Switching structures or switching networks operating according to an asynchronous transfer mode are provided for future communication systems, particularly broadband networks. In this asynchronous transfer mode, packets having a fixed length, these being referred to as cells in the technical field, are transmitted in uninterrupted fashion on every transmission section. These cells are composed of 48 octets for the useful information and of 5 octets of cell routing information for the cell header. When no useful information is to be transmitted at the moment, specifically marked idle signals are transmitted.
A switching network operating according to the asynchronous transfer mode is structured into one or more switching stages, similar to the switching network of traditional digital communication systems, whereby the individual switching stages are meshed with one another such that a largely blocking-free switching structure arises. The input and output lines of such a switching structure are identified from the cell routing information recited in the cell header of the cell, i.e. from virtual routing information and virtual channel information. These switching-oriented information are derived from the multi-addressing and destination information signalized by the subscribers of a communication system, i.e. telephone numbers of the destination subscribers.
It is known from the publication "ATM-Technologie fuer zukuenftige Breit-bandnetze" of Siemens AG, page 17, right-hand column, to additionally identify routing information for the switching of a cell through a switching structure from the cell routing information recited in the cell header of the cell and to attach this to the cell. With the assistance of these internal routing information, the respective cell seeks the defined path through an n-stage switching structure under self-control, i.e. without the cooperation of a central communication system controller. As used herein the term "self-control" refers to the self-routing of cells. The additional, internal routing information are inserted into an internal cell header of the communication system and are set in front of the respective cell. After the self-switching of the cell through the switching structure, the internal cell header of the communication system is again removed.
The data scope of the cell routing information or of the internal cell header of the communication system is essentially defined by the plurality of switching stages, whereby one information string, for example, one byte is usually provided for a switching stage, these being compiled to form a block. Internal cell headers of the communication system are being defined to an increasing degree that have a prescribed plurality of information strings matched to the maximum plurality of switching stages, for example 5 bit octets or bytes for 5 switching stages.
In the case of multi-address transmission of cells to a plurality of output lines of the switching structure, the self-control principle of the cells can no longer be maintained without further measures given internal cell headers of the communication system structured in this way.