WO1998038813A2

WO1998038813A2 - Apparatus and method for a multipoint dsl modem

Info

Publication number: WO1998038813A2
Application number: PCT/US1998/003863
Authority: WO
Inventors: Gordon Bremer; James S. Alexander; Joseph Q. Chapman; Robert E. Scott; Edward Thoenes
Original assignee: Paradyne Corporation
Priority date: 1997-02-26
Filing date: 1998-02-26
Publication date: 1998-09-03
Also published as: WO1998038813A3; EP0983691A2; JP2002513532A

Abstract

A data communications apparatus and method to allow a single central site modem (18) to handle numerous DSL multiple modems (51) connected to a single subscriber line (27). The data communications apparatus and method that are implemented via logic that performs selected program routine sequences. These sequences include the transmission of packets from multiple DSL modems (51) directly connected, at a premises, to a single subscriber line to simultaneously provide data sessions with a single DSL modem (18) at the central office (11).

Description

APPARATUS AND METHOD FOR A MULTIPOINT DSL

MODEM BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

The present invention generally relates to an apparatus and method that enables multiple modems, connected at a premise to a single subscriber line, to simultaneously communicate data with a single modem at the central office end of the subscriber line.

BACKGROUND OF RELATED ART

Data communication on a subscriber line is typically referred to as DSL (digital subscriber line) communication. Examples of DSL technologies are ADSL, RADSL, HDSL, basic rate ISDN, etc. All DSL communication in the prior art is point-to-point, in that there is a single operating DSL modem at each end of the subscriber line with no provision for multiple operating DSL modems at either end. The physical layer transmissions are continuous and are decoupled from and independent of the higher layers.

Some leased line voiceband modems in the prior art provide for a single central site modem which communicates with multiple remote modems: a concept referred to as "four-wire multipoint communications." An example of such a modem is one that complies with the industry standard ITU V.27bis. The communication channel to each remote modem is a four-wire connection and the modems are typically widely geographically dispersed.

Similarly, some dial line voiceband modems in the prior art provide for a single central site modem which communicates with a multiple remote modems, which is a concept referred to as "two-wire PSTN communications." The communication channel to each remote modem is a two-wire PSTN connection and the modems are typically widely geographically dispersed. The physical layer is half duplex, and the data protocol is half duplex.

Importantly, in both prior art voiceband modem cases above, the central modem and the remote modems are never at both ends of a single subscriber loop, and the communication channel includes four-wire backbone circuits.

In the dial line prior art case, central modem transmission is controlled by an attached central site computer which uses non-data control signals such as those prescribed in industry standard ITU V.24 CT105 to control the start and end of transmissions; and the remote transmission is controlled by an attached remote computer which also uses non-data control signals such as those described in industry standard ITU V.24 CT105 to control the start and end of transmissions. In the leased line prior art cases, the central site transmission is continuous and the remote transmission is controlled as in the dial line case. In both these cases, the attached computers must ensure that transmissions do not overlap by monitoring the ends of received signals, for example via ^'% ITU V.24 CT109, and delaying CT105 accordingly.

Note especially above that the prior art voiceband modem communications for multiple remote users is not on the subscriber line and involves transmission controls from attached multiple computers via non-data interfaces.

Another prior art technology is Ethernet local area network communication wherein the physical channel can be a short two-wire channel, never a subscriber line. Here, transmissions are derived directly from the upper layer data protocol, but there is no central control, and therefore, the signals may collide. A special upper layer protocol must manage the detrimental effects of collisions.

Another aspect in the prior art is that the Point to Point Protocol (PPP) defined in Internet Engineering Task Force (IETF) specification Request for Comment(RFC) 1661 is defined to operate as follows: "The Point-to-Point Protocol is designed for simple links which transport packets between two peers. These links provide full-duplex simultaneous bi-directional operation." Up to this time, the Point-to-Point Protocol has not been used in connection with links.

Heretofore, modems have lacked the ability to couple multiple modems, connected at one or more premises to a single subscriber line, to simultaneously communicate data with a single modem at the central office end of the subscriber line. SUMMARY OF THE INVENTION ₃

Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentality's and combinations particularly pointed out in the appended claims.

To achieve the advantages and novel features, the present invention is generally directed to a data communications apparatus and method that are implemented via logic that performs selected program routine sequences. These sequences include the transmission of packets from multiple DSL modems directly connected, at a premises, to a single subscriber line to simultaneously provide data sessions with a single DSL modem at the central office end of the subscriber line.

In accordance with another aspect of the preferred embodiment, the apparatus and method create the appearance to each premises DSL modem user that each DSL modem has an independent communication channel such that the data rate for each user may be equal to the capacity of the subscriber line itself at moments when no other user communication is in progress and that the subscriber line data rate capacity is shared between any number of users at moments when such users require simultaneous communications. In another alternate embodiment, the apparatus and method ^ provide for control of all communications on the subscriber line by the central office DSL modem in such a way that the subscriber line data rate capacity is optimally utilized at all moments, that collisions between all DSL modems are avoided, and that the data throughput between each user and the central office DSL modem can be selected to offer service priorities.

In accordance with another aspect of the preferred embodiment, the apparatus and method provide for direct control of all DSL modem subscriber line signals from the sensing of data transmission needs of the higher layer data protocols. The transmissions directives are thus derived from higher layer protocols without need for non-data interfaces.

In accordance with another aspect of the preferred embodiment, the apparatus and method provides utilization of point-to-point full duplex data protocols, for example but not limited to, the PPP.

In accordance with another aspect of the preferred embodiment, the apparatus and method provides data transmission in the multi-point environment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a view of the central office (CO) wire centers and user premises layout of the prior art.

FIG. 2 is a block diagram of the CO wire center and user premises DSL modem connections of FIG. 1.

FIG. 3 is a view of the CO wire centers and user premises layout of the present invention.

FIG. 4 is a block diagram of the CO wire center and user premises DSL modem connections of FIG. 3.

FIG. 5 is a block diagram of the OSI layers of the present invention.

FIG. 6A is a block diagram of the transmission convergence and physical media dependent functions of the CO wire center DSL modem of the present invention.

FIG. 6B is a block diagram of the transmission convergence and physical media dependent layers of the user premises DSL modem of the present invention.

FIG. 7A is a block diagram of the multipoint DSL poll or response frame with data.

FIG. 7B is a block diagram of the multipoint DSL poll or response frame without data.

FIGS. 8A to 8D are graphs showing the modes of poll and response modulations that are placed on the local loop by the DSP logic in FIGS. 6A and 6B; more particularly: FIG. 8A is a schematic diagram showing a poll with no central site - user data, followed by a response with no premises user data;

FIG. 8B is a schematic diagram showing a poll with central site user data, followed by a response with no premises user data;

FIG. 8C is a schematic diagram showing a poll with no central site user data, followed by a response with premises user data;

FIG. 8D is a schematic diagram showing a poll with central site user data, followed by a response with premises user data.

FIG 9 is a graph showing the frequency spectrum of the DSL modem and the POTS channel.

FIG 10 is a graph showing the frequency spectrum of the DSL modem when POTS devices are all "on-hook".

Reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims. Note specifically that the figures imply central office data is sent to multiple DSL modems at one premise, but this invention also applies to a DSL modem that can support multiple users at multiple premises. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Having summarized the invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims.

FIG. 1 illustrates the plain old telephone system (POTS) network with data communication digital subscriber line (DSL) modems 16 and 45 of the prior art. The POTS network includes user premises 41 connected to a central office wire center 11, via a subscriber line 27. Each subscriber line 27 is connected to the user premises 41, which further connects to a user premises line 47, for distribution of POTS service and DSL service throughout the user premises. There is only one DSL modem connected to each premises line 47. Usually, there are numerous POTS devices connected to each user premises line 47, such as telephones 44, facsimile (fax) machines 42, and the like.

It is noted that POTS splitters can be utilized at the premises, when required, to separate the POTS lower frequency band between about 0 kHz and about 4 kHz, from the DSL signals at a higher frequency level than the POTS frequency band. In applications where the premises POTS splitter is required, the splitter would be on the incoming line 27, with the modem 45 coming off one splitter line and the two phones 44 and fax 42 off the other.

As noted previously, each user premises is connected via a subscriber line 27 to a central office wire center 11. The subscriber line 27 is connected to a POTS splitter device 15 that separates the analog POTS signals from data signals. The POTS signals are sent to a POTS switch 14 that is connected to the other central office wire centers, via the public switched telephone network (PSTN) 28. DSL modem data signals are separated from the POTS analog signals at POTS splitter 15, and are connected to DSL modems 16 within the central office wire center 11. DSL modems 16 are further connected to digital data networks such as the Internet 29 through a remote access server (RAS) 17.

A brief discussion of an example for the signals generated in the applied system environment for the prior art from the user premises and transmitted through the central office wire center, via either the PSTN or Internet networks and back to a user premises will now be detailed.

When a user wishes to place a telephone call on device 44, the user picks up the telephone and puts the subscriber line 27 in an off-hook condition that is detected at the central office wire center 11, by closed switch hooks (not shown). The off- hook condition signals the central office wire center 11, via subscriber line 27, to accept an outgoing call by allowing a flow of D.C. current and a dial tone of 480 Hz to be sent to device 44. The outgoing telephone call signals are transmitted, as described before, via subscriber line 27 to POTS splitter 15. The analog POTS system signals are separated from the DSL modem signals, and the POTS signals are directed towards the POTS switch 14 for transmission, via the PSTN network 28, to another telephone.

Now, a description of digital signals to/from the user premises will be described. When a user desires to transmit data over a digital network via his personal PC 46 or the like, the digital signals from the digital device are transformed into analog signals, via modulation by DSL modem 45. The signals are transmitted over the user premises line 47 to the subscriber line 27 for final delivery to the local central office wire center 11. The digitally modulated analog signals going into POTS splitter 15, are separated from the analog POTS signals, and are directed to DSL modems 16. DSL modems 16 demodulate the analog signals back to their original digital data signals. The DSL modems 16 transmit the digital data over the Internet 29 via the RAS 17. The digital data signals sent via the Internet 29 are typically received by a website server 48, which returns information to the user.

As discussed above in the prior art, it is necessary to have multiple subscriber lines 27 connected to a user premises to be able to have multiple DSL modems 45 at the same premises simultaneously communicating data with the central office.

FIG. 2 illustrates the CO wire center and user premises DSL modem connections used in the prior art which includes multiple subscriber lines 27 connected to an user premises to be able to have multiple DSL modems 45 simultaneously communicating data with the central office 11.

Also illustrated in FIG. 2 is the type of communication traffic occurring. In the CO wire center 11, communication between remote access server (RAS) 17 and each individual DSL modem 16 occurs with multiple full duplex Point to Point Protocol (PPP) sessions over interface lines 31. The input and output from each DSL modem 16 on subscriber lines 27 to DSL modems 45 occurs using multiple full duplex PPP sessions. Furthermore, communication between DSL modems 45 and digital devices 46 occurs utilizing multiple full duplex PPP sessions over interface lines 32.

FIG. 3 illustrates the CO wire centers and user premises layout of the present invention, that enables multiple DSL modems 51, connected at a premises 41 to a single subscriber line 27, to simultaneously communicate data with a single DSL modem 18 at the central office 11 end of the subscriber line 27.

FIG. 4 illustrates the CO wire center and user premises DSL modem connections used in the present invention. The present invention enables multiple DSL modems 51 connected to multiple digital devices 46 connected at a premises 41 to a single subscriber line 27, to simultaneously communicate data with a single DSL modem 18 at the central office 11 end of the subscriber line 27.

As also illustrated in FIG. 4, the communication between RAS 17 and the single DSL modem 18 occurs utilizing multiple full duplex PPP sessions over interface lines 31. Communication between the single central site DSL modem 18 and the multiple DSL modems 51 at the user premises across the single subscriber line 27 occurs utilizing multiple half duplex PPP sessions. These half-duplex sessions utilize point-to-point full duplex data protocols, for example but not limited to the Point to Point Protocol (PPP) defined in Internet Engineering Task Force (IETF) specification Request for Comment(RFC) 1661. The communications between the user premises DSL modem 51 and the user premises digital device 46 occurs utilizing multiple full duplex PPP sessions over interface lines 32.

Illustrated in FIG. 5 is the OSI 7-layer model, including discussion of the physical and data link layers with regard to the present invention. As shown in FIG. 5, the Physical Layer 61 contains two distinct sublayers, the Transmission Convergence (TC) Sublayer 67 and the Physical Media Dependent (PMD) Sublayer 66. The PMD 66 deals with the aspects that are dependent on the transmission medium selected, i.e., the subscriber line.

The PMD 66 specifies the physical medium in the transmission characteristics (e.g., bit timing, line coding) and does not include framing or overhead information.

The TC layer 67 deals with the physical layer aspects which are independent of the transmission medium characteristics. Most of the functions comprising the TC layer 67 are involved with the generation and processing of some overhead information contained within the frame. The Data Link Layer 62 uses PPP 68. The invention described herein specifies techniques that enable PPP to operate half-duplex over the subscriber line 27. One central site DSL modem 18 can service multiple subscriber DSL modems 51, with each subscriber DSL modem 51 appearing to receive a unique PPP session.

FIG. 6A is a block diagram of a CO wire center multichannel data communications device DSL modem 18 constructed in accordance with the present invention. The typical configuration of the central wire office 11 multichannel data communication device 18 is connected via a POTS splitter 15 (FIG. 3) to the subscriber lines 27. In FIG 6A, multiple full duplex PPP sessions are transported over interface lines 31 to the Full Duplex Buffers 75. The full duplex buffers 75 include circuitry to convert serial data streams in to parallel data. Each full duplex PPP session is carried over a separate interface line 31. Upon detection of a PPP frame in any of the full duplex buffers 75, the control processor/digital mux 74 will encapsulate this PPP frame as described below in FIG 7A and send it to the modulator/demodulator 71 via line 78. The modulator/demodulator 71 will transmit this frame onto the subscriber line 27 to far end subscriber DSL modem 51.

FIG 7A illustrates the method that the central-site DSL modem 18 uses to address the various subscriber DSL modems 51. The control processor/ digital mux 74 (FIG. 6A) creates a multipoint DSL frame 91 by encapsulating the PPP frame 92 within a TC layer circuitry 66. This TC layer circuitry 66 (FIG 6A) includes digital mux 74 circuitry to generate an address header 93 and a frame check sequence (FCS) 95. The digital ^" mux 74 circuitry looks to the source line 31 and determines the appropriate address header 93 for the destination device. The address header 93 allows one of the plurality of endpoints to know which multipoint DSL frame 91 is meant for it. The FCS 95 octets assures that the entire multipoint DSL frame 91 is correct.

The apparatus and method to generate the address header 93 and the frame check sequence 95 are described in commonly assigned and co- pending U.S. Patent Application (Attorney Docket 61606-1431) entitled "SYSTEM AND METHOD FOR DYNAMIC ALLOCATION OF LINK LAYER ADDRESSES IN A MULTI-POINT PROTOCOL INCLUDING VARIABLE BACK OFF TIMING", Serial Number xx/xxxxxx filed on, xxxx.xx, 1997, herein incorporated by reference. The TC layer in the present invention is also known as the data link line layer of the above- incorporated U.S. Patent Application.

FIG 7B shows the case where either the central-site DSL modem 18 or remote DSL modem 51 has no data to send. The address header 93 and FCS 95 are still included, but no PPP information is sent. No data multipoint DSL frame 96 is used for cases where the subscriber DSL modem 51 has no PPP data to send in a response. It can also be used by central office DSL modem 18 to poll a subscriber DSL modem 51 for PPP information, even though central office DSL modem 18 has no PPP frames to send. FIG. 6B is a block diagram of the premises DSL modem 51 constructed in accordance with the present invention. DSL modem 51 will demodulate the signal transmitted by DSL modem 18 over subscriber line 27 using modulator/demodulator 81. The demodulated data is sent to control processor 84 via line 88. Control processor 84 will check for errors via FCS 95. If no errors exist, then control processor 84 will determine if this poll is meant for it via Address Header 93. If the address header 93 indicates this DSL modem, it will check for a PPP frame 92. If this PPP frame 92 exists, it will be placed into full duplex buffer 85 via line 86. The full duplex buffer 85 will transfer this PPP frame to PC 46 via line 32.

Since the PPP session on line 32 operates in full duplex mode, the PC 46 can at any time transfer a PPP frame into full duplex buffer 85 via line 32. After receiving a poll on subscriber line 27, subscriber DSL modem 51 knows that it is its turn to transfer information. If a PPP frame exist in the full duplex buffer 85, the PPP frame is encapsulated into a multipoint DSL frame 91 by control processor 84, sent to modulator/demodulator 81 for modulation onto the subscriber line 27. If no PPP frames are available to send, the control processor 84 will send a signal indicative of no data multipoint DSL frame 96 to modulator/demodulator 81. Modulator/demodulator 81 will transfer this response to subscriber line 27.

Illustrated in FIGS. 8A through 8D are the polling algorithms that allow modulator/demodulator logic 71 and 81 to simultaneously support multiple premises DSL modems. The modulation used in the preferred embodiment of this invention is referred to herein as "time division duplexing" (TDD), whereby the transmission on a single local loop can only occur in one direction at a time. The specific version of TDD is a poll/response modulation, whereby the central-site DSL modem controls which of the premises DSL modems on the subscriber line is allowed to transmit. A "poll" is a transmission from the central-site DSL modem 18, while a "response" is a transmission from a user premise DSL modem 51. To avoid simultaneous transmissions on the line, a poll will always occur followed by a response. For cases in which a response has no data, "silence" is a legitimate response. The central-site DSL modem 18 will recognize this as a response with no data. In the simple case, two DSL modems exist on the line 27 the central-site DSL modem 18 and the user premise DSL modem 51. However, those skilled in the art will recognize that poll/response modulation can allow multiple user premise DSL modems to exist on the same local loop.

The start of a poll or a response is indicated by the PMD layer 66 (FIG. 5) turning on the carrier. The end of a poll or a response is indicated by the PMD layer 66 (FIG. 5) turning off the carrier. As shown in FIGs. 7A and 7B, the multipoint DSL frames 91 and 96 do not need flag delimiters, as are normally found in PPP frames. Instead, the turning on and off of the carrier indicates the start and the stop respectively of a PPP frame. The method used to accomplish the PMD layer as described in commonly assigned U.S. Patent No. 4,669,090, issued May 26, 1987, entitled "Half- Duplex Modem Without Turnaround Delay", herein incorporated by reference, and U.S. Patent No. 4,744,092, issued May 10, 1988, entitled "Transparent Error Detection In Half Duplex Modems", herein incorporated by reference.

The method used to accomplish the PMD layer is also described in commonly assigned and co-pending U.S. Patent Application entitled "Circular Constellations For Uncoded Modulation", Serial Number 08/915,980 filed on August 21, 1997, herein incorporated by reference, and U.S. Patent Application entitled "System And Method For Transmitting Special Marker Symbols", Serial Number 08/ 979,455 filed on November 26, 1997, herein incorporated by reference.

FIGS. 8A through 8D graphically show four respective modes for the poll/response cycle: FIG. 8A shows a poll with no user data step 111, followed by a response with no user data step 112. FIG. 8B shows a poll with user data at step 113, followed by a response with no user data at step 114. FIG. 8C shows a poll with no user data at step 115, followed by a response with user data at step 116. FIG. 8D shows a poll with user data at step 117, followed by a response with user data at step 118.

FIG. 9 is a diagram illustrating frequency band communications. The term frequency band communications is used here to indicate communication of information within a certain defined, frequency band. As is known in the prior art, POTS communications are transmitted in the frequency band 121 defined between about 0 Hz (DC) and about 4 kHz. A second transmission frequency band 122 is defined at a higher frequency level than the POTS frequency band 121, and is used in the transmission of digital subscriber line (DSL) communications. A guard band 123 is required to separate the two transmission frequency bands 121 and 122. The DSL transmission frequency band 122 is more broadly denominated as "xDSL", wherein the "x" generically denominates any of a number of transmission techniques within the DSL family. For example, ADSL - asymmetric digital subscriber line, RADSL - rate adaptive digital subscriber line, HDSL - high-bit-rate DSL, etc. As is known, xDSL transmission frequency bands may encompass a bandwidth of greater than about 1 MHz. As a result, and for the reasons described above, without the addition of extra equipment, such as POTS filters, splitters, etc. The xDSL signals are not compatible with attached POTS type equipment, such as telephones, PSTN modems, facsimile machines, etc.

As will be discussed in more detail below, an alternative embodiment of the present invention provides an upper transmission band having an upper frequency boundary that is much lower than the 1 MHz frequency boundary often encountered in xDSL transmissions., the upper frequency boundary of the present Indeed invention is defined in a range that is readily supported by, or compatible with, transmission systems (and attached POTS-type equipment) presently in place between a customer premises and a central office, without the need for extraneous devices such as POTS filters and POTS splitters.

In accordance with one aspect of the invention, a multichannel data communication device, DSL modem 51, is provided for achieving efficient data communications between a customer premises 41 and a central office 11 across a local loop 27, by dynamically allocating a transmission frequency bandwidth for transmitting data. Certainly, one of the factors motivating the development of the present invention is the expanded demand for higher speed communications in recent years. This enhanced demand is primarily attributed to communications over the Internet.

The present invention may utilize dynamic allocation of the data transmission frequency band in response to POTS communications activity across the same line as described in commonly assigned and co- pending U.S. Patent Application (Attorney Docket 61605-620) entitled, "Digital Subscriber Loop Data Communications Method Enabling Simultaneous Data And POTS Without POTS Filters/Splitters Or Special Premise Wiring", Serial Number 08/962,796 filed on November 3, 1997, herein incorporated by reference.

More particularly, the present invention may utilize the frequency band otherwise allocated for POTS/voice transmission, at times when there is no present demand for transmitting voice information as illustrated in FIG. 10. When, however, there is a demand for voice transmissions, then the present invention reallocates the transmission frequency band for the data communications so that there is no overlap or interference with the POTS transmission frequency band 124, and so that there is not significant interference to POTS-type attached equipment.

The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.

Claims

CLAIMSWhat is claimed is:

1. A data communications apparatus for multipoint operation comprising interface circuitry connectable to a subscriber line.

2. The apparatus of claim 1, wherein said data communications apparatus further comprises control logic; and buffer memory, wherein said buffer memory and said control logic emulate a full duplex point-to-point protocol connection on an interface while operating in half-duplex point-to-point protocol mode over said subscriber line.

3. The apparatus of claim 1, wherein said interface circuitry provides a physical layer carrier to start a half duplex point-to-point protocol frame, and wherein said interface circuitry terminates said physical layer carrier to end said point-to-point protocol frame.

4. The apparatus of claim 1, wherein said data communications apparatus further provides simultaneous communications sessions between two or more points on a subscriber line.

5. The apparatus of claim 1, wherein said subscriber line is inclusive of premises wiring.

6. The apparatus of claim 1, wherein said subscriber line further comprises a premises wiring, and wherein said apparatus is located at a premises and is plugged into telephone jacks.

7. The apparatus of claim 1, wherein a data rate between two points is substantially equal to the data rate capacity of the subscriber line when no other communication is in progress.

8. The apparatus of claim 1, wherein the data rate capacity of the subscriber line is shared between communicating pairs of points at times when more than one pair are communicating.

9. The apparatus of claim 1, wherein line signals are controlled such that multiple transmitted signals do no appear on the subscriber line at the same time.

10. The apparatus of claim 1, wherein line signals are controlled such that communications between a first pair of points has priority over communications between other pairs of points.

11. The apparatus of claim 1, wherein multipoint operation is provided without use of a non-data control interface to control line signals.

12. The apparatus of claim 1, wherein the data comprises digitized analog signals.

13. The apparatus of claim 1, further comprising:

a POTS splitter at one or more points of the subscriber line.

14. A data communications apparatus for multipoint operation comprising:

interface circuitry connectable to a subscriber line; and a modulation circuitry to modulate and demodulate a half duplex signal over said subscriber line using a full duplex protocol at a link layer to carry higher layer protocols and information.

15. A data communications apparatus for multipoint operation comprising: interface circuitry connectable to a subscriber line; and modulation circuitry to modulate and demodulate a signal over said subscriber line using a point-to-point protocol at a link layer to carry higher layer protocols and information.

16. A data communications apparatus for multipoint operation comprising: interface circuitry connectable to a subscriber line; and modulation circuitry to modulate and demodulate a half duplex signal over said subscriber line using a point-to-point protocol at a link layer to carry higher layer protocols and information.

17. A method for use in a data communications apparatus capable of multipoint operation, the method comprising the steps of: providing an interface to a subscriber line; and modulating and demodulating a half duplex signal over said subscriber line using a full duplex protocol at a link layer to carry higher layer protocols and information.

18. The method of claim 17, further comprising the step of: emulating a full duplex point-to-point protocol connection on said interface while operating in half-duplex point-to-point protocol mode over said subscriber line.

19. The method of claim 17, further comprising the steps of: providing a physical layer carrier to start a half duplex point-to-point protocol frame; and terminating said physical layer carrier to end said point-to-point protocol frame.

20. The method of claim 17, further comprising the step of: providing simultaneous communications sessions between two or more points on a subscriber line.

21. The method of claim 17, wherein said subscriber line includes premises wiring.

22. The method of claim 21, wherein said apparatus is plugged into telephone jacks.

23. The method of claim 17, further comprising the step of: maintaining a data rate between two points that is equal to a data rate capacity of the subscriber line when no other communication is in progress.

24. The method of claim 17, further comprising the step of:

sharing a data rate capacity of the subscriber line between communicating pairs of points at times when more than one pair are communicating.

25. The method of claim 17, further comprising the step of:

controlling line signals such that multiple transmitted signals do not appear on said subscriber line at the same time.

26. The method of claim 17, further comprising the step of:

controlling line signals such that communications between a first pair of points has priority over communications between other pairs of points.

27. The method of claim 17, further comprising the step of:

providing multipoint operation without use of a non-data control interface to control line signals.

28. The method of claim 17, wherein the data comprises digitized analog signals.

29. The method of claim 17, further comprising the step of:

providing a POTS splitter at one or more points of the subscriber line.

30. A data communications apparatus capable of multipoint operation comprising: a means for connecting an interface to a subscriber line; and a means for modulating and demodulating a half duplex signal over said subscriber line using a full duplex protocol at a link layer to carry higher layer protocols and information.

31. The apparatus of claim 30, further comprising: a means for emulating a full duplex point-to-point protocol connection on said interface while operating in half-duplex point-to-point protocol mode over said subscriber line.

32. The apparatus of claim 30, further comprising: a means for providing a physical layer carrier to start a half duplex point-to-point protocol frame; and a means for terminating said physical layer carrier to end said point- to-point protocol frame.

33. The apparatus of claim 30, further comprising: a means for providing simultaneous communications sessions between two or more points on a subscriber line.

34. The apparatus of claim 30, further comprising: means for maintaining a data rate between two points that is equal to a data rate capacity of the subscriber line when no other communication is in progress.

35. The apparatus of claim 30, further comprising:

means for sharing a data rate capacity of the subscriber line between communicating pairs of points at times when more than one pair are communicating.

36. The apparatus of claim 30, further comprising:

means for controlling line signals such that multiple transmitted signals do not appear on said subscriber line at the same time.

37. The apparatus of claim 30, further comprising:

means for controlling line signals such that communications between a first pair of points has priority over communications between other pairs of points.

38. The apparatus of claim 30, further comprising:

means for providing multipoint operation without use of a non-data control interface to control line signals.

39. The apparatus of claim 30, further comprising:

means for providing a POTS splitter at one or more points of the subscriber line.

40. A computer program product for directing a data communications apparatus to perform half duplex multipoint operation, said program product comprising: a computer readable recording medium; and a means recorded on the medium for directing the data communications apparatus to modulate and demodulate a half duplex signal over said subscriber line using a full duplex protocol.

41. The computer program product of claim 40, wherein the means for directing includes: a routine means, responsive to said means for directing, for emulating a full duplex point-to-point protocol connection on said interface while operating in half-duplex point-to-point protocol mode over said subscriber line.

42. The computer program product of claim 40, wherein the means for directing includes: a routine means, responsive to the means for directing, for a means for providing a physical layer carrier to start a half duplex point-to-point protocol frame and for terminating said physical layer carrier to end said point-to-point protocol frame.

43. The computer program product of claim 40, wherein the means for directing includes: a routine means, responsive to the means for directing, for providing simultaneous communications sessions between two or more points on a subscriber line.

44. The computer program product of claim 40, wherein the means for directing includes: a routine means, responsive to the means for directing, for maintaining a data rate between two points that is equal to a data rate capacity of the subscriber line when no other communication is in progress.

45. The computer program product of claim 40, wherein the means for generating includes: a routine means, responsive to the means for generating, for sharing a data rate capacity of the subscriber line between communicating pairs of points at times when more than one pair are communicating.

46. The computer program product of claim 40, wherein the means for generating includes: a routine means, responsive to the means for generating, for controlling line signals such that multiple transmitted signals do not appear on said subscriber line at the same time.

47. The computer program product of claim 40, wherein the means for generating includes: a routine means, responsive to the means for generating, for controlling line signals such that communications between a first pair of points has priority over communications between other pairs of points.

48. The computer program product of claim 40, wherein the means for generating includes:

a routine means, responsive to the means for generating, for providing multipoint operation without use of a non-data control interface to control line signals.