Method and equipment for prioritizing traffic in an ATM network

Details Method and equipment for prioritizing traffic in an ATM network Method and equipment for prioritizing traffic in an ATM network

1996-11-21

1999-02-09

Hsu, Alpus H.

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

370397, H04L 1256

Patent

active

058703845

DESCRIPTION:

BRIEF SUMMARY
This application is the national phase of international application PCT/FI195/00282 filed May 23, 1995 which designated the U.S.


BACKGROUND OF INVENTION

The invention relates to a method and an equipment for prioritizing traffic in an ATM network.
ATM (Asynchronous Transfer Mode) is a new connection-oriented packet-switching technique which the international telecommunication standardization organization ITU T has chosen to be the target solution of a broadband integrated services digital network (B-ISDN). The problems of conventional packet networks have been eliminated in the ATM network by starting to use short packets of a standard length (53 bytes) known as cells.
FIG. 1a shows the structure of one cell to be transmitted in an ATM network. Each cell transmitted in the network contains a payload part of 48 bytes and a header of 5 bytes in length. However the more exact structure of, the header (the contents of the header) depends on which part of the ATM network is being used at the time. The ATM network architecture comprises a group of interfaces exactly specified in the standards, and the header structure used in an ATM cell depends on the interface (that is, the part of the network) in question.
FIG. 1b shows the structure of the header of a cell at a UNI interface (User-to-Network Interface) of the ATM network that is an interface between an ATM terminal equipment (such as a computer, a router or a telephone exchange) and an ATM node. FIG. 1c shows the structure of the header at an NNI interface (Network-to-Network Interface) of the ATM network that is an interface between two ATM nodes, either inside the network or between two different networks. The most significant part of the header for the present invention is a routing field that comprises a virtual path identifier VPI and a virtual channel identifier VCI.
In the header structure of FIG. 1b, which is used only at a subscriber interface, 24 bits in all are reserved for the routing field (VPI/VCI). In the header structure of FIG. 1c, which is used anywhere else in the ATM network, 28 bits are reserved for the routing field (VPI/VCI). As the name suggests, the routing field is the basis for the routing of cells in the ATM network. The inner parts of the network primarily use the virtual path identifier VPI which, in practice, often defines to which physical connection a cell is to be routed. On the other hand, the virtual channel identifier VCI is used in routing only at the boundary of the network, for example when connecting FR connections (FR=Frame Relay) to the ATM network.
However, it is to be noted that only the VPI and VCI together define the route of the cell unambiguously.
Other fields in the header of the ATM cell defined by the specifications are subscriber interface, not yet exactly defined, administrative cells of the network and the information cells of the subscribers but part of the field can possibly be used for transmitting virtual-path-specific and virtual-channel-specific congestion notices, discard probability (which closely corresponds to the DE bit of the Frame Relay network),
Of these other fields, the present invention is solely concerned with the CLP bit, by means of which cells can be prioritized in relation to the probability of loss. In practice, this field has two different meanings. Primarily, applications can distinguish cells with a CLP bit with regard to how important their throughput is for the application (Service Oriented Marking). On the other hand, the CLP bit can be set by the network on those cells that exceed the traffic sold to the subscriber. In this case it is a question of usage parameter control (UPC).
The use of the CLP bit closely corresponds to the use of the DE bit in the Frame Relay network. However, the biggest difference is that in the ATM network, applications also make use of the possibility provided by the CLP bit for prioritizing cells. This is an especially common practice for video coders and generally, transmission sources with a variable bit rate (VBR). In coders, the CLP bit is n

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ITU-T 1.610, Mar. 1993, "B-ISDN Operation and Maintenance Principles and Functions".
ITU-T 1.361, Mar. 1993, "B-ISDN ATM Layer Specification".

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