Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Patent
1996-10-22
1999-06-22
Hsu, Alpus H.
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
370236, 370355, 370397, 370410, 370467, H04L 1256, H04Q 1104
Patent
active
059149370
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
When the Asynchronous Transfer Mode (ATM) standards were being formulated the Virtual Path Identifier (VPI) field was intended to serve two purposes; to provide an independent non-interacting Transport Layer, and to enable an access sub-network which provides the equivalent functions to Concentrators and Grooming Switches in the Public Switched Telephone Network (PSTN).
Multiplexers in the PSTN provide a one-to-one bandwidth relationship between the subscriber line and an upstream multiplex; a multiplexer is a managed entity. Statistical Multiplexers, used in ATM and other packet-mode networks are also managed entities but they do provide statistical gain, that is the total upstream bandwidth occupied can be less than the sum of the peak bandwidth of the inputs; this is because the process of merging many sources onto one bearer results in a smoothing of the distribution and hence, the peaks are less significant. A statistical multiplexer therefore provides a similar function to a concentrator in the PSTN.
Switches which operate on the VPI field form a managed network and statistical multiplexing (concentration) and grooming are managed network functions, thus routing upstream on the VPI field in the access network is an obvious choice. The choice of VPI for routing downstream is less obvious but there are two reasons why this should be so; firstly, the same switches are likely to be used for handling routing upstream and downstream and to route on VPI upstream and VCI downstream would affect the complexity, and hence the cost, of the switches. Secondly the downstream path would, in many cases, make connection to the equivalent of an S-bus serving several terminals, requiring many virtual channels which can also be contained in one virtual path.
Another feature often specified for PSTN multiplexers and concentrators is own-unit switching capability, usually in order to provide a limited service if the upstream link(s) fail. In the above scenario for Broadband-Integrated Services Digital Network (B-ISDN) access, since there must be VPI addresses for all the ports in the downstream direction, and since switches rather than simple statistical multiplexers are used in the access network in order to provide grooming, all that is necessary to provide an own-unit switching capability is to place the "upstream" (grooming) ports and the "downstream" (subscriber) ports in a common address group.
SUMMARY OF THE INVENTION
According to the present invention there is provided a Broadband-Integrated Services Digital (B-ISDN) access network using Asynchronous Transfer Mode (ATM) technology where a Concentration Function is provided by statistical multiplexers, a Grooming Function by ATM switches and own-access-network connections is provided by combining "upstream" ports into the core network(s) and the "downstream" ports to subscribers into a common address group and where each subscriber port and each core network(s) access port is allocated a unique OSI Layer 2 address and where the access network destination address is carried in the Virtual Path Identifier (VPI) field of each ATM cell formatted according to relevant CCITT recommendations for the User Network Interface (UNI) or the Network to Network Interface (NNI) and where the Virtual Channel Identifier (VCI) field of said recommendations is divided into two sub-fields which carry the OSI Layer 2 source address and a Terminal Equipment Identifier (TEI) field respectively, said TEI field being used to identify a virtual channel at the source and destination ends of a path.
There is further provided a B-ISDN network wherein the UNI format, characterised by an 8-bit VPI field and 4 bits reserved for an independent Generic Flow Control (GFC) channel, is used throughout the access network and the maximum number of network port addresses available is 256, where a network port may be serving a subscriber or an access port to a core network, and where the application of a flow-control protocol is enabled over network port access links and in
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Hsu Alpus H.
Marconi Communications Limited
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