Multiplex communications – Wide area network – Packet switching
Patent
1992-07-29
1994-04-26
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 59, H04Q 1104
Patent
active
053073436
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention refers to telecommunication systems employing digital signals for the transmission of speech, video and data signals, and in particular it refers a basic element for the connection network of a fast packet switching node.
BACKGROUND
The fast packet switching techniques, called ATM from the first letters of the wording in the English language "Asynchronous Transfer Mode", is going to take on an ever growing importance in the integrated switching of digital streams, belonging to the services for speech signal transmission, video and data signals, with different bandwith requirements and differentiated traffic characteristics. The network foreseeing this kind of service integration, with even more wide bandwith, is called B-ISDN (Broadband Integrated Service Digital Network). This technique meets better than others the requirements of the above mentioned services using an integrated switching structure, open to possible future services with not yet defined characteristics. The resources offered by the switching system are not strictly dedicated to a single call for its all length of time, as in the circuit switching systems, but are used only on demand, when the need arises to transfer information.
As known, this technique foresees that information relevant to the various services is organised in contiguous units with a fixed length of approximately 400 bits, called cells. These are composed by information field and a routing field, called header, carrying the information necessary to the route selection through the connection network and other service information.
Cells are received by line interfaces placed at the input of a switching node, essentially consisting of a control unit and of a structure performing the real switching function. The control unit performs all high level functions related to the call processing, to the configuration of the connection network and to the control of other services. Among these functions, a fundamental is the path finding. This path is decided at the call setup phase and is common to all the cells belonging to the same call. The choice is determined call by call by routing bounds throughout the geographical network and by the bandwith allocation state within the interconnection network.
The structure performing the cells switching operates by converting the header, which validity is just link by link, and the routing of cells of the same call towards the appropriate output through the connection network.
The connection network, which has the function to obtain the space switching of the cells from an input port to an output port, must be able to deliver large traffic volumes, in the range of some hundred Gbit/s, with a low cell loss probability, and low blocking probability. Furthermore, the connection network must show a minimum crossing time and has to be open to further modular growth.
Some connection networks are known at present, based on multistage structures almost non blocking, which employ unblocking switching elements of NN capacity, where N is higher equal to 8.
Each one of these elements controls the space switching of the cells belonging to the same call, which are sent following a path unique per each input-output pair. It works in a self-routing way, since a portion of the header of the cell, called TAG, describes the route of the cell itself through the connection network and in particular the output port of each element, where the cell has to be delivered.
Since it can occur that two or more cells, arrived at different inputs, want to access to the same output port at the same time, it is necessary to foresee an intermediate storage function for the cells which cannot be immediately transferred. One cell can therefore be sent at once to the subsequent stage, while the remaining ones stand-by waiting for the availability of the output port. The known switching elements essentially differ in the way the intermediate storage of cells in conflict is performed.
According to a first method, cells are held in intermedi
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Bostica Bruno
Daniele Antonella
Vercellone Vinicio
Hom Shick
Italtel Societa Italiana Telecommunicazioni S.p.A.
Olms Douglas W.
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