Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Patent
1997-07-07
2000-03-28
Kizou, Hassan
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
370399, H04L 1228, H04L 1256
Patent
active
060440775
DESCRIPTION:
BRIEF SUMMARY
An Asynchronous Transfer Mode (henceforth ATM) network has switching points within the network. The "switching" performed by these switching points is in fact the action of passing on a communication received by that switching point to a further link in the network. Such switching actions are the means by which a communication is moved through the ATM network. The method and apparatus of the invention relate to a way of performing one type of switching operation at a switching point in an ATM network.
BACKGROUND OF THE INVENTION
The ATM system has a broadly accepted set of standards which ensure compatibility of ATM networks and their components. The book "ATM (broadband-ISDN) a technical overview", published as publication GG24-4330-00, can be consulted in order to gain familiarity with the ATM system.
The ATM standards define the following basic characteristics of ATM communication:
All digital information is converted into cells (henceforth simply "cells"). These cells are transferred via a transmission medium.
Each cell has a fixed data length. The cell consists of a 5-byte header and a 48-byte information field. One part of the header carries data which is termed a "Virtual Path Identifier" (henceforth the "VPI"). Another part of the header carries data termed a "Virtual Channel Identifier" (henceforth the "VCI").
FIG. 1 (prior art) illustrates the parts of the header recognised as belonging to the VPI and VCI. At certain points in the ATM network, the region of the header labelled "GFC" (Generic Flow Control) is also interpreted as part of the VPI.
The path to be followed by a cell through an ATM network is defined by a series of "look-up tables" which are prepositioned in the switching points of the network. These look-up tables contain routing information to be consulted when a cell arrives at the switch point.
The ATM network has some switching points called "Virtual Channel Switches". A "Virtual Channel Link" is the link between two successive virtual channel switches in the ATM network. A "Virtual Channel Connection" (VCC) is a route through the ATM network consisting of a particular set of virtual channel links. An example of such a virtual channel connection is the route from the point of origin of a communication in the ATM network via two or more virtual channel links to the destination of the communication in the ATM network. It should be clearly understood that the virtual channel "connection" here refers to a route through the ATM network and not to the action of making a connection.
A switching action performed at a virtual channel switch in the ATM network is made in dependence on the data in both the VPI and VCI fields of the cell's header.
The ATM network also has some switching points called "Virtual Path Switches". A "Virtual Path Link" is the link between two successive virtual path switches in the ATM network. There may be several virtual path switches within one virtual channel link. The "Virtual Path Connection" (VPC) is the route through several virtual path switches followed by a particular cell. A switching action performed at a virtual path switch in the ATM network is made in dependence on only the data in the VPI field of the cell's header. In short, a VPI bundles several VCIs.
The prior art FIG. 2 illustrates the differences in the VP and the VC switching using a layer model. The lowest level of the model consists of the physical layer, i.e., the layer on which signals are exchanged. The virtual path connection layer (ATM VP) can be regarded as being mounted on the physical layer. A virtual path connection is marked VPC. The virtual channel connection layer (ATM VC) can be seen as third layer. A virtual channel connection is marked VCC. The origin of the cells in the simplified network of FIG. 2 is marked ORIG and their destination DEST. FIG. 2 recalls that virtual channel switching and virtual path switching are separate layers in the ATM hierarchy, even though some switches may act as either virtual channel or virtual path switch. However, the standard operation of a
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Luijten Ronald P.
Webb David J.
International Business Machines - Corporation
Kizou Hassan
Pezzlo John
Woods Gerald R.
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