Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Patent
1997-03-21
1999-06-29
Nguyen, Chau
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
370466, 370474, H04J 1256
Patent
active
059178248
DESCRIPTION:
BRIEF SUMMARY
This invention relates to digital communications systems and in particular to systems embodying asynchronous transfer mode (ATM) technology.
The asynchronous transfer mode (ATM) technology is a flexible form of transmission which allows any type of service traffic, voice, video or data, to be multiplexed together on to a common means of transmission. In order for this to be realised, the service traffic must first be adapted typically into 53 byte cells comprising 5 byte headers and 48 byte payloads such that the original traffic can be reconstituted at the far end of an ATM network. This form of adaptation is performed in the ATM adaptation layer (AAL). Five types of adaptation layer have been defined, this invention relates to adaptation layer 1 which is used to adapt constant bit rate traffic to the ATM standard.
A general description of a host interface for an ATM network is given in specification number WO-A-9222034 which describes a method of transmitting traffic carried in channels. A discussion of a hardware implementation of AAL and ATM protocol layers is given by G Marino et al. in Proceedings of Interworking '92, Amsterdam, 18 to 20 November 1992, pages 166 to 178. The prototyping of an ATM adaptation layer in a multimedia terminal is discussed by G Armitage et al. in International Journal of Digital and Analog Communication Systems, Vol. 6 No. 1, January 1993, pages 3 to 14.
An ATM exchange may support POTS or ISDN services as well as B-ISDN services. The H320 Video conference standard is a typical user of an n.times.64 Kb/s service, this may well be embedded within a B-ISDN workstation and can also be supported by the N-ISDN. In an ATM exchange with 2 Mb/s trunk circuits with independent calls on each 64 kb/s channel it is desirable that traffic once adapted to ATM should remain in ATM up to the destination narrowband port. It is further desirable that a physical trunk at e.g. 155 Mb/s should be able to carry logical routes to more than one destination as 155 Mb/s is generally too large a capacity for trunking within a narrowband service network. If the logical routes are of n.times.64 kb/s where n.gtoreq.6 then the cell assembly delay is reduced to the point that echo cancellation is no longer necessary. The cell assembly delay of a single 64 kb/s circuit is 6 msec which requires echo cancellation for interworking with the existing narrowband network.
The object of the invention is to provide a flexible means to implement the network requirements outlined above.
According to one aspect of the present invention there is provided an asynchronous transfer mode (ATM) communications system supporting both broadband and narrowband services carried in respective channels, the system including means for adapting a plurality of channels into groups, each said group comprising a virtual channel for transmission purposes, ingress and egress frame memories, means for staticising a synchronous transport mode (STM) stream into the egress frame memory, means for distributing the content of the ingress frame memory as an STM stream, and means for readapting each said group back to individual channels, wherein the adaptation and readaptation processes are controlled by a chain structure, each link in the chain comprising two bidirectional pointers and an address in the egress or ingress frame memory, there being one link per channel in each of the egress or ingress chains, wherein a said chain is assembled for each active ATM virtual circuit, and wherein the system is such that any individual channel can be associated with any virtual channel, and that any said group of channels maintains time slot integrity throughout the adaptation and transmission process
According to another aspect of the invention there is provided a method of transmitting traffic carried in channels in an asynchronous transfer mode (ATM) communications system supporting both broadband and narrowband services carried in respective channels, the method including for adapting a plurality of channels into groups, each said group comprising
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Brueckheimer Simon Daniel
Mauger Roy Harold
Nguyen Chau
Northern Telecom Limited
Vanderpuye Kenneth
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