CA1208735A - Timed token ring with multiple priorities - Google Patents

Abstract

TIMED TOKEN RING WITH MULTIPLE PRIORITIES

Abstract A timed token protocol for use in a local area loop communications network is disclosed. The protocol provides three classes of service with a priority relationship between classes. The three classes allow guaranteed bandwidth, interactive and batch services. The classes are implemented by timing the rotation time of a write token to measure instantaneous load. Transmission of information is limited by class of service and the measured write token rotation time.
Also disclosed is a hardware embodiment of a loop communications station which implements the timed token protocol.

Description

73~

TXMED TOKEN RING WITH MULTIPLE PRIORITIES

Background of the Invention The present invention relates in general to a system and method for communicating information between distributed stations. More particularly, the present invention relates to a timed token loop which provides three or more classes of service with a priority relationship between classes. The thxee classes of service provided allow guaranteed bandwidth, interactive and batch services. These classes are implemented by timing the rotation time of a write token to measure instantaneous load and limiting transmission of information by class of service and the observed write token rotation time.
The synthesis of the architecture for future office automation systems will be effected to a large extent by the available communication mechanisms supporting those systems.
Circuit switched communication as provided by PBXs i5 efficient for handling voice traffic, but is limited by the maximum bandwidth available for data traffic~ The inefficiencies inherent in using circuit switched service for communication of bursty data traffic are being solved for low data rate devices through submultiplexing in the PBX. In contrast, local area networks have been optimized for efficient transmission of data at high hurst rates with little consideration for handling of digital voice.
~ .-.'~, I - 2 ~2~ 3~

Broadband systems provide the capability for carrying both voice and data over the same media through separate logical networks for voice and data on the same physical media. This hybrid approach solves some problems by using a single media, but does not allow the flexibility given by integration of data on the same logical network.
Distributed communication systems based on token loop structures are well known in the prior art. Thus, in the article by Davia J~ Farber titled "A Ring Network", Datamation, February 1975, pp. 44-46, a collection of minicomputers connected by a ring-like digital communication system is disclosed. Similarly, the work by Newhall and Farmer on toke~ controlled rings is exemplified in a paper titled "An Experimental Distributed Switching System To Handle Bursty Computer Traffic, in Proc. ACM Symp. Problems in the Optimization of Data Communications Systems (Pine Mountain, GA, Oct. 1~69), pp. 31-34.
The work of both Newhall and Farber was primarily applicable to data type traffic where all stations were given an essentially equal opportunity to transmit. Thus the drawback of both systems is that they cannot support a guarantee o~ bandwidth.
The inability to guarantee bandwidth is also a drawback of the Ethernet system and all CSMACD-type protocols for local area networks.
The Cambridge ring, which is based on the work of Pierce, is more adapted to a circuit type of service. In such a system, you essentially have a boxcar (which corresponds to available bandwidth) into which data may be inputted or extrscted. A fixed allocation procedure may be implemented which reserves the boxcar for a station to use. The drawback of the Cambridge ring is that there's no simple or obvious way to use the boxcar when its not being used by the station that has a fixed reservation on it.

~ l _ 3 _ ~2~ 73~

It is the general object of the presen-t invention to overcome these and other drawbacks of the prior art by providing a timed token protocol method and apparatus which integrates the favorable characteristics of both circuit switched and packet switched communications and provides these characteristics to a station through a single physical and logical interface.
It is another object of the present invention to provide a protocol adaptable to either a physical or logical loop which provides three or more classes of service with a priority relationship between classes, the three classes allowing guaranteed bandwidth, interactive and batch services.
It is still another object of the present invention to provide a timed to~en protocol for a loop communications network which allows the bandwidth guaranteed to a first station to be used by that first station when needed and further allows the same guaranteed bandwidth to be u~ed by another station when it is not needed by the first station.
It is yet another object of the present invention to provide a token controlled loop which provides efficient ~tilization of available bandwidth by the stations configured on the loop.
It is an additional object of the p~esent invention to provide a timed token protocol adaptable to either a physical or logical loop which provides for stations configured on the loop, each being of one or more of multiple classes of priority.
It is a further object of the present inven-tion to provide a timed token protocol for stations interconnected in a continuous loop structure, the protocol providing for stations with different priority levels, wherein stations of the highest priority level are capable of allocating a guaranteed minimum bandwidth to themselves to the exclusion of other stations of the same priority.

7;~

It is still a further object of the present invention to provide a timed token protocol for stations interconnected in a continuous loop structure, the protocol providing for stations with different priority levels, wherein stations not of the highest but of equal prlority level are guaranteed a pool of bandwidth which may be fairly shared between them.
These and other objects, features and advantages of the present invention will become more apparent from the detailed description of the preferred embodiment when read in conjunction with the drawings.

Summary of the Invention According to the invention, a timed token protocol is provided to allow for the integration of three or more classes of service on the same loop communications network.
The highest class of service (Class 1) is for information which requires a guarantee of bandwidth and/or deterministic delay and jitter characteristics. This class of service is used for information that is represented in the time domain (e~g., pulse code modulated voice), or where minimal queuing delay is important te.g., process control). The second class of information (Class 2) is that which is non-real time, but of an interactive nature. Traditional data cornmunications between terminals and computers falls into this classiication.
That is, Class 2 information requires some minimum throughput, but the a~solute guarantee of bandwidth is not a requirement.
The third class of service (Class 3) is for batch information where no minimum throughput is required and transmission of information may be delayed until network load is light.
The timing of a write token is the mechanism used for measuring instantaneous load. The measurement of load allows for the establishment of the three classes of service.

~Z~8~3S

Each class of service uses a dlfferent set of rules fox determining when information may be transmitted.
An initial value called the target token rotation time (TTRT) must be selected for the network. The network S protocols are designed so that under 100~ offered load! the write token will revolve at the TTRT. The ~TRT must be chosen to be less than or equal to the rate at which devices operating at a Class 1 priority require service.
As in all token controlled communications systems, the right to service new information into the network is controlled by passing a priviledge to transmit (the write token) ~rom one station to anotherO The passing of the write to~en is controlled by the communication protocol.
Class 1 (Cl) informatlon may be transmitted upon every write token reception. The amount of Cl information transmitted with each write token reception is limited by a bandwidth allocation procedure to be explained below. Other classes of information control their transmission by using a timer for each class. The timer for Class 2 is the target token rotation time minus the time for transmission of the maximum length frame (TTRT - MAXFRAME) (or the Class 2 target time).
The target time for Class 3 would be some percentage of the target token rotation time related to load minus the maximum sized frame transmission time; (e.g., .6 x TTR~ - MAXFRAME).
Stations of Class 2 or lower priority control their transmission of information by timing between arrivals of the write token. Each time the write token arrives at a station, prlority class timers are reset to their initial values if no information is to be transmitted, and the write token is passed on unimpeded. If, at arrival of the write token, timers have not decremented to zero and information is queued for transmission, queued information may be transmitted for any priority class (other than Class 1) with a non-zero timer value.

- 6 - ~2~73~

A station which simultaneously services multiple classes of information transmits lowest priority first and highest priority last. For example, in a station which has Class l, Class 2 and Class 3 traffic, if when the write token arrives the Class 3 (C3) timer has not decremented to zero, the residual value in the C3 timer is loaded into a token holding timer, the C3 timer is reset, and all timers continue to decrement. New frames may be sourced at C3 priority level onto the ring as long as the token holding timer ha~ not decremented to zero. When the holding timer has decremented to zero, the current frame in transmission is completed.
At that time the residual in the Class 2 (C2) timer is loaded into the holding timer and the C2 timer is reinitialized~
Transmission of C2 information then proceeds as described for C3. Class l (Cl) information is then transmitted. The write token is transmitted after all the allowed Cl frames. If at write token arrival the C3 timer had decremented ~o zero, the protocol begins with service to Class 2. If both the C3 and C2 timers had decremented to zero, transmission begins with Cl.
At design or configuration time, paremeters must be chosen to allow for the quality of service desired for the classes of information. A value representing allocatable bandwidth is used for the control of Class 1 traffic. This value (ALLOC) i5 less than the target token rotation time.
The amount of difference dpends upon two factors~ One is the amount o~ bandwidth wished for Class 2 devices to guarantee minimum throughput (C2POOL), and the other is the latency (LATEN) of the physical or lo~ical ring. Latency is the amount of time it takes for the token to go around the ring with zero load.
~30 The sum of allocatable bandwidth, the Class 2 pool, and latency is equal to the target token rotation time (TTRT = ALLOC ~
~2POOL + LATEN). Normally the timer value for Class 3 would be less than the available bandwidth for Class 1 (C3TIMER ~ ALI.OC).
In such case, no minimum bandwidth is guaranteed ~or Class 3.

Y3~

If the C3 timer is greater than allocatable bandwidth, some minimum bandwidth has been guaranteed for Class 2 or Class 3.
By limiting tra~fic through the described mechanisms, Class 1 service is that of a minimum guaranteed bandwidth, since the guarantee is for each Class 1 station that has received a portion of the allocatable bandwidth to be able to transmit some fixed amount of information every rotation of the write token. If the write token is rotating faster than the target token rotation time, the bandwidth usable by Class 1 would therefore be greater than the guaranteed minimum.
Class 2 devices have a pool of bandwidth guaranteed to them which is shared fairly by all devices designed to use that quality of service. In addition, the timing of the write token allows any unused Class 1 bandwidth to be used by lower priority stations. This includes both allocated and unused bandwidth as well as unallocated Class 1 bandwidth.
Class 3 priority has no guaranteed throughput, but would only transmit when the load falls below the arbitrary percentage estalished for that class.
In the preferred embodiment, the mechanism for allocation of bandwidth for Class 1 service is to use a special token which is transmitted around the loop. When a Class 1 station desires to allocate additional bandwidth to itself, the write token is captured and a bandwidth allocation token is transmitted. Each station on the loop takes this bandwidth allocation token, adds to it the amount of bandwidth which is currently allocated by that station for Class 1, and forwards the allocation token to the next station. When the bandwidth allocation token returns to the station attempting to allocate ` 30 bandwidth, the write token is regenerated and passed on to `the next station. If the current allocation of bandwidth returned in the bandwidth allocation token plus the desired allocation is less than the allocatable bandwidth, then the allocation is granted. The bandwidth desired is then added to the total allocated for that station.

.;

~Z~73~

In addition to the presen-t invention providing a protocol method for the integration of different classes of service on the same communication network, a preferred hardware embodiment of the station logic is also described.
Details of the hardware implemention is contained in the detailed description of the preferred embodiment.

Brief Description of the Drawings Figure 1 illustrates the interconnection of a plurality of stations in a communications loop as employed in the present invention.
Figure 2 illustrates a plurality of Class 1 stations interconnected in a loop structure, each station having a current Class 1 allocation of the number of units indicated.
Figure 3 shows the formats of the data frame, recovery token, bandwidth allocation token and write token as used in the preferred ~n~odiment of the present invention.
Figure 4A illustrates a single loop with redundant transmission paths, having been restructured into two separate fragmentary loops after the occurrence of the two lndicated faults and the invocation of loopback. Each station shown is Class 1 priority and has a current Class 1 allocation as indicated.
Figure 4B is similax to Figure 4A, but illustrates the configuration after the failure betwen stations C and D
has been repaired, wherein the two separate loops of Figure 4A
have begun to function as a single loop.
Figure 5 shows a block diagram of the loop logic included in each station attached to the loop.

9 .~ 35 Jetailed Description of the Preferred Embodiment The protocol of the present invention is designed to operate in a token con-trolled loop (or ring) communications network. Those skilled in the art will appreciate that the protocol of the present invention may be implemented either on a physical loop or on a logical loop (or ring) superimposed on a physical bus. Such a loop communica~ions network may u~ilize a single loop (or ring) architecture or one incorpora~ing a second redundant loop with network components that route the data around any network faults. The following description will consider the implementation of the present invention in a single loop archi-tecture. However, those skilled in the art will appreciate that the present invention may be readily adapted for use in loop architecture employing a second redundant loop.
The timed token protocol of the present invention allows for the integration of different classes of service on the same communications network. The preferred embodiment of the protocol supports three basic priority classes of service. The first class (Class 1) is for that type of information which re-quires a guarantee of bandwidth and deterministic delay and jitter characteristics. This class of service is used for inform-ation which is represented in the time domainO Thus, for example, Class 1 information may include real-time audio applications such as pulse code modulated (PCM) voice. Such Class 1 information is sometimes referred to as synchronous information.
The second priority class of infoxmation (Class 2) supports non-real -time applications requiring interactive response.
Typical of such an application is traditional data communications between terminals and a computer. Thus, in this class some minimum throughput is required, but an absolute guarantee of band-width is not a requirement. This class of traffic is sometimes referred to as asynchronous.
The third class of service (Class 3) is that of batch traffic which requires no minimum throughput, but can be transported X

~Z~3735 throu~h the network when load is light. Background communications such as electronic mail or file transfers are typical applications where Class 3 service would be appropriate. The protocol of the present invention allows ~or the creation of additional priori~ies within this class of service for ~atch traffic. Thus, Class 4 .... Class N, all subclasses of Class 3, may be established.
As will be discussed below~ the timing of a write token is the mechanis~ used for measurina instantaneous load on the loop.
This measurement of load allows for the establishment or the classes of service discussed above. Each class of service uses a different set of rules for determinins when information may be transmitted.
The speed at which the write token rotates around the loop determines the rate at which the network services each station, the network's queing delay, and the bandwidth lost to passing the write token from station to station. An initial value called the taraet token rotation time (TRTT) must be selected for the network. The loop protocols guarantee that the short-term average rotation ti~e will vary fro~. the minimum orbit time with no load, to the target token rotation time (TRTT) under full load conditions. The TRTT is important since it defines the ~aximum average write token rotation time. Thus, under 100~ offered load, the write token will revolve at the TTRT. In the preferred e~bodiment of the present invention, the TRTT is loaded into each station during network initialization.
The TTRT is related to the rate at which devices operating at a Class l priority require service. For Class 1 priority, information may be transmitted once every write token arrival. Thus, the protocol guarantees that Class 1 (Cl) information may be sent at least once every TTRT for each Class 1 station on the loop that has received a guarantee o~ bandwidth. This means that the TRTT determines the guaranteed service rate for Cl transmissions.

373~

As previously mentioned, the TTRT is related to the rate at which devices operating at a Class 1 prlority re~uire service. For example, if service is only required every eight milliseconds, a 64X bits per second information rate would be transmitted using a packet size of 64 bytes (or 512 bits). Thus, the time to accumulate 512 bits at a rate o~ 64K bits/second is 8 milliseconds. If the information generation rate was 32K
bits per second instead of 64K bits per second (bps), a packet size o~ 3~ bytes (ox 256 bits) would be used with this eight millisecond TTRT. Similarly, a chosen service time of four milliseconds would require 32 bytes (or 256 bits) per packet to suppoxt a 64K bps information rate/ or 15 bytes (or 128 bits) per packet for a 32X bps information rate.
The value used for the target token rotation time must be less than or equal to the selected service time in order to guarantee that each station is serviced within the selected service time. If error free bandwidth is desired for Class 1, the error rate of the media must be taken into consideration.
In such case, the target token rotation time would be correspondingly less than the rate at which packets are produced.
As in all prior art token controlled communications systems, the right to source new information into the network of the present invention is controlled by passing a privileae to transmit (or write token) from one station to another. In the present invention, the passing of the write token is controlled by the communication protocol.
FIG. 1 shows a single loop communications system as employed in the present invention. In such a system, station A 10 passes a write token to station B 12, station B 12 passes the write token to station C 14 .... and station Z 16 passes the write token to station A 10, and the cycle is therea~ter repeated.
Each station on the loop may interconnect devices for handling one or more priority classes of data. Thus, a single station may handle classes 1 or 2 or 3, or any co~bination of the three classes.

Class 1 information may be transmitted upon every write token reception by a Class 1 station. The amount of Cl information that a Class 1 station may transmit upon each write token reception is limited by a bandwidth allocation procedure to be explained below. Other cla-sses of information transmission are controlled by using a timer for each class, each station capable of transmitting non-Class 1 information must have a timer for each non-class 1 priority of information it is capable of transmitting.
The inltial value (or target time) for each Class 2 timer is set to the target token rotation time (TTRT) minus the time for transmission of the maximum length frame (TRTT-MAXFRAME).
As will be obvious to those skilled in the art, MAXFRAME is dependent on the quality of crystals used in the network, the amount of padding inserted between frames, the coding and synchronization system utilized, and other characteristics of the network. I~ the network uses a central clock, the maximum length frame could be arbitrarily long. In the preferred embodiment of the invention, the maximum length frame has been chosen to be 1024 bytes in the information field.
In the preferred embodiment, the timer value for Class

2 is chosen to assure efficient network utilization and prevent starvation of stations. Thus, if the timer value for Class 2 is not TTRT-MAXFRAME, the network will give smaller frames a greater probability of transmission. This would tend to encourage inefficient network utilization since the overhead to information ratio is higher for smaller frames. It also might prevent some Class 2 stations from transmitting at all.
The target time for e~ery Class 3 timer is set to some percentage of the target token rotation time minus the maximum 3o sized frame transmission time. For example, the tar~et time for Class 3 might be 0.6 X TRTT - ~FRAME. The percentage of the TRTI~ used in the calculation of the Class 3 target time is related to the load on the network. Thus, each timer within the same Class is set to the same initial value, the value being set when the network is configuredO

~ ~ U ~ ~ 3 S

The timer value for any other priorities of batch information would follow the same pattern as used for Class 3, with each priority using a smaller percentaye of TTRT for its initial timer value~ For ex~mple, if a Class 4 priority was included, the initial Class 4 timer value (or target time) might be O.4 X TRTT - MAXFRAME.
Note that in the present invention all timers in all stations are continually decrementing until they have decremented to zero (at which time a timer ceases to decrement).
Stations of Class 2 or lower priority control their transmission of information by timing the write token from arri~al to arrival. Each time the write token arrives at a station, priority class timers are reset to their initial values. If no information is to be transmitted, the write token is passed back onto the loop unimpeded. If, at arrival of the write token, the timers have not decremented to zero and information is queued for transmission, queued information may be transmitted for any priority class (other than Class l) whose corresponding timer has a non-zero value. Thus, a station can transmit Class 2 (or Class

3) information as long as the time since the previous write token arrival is less than the Class 2 (or Class 3) target time. If the write token arrives later than a Class 2 (or Class 3) target time since its previous arrival, the station must refrain from transmitting any Class 2 (or Class 3) information onto the loop.
A station which simultaneously services multiple classes of information transmits lowest priority first and highest priority last. For example, in a station which has Class l, Class 2 and Class 3 traffic, when the write token arrives, if the timer for Class 3 has not decremented to zero, the residual value in the Class 3 timer is loaded into a token holding ~imer, the Class 3 timer is simultaneously reset to its initial value, and the Class 3 timer and token holding timer immediately begin to decrement. Note that during this time the Class 2 timer and all timers in other stations are continuously decrementing. Multiple new frames may be ~2~ 73S

sourced at Class 3 priority level onto the loop as long as the token holding timer has not decremented to zero.
When the token holding timer has decremented to zero, the current Class 3 frame in transmission is completed. At that time the residual value in the Class 2 timer is loaded into the token holding timer, the Class 2 timer is simultaneously reset to its initial value, and the Class 2 timer and token holding timer immediately begin to decrement. Note that during this time the Class 3 timer and all timers in other stations are continually decrementing. Transmission of Class 2 information then proceeds in the same manner as described for Class 3, the transmission of Class 2 information ceasing after completing transmission of the frame being transmitted when the token holding timer goes to zero.
Note that if at the time the write token arrives there is no Class 2 information to transmit, the Class 2 timer still would not be reset until after Class 3 is serviced.
After Class 2 transmission is ended, the station nèxt transmits Class 1 information. Details of when Class l information may be transmitted will be discussed below. After all of the allowed Class 1 frames have been transmitted, the write token is retransmitted back onto the loop.
Note that in the above description, if at the arri~al of the write token the C3 timer had already decremented to zero or there was no Class 3 information to transmit, the station would immediately reset the C3 timer to its initial value and begin with service to Class 2. If when the write token arrived both the Class 3 and Class 2 timers had decremented to zero or there was no Class 2 or Class 3 in~ormation to transmit, the station would immediately reset the C~
and C3 timers and transm~ssion would begin with Class 1 information.
To improve the fairness within a class of service, a method of accumulating lateness is preferred. Such a me~hod may be optionally implemented in the present invention as ~ollows. Thus, after transmission of Class 2 (or Class 3) information, if on the next rotation of the write token the timer for a class that ~15- ~2~ S
transmitted decrements to zero, it will cause a class lateness register (not shown) to increment until write token arrival. This lateness must be removed before transmission can occur for that class again. The measure of token earliness (the residual of the target timer normally transferred to the token holding timer) is subtracted from the lateness register. This continues until the lateness has been compen.sated for by earliness. Then transmission can resume either on the same rotation that lateness is completely removed or on the next rotation after lateness is completely removed.
When the network is configured, parameters must be chosen to allow for the quality of service desired for the classes of information. As previously mentioned, the amount of Class l inrormation that may be transmitted upon each write token reception is limited by a value representing allocatable bandwidth. This value, ALLOC, is less than the target token rotation time. The amount that ALLOC differs from the target token rotation time is dependent on three factors. These three factors are the amount of bandwidth to be allocated for Class 2 devices to guarantee minimum throughput (C2POOL), the latency (LATEN) of the physical or logical ring, and any bandwidth for system administration (SYSADM).
System administration would include functions required to construct a logical loop or for bandwidth allocation procedures. Latency (LATEN) is the amount of time it takes for the token to go around the loop with zero load. The sum of allocatable bandwidth (ALLOC), the Class 2 pool (C2POOL), latency (LATEN) and system administration (SYSADM) is equal to the target token rotation time. Thus, TTRT = ALLOC + C2POOL + LATEN + SYSADM
In practice, latency and system administration will be a small factor for most systems. Thus, allocatable bandwidth (ALLOC) is selected primarily on how much Class 2 traffic is anticipated on the loop. By selecting the size of C2POOL, you determine the minimum throughput per Class 2 station. The remainder (ALLOC) is the bandwidth which is available for all Class l (Cl) traffic.

3~;
-16_ Normally, the timer value for Class 3 and any lower priority classes will be less than the available bandwldth for Class 1 (C3TIMER ~ ALLOC). In such case, no minimum bandwidth is guaranteed for Class 3. If this is not the case, then the actual Class 2 pool (C2POOL) is C2POOL = TTRT - LATEN - (C3TIMER-ALLOC) = TTRT - LATEN - C3TIMER + ALLOC
Thus, if the Class 3 timer value is greater than the allocatable bandwidth, some minimum bandwidth has been guaranteed for Class 2 ~r Class 3.
Class 1 service is that of a minim~tm guaranteed bandwidth. Each Class l station that has re eived a portion of the allocatable bandwidth (ALLOC) guarantees it will be able to transmit some fixed amount of information coxresponding to the siæe of its allocation for every rotation o the write token. Thus, if the write token is rotating faster than the target token rotation time, the bandwidth usable by Class l stations would be greater than the guaranteed minimum bandwidth available for Class l information.
The Pol of bandwidth guaranteed to Class 2 stations (C2POOL) is shared by all stations designed to use Class 2 service. In addition, the timing of the write token allows any unused Class l bandwidth to be used by lower priority stations.
This is accomplished by lower priority stations timing the write token and measuring load as previously described. Thus, when the write token arrives at a lower priority station, the token holding timer basicly says how much bandwidth was not used on the last rotation. Note that this has no bearing on what is allocated or what was even allocatable; it is just what was used, and so by measuring the current load (via the C2 and C3 timers) lower priority stations are able to use that unused Class 1 bandwidth which is either not allocated to Class 1 or allocated and not used. In other words, the transmission algorithm used by Class 2 and 3 stations does not even look at ALLOC; only the allocation algorithm for Class 1 looks at ALLOC.

lZ~3~ii Class 3 and lower priority s-tations have no guaranteed pool of bandwidth available to them and hence have no guaranteed throughput. Thus, they may only trans~ut when the load falls below the arbitrary percentage established for that class. As previously discussed, Class 3 and lower priority stations make this determination based on the target time (or timer value) established for that class. For example, if the Class 2 target time is 8 milliseconds and the class 3 target time equated to 6 milliseconds, then whenever Class 2 load ~ell below 75 percent Class 3 would be able to transmit.
There are situations where a Class 1 station may want to increase the amount of Class 1 bandwidth allocated to it. For example, if a device such as a PBX is attached to a station, each time you establish a call or terminate a call the station would want to change the amount of allocated Class 1 bandwidth ~or that station to reflect the current load.
Those skilled in the art will appreciate that the allocatlon of bandwidth for Class 1 service can be accomplished in one of at least five ways:
~ Through configuration limitation.
- Through a central device which controls the allocation of bandwidth.
- By including in the write token a field representing the current allocated bandwidth.
- By a special token which circulates around the loop and collects the currently allocated bandwidth from all s-tations.
- By a distributed message passing algorithm for determining the current allocation of bandwidth.
In the preferred embodiment of the present invention, the mechanism used for allocation o~ bandwidth for Class 1 service is to use a special token which is transmitted around the loop.
When a station desires to allocate additional Class 1 bandwidth, it captures the write token and transmits a bandwidth ~2t~ 3 allocation token (FIG. 3). This bandwidth allocation token includes a field for accumulating the allocated bandwldth of all stations (ALLOCATED). This field is initialized to the current allocation of the station transmitting the bandwidth allocation token. Each Class 1 station on the loop takes the bandwidth allocation token, adds to the allocated field (ALLOCATED) the amount of bandwidth which is currently allocated by that station to Class l, and forwards the bandwidth allocation token to the next station. When the bandwidth allocation token returns to the station attempting to allocate bandwidth, the write token is regenerated and passed on to the next station. If the current allocation of bandwidth returned in the bandwidth allocation token (ALLOCATED) field plus the desired additional allocation is less than or equal to the allocatable bandwidth (ALLOC), then the allocation is granted. In such case the additional bandwidth desired is then added to the total bandwidth currently allocated for that statin.
As an example of the above operation, assume we have a loop as shown in FIG. 2 with all stations A, B, ..., E being of Class 1, each station having the number of Class 1 units of bandwidth allocated to it as shown in the figure. Further assume that the loop has a capacity of 12 allocatable units of Class 1 bandwidth (- ALLOC). I~ station C wants to allocate additional bandwidth to itself, it captures the write token, and sends out a bandwidth allocation token with O in the allocation field ALLOCATED (since C
currently has O units allocated to it). When the allocation token is received by statlon D, 5 units are added to the ALLOCATED field and the allocation token is transmitted to station E. This process continues until the bandwidth allocation token arrives back at station C with a value of 9 in the ALLOCATED ~ield. Station C
compares the value in the allocation field ALLOCATED a~ainst the loop capacity of 12 (as specified by ALLOC). Since there is a difference of 3 units between th~ ~alue of the ALLOCAT~D field and ALLOC, station C may allocate up to three additional units of ~ 2~ 73 Class 1 bandwidth. If C was trying to allocate only one additional unit, it would change its current allocation register from O to 1.
Subsequently, if station C received a bandwidth allocation token, it would add 1 unit to the ALLOCATED field; viz., its current allocation~ Note that when sta~ion C is finished using its 1 unit of allocated Class 1 bandwidth, it will change its current allocation register back to O units. Similarly, when other Class 1 stations no longer require part or all of their currently allocated bandwidth, they will also reduce the value in their current allocation regis~er accordingly.
Under one particular failure condition it is possible for a Class 1 station to receive a bandwidth allocation token wherein the value in the ALLOCATED field exceeds the total allocatable Class 1 bandwidth (ALLOC). Thus for example, a loop having redundant transmission paths and using loopback or reliability will fragment into separate loops when multiple failures occur (FIG. 4A). A
description o the loopback mechanism is contained in U. S. Patent

4,190,821, issued to Thomas R. Woodward on Feb. 26, 1980.
Upon ~epa~r o~one of the failures, the two separate loops will begin functioning as a single loop (FIG. 4B).
Before repair, the two loop fragments operate using the same bandwidth allocation procedure. Hence both loop fragments in FIG. 4A have less than the ALLOC amount ( = 12 units) of bandwidth allocated. But when repair of the fault between stations C and D rejoins the loops (FI&~ 4B), the current allocation is larger than ALLOCo As an example, assume in FIG. 4B that station C wanted to allocate additional bandwidth. When the allocation token arrived at station A, the ALLOCATED field would specify 11 units. In such case, station A would detect that the currently allocated Class 1 bandwidth exceeded ALLOC, and would respond by terminating all sessions since it could only have a current allocation of 1 unit.
Since station A terminated all sessions, it would change its current allocation to O and when the allocation token arrived at station B the ALLOCATED field would still specify 11 units.
Station B would not be required to terminate its sessions since , s it could still maintain its current allocation of 1 unit without the total current allocation exceeding ALLOC ( = 12 Units). However, the request for additional allocation made by station C could not be granted since if granted the total current allocation would exceed ALLOC.
Alternatively, station ~ could deallocate 1 unit of bandwidth and maintain a portion of its sessions. In such case, station A would add 1 unit to the ALLOCATED field of the allocation token. Thus, when the allocation token rearched station B, the ALLOCATED field would specify 12 units. Station B would detect that the currently allocated Class 1 bandwidth exceeded ALLOC (if station B maintained its current allocation), and repond by terminating all of its sessions since it could no longer have a current allocation of 1 unit. Thus when the allocation token -15 arrived at station C, the ALLOCATED field would specify 12 units, and the re~uest made by station C could not be granted since ALLOCATED was already equal to ALLOC.
In the preferred embodiment of the present invention, under normal conditions only one write token circulates around the loop. Station failures or transmission errors may cause the loss of the write token. The determ.ination of when the write token has been lost is quite simple in the present timed token loop bacause of the target token rotation time. Thus, the absolute worst case time for rotation of the write token is less than or equal to two times the target token rotation time (TRTT).
This worst case time occurs under the extremely unlikely conditions that all o~ the bandwidth is currently allocated to Class 1 (no C2POOL) and all o~ the bandwidth is being used by Class 1 stations on one rotation and on the next rotation all stations cease to transmit.
Therefore, if the time since the previous arrival of a write token at a station (of any class or classes) is greater than two times the target token rotation time, the station knows that the write token has been lost. In response to detecting the loss of the write token, the station will initiate a bidding cycle to recover the token. The bidding cycle is initiated by the station transmitting a recovery token (FIG. 3) with its individual address in the destination address (DA) field. The next station receiving the recovery token passes it on if the destination addxess in the recovery token is greater than its own individual address, replaces the destination address with its own individual address if the destination address is smaller than its own individual address, or wins the bid and regenerates the write token when the destination address in the recovery token is equal to its own individual address. Thus, the station with the highest individual address wins the bid and regenerates the write token.
Those skilled in the art will appreciate that the bidding algorithm may easily be modified so that the station having the lowest individual address will win the bid and regenerate the write token.
It should be noted that the same biddincJ process used to regenerate a lost write token may also be utilized to generate a write token when the network is initialized.
The discussion will next briefly consider the formats of the tokens and data frame (FIG. 3) and the station's response ~o upon the receipt of incoming information.
All stations on the loop look at all incoming information.
If the destination addressed (DA) specified in a data frame equals the receiving station's individual address, the data frame will be buffered if there is no room in the station's buffer. The network allows for creation of status indications (in the EFD field) for error control and flow control on data frames. If a received data frame has a bad cyclic redundancy check (in the frame check sequence field), a status bit in the EFD field will be set to NAK.
If the station has no room to buffer the frame, a status bit in the EFD field will be set to indicate the buffer full condition. On the other hand, if the frame is buffered a status bit in the EFD
field will be set to ACK. If the destination address of a frame ~2~ 73~

is not that of the station, the frame is repeated to the next station without change, except in the case described below.
Each station also looks at the source address of every received data frame. If the source address is equal to the station's individual address, the frame has made one complete,revolution of the loop. The status indicated in the EFD field is captured and used to control retransmission. The station invalidates the frame by either placing an abort sequence in the frame or by removing the frame from the loop. This prohibits multiple receptions of the same frame by its continuing to rotate around the loop under very light load.
The following description describes the characteristics of the hardware used to implement a station. Although a detailed description of the hardware is not included, the description is sufricient to enable those skilled in the art to make and use the invention.
Referring to FIG. 3, information is carried on the loop (or ring~ in frames which include unique identifiers for start of frame and end of frame. The start frame delimiter (SFD) indicates whether the frame is one of the tokens used for management of the loop or is a data frame. The end frame delimiter (EFD) includes a s-tatus field which is used to indicate positive or negative acknowledsment of the frame, buffer status and other status indications. The data frame has two addresses, the destination address (DA) and the source address (SA). User data and any user control information is carried in the information field (INF0) of the data frame. The frame check sequence field (FCS) is used to detect errors in transmission.
The various fields in the token formats have functions similar to those described for correspondingly named fields in the data frame format. The exact positioning of the fields in the token and data forma-ts and the meaning assigned to the various status bits is not critical to the operation of the present invention. Thus, those skilled in the art will appreciate that modifications to the formats shown in FIG. 3 may be made without departing ~rom the spirit of the present inventionO
In the preferred embodiment of the present invention, information transmitted on the loop ls encoded in a dual frequency format which produces three values, "1", "0", and "violation". The violation value is used to define SFD and EFD. However, ~hose skilled in the art will appreciate that other data transmission formats may be more appropriate to a particular application.
FIG. 5, shows a block diagram of the ring logic provided for each station on the loop. In FIG. 5, solid lines indicate actual data flow and broken lines indicate control information.
The broken line entering the bottom of the transmit priority logic 32 is the control interface from the data device(s) (not shown) supported by and included in each station. The data lines leaving the bottom of the receive buffer logic 42 and entering the bottom of the transmit buffer logic 34 are data interfaces which allow the data device(s) (i.e., facsimile units, storage devices, etc.) to receive/transmit information from/to the ring logic. As will be obvious to those skilled in the art, these data interface lines are normally coupled to some logic on the data bus of the data device(s).
Signals received from the loop are fed into a decoder 20 where a clock is extracted and the data is clocked into the first in/first out queing unit (FIF0) 22. The choice of whether a centralized or decentralized clock is utilized is not important. In the preferred embodiment of the invention a decentralized clock is utilized; viz., each station runs off of an independent clock. In such a situation, the difference in rates between the received clock and a station's internal clock can cause the need to insert or delete bits between frames. This is accomplished by the FIF0 22. Thus, the FIF0 22 will add or delete bits between frames to compensate for rate disparities between ~l~0~3~

crystals in different stations. The d~sign of the FIF0 22 is dependent on the clocking system being used, the quality of crystals and other parameters. The design of a FIF0 22 to accommodate the particular network's characteristics will be obvious tG those skilled in the art.
It should be noted that the FIFO's 22 length is an important factor in determining the maximum frame length MAXFRA~.
Thus, MAXFRAME is dependent on how many bits of padding the frame creation logic 36 inserts between frames, the length of the FIF0 22 and other factors such as how many stations are in the loop and the method of clocking used. The tradeoff between these variables will be apparent to those skilled in the art.
The data output from the FIF0 22 sources four parallel sections of logic: the token management logic 24; the frame synchronization logic 26; the address reco~nition logic 28; and the error detection logic 30. The frame synchronization logic 26 scans the data coming in from ~IF0 22 looking for start frame delimiters (SFDs). Upon de-tection of a start frame delimiter, the frame synchroni~ation logic determines whether the frame is a data frame or a token ba5ed on the coding of the start frame delimiterO
The design of the frame synchronization logic is dependent on the coding scheme used to indicate start frame delimiters (SFDs) and end frame delimiters (EFDs). Thus for example, if a HDLC/BDLC
type of zero insertion was used to create the unique patterns identiying SFD and EFD, the frame synchronization logic 26 would have to find those flag patterns and also remove the insexted zeros in non-flag fields. In the preferred embodiment, illegal coding sequences are used to indicate delimiters and identify whether a data frame ox one of the three types of tokens has been received.
If the fxame synchronization logic 26 detects a token, the token mana~ement logic 24 is notified by the frame synchronization logic 26. The token can be one of three types:
a write token, a recovery token, or a bandwidth allocation token.

-25_ ~Z~873~
In response to the frame synchronization logic 26 notifying the token management logic 24 that a write token has been received, the token management logic 24 will reset an internal timer (not shown) which is doing timeouts for recovery of the write token.
That is, the internal timer will be reset to its initial value of two times the TTRT. Note that this internal timer is also set to its initial value when a station joins the loop. If a write token is received, the transmit priority logic 32 is notified by the token management logic 24. The transmit priority logic 32 includes the C2 timer, C3 timer, token holding timer, and lateness register, none of which are shown. Upon the transmit priority logic 32 being notified of the receipt of a write token, the transmit priority logic 32 will load the token holding timer and reset the C2 and C3 timers in accordance with the procedure specified earlier.
If information has been queued for transmission in the transmit buffer logic 34 and the timers for the classes queued have not decremented to zero, information will be taken from the buffers (not shown) in the transmit buffer logic 3~ and run through the frame creation logic 36 where a start frame delimiter, the source address, the frame check sequence and end ~rame deli~iter are appended.
The design of the frame creation logic 36 is dependent on the data structure used in the transmit buffer logic 34, the ordering of fields of the data frame, and the method used for 2S creating frame delimiters. In the preferred embodiment, the only information stored in the transmit buffer logic 34 is the information field and the destination address. Thus, the frame creation logic 36 p~ts on a start frame delimiter (SFD), adds the source address (SA), generates the frame check sequence (FCS) and adds the end frame delimiter (EFD). With the functions performed by the frame creation logic 36 now understood, suffice it to say that ~he design of the frame creation logic 36 will be obvious to those skilled in the art.

_26~ 873~
The frame constructed in the ~rame creation logic 36 is transferred to the output control logic 38 which in turn supplies the data ~rame to the encoder 40. The output control logic 38 is a multiplexor, responsive to inputted control signals, for gating to the encoder 40 one of the output control logic's 38 data inputs in accordance with the received control signals. Its design is well known to those skilled in the art. The encoder 40 encodes the data frame into whatever data transmission format is being utilized (i.e., NAZ, dual frequency) and transmits the encoded data frame onto the loop. The transmission of information continues until the allowed holding time-for the write token (as indicated by the token holding timer) has expired or until all queues information in the transmit buffer logic 34 has been transmitted. The output con~rol logic 38 then causes the write token to be regenerated by the token management logic 24, and the regenerated write token is gated ~rom the token management logic 2~ through the output control logic 38 to the encoder ~0.
If the token rec~ived is a recovery token, the token management logic 24 uses the control signals from the address recognition logic 28 to determine whether the destination address (DA) in the recovexy token is less than, equal to, or greater than the station's address. The address recognition logic 28 includes a simple comparator to perform the comparison and supplies the token management logic 24 with control signals indicating the result of the comparison. If the destination address is greater than the station's address, the recover~ ~oken is gated through the output control logic 34 into the encoder 40 and back onto the loop unimpeded. I~ the destination address in the recovery token is less than the station's address, the recovery token's DA is replaced with the station's address and the modified xecovery token is gated out onto the loop. If the destination address in the recovery token is equal to the station's address, the station has won the bid to recover the write token. In such case, a new write token is generated tby the same mechanism use~ to generate a write token after completing the transmission of data frames) and gated out onto the loop. As previously mentioned, this bid mechanism allows only the station with the highest address to regenerate a write token after it is lost.
If the token received is a bandwidth allocation token, the allocation field ~ALLOCATED) in the token is added to the current allocation for the station (which is stored in the token management logic 24~ by the token management logic 24. If the result of this calculation is greater than total amount of Class 1 bandwidth which is allowed to be allocated on the ring (ALLOC), the token management logic 24 notifies the transmit priority logic 32 and the unaltered bandwldth allocation token is immediately transmitted out on the ring through the output control logic 38. As previously discussed, the latter situation can occur -~nder the anomaly when two loops are joined together. If the result of this calculation is less than or equal to the total allocatable Class 1 bandwidth, the bandwidth allocation token is fo~warded out onto the loop with the new total in the ALLOCATED field.
If the frame coming out of the FIFO 22 is not a token (viz., it's a data frame or a frame fragment), the address recognition logic 28 will buffer the frame in the receive buffer Iogic 42 if the frame's destination address is equal to (one of) the address(es) of the station, or cause the frame to be aborted if the station was the source of the frame (SA = station address). Note that a station may recognize multiple addresses; viz.; its station address, a broadcast address and (in some network implementations) a generic address. If the station's address is neither the source nor the destination specified in the frame, the frame is transmitted through the station unimpeded.
The address recognition logic 28 uses timing signals from the frame synchronization logic 26 to supply signals from the address recognition logic 28: to the token management logic 24 indicating the result of recovery token address comparison; to the frame creation logic 36 for aborting frames, and to the receive bu~fer logic 42 ~or frame and acknowledgment reception.
I~ the frame's destination address is equal to the station's addresstes), the receive buffer logic 42 will attempt to store the frame. If the station was the source of the frame, the frame creation logic 36 inserts an abort sequence into the frame. The aboxt sequence in the preferred embodimen-t is a frame delimiter (not shown in FIG. 3). After modifying the frame to indicate an abort condition, the station retransmits the modified frame back onto the loop.
When comparing for destination addresses, the address recognition logic 28 will match both a unique station identifier as well as any broadcast addresses which the station has been conditioned to recognize. If the destination address of the frame matches the stationls unique identifier or broadcast address, the received buffer logic 42 causes an update of the status field of the frame that i5 being received based on internal buffer conditions and control signals the receive buffer logic 42 receives from the error detection logic 30 (which computes the CRC~. The receive buffer logic 42 accomplishes this status update by signaling the frame creation logic 36 to modify the end frame delimiter. In both the case of broadcast frames and non-broadcast frames, after updating the status the modified frame will be txansmitt.ed back onto the loop.
~hose skilled in the art will appreciate that it is possible to impleMent all protocol functions (except token recovery and bandwidth allocation) in 1 bit of delay from FIF0 22 output to encoder 40 input b~ performing functions ln parallel.
~ aving shown and described the preferred embodiment of the present invention, those skilled in the art will realize that various 3o omissions, substitutions and changes in forms and details may be made without departing from the spirit of the invention. It i5 the intention, therefore, for the invention to be limited only as indicated by ~he scope of the following claims.

Claims (190)

What is claimed is:

1. A method of allocating bandwidth in a loop communications network, said network including a loop-connected set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the loop, extracting data from the loop or injecting data into the loop, each of said stations having associated with it at least one identifier address, each of said stations being assigned a Class 1 priority, a Class 2 priority, or both of said Class 1 and Class 2 priorities, the right of each of said stations to source new information into the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. each of said Class 2 stations timing the rotation time of the write token to measure instantaneous load; and b. each of said Class 2 stations limiting the transmission of information onto the loop based on the observed write token rotation time.

2. The method in accordance with Claim 1 further including the step of allocating to the set of stations including all Class 1 stations a first portion of the bandwidth available on said loop.

3. The method in accordance with claim 2 further including the step of each Class 1 station requiring bandwidth reserving a portion of the first portion of bandwidth, wherein the sum of the reserved Class 1 bandwidth does not exceed the first portion of the bandwidth.

4. The method in accordance with claim 3 further including a step wherein each Class 1 station that has reserved bandwidth and subsequently determines that it does not require its reserved bandwidth may surrender a portion of its reserved bandwidth.

5. The method in accordance with claim 2 further including the step of allocating to the class of stations including all Class 2 stations a second portion of the bandwidth available on said loop.

6. The method in accordance with claim 5 wherein:
each Class 2 station upon the receipt of a write token measures the time duration since the previous receipt of a write token; and if the measured time duration is less than a predetermined time and that Class 2 station has queued information to transmit, the Class 2 station having received the write token will transmit said queued information onto the loop.

7. The method in accordance with claim 6 wherein that said Class 2 station having received the write token will transmit its said queued information onto the loop until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

8. The method in accordance with claim 6 or 7 further including the step of said Class 2 station transmitting a new write token onto the loop after transmitting said queued information.

9. The method in accordance with claim 5 wherein:
each Class 2 station upon the receipt of a write token measures the time duration since the previous receipt of a write token; and if the measured time duration is at least equal to a predetermined time, that Class 2 station will transmit a new write token onto the loop.

10. The method in accordance with claim 9 wherein:
if after transmission of information the measured time duration at the next write token reception is greater than the predetermined time, the Class 2 station will accumulate this lateness time;
on the next receipt of the write token by said Class 2 station, if the measured time duration is at least equal to said predetermined time, the difference in time will be added to the lateness time;
if the measured time duration is less than the predetermined time, the Class 2 station will subtract the difference from the lateness time; and if the accumulated lateness time is not greater than zero, the Class 2 station will then transmit any queued information.

11. The method in accordance with claim 1 further including the steps of:
each station measuring the time since that said station's last receipt of a write token; and if the measured time since that said station last received a write token exceeds a lost token time, that said station will initiate a write token recovery bidding process.

12. The method in accordance with claim 3 further including the steps of:
each Class 1 station checking whether the bandwidth reserved by Class 1 stations exceeds the first portion of the bandwidth; and if the Class 1 bandwidth reserved exceeds the first portion, each said Class 1 station will surrender a portion of its reserved bandwidth.

13. A station for use in a loop communications network, said network including a loop connected set of said stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the loop, extracting data from the loop or injecting data into the loop, each of said stations having associated with it at least one identifier address, the right of each of said stations to source new information into the network controlled by passing a write token from one of said stations to another, wherein the improvement in each of said stations comprises:
means for assigning each of said stations a Class 1 priority, a Class 2 priority, or both a Class 1 and 2 priority;
means in each Class 2 priority station for timing the rotation time of the write token for measuring instantaneous load on the loop; and means in each Class 2 priority station for limiting the transmission of information onto the loop in response to the observed write token rotation time.

14. The station in accordance with claim 13 wherein each of said Class 1 stations includes means for specifying a first portion of the bandwidth available on said loop, said first portion corresponding to the bandwidth allocated to the set of stations including all Class 1 stations.

15. The station in accordance with claim 14 wherein each Class 1 station further includes means for reserving a portion of the first portion of bandwidth, wherein the sum of reserved Class 1 bandwidth does not exceed the first portion of the bandwidth.

16. The station in accordance with claim 15 wherein each Class 1 station that has reserved bandwidth includes means for determining that it no longer requires its reserved bandwidth and means for surrendering a portion of its reserved bandwidth.

17. The station in accordance with claim 14 wherein each of said Class 2 stations includes means for specifying a second portion of the bandwidth available on said loop, said second portion corresponding to the pool of bandwidth allocated to the set of including all Class 2 stations.

18. The station in accordance with claim 17 wherein each Class 2 station includes:
means for measuring the time between the receipt of one of said write tokens and the previous receipt of one of said write tokens; and means, responsive to the measured time duration being less than a predetermined time and said Class 2 station having queued information to transmit, for the Class 2 station having received said write token to transmit said queued information onto said loop.

19. The station in accordance with claim 18 wherein each of said Class 2 stations further includes means, responsive to having received one of said write tokens, said means for transmitting its said queued information onto the loop until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

20. The station in accordance with claim 18 or 19 wherein each of said Class 2 stations includes means for transmitting a new write token onto the loop after transmitting said queued information.

21. The station in accordance with claim 17 wherein:
each of said Class 2 stations includes means, responsive to the receipt of a write token, for measuring the time duration since the previous receipt of a write token; and means, responsive to the measured time duration being at least equal to a predetermined time, for transmitting a new write token onto the loop.

22. The station in accordance with claim 21 wherein each of said Class 2 stations further includes:
means, responsive to the measured time duration being greater than the predetermined time at the next write token reception following transmission of information, said means for accumulating this lateness time;
means, responsive to the next receipt of one of said write tokens and a measured time duration at least equal to said predetermined time, for adding the difference in time to the lateness time;
means, responsive to the measured time duration being less than the predetermined time, said means for subtracting the difference from the lateness time; and means, responsive to the accumulated lateness time not being greater than zero, for transmitting any queued information.

23. The station in accordance with claim 13 further including:
means for measuring the time since that said station's last receipt of a write token; and means, responsive to the measured time since that said station last received a write token exceeding a lost token time, for initiating a write token recovery bidding process.

24. The station in accordance with claim 15 wherein each Class 1 station includes:
means for checking whether the bandwidth reserved by Class 1 stations exceed the first portion of the bandwidth; and means, responsive to the reserved Class 1 bandwidth exceeding the first portion, for surrendering a portion of its reserved bandwidth.

25. A method of allocating bandwidth in a communications network, said network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the network, extracting data from the network or injecting data into the network, each of said stations having associated with it at least one identifier address, each of said stations being of a Class 1 priority, a Class 2 priority, a Class 3 priority, or any combination of the three classes of priorities, each frame of data to be transmitted being associated with one of said three classes of priority, the right of each of said stations to source new data into the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. allocating to the set of stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said network;
b. allocating to the set of stations including all of said Class 2 priority stations a second portion (C2POOL) of the bandwidth available on said network, said second portion (C2 POOL) being less than or equal to the difference between the available bandwidth and the first portion (ALLOC) of the available bandwidth.

26. The method in accordance with claim 25 further including the step of reserving for each one of said Class 1 stations that desires to reserve bandwidth to itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said Class 1 stations does not exceed the first portion (ALLOC) of the bandwidth.

27. The method in accordance with claim 26 further including the steps of:
each of said Class 3 stations measuring the network's instantaneous load by timing the write token rotation from arrival to arrival;
if upon arrival of a write token at one of said Class 3 stations the write token rotation time exceeds a Class 3 threshold time (C3TIMER), said Class 3 station will retransmit the received write token back onto the network without transmitting any data, and if upon arrival of a write token at one of said Class 3 stations the write token rotation time is less than said Class 3 threshold time (C3TIMER) and if said Class 3 station has queued data to transmit, said Class 3 station will transmit said queued data onto the network as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER).

28. The method in accordance with claim 27 further including the step of:
if upon arrival of the write token at one of said Class 3 stations the write token rotation time is less than the Class 3 threshold time (C3TIMER) and if said Class 3 station has no queued data to transmit, said Class 3 station will transmit said received write token back onto the network.

29. The method in accordance with claim 25 further including the following steps:
each of said stations being assigned both Class 2 and Class 3 priority measuring the network's instantaneous load by timing the write token rotation from arrival to arrival, each of said stations assigned both Class 2 and Class 3 priority identified as a Class 2/3 station;
if upon arrival of the write token at one of said Class 2/3 stations the write token rotation time is less than a Class 3 threshold time (C3TIMER) and said Class 2/3 station has queued Class 3 data to transmit, said Class 2/3 station will transmit said queued Class 3 data onto the network as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER); and if upon arrival of the write token at one of said Class 2/3 stations the write token rotation time exceeds said Class 3 threshold time (C3TIMER) and the write token rotation time is less than a Class 2 threshold time (C2TIMER) and said Class 2/3 station has queued Class 2 data to transmit, said Class 2/3 station will transmit said queued Class 2 data onto the network as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

30. The method in accordance with claim 29 further including the additional step of:
if upon arrival of the write token at one of said Class 2/3 stations there is not any queued Class 3 data and if the write token rotation time is less than said Class 2 threshold time (C2TIMER) and if said Class 2/3 station has queued Class 2 data to transmit, said Class 2/3 station will transmit said queued Class 2 data onto the network as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

31. The method in accordance with claim 29 or 30 further including the additional step of:
after completing the transmission of all queued Class 3 data, if the time since the previous write token arrival is less than the Class 2 threshold time (C2TIMER) and said Class 2/3 station has queued Class 2 data to transmit, said Class 2/3 station will transmit said queued Class 2 data onto the network as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

32. The method in accordance with claim 26 further including the following steps:
each of said stations being assigned all three of said Classes of priority measuring the network's instantaneous load by timing the write token rotation from arrival to arrival, each of said stations being assigned all three priorities identified as a Class 1/2/3 station;
if upon arrival of the write token at one of said Class 1/2/3 priority stations the write token rotation time is less than a Class 3 threshold time (C3TIMER) and said Class 1/2/3 station has queued Class 3 data to transmit, said Class 1/2/3 station will transmit said queued Class 3 data onto the network as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER); and if upon arrival of the write token at one of said Class 1/2/3 priority stations if the write token rotation time exceeds said Class 3 threshold time (C3TIMER) and the write token rotation time is less than a Class 2 threshold time (C2TIMER) and said Class 1/2/3 station has queued Class 2 data to transmit, said Class 1/2/3 station will transmit said queued Class 2 data onto the network as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

33. The method in accordance with claim 32 further including the additional step of:
if upon arrival of the write token at one of said Class 1/2/3 stations there is not any queued Class 3 data and if the write token rotation time is less than said Class 2 threshold time (C2TIMER) and if said Class 1/2/3 station has queued Class 2 data to transmit, said Class 1/2/3 station will transmit said queued Class 2 data onto the network as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

34. The method in accordance with claim 32 or 33 further including the additional step of:
after completing the transmission of all queued Class 3 data, if the time since the previous write token arrival is less than the Class 2 threshold time (C2TIMER) and if said Class 1/2/3 station has queued Class 2 data to transmit, said Class 1/2/3 station will transmit said queued Class 2 data onto the network as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

35. The method in accordance with claim 33 further including the following additional steps after said Class 1/2/3 station completes any permitted transmission of said Class 2 and/or Class 3 queued data:
said Class 1/2/3 station testing whether it has reserved to itself a portion of the first portion of bandwidth (ALLOC); and if said Class 1/2/3 station has reserved bandwidth available, said Class 1/2/3 station will transmit any queued Class 1 data onto the network as long as it does not exhaust its Class 1 queued data ox exceed the portion of the Class 1 bandwidth (ALLOC) reserved for said Class 1/2/3 station.

36. The method in accordance with claim 35 further including the step of said Class 1/2/3 station retransmitting the write token onto the network after completing any allowed transmission of queuea Class 1 data.

37. The method in accordance with claim 35 further including the step of:
if said Class 1/2/3 station does not have any reserved bandwidth, said Class 1/2/3 station will retransmit said write token back onto the network.

38. The method in accordance with claim 25 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

39. The method in accordance with claim 25 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

40. A method of allocating bandwidth in a logical loop communications network, said network including a bus connected set of stations on a broadcast medium wherein a logical ordering of said stations is enforced by passing a write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order, each of said stations being capable of passing data through itself along the logical loop, extracting data from the logical loop or injecting data into the logical loop, each of said stations having associated with it at least one identifier address, each of said stations being of a Class 1 priority, a Class 2 priority, or both of said Class 1 and Class 2 priorities, said method comprising the steps of:
a. allocating to the set of stations being of said Class 1 priority a first portion (ALLOC) of the bandwidth available on said logical loop;

b. allocating to the set of stations being of said Class 2 priority a second portion (C2POOL) of the bandwidth available on said logical loop, said second portion (C2POOL) being less than or equal to the difference between the available bandwidth and the first portion (ALLOC) of the available bandwidth.

41. The method in accordance with claim 40 further including the step of reserving for each one of said stations being of said Class 1 priority that desires to reserve bandwidth to itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said stations being of said Class 1 priority does not exceed the first portion (ALLOC) of the bandwidth.

42. A method of allocating bandwidth in a loop communications network, said network including a loop-connected set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the loop, extracting data from the loop or injecting data into the loop, each of said stations having associated with it at least one identifier address, each of said stations being of a Class 1 priority, a Class 2 priority, or both of said Class 1 and Class 2 priorities, the right of each of said stations to source new data into the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:

a. allocating to the set of stations being of said Class 1 priority a first portion (ALLOC) of the bandwidth available on said loop;
b. allocating to the set of stations being of said Class 2 priority a second portion (C2POOL) of the bandwidth available on said loop, said second portion (C2POOL) being less than or equal to the difference between the available bandwidth and the first portion (ALLOC) of the available bandwidth.

43. The method in accordance with claim 42 further including the step of reserving for each one of said stations being of said Class 1 priority that desires to reserve bandwidth to itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said stations being of said Class 1 priority does not exceed the first portion (ALLOC) of the bandwidth.

44. A station for use in a communications network, said network including a set of said stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the network, extracting data from the network or injecting data into the network, each of said stations having associated with it at least one identifier address, the right of each of said stations to source new information into the network controlled by passing a write token from one of said stations to another, wherein the improvement in each of said stations comprises:

means for assigning each of said stations a Class 1 priority, a Class 2 priority, a Class 3 priority, or any two or all three of said latter mentioned priorities, each frame of data to be transmitted on said loop being associated with one of said three classes of priority;
means for timing the rotation time of the write token in order to measure instantaneous load on the network;
means for limiting the transmission of data associated with said Class 2 of priority onto the network in response to the observed write token rotation time; and means for limiting the transmission of data associated with said Class 3 of priority onto the network in response to the observed write token rotation time.

45. The station in accordance with claim 44 wherein said Class 3 limiting means includes:
Class 3 timer means for determining whether a first preset amount of time (C3TIMER) has elapsed since the last receipt of a write token; and Class 3 transmitting means, responsive to the receipt of the write token and to said first preset amount of time (C3TIMER) not having elapsed, said Class 3 transmitting means for transmitting any queued Class 3 data onto the network until the earlier of either all of said queued Class 3 data having been transmitted or the said first preset amount of time (C3TIMER) having elapsed.

46. The station in accordance with claim 45 wherein said Class 3 transmitting means includes Class 3 loading means, responsive to the receipt of the write token and said first preset amount of time (C3TIMER) not having elapsed, said Class 3 loading means for loading the residual value in said Class 3 timer means into a token holding timer and simultaneously resetting said Class 3 timer means to said first preset amount (C3TIMER).

47. The station in accordance with claim 46 wherein said Class 3 timer means and said token holding timer each include a timer which continuously decrements until it has decremented to zero.

48. The station in accordance with claim 43 wherein said Class 2 limiting means includes:
Class 2 timer means for determining whether a second preset amount of time (C2TIMER) has elapsed since the last receipt of a write token; and Class 2 transmitting means, responsive to said first preset amount of time (C3TIMER) having elapsed at the time a write token is received, said Class 2 transmitting means for transmitting any queued Class 2 data onto the network until either all of said queued Class 2 data has been transmitted or said second preset amount of time (C2TIMER) has elapsed.

49. The station in accordance with claim 48 wherein said Class 2 transmitting means further includes Class 2 loading means, responsive to said first preset amount of time (C3TIMER) having elapsed at the time the write token is received, said Class 2 loading means for loading the residual value in said Class 2 timer means into said token holding timer and simultaneously resetting said Class 2 timer means to said second preset amount (C2TIMER).

50. The station in accordance with claim 49 wherein said Class 2 timer means includes a timer which continuously decrements until it has decremented to zero.

51. The station in accordance with claim 48 wherein said Class 2 transmitting means further includes no-Class 3 means, responsive to there being no queued Class 3 data at the time the write token is received, said no-Class 3 means for transmitting any queued Class 2 data onto the network until the earlier of all of said queued Class 2 data having been transmitted or said second preset amount of time (C2TIMER) having elapsed.

52. The station in accordance with claim 51 wherein said Class 3 transmitting means further includes Class 3 reset means, responsive to there being no queued Class 3 data at the time the write token is received, said Class 3 reset means for resetting the Class 3 timer means to said first preset amount (C3TIMER).

53. The station in accordance with claim 51 wherein said Class 2 transmitting means further includes simultaneous reset means, responsive to the receipt of the write token and there being no queued Class 2 or Class 3 data to transmit, said simultaneous reset means for simultaneously resetting said Class 3 and Class 2 timer means to their first (C3TIMER) and second (C2TIMER) values, respectively.

54. The station in accordance with claim 51 wherein said Class 2 transmitting means further includes Class 3 transmitted means t responsive to the receipt of the write token and the completion of transmission of queued Class 3 data, said Class 3 transmitted means for transmitting any queued Class 2 data onto the network until the earlier of all of said queued Class 2 data having been transmitted or said second preset amount of time (C2TIMER) having elapsed.

55. The station in accordance with claim 49 further including reserved bandwidth means, responsive to the receipt of the write token and there either being no remaining queued Class 3 data to be transmitted or said first preset amount of time (C3TIMER) having elepased, and further responsive to there either being no remaining queued Class 2 data to be transmitted or said second preset amount of time (C2TIMER) having elapsed, said reserved bandwidth means for determining whether a portion of the bandwidth available on said network has been reserved to said station for the transmission of data associated with said Class 1 priority.

56. The station in accordance with claim 55 further including means, responsive to said reserve bandwidth means indicating that no bandwidth has been reserved for said station, said means for retransmitting the received write token back onto the network.

57. The station in accordance with claim 55 further including Class 1 transmitting means, responsive to said reserved bandwidth means indicating that bandwidth has been reserved for Class 1 data transmission by said station, said Class 1 transmitting means for transmitting any queued Class 1 data onto the network until the earlier of all of said queued Class 1 data having been transmitted or an amount of queued Class 1 data corresponding to the reserved bandwidth having been transmitted.

58. The station in accordance with claim 57 wherein said Class 1 transmitting means further includes Class 1 retransmit means, responsive to the earlier of completing the transmission of all queued Class 1 data or the transmission of an amount of queued Class 1 data corresponding to the bandwidth reserved for said station, said Class 1 retransmit means for retransmitting the write token back onto the network.

59. The station in accordance with claim 58 further including surrender means for reserving and surrendering for said station a portion of a block of the bandwidth available on said network which has been allocated to the set of all stations on said network for the transmission of Class 1 data.

60. The station in accordance with claim 44 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

61. The station in accordance with claim 44 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

62. In a communications network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself, extracting data from the network or injecting data into the network, each of said stations having associated with it at least one individual address, the right of each of said stations to source new information onto the network controlled by passing a write token from one of said stations to another, only one of said write tokens on the network under normal conditions, a method of generating said write token at initialization of said network or regenerating a lost write token, said method comprising the steps of:
each station measuring the time duration since the last receipt of said write token; and in response to a first one of said stations detecting that said measured time duration exceeds a preset amount of time, said first one of said stations will initiate a bidding cycle to recover the write token.

63. The method in accordance with claim 62 wherein said bidding cycle includes the following steps:
said first station generating a recovery token, said recovery token including a destination address, the destination address in the recovery token generated including the individual address associated with said first station;
said first station transmitting said generated recovery token onto the network.

64. The method in accordance with claim 63 further including the following additional steps:
each one of said stations receiving one of said recovery tokens comparing the destination address in that said received recovery token with the individual address associated with that said receiving station;
if the destination address in that said received recovery token is greater than the individual address associated with that said receiving station that said receiving station will transmit that said received recovery token back onto the network with the destination address unaltered; and if the destination address in that said received recovery token is less than the individual address associated with that said receiving station, that said receiving station will replace the destination address in that said recovery token with the individual address associated with that said receiving station and transmit the modified recovery token back onto the network.

65. The method in accordance with claim 63 further including the following additional steps:
each one of said stations receiving one of said recovery tokens comparing the destination address in that said received recovery token with the individual address associated with that said receiving station;
if the destination address in that said received recovery token is less than the individual address associated with that said receiving station, that said receiving station will transmit that said received recovery token back onto the network with the destination address unaltered; and if the destination address in that said received recovery token is greater than the individual address associated with that said receiving station, that said receiving station will replace the destination address in that said recovery token with the individual address associated with that said receiving station and transmit the modified recovery token back onto the network.

66. The method in accordance with claim 64 further including the following additional steps:
if the destination address in that said received recovery token is equal to the invidual address of that said receiving station, that said receiving station will generate a new write token and transmit the new write token onto the network.

67. The method in accordance with claim 66 further including the steps of:
assigning to each of said station on the network a Class 1 priority, a Class 2 priority, or both of said Class 1 and Class 2 priorities; and each of said Class 2 stations limiting the transmission of information onto the network based on the observed write token rotation time.

68. The method in accordance with claim 67 further including the steps of:
allocating to the set of stations including all Class 1 stations a first portion of the bandwidth available on said network; and each Class 1 station requiring bandwidth reserving a portion of the first portion of bandwidth, wherein the sum of the reserved Class 1 bandwidth does not exceed the first portion of the bandwidth.

69. The method in accordance with claim 62 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

70. The method in accordance with claim 62 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

71. A method of allocating bandwidth in a communications network, said network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the network, extracting data from the network or injecting data into the network, each of said stations having associated with it at least one identifier address, a number of said stations being of a Class 1 priority, the right of each of said stations to source new data into the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
allocating to the number of said stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said network;
and reserving for each one of said Class 1 stations that desires to reserve bandwidth for itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said Class 1 stations does not exceed the first portion (ALLOC) of the bandwidth.

72. The method in accordance with claim 71 wherein one of said Class 1 stations desiring to reserve an additional amount of the ALLOC bandwidth performs the following steps:
that one of said Class 1 stations captures the write token;
that one of said Class 1 stations generates a bandwidth allocation token, the generated bandwidth allocation token including first and second information fields specifying the identifier address of that one of said Class 1 stations and the amount of the ALLOC bandwidth currently reserved by that one of said Class 1 stations, respectively; and that one of said Class 1 stations transmits the generated bandwidth allocation token onto the network.

73. The method in accordance with claim 72 wherein each one of said Class 1 stations receiving one of said bandwidth allocation tokens:
compares the address in the first information field with its own identifier address:
if the two latter mentioned addresses are unequal, the receiving station modifies the second information field by adding to it the amount of the ALLOC
bandwidth currently reserved by the receiving station and then retransmits the modified bandwidth allocation token back onto the network.

74. The method in accordance with claim 73 wherein if the two latter mentioned addresses are equal, the receiving station:
compares the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station with the ALLOC bandwidth; and if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station is less than the ALLOC bandwidth, the receiving station will add the additional amount of the ALLOC
bandwidth sought to be reserved to the amount of ALLOC
bandwidth currently reserved for that receiving station.

75. The method in accordance with claim 74 wherein if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC
bandwidth sought to be reserved by said receiving station is greater than the ALLOC bandwidth, the receiving station will regenerate and transmit a new write token without reserving the additional amount of ALLOC bandwidth for itself.

76. The method in accordance with claim 74 wherein if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC
bandwidth sought to be reserved by said receiving station is greater than the ALLOC bandwidth, the receiving station will reserve additional ALLOC bandwidth for itself, the amount of additional ALLOC bandwidth reserved by the receiving station being limited to the difference between the ALLOC bandwidth and the amount of bandwidth specified in the second information field.

77. The method in accordance with claim 72 further including the step of each one of said Class 1 stations having a currently reserved amount of ALLOC bandwidth which is greater than it needs reducing the amount of its reserved ALLOC bandwidth to a lesser amount.

78. The method in accordance with claim 71 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

79, The method in accordance with claim 71 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

80. A method of allocating bandwidth in a communications network, said network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself, extracting data or injecting data, the right of each of said stations to source new information onto the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. each of said stations timing the rotation time of the write token to measure instantaneous load; and b. each of said stations limiting the transmission of information onto the network based on the observed write token rotation time.

81. The method in accordance with claim 80 wherein each station upon receipt of the write token measures the time duration since the previous receipt of the write token; and if the measured time duration is less than a predetermined time and that said station having received the write token has queued information to transmit, that said station having received the write token will transmit said queued information onto the network.

82. The method in accordance with claim 81 wherein that said station having received the write token will transmit its said queued information onto the network until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

83. The method in accordance with claim 82 further including the step of that said station having received the write token transmitting the write token onto the network after transmitting said queued information.

84. The method in accordance with claim 81 wherein if the measured time duration is at least equal to the predetermined time, that said station having received the write token will transmit the write token onto the network.

85. The method in accordance with claim 84 wherein:
if after transmission of information the measured time duration at the next write token reception by that said station is greater than the predetermined time, that said station having received the write token will accumulate the difference between the latter two times as a lateness time;
on the next receipt of the write token by that said station, if the measured time duration is at least equal to said predetermined time, the difference in time will be added to the lateness time;
if the measured time duration is less than the predetermined time, that said station will subtract the difference from the lateness time; and if the accumulated lateness time is not greater than zero, that said station will then transmit any queued information onto the network.

86. The method in accordance with claim 80 further including the steps of:
each station measuring the time since that said station's last receipt of the write token; and if the measured time since that said station last received the write token exceeds a lost token time, that said station will initiate a write token recovery bidding process.

87. The method in accordance with claim 80 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

88. The method in accordance with claim 80 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

89. A station for use in a communications network, said network including a set of said stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself, extracting data or injecting data, the right of each of said stations to source new information onto the network controlled by passing a write token from one of said stations to another, wherein the improvement in each of said stations comprises:
means in each station for timing the rotation time of the write token for measuring instantaneous load;
and means in each station for limiting the transmission of information in response to the observed write token rotation time.

90. The station in accordance with claim 89 wherein each station includes:
means for measuring the time between the receipt of said write token and the previous receipt of said write token; and means, responsive to the measured time duration being less than a predetermined time and said station having queued information to transmit, for the station having received said write token to transmit said queued information onto the network.

91. The station in accordance with claim 90 wherein each of said stations further includes means, responsive to having received said write token, said means for transmitting its said queued information onto the network until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

92. The station in accordance with claim 91 wherein each of said stations includes means for transmitting the write token after transmitting said queued information.

93. The station in accordance with claim 90 wherein each of said stations includes means, responsive to the measured time duration being at least equal to said predetermined time, for transmitting the write token onto the network.

94. The station in accordance with claim 93 wherein each of said stations further includes:
means, responsive to the measured time duration being greater than the predetermined time at the next write token reception following transmission of information, said means for accumulating the difference between the latter two times as a lateness time;
means, responsive to the next receipt of said write token and a measured time duration at least equal to said predetermined time, for adding the difference in time to the lateness time;
means, responsive to the measured time duration being less than the predetermined time, said means for subtracting the difference from the lateness time; and means, responsive to the accumulated lateness time not being greater than zero, for transmitting any queued information.

95. The station in accordance with claim 94 further including:
means for measuring the time since that said station's last receipt of the write token; and means, responsive to the measured time since that said station last received the write token exceeding a lost token time, for initiating a write token recovery bidding process.

96. The method in accordance with claim 89 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

97. The method in accordance with claim 89 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

98. A method of allocating bandwidth in a communications network, said network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the network, extracting data from the network or injecting data into the network, each of said stations being a Class 1 priority or a Class 2 priority, the right of each of said stations to source new information onto the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. each of said Class 2 stations timing the rotation time of the write token to measure instantaneous load; and b. each of said Class 2 stations limiting the transmission of information onto the network based on the observed write token rotation time.

99. The method in accordance with claim 98 further including the step of allocating to the set of stations including all Class 1 stations a first portion of the bandwidth available on said network.

100. The method in accordance with claim 99 further including the step of each Class 1 station requiring bandwidth reserving a portion of the first portion of bandwidth, wherein the sum of the reserved Class 1 bandwidth does not exceed the first portion of the bandwidth.

101. The method in accordance with claim 98 wherein:
each Class 2 station upon the receipt of the write token measures the time duration since the previous receipt of the write token; and if the measured time duration is less than a predetermined time and that said Class 2 station having received the write token has queued information to transmit, that said Class 2 station having received the write token will transmit said queued information onto the network.

102. The method in accordance with claim 101 wherein that said Class 2 station having received the write token will transmit its queued information onto the network until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

103. The method in accordance with claim 102 wherein:
if after transmission of information the measured time duration at the next write token reception by that said Class 2 station is greater than the predetermined time, that said Class 2 station having received the write token will accumulate the difference between the latter two times as a lateness time;
on the next receipt of the write token by that said Class 2 station, if the measured time duration is at least equal to said predetermined time, the difference in time will be added to the lateness time;
if the measured time duration is less than the predetermined time, that said Class 2 station will subtract the difference from the lateness time; and if the accumulated lateness time is not greater than zero, that said Class 2 station will then transmit any queued information.

104. The method in accordance with claim 98 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

105. The method in accordance with claim 98 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

106. A method of allocating bandwidth in a communications network, said network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself, extracting data or injecting data, the right of each of said stations to source new information onto the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. each of said stations timing the rotation time of the write token to measure instantaneous load; and b. each of said stations limiting the transmission of information onto the network based on the ob-served write token rotation time.

107. The method in accordance with claim 106 wherein each station upon receipt of the write token measures the time duration since the previous receipt of the write token; and if the measured time duration is less than a predetermined time and that said station having received the write token has queued information to transmit, that said station having received the write token will transmit said queued information onto the network.

108. The method in accordance with claim 107 wherein that said station having received the write token will transmit its said queued information onto the network until the earli-er of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

109. The method in accordance with claim 108 further including the step of that said station having received the write token transmitting the write token onto the network after transmitting said queued information.

110. The method in accordance with claim 107 wherein if the measured time duration is at least equal to the predeter-mined time, that said station having received the write token will transmit the write token onto the network.

111. The method in accordance with claim 110 wherein:
if after transmission of information the measured time duration at the next write token reception by that said station is greater than the predetermined time, that said station having received the write token will accumulate the difference between the latter two times as a lateness time;
on the next receipt of the write token by that said station, if the measured time duration is at least equal to said predetermined time, the difference in time will be added to the lateness time;
if the measured time duration is less than the predetermined time, that said station will subtract the dif-ference from the lateness time; and if the accumulated lateness time is not greater than zero, that said station will then transmit any queued infor-mation onto the network.

112. The method in accordance with claim 106 further including the steps of:
each station measuring the time since that said station's last receipt of a write token; and if the measured time since that said station last received a write token exceeds a lost token time, that said station will initiate a write token recovery bidding process.

113. The method in accordance with claim 106 wherein said network is a logical loop communications network, said set of station being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order pass-ing the write token to the first station in the order.

114. The method in accordance with claim 106 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

115. A station for use in a communications network, said network including a set of said stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself, extracting data or injecting data, the right of each of said stations to source new information onto the network control-led by passing a write token from one of said stations to another, wherein the improvement in each of said stations comprises:
means in each station for timing the rotation time of the write token for measuring instantaneous load; and means in each station for limiting the transmission of information in response to the observed write token ro-tation time.

116. The station in accordance with claim 115 wherein each station includes:
means for measuring the time between the receipt of said write token and the previous receipt of said write token; and means, responsive to the measured time duration being less than a predetermined time and said station having queued information to transmit, for the station having recei-ved said write token to transmit said queued information onto the network.

117. The station in accordance with claim 115 wherein each of said stations further includes means, responsive to having received said write token, said means for trans-mitting its said queued information onto the network until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the differ-ence between said predetermined time and said measured time duration.

118. The station in accordance with claim 117 wherein each of said stations includes means for transmitting the write token after transmitting said queued information.

119. The station in accordance with claim 118 wherein each of said stations includes means, responsive to the measured time duration being at least equal to said predeter-mined time, for transmitting the write token onto the network.

120. The station in accordance with claim 119 wherein each of said stations further includes:
means, responsive to the measured time duration being greater than the predetermined time at the next write token reception following transmission of information, said means for accumulating the difference between the latter two times as a lateness time;
means, responsive to the next receipt of said write token and a measured time duration at least equal to said predetermined time, for adding the difference in time to the lateness time;
means, responsive to the measured time duration being less than the predetermined time, said means for sub-tracting the difference from the lateness time; and means, responsive to the accumulated lateness time not being greater than zero, for transmitting any queued information.

121. The station in accordance with claim 120 further including:
means for measuring the time since that said station's last receipt of the write token; and means, responsive to the measured time since that said station last received the write token exceeding a lost token time, for initiating a write token recovery bidding process.

122. The method in accordance with claim 115 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

123. The method in accordance with claim 115 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirec-tionally from one of said stations to the next.

124. A method of allocating bandwidth in a communica-tions network, said network including a set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the network, extract-ing data from the network or injecting data into the network, each of said stations being a Class 1 priority or a Class 2 priority, the right of each of said stations to source new information onto the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. each of said Class 2 stations timing the rotation time of the write token to measure instantaneous load; and b. each of said Class 2 stations limiting the trans-mission of information onto the network based on the observed write token rotation time.

125. The method in accordance with claim 124 further including the step of allocating to the set of stations including all Class 1 stations a first portion of the band-width available on said network.

126. The method in accordance with claim 125 further including the step of each Class 1 station requiring band-width reserving a portion of the first portion of bandwidth, wherein the sum of the reserved Class 1 bandwidth does not exceed the first portion of the bandwidth.

127. The method in accordance with claim 124 wherein:
each Class 2 station upon the receipt of the write token measures the time duration since the previous receipt of the write token; and if the measured time duration is less than a pre-determined time and that said Class 2 station having received the write token has queued information to transmit, that said Class 2 station having received the write token will transmit said queued information onto the network.

128. The method in accordance with claim 127 wherein that said Class 2 station having received the write token will transmit its said queued information onto the network until the earlier of the transmission of all of its said queued information or the expiration of a time equal to the difference between said predetermined time and said measured time duration.

129. The method in accordance with claim 128 wherein:
if after transmission of information the measured time duration at the next write token reception by that said Class 2 station is greater than the predetermined time, that said Class 2 station having received the write token will accumulate the difference between the latter two times as a lateness time;
on the next receipt of the write token by that said Class 2 station, if the measured time duration is at least equal to said predetermined time, the difference in time will be added to the lateness time;
if the measured time duration is less than the pre-determined time, that said Class 2 station will subtract the difference from the lateness time; and if the accumulated lateness time is not greater than zero, that said Class 2 station will then transmit any queued information.

130. The method in accordance with claim 124 wherein said network is a logical loop communications network, said set of stations being bus connected on a broadcast medium, and wherein a logical ordering of said stations is enforced by passing the write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order.

131. The method in accordance with claim 124 wherein said network is a loop communications network, said set of stations being loop connected to provide data flow unidirectionally from one of said stations to the next.

132. A method of allocating bandwidth in a loop communi-tions network, said network including a loop-connected set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the loop, extracting data from the loop or injecting data into the loop, each of said stations having associated with it at least one identifier address, each of said stations being assigned a Class 1 prior-ity, a Class 2 priority, or both of said Class 1 and Class 2 priorities, the right of each of said stations to source new data into the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
allocating to the set of stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said loop; and reserving for each one of said Class 1 stations that desires to reserve bandwidth for itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said Class 1 stations does not exceed the first portion (ALLOC) of the band-width.

133. The method in accordance with claim 132 wherein one of said Class 1 stations desiring to reserve an additional amount of the ALLOC bandwidth performs the following steps:
that one of said Class 1 stations captures the write token;
that one of said Class 1 stations generates a band-width allocation token; and.
that one of said Class 1 stations transmits the generated bandwidth allocation token onto the loop.

134. The method in accordance with claim 133 wherein the generated bandwidth allocation token includes first and second information fields specifying the identifier address of that one of class 1 stations and the amount of the ALLOC

bandwidth currently reserved by that one of said Class 1 stations, respectively.

135. The method in accordance with claim 134 wherein each one of said Class 1 stations receiving one of said bandwidth allocation tokens:
compares the address in the first information field with its own identifier address;
if the two latter mentioned addresses are unequal, the receiving station modifies the second information field by adding to it the amount of the ALLOC bandwidth currently reserved by the receiving station and then retransmits the modified bandwidth allocation token back onto the loop.

136. The method in accordance with claim 135 wherein if the two latter mentioned addresses are equal, the receiving station:
compares the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station with the ALLOC bandwidth; and if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC
bandwidth sought to be reserved by said receiving station is less than the ALLOC bandwidth, the receiving station will add the additional amount of the ALLOC bandwidth sought to be reserved to the amount of ALLOC bandwidth currently reserved for that receiving station.

137. The method in accordance with claim 136 wherein if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station is greater than the ALLOC bandwidth, the receiving station will regenerate and trans-mit a new write token without reserving the additional amount of ALLOC bandwidth for itself.

138. The method in accordance with claim 136 wherein if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station is greater than the ALLOC bandwidth, the receiving station will reserve additional ALLOC bandwidth for itself, the amount of additional ALLOC band-width reserved by the received station being limited to the difference between the ALLOC bandwidth and the amount of band-width specified in the second information field.

139. The method in accordance with claim 136 further including the additional step of the receiving station regener-ating and transmitting a new write token.

140. The method in accordance with claim 138 further in-cluding the additional step of the receiving station generat-ing and transmitting a new write token.

141. The method in accordance with claim 133 further including the step of each one of said Class 1 stations having a currently reserved amount of ALLOC bandwidth which is greater than it needs reducing the amount of its reserved ALLOC bandwidth to a lesser amount.

142. The method in accordance with claim 136 wherein if the amount of bandwidth specified in the second information field is greater than the ALLOC bandwidth, the receiving station will reduce its currently reserved amount of ALLOC
bandwidth by the difference between the bandwidth specified in the second information field and ALLOC.

143. The method in accordance with claim 134 wherein each of said Class 1 stations receiving one of said band-width allocation tokens:
compares the address in the first information field with its own identifier address; and if the two latter mentioned addresses are unequal, the receiving station compares the amount of bandwidth speci-fied in the second information field with the ALLOC band-width.

144. The method in accordance with claim 143 wherein if the amount of bandwidth in the second information field is greater than the ALLOC bandwidth, the receiving station will reduce the amount of its currently reserved ALLOC bandwidth by:
the difference between the ALLOC bandwidth and the amount of ALLOC bandwidth currently reserved by the receiving station if the difference is less than or equal to the current amount of ALLOC bandwidth reserved by the receiving station, or the current amount of ALLOC bandwidth reserved by the receiving station if the difference is greater than the current amount of ALLOC bandwidth reserved by the receiving station.

145. The method in accordance with claim 144 further including the steps of:
the receiving station modifying the second informa-tion field by subtracting from it the amount of ALLOC band-width it has reduced its currently reserved amount of ALLOC
bandwidth by; and the receiving station retransmitting the modified allocation token back onto the loop.

146. The method in accordance with claim 132 wherein one of said Class 1 stations desiring to reserve an additional amount of the ALLOC bandwidth performs the following steps:
that one of said Class 1 stations captures the write token;
that one of said Class 1 stations generates a band-width allocation token, the generated bandwidth allocation token including first and second information fields specifying the identifier address of that one of said Class 1 stations and the amount of the ALLOC bandwidth currently reserved by that one of said Class 1 stations, respectively; and that one of said Class 1 stations transmits the generated bandwidth allocation token onto the loop.

147. The method in accordance with claim 146 wherein each one of said Class 1 stations receiving one of said bandwidth allocation tokens:
compares the address in the first information field with its own identifier address;
if the two latter mentioned addresses are unequal, the receiving station modifies the second information field by adding to it the amount of the ALLOC bandwidth currently reserved by the receiving station and then retransmits the modified bandwidth allocation token back onto the loop.

148. The method in accordance with claim 147 wherein if the two latter mentioned addresses are equal, the receiving station:
compares the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station with the ALLOC bandwidth; and if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station is less than the ALLOC bandwidth, the receiving station will add the additional amount of the ALLOC bandwidth sought to be reserved to the amount of ALLOC bandwidth currently reserved for that receiving station.

149. The method in accordance with claim 147 wherein if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station is greater than the ALLOC bandwidth, the receiving station will regenerate and transmit a new write token without reserving the additional amount of ALLOC bandwidth for itself.

150. The method in accordance with claim 148 wherein if the amount of bandwidth specified in the second information field plus the additional amount of the ALLOC bandwidth sought to be reserved by said receiving station is greater than the ALLOC bandwidth, the receiving station will reserve addition-al ALLOC bandwidth for itself, the amount of additional ALLOC
bandwidth reserved by the received station being limited to the difference between the ALLOC bandwidth and the amount of bandwidth specified in the second information field.

151. The method in accordance with claim 146 further including the step of each one of said Class 1 stations having a currently reserved amount of ALLOC bandwidth which is greater than it needs reducing the amount of its reserved ALLOC bandwidth to a lesser amount.

152. A method of allocating bandwidth in a loop com-munications network, said network including a loop-connected set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the loop, ex-tracting data from the loop or injecting data into the loop, each of said stations having associated with it at least one identifier address, a number of said set of stations being of a Class 1 priority, the right of each of said stations to source new data into the network controlled by passing a write token from one of said stations to another, said method com-prising the steps of:
allocating to the number of said stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said loop; and reserving for each one of said Class 1 stations that desired to reserve bandwidth for itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said Class 1 stations does not exceed the first portion (ALLOC) of the bandwidth.

153. A method of allocating bandwidth in a logical loop communications network said network including a bus connected set of stations on a broadcast medium wherein a logical order-ing of said stations is enforced by passing a write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order, each of said stations being cap-able of passing data through itself along the logical loop, extracting data from the loop or injecting data into the logical loop, each of said stations having associated with at least one identifier address, a number of said stations being of a Class 1 priority, said method comprising the steps of:
allocating to the number of said stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said logical loop; and reserving for each one of said Class 1 stations that desires to reserve bandwidth for itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth received by all of said Class 1 stations does not exceed the first portion (ALLOC) of the bandwidth.

154. The method in accordance with claim 153 wherein one of said Class 1 stations desiring to reserve an additional amount of the ALLOC bandwidth performs the following steps:
that one of said Class 1 stations captures the write token;
that one of said Class 1 stations generates a band-width allocation token, the generated bandwidth allocation token including first and second information fields speci-fying the identifier address of that one of said Class 1 stations and the amount of the ALLOC bandwidth currently reserved by that one of said Class 1 stations, respectively;
and that one of said Class 1 stations transmits the generated bandwidth allocation token onto the logical loop.

155. A method of allocating bandwidth in a loop communi-cations network, said network including a loop-connected set of stations providing data flow unidirectionally from one of said stations to the next, each of said stations being cap-able of passing data through itself along the loop, extract-ing data from the loop or injecting data into the loop, each of said stations having associated with it at least one identi-fier address, each of said stations being assigned a Class 1 priority, a Class 2 priority, a Class 3 priority, or any combination of the three classes of priorities, each frame of data to be transmitted on said loop being associated with one of said three classes of priority, the right of each of said stations to source new data into the network controlled by passing a write token from one of said stations to another, said method comprising the steps of:
a. allocating to the set of stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said loop;

b. allocating to the set of stations including all of said Class 2 priority stations a second portion (C2POOL) of the bandwidth available on said loop, said second portion (C2POOL) being less than or equal to the difference between the available bandwidth and the first portion (ALLOC) of the available bandwidth.

156. The method in accordance with claim 155 wherein:
each one of said Class 1 priority stations can ac-commodate data communications requiring a guaranteed band-width;
each one of said Class 2 priority stations can ac-commodate data communications requiring guaranteed minimum throughput, but no absolute guarantee of bandwidth; and each one of said class 3 priority stations can ac-commodate data communications where no minimum guaranteed throughput is required.

157. The method in accordance with claim 155 further in-cluding the step of reserving for each one of said Class 1 stations that desires to reserve bandwidth to itself a por-tion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation procedure, wherein the sum of the bandwidth reserved by all of said Class 1 stations does not exceed the first portion (ALLOC) of the band-width.

158. The method in accordance with claim 157 further including the steps of:
each of said class 3 stations measuring the network's instantaneous load by timing the write token rotation from arrival to arrival;
if upon arrival of the write token at one of said Class 3 stations the write token rotation time exceeds a Class 3 threshold time (C3TIMER), said Class 3 station will retransmit the received write token back onto the loop without transmitting any data; and if upon arrival of the write token at one of said Class 3 stations the write token rotation time is less than said Class 3 threshold time (C3TIMER) and if said Class 3 station has queued data to transmit, said Class 3 station will transmit said queued data onto the loop as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER).

159. The method in accordance with claim 158 further including the step of:
if upon arrival of the write token at one of said Class 3 stations the write token rotation time is less than the Class 3 threshold time (C3TIMER) and if said Class 3 station has no queued data to transmit, said Class 3 station will transmit said received write token back onto the loop.

160. The method in accordance with claim 155 further including the following steps:
each of said stations being assigned both Class 2 and Class 3 priority measuring the network's instantaneous load by timing the write token rotation from arrival to arrival, each of said stations assigned both Class 2 and Class 3 priority identified as a Class 2/3 station;
if upon arrival of the write token at one of said Class 2/3 stations the write token rotation time is less than a Class 3 threshold time (C3TIMER) and said Class 2/3 station has queued Class 3 data to transmit, said Class 2/3 station will transmit said queued Class 3 data onto the loop as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER); and if upon arrival of the write token at one of said Class 2/3 stations the write token rotation time exceeds said Class 3 threshold time (C3TIMER) and the write token ro-tation time is less than a Class 2 threshold time (C2TIMER) and said Class 2/3 station has queued Class 2 data to trans-mit, said Class 2/3 station will transmit said queued Class 2 data onto the loop as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

161. The method in accordance with claim 160 further including the additional step of:
if upon arrival of a write token at one of said Class 2/3 stations there is not any queued Class 3 data and if the write token rotation time is less than said Class 2 threshold time (C2TIMER) and if said Class 2/3 station has queued Class 2 data to transmit, said Class 2/3 station will transmit said queued Class 2 data onto the loop as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

162. The method in accordance with claim 160 or 161 fur-ther including the additional step of:
after completing the transmission of all queued Class 3 data, if the time since the previous write token arrival is less than the Class 2 threshold time (C2TIMER) and said Class 2/3 station has queued Class 2 data to transmit, said Class 2/3 station will transmit said queued Class 2 data onto the loop as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

163. The method in accordance with claim 157 further including the following steps:
each of said stations being assigned all three of said Classes of priority measuring the network's instantaneous load by timing the write token rotation from arrival to arrival, each of said stations being assigned all three prior-ities identified as a Class 1/2/3 station;
if upon arrival of the write token at one of said Class 1/2/3 priority stations the write token rotation time is less than a Class 3 threshold time (C3TIMER) and said Class 1/2/3 station has queued Class 3 data to transmit, said Class 1/2/3 station will transmit said queued Class 3 data onto the loop as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER);
and if upon arrival of the write token at one of said Class 1/2/3 priority stations if the write token rotation time exceeds said Class 3 threshold time (C3TIMER) and the write token rotation time is less than a Class 2 threshold time (C2TIMER) and said Class 1/2/3 station has queued Class 2 data to transmit, said Class 1/2/3 station will transmit said queued Class 2 data onto the loop as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

164. The method in accordance with claim 163 further in-cluding the additional step of:
if upon arrival of the write token at one of said Class 1/2/3 stations there is not any queued Class 3 data and if the write token rotation time is less than said Class 2 threshold time (C2TIMER) and if said Class 1/2/3 station has queued Class 2 data to transmit, said Class 1/2/3 station will transmit said queued Class 2 data onto the loop as long as the time since the previous write token arrival is less than said Class 2 threshold time (C2TIMER).

165. The method in accordance with claim 163 or 164 fur-ther including the additional step of:
after completing the transmission of all queued Class 3 data, if the time since the previous write token arrival is less than the Class 2 threshold time (C2TIMER) and if said Class 1/2/3 station has queued Class 2 data to transmit, said Class 1/2/3 station will transmit said queued Class 2 data onto the loop as long as the time since the previous write token arrival is less than said Class 2 thres-hold time (C2TIMER).

166. The method in accordance with claim 163 or 164 further including the following additional steps after said Class 1/2/3 station completes any permitted transmission of said Class 2 and/or Class 3 queued data:
said Class 1/2/3 station testing whether it has reserved to itself a portion of the first portion of band-width (ALLOC); and if said Class 1/2/3 station has reserved bandwidth available, said Class 1/2/3 station will transmit any queued Class 1 data onto the loop as long as it does not exhaust its Class 1 queued data or exceed the portion of the Class 1 bandwidth (ALLOC) reserved for said Class 1/2/3 station.

167. The method in accordance with claim 166 further including the step of said Class 1/2/3 station retransmitting the write token onto the loop after completing any allowed transmission of queued Class 1 data.

168. The method in accordance with claim 166 further in-cluding the step of:
if said Class 1/2/3 station does not have any re-served bandwidth, said Class 1/2/3 station will retransmit said write token back onto the loop.

169. The method in accordance with claim 161 or 163 wherein said Class 2 threshold time (C2TIMER) is dependent on the difference between the maximum average write token rotation time under 100% load (TTRT) and the time for transmission of a maximum length frame (MAXFRAME).

170. The method in accordance with claim 169 wherein the Class 3 threshold time (C3TIMER) is dependent on the differ-ence between a percentage of the TTRT and MAXFRAME.

171. The method in accordance with claim 170 wherein:
TTRT=ALLOC+C2POOL+LATEN+SYSADM
where LATEN is the amount of time it takes for the write token to go around the loop with zero load and SYSADM is dependent on any bandwidth required for system administration.

172. A station for use in a loop communications network, said network including a loop connected set of said stations providing data flow unidirectionally from one of said stations to the next, each of said stations being capable of passing data through itself along the loop, extracting data from the loop or injecting data into the loop, each of said stations having associated with it at least one identifier address, the right of each of said stations to source new information into the network controlled by passing a write token from one of said stations to another, wherein the improvement in each of said stations comprises:
means for assigning each of said stations a Class 1 priority, a Class 2 priority, a Class 3 priority, or any two or all three of said latter mentioned priorities, each frame of data to be transmitted on said loop being associated with one of said three classes of priority;
means for timing the rotation time of the write token in order to measure instantaneous load on the loop;
means for limiting the transmission of data associ-ated with said Class 2 of priority onto the loop in response to the observed write token rotation time; and means for limiting the transmission of data associ-ated with said Class 3 of priority onto the loop in response to the observed write token rotation time.

173. The station in accordance with claim 172 wherein said Class 3 limiting means includes:
Class 3 timer means for determining whether a first preset amount of time (C3TIMER) has elapsed since the last receipt of the write token; and Class 3 transmitting means, responsive to the re-ceipt of the write token and to said first preset amount of time (C3TIMER) not having elapsed, said Class 3 transmitting means for transmitting any queued Class 3 data onto the loop until the earlier of either all of said queued Class 3 data having been transmitted or the said first preset amount of time (C3TIMER) having elapsed.

174. The station in accordance with claim 173 wherein said Class 3 transmitting means includes Class 3 loading means, responsive to the receipt of the write token and said first preset amount of time (C3TIMER) not having elapsed, said Class 3 loading means for loading the residual value in said Class 3 timer means into a token holding timer and simul-taneously resetting said Class 3 timer means to said first preset amount (C3TIMER).

175. The station in accordance with claim 174 wherein said Class 3 timer means and said token holding timer each include a timer which continuously decrements until it has decremented to zero.

176. The station in accordance with claim 173 wherein said Class 2 limiting means includes:
Class 2 timer means for determining whether a second preset amount of time (C2TIMER) has elapsed since the last receipt of the write token; and Class 2 transmitting means, responsive to said first preset amount of time (C3TIMER) having elapsed at the time the write token is received, said Class 2 transmitting means for transmitting any queued Class 2 data onto the loop until either all of said queued Class 2 data has been trans-mitted or said second preset amount of time (C2TIMER) has elaps-ed.

177. The station in accordance with claim 176 wherein said Class 2 transmitting means further includes Class 2 loading means, responsive to said first preset amount of time (C3TIMER) having elapsed at the time the write token is received, said Class 2 loading means for loading the residual value in said Class 2 timer means into said token holding timer and simul-taneously resetting said Class 2 timer means to said second preset amount (C2TIMER).

178. The station in accordance with claim 177 wherein said Class 2 timer means includes a timer which continuously de-crements until it has decremented to zero.

179. The station in accordance with claim 176 wherein said Class 2 transmitting means further includes no-Class 3 means, responsive to there being no queued Class 3 data at the time the write token is received, said no-Class 3 means for trans-mitting any queued Class 2 data onto the loop until the earl-ier of all of said queued Class 2 data having been transmitted or said second preset amount of time (C2TIMER) having elapsed.

180. The station in accordance with claim 179 wherein said Class 3 transmitting means further includes Class 3 reset means, responsive to there being no queued Class 3 data at the time the write token is received, said Class 3 reset means for resetting the Class 3 timer means to said first preset amount (C3TIMER).

181. The station in accordance with claim 179 wherein said Class 2 transmitting means further includes simultaneous reset means, responsive to the receipt of the write token and there being no queued Class 2 or Class 3 data to trans-mit, said simultaneous reset means for simultaneously re-setting said Class 3 and Class 2 timer means to their first (C3TIMER) and second (C2TIMER) values, respectively.

182. The station in accordance with claim 179 wherein said Class 2 transmitting means further includes Class 3 transmitted means, responsive to the receipt of the write token and the completion of transmission of queued Class 3 data, said Class 3 transmitted means for transmitting any queued Class 2 data onto the loop until the earlier of all of said queued Class 2 data having been transmitted or said second preset amount of time (C2TIMER) having elapsed.

183. The station in accordance with claim 177 further including reserved bandwidth means, responsive to the receipt of the write token and there either being no remain-ing queued Class 3 data to be transmitted or said first pre-set amount of time (C3TIMER) having elapsed, and further responsive to there either being no remaining queued Class 2 data to be transmitted or said second preset amount of time (C2TIMER) having elapsed, said reserved bandwidth means for determining whether a portion of the bandwidth available on said loop has been reserved to said station for the trans-mission of data associated with said Class 1 priority.

184. The station in accordance with claim 183 further including means, responsive to said reserved bandwidth means indicating that no bandwidth has been reserved for said station, said means for retransmitting the received write token back onto the loop.

185. The station in accordance with claim 183 further including Class 1 transmitting means, responsive to said reserved bandwidth means indicating that bandwidth has been reserved for Class 1 data transmission by said station, said Class 1 transmitting means for transmitting any queued Class 1 data onto the loop until the earlier of all of said queued Class 1 data having been transmitted or an amount of queued Class 1 data corresponding to the reserved band-width having been transmitted.

186. The station in accordance with claim 185 wherein said Class 1 transmitting means further includes Class 1 retransmit means, responsive to the earlier of completing the transmission of all queued Class 1 data or the transmission of an amount of queued Class 1 data corresponding to the band-width reserved for said station, said Class 1 retransmit means for retransmitting the write token back onto the loop.

187. The station in accordance with claim 186 further including surrender means for reserving and surrendering for said station a portion of a block of the bandwidth available on said loop which has been allocated to the set of all stations on said loop for the transmission of Class 1 data.

188. A method of allocating bandwidth in a logical loop communications network, said network including a bus-oriented set of stations on a broadcast medium wherein a logical order-ing of said stations is enforced by passing a write token from one of said stations to another in a predictable order with the last station in the order passing the write token to the first station in the order, each of said stations being capable of passing data through itself along the logical loop, extracting data from the logical loop or injecting data into the logical loop, each of said stations having associated with it at least one identifier address, each of said stations being of a Class 1 priority, a Class 2 priority, a Class 3 priority, or any combination of the three classes of priori-ties, each frame of data to be transmitted on said logical loop being associated with one of said three classes of priority, said method comprising the steps of:
a. allocating to the set of stations including all of said Class 1 priority stations a first portion (ALLOC) of the bandwidth available on said logical loop;
b. allocating to the set of stations including all of said Class 2 priority stations a second portion (C2POOL) of the bandwidth available on said logical loop, said second portion (C2POOL) being less than or equal to the difference between the available bandwidth and the first portion (ALLOC) of the available bandwidth.

189. The method in accordance with claim 188 further in-cluding the step of reserving for each one of said Class 1 stations that desires to reserve bandwidth to itself a portion of the first portion (ALLOC) of bandwidth, the reservation of portions of the first portion (ALLOC) of bandwidth done in accordance with a bandwidth allocation pro-cedure, wherein the sum of the bandwidth reserved by all of said Class 1 stations does not exceed the first portion (ALLOC) of the bandwidth.

190. The method in accordance with claim 189 further including the steps of:
each of said Class 3 stations measuring the network's instantaneous load by timing the write token rotation from arrival to arrival;
if upon arrival of the write token at one of said Class 3 stations the write token rotation time exceeds a Class 3 threshold time (C3TIMER), said Class 3 station will retransmit the received write token back onto the logical loop without transmitting any data; and if upon arrival of the write token at one of said Class 3 stations the write token rotation time is less than said Class 3 threshold time (C3TIMER) and if said Class 3 station has queued data to transmit, said Class 3 station will transmit said queued data onto the logical loop as long as the time since the previous write token arrival is less than said Class 3 threshold time (C3TIMER).