Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Patent
1997-06-18
2000-05-16
Patel, Ajit
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
370401, 370410, G01R 3108
Patent
active
060646489
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for notifying an FR network of traffic congestion in an ATM network.
2. Description of Related Art
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 using short packets of a standard length (53 bytes) known as cells.
FIG. 1a shows the basic structure of one cell to be transmitted in an ATM network. Each cell transmitted in the network contains a payload section of 48 bytes and a header of 5 bytes in length, but the more detailed 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 accurately specified in the standards, and the header structure used in an ATM cell depends on the interface (i.e. the part of the network) in question.
FIG. 1b shows the structure of the cell header at a UNI interface (User-to-Network Interface) of the ATM network, which is the 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, which is the interface between two ATM nodes, either inside the network or between two different networks.
The routing field of the cell header consists of the Virtual Path Identifier VPI and the 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 everywhere else in the ATM network, 28 bits are reserved for the routing field (VPI/VCI). As the name suggests, the routing field serves as 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 determines to which physical connection a cell is to be routed. On the other hand, the virtual channel identifier VCI is often used for 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 VPI and VCI together define the route of the cell unambiguously.
The other fields in the header of an ATM cell as defined by the specifications are subscriber interface, not yet accurately defined, management cells of the network and the information cells of the subscribers, but it is also possible to distinguish information cells of the subscribers on the basis of whether or not congestion has been detected on the way, discard probability (closely corresponds to the DE bit of the Frame Relay network),
Of these other fields, the present invention is solely concerned with the PTI field, which can be used for transmitting congestion notifications specific for a virtual path or a virtual channel.
The Frame Relay (FR) technique is a packet-switched network technique used for the transmission of frames of varying length in place of the packet-switched network connections presently in use. The protocol (X.25) applied generally in the present packet-switched networks requires plenty of processing and the transmission equipment is expensive, as a result of which the speeds also remain low. These matters are due to the fact that the X.25 standard was developed when the transmission connections used were still rather prone to transmission errors. The starting point of the frame relay technique was a considerably lower transmission line error probability. It has therefore been possible to discard a number of unnecessary functions in the frame relay technique, which makes the delivery of frames rapid and efficient. The Frame Mod
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Flinck Hannu
Hellman Esko
Nokia Telecommunications Oy
Patel Ajit
Phunkulh Bob A.
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