1 2
TELECOMMUNICATIONS NETWORK (PVCs) for inter-site links). This means that the Source
Mini-Network address is carried in the source Mini-Network
BACKGROUND OF THE INVENTION where it is redundant, being implicit, and similarly the
„.,„., „ ... ,T „„„„ Destination Mini-Network address is carried in the destina
In United Kingdom Patent Application No. GB 2255257 tion j^N^t nG. 2 shows how, by eliminating this
is described an earlier concept for an Asynchronous Transfer redundancy, in accordance with the present invention, the
Mode (ATM) self-routing network which may be used for address capabmty may be expanded.
Private Networks, Virtual Private Networks and distributed ^ ±e flgures shaded ^ show where ch haye been
Local Area Switches in the Public Network. The service is made from the earlier format
connectionless using a, special format of the address octets TwQ gU h maaafanasbi ^ used for the Source and
i n the cell header; cells are directed to their respective Destination Mini-Networks respectively and, since a Mini
destinations by an Interpreter held in each elemental switch , T . , . ... , . . ,. . „ ...
or at each switch in ut ort de endin u on im lementa Network is relatively unstructured internally, it is necessary
or a eac swic inpu po , epen ng upon imp emen a- to infonn the mteipreters which format is being used and this
tion. No overhead is required in the ceU Mor^tion Field [& done ^ me ^ ^ ^ ^ most
which therefore corresponds to the payload m the ATM layer si ^can/octet 06f the ceU heJa as a Source/Destination
or a composite network; hence the use of standard adaption- ^ fomat ^ ^.^^ ranction
layer formats is not compromised. This application is bom ... and ... Mini-Network identities must
included herein by reference. be ^ sjnce {he ^ Mormation required t0 be held
The network is divided into Mini-Networks typically with exceeds the capacity of the standard cell header format, the
up to 256 user Network Ports. The size of the address field 2Q function must be internal to a switch element.
The rules for Interpretation are as follows:
If the S/D bit is zero AND the D-Minet 1,2 field indicates
It will be seen that such a network is limited to a own Mini-Network then route on D-Port 1,2.
maximum of 4k (4,096) User Network Ports, although thee ff the S/D bit h zero ^ thg 12 fidd mdicates
use of multiplexers can substantially increase this number. 25 thatthedestination is NOT own Mini-Network then route on
D-Minet 1.2.
If the S/D bit is one then route on D-Port 1,2.
According to the present invention there is provided a xhe theoretical maximum addressing capability using the
telecommunications switching network comprising a plural- ceu header formats of the present invention is 128 Mini
ity of sub-networks, each sub-network having a plurality of 30 Networks with 256 User Network Ports (UNPs) each. The
User Network Ports wherein the Destination and Source resultant maximum address range is 32k UNPs which is a
addresses in a cell-header carried by a cell switched by the verv i^ge number for a private broadband network,
network are each divided into a Port Address part and a ^ order t0 improve fault tolerance and to simplify con
Sub-network Address part and wherein the Source Sub- gestion avoidance haif of ^ capacity is sacrificed by
network part is implicit whilst the cell remains in the Source 35 pairing Mini-Networks so that two adjacent addresses serve
Sub-network and similarly the Destination Sub-network part the same of ... Ls bit of me Miner field is
is implicit from when the cell arrives in the Destination used t0 sepaiate the two, this bit is referred to as the 'A' (for
Sub-network, wherein the Source and the Destination Sub- Alternative route) bit
networks are linked via a cross-connect switching device The A.Wt h &m in (he int tation of me
wherein the address formats are changed. 40 ^ ^ ^ fc ^ ^ ... of me port
BRIEF DESCRIPTION OF THE DRAWINGS ^e^' ^ means alternate paths are provided both for
intra-Mini-Network and to cross-connect switches and pub
The present invention will now be described by way of lie network ports,
example, with reference to the accompanying drawings, in 45 The rules for interpretation are therefore modified as
which: follows:
FIG. 1 shows an example of a prior art cell header format; If the S/D bit is Zero AND the D-Minet 1,2 field indicates
FIG. 2 shows a variation of the format shown in FIG. 1 own Mini-Network then route on D-Port t,2 and the
with the cross-connect function of the present invention; A-bit.
FIG. 3 shows a further variation of the format shown in 50 If the S/D bit is zero AND the D-Minet 12 field indicates
FIG. 1 having a modified cross-connect function; that the destination is NOT own Mini-Network then
FIG. 4 shows diagrammatically the paths between users route on G-Mi^t1-2 ^ ^ A"bit
on two mini-networks ^ ^e ^ *s one tnen route 011 D-Port 1,2 and the A-bit
_ . .. „ ^_ , It will be seen that the A-bit is included in the interpre
FIGS 5 and 6 show diagrammatically the transmit and 5J ^ ... ^ ^
receive functions for a public network link; T~ = , ,. u.t . „„m„11l7 „„+= „0=,'0 „„„„„„
r The value or the A-bit is normally not the user s concern,
FIG. 7 shows diagrammatically the signalling system being set tne Exchange Terminator (ET) from a table for between peripheral nodes for the present invention; the 16 possible Virtual Connections (VCs) and maintained
FIG. 8 shows diagrammatically the use of a Public by the Resource Manager. However, for certain functions Network Port address with addresses allocated in site net- 60 (for example Multicast codes), the two addresses may be works. used individually. The S/D bit, normally used to identify the
header format, is redundant in the upstream UNP link; and is used instead to inform the ET that the A-bit value given is real. Note that this feature is implemented by user choice, The earlier network, as described above, uses a common 65 in a network where the address range is not a pressing address format throughout (apart from changes at the Public problem users may prefer to leave the choice up to the Network Port used in mapping to Public Virtual Circuits manager.
