Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Patent
1997-12-01
1999-07-27
Ton, Dang
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
370419, H04L 1228, H04L 1256
Patent
active
059302534
DESCRIPTION:
BRIEF SUMMARY
This invention relates to digital communications systems and in particular to systems embodying asynchronous transfer mode (ATM) technology. The invention further relates to an apparatus and method of switching narrow band traffic in such a system.
BACKGROUND OF THE INVENTION
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. In particular, adaptation layer 1 is used to adapt constant bit rate traffic to the ATM standard.
A general description of a large capacity ATM cross connect system with an STM-ATM conversion function is given by Kurano et al. in Proceedings of Globecom 93, IEEE Global Communications Conference (ISBN 0-7803-0917-0) Vol.3, pages 1461 to 1467. A discussion of bridge functions used in the implementation of ATM networks is given by Nishara et al. in Proceedings of Globecom 93, IEEE Global Communications Conference (ISBN 0-7803-0917-0) Vol.2, pages 888 to 892. Reference is also directed to our co-pending United Kingdom applications No. 9410294.4, No. 9410295.1 and No. 9411894.0 which relate to integrated broad band and narrow band access arrangements.
ATM switches provide point-multipoint capability as a basic function. A combination of an ATM switch and a narrow band to broad band service interworking capability can therefore achieve point-multipoint in the narrow band network. This solution however has the problem that each narrow band to ATM adaptation incurs a 6 millisecond cell assembly delay which means that voice connections through the existing narrow band network will suffer from delay problems which require the use of additional equipment to effect for cancellation.
The object of the invention is to minimise or to overcome this disadvantage.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a narrow band ATM switch for a communications network and adapted to work into a backplane bus associated with a backplane having ingress and egress facilities so as to separate switching from circuit adaptation and including a number of ports each of which is coupled to a respective adaptive virtual junctor, the switch having means for disassembly and reassembly of ATM narrow band channel payloads by providing a mapping between channel addresses and virtual circuit payloads, means for allocating any channel on the backplane to any time slot in a plurality of virtual circuits whereby to provide a multicast facility, and wherein each said adaptive virtual junctor has a junctor virtual circuit with each of the other said adaptive virtual junctors.
According to another aspect of the invention there is provided a method of switching narrow band channels in an ATM communications network, the method including allocating said channels to time slots in a plurality of broad band virtual circuits by providing a mapping between channel addresses and virtual circuit payloads.
In a further aspect, the invention provides a narrow band ATM switch for a communications network which provides point to multipoint capability on a narrow band channel basis in combination with bulk adaptation to ATM. The switch may be adapted whereby to perform a cell relay function into a narrow band switching fabric and may incorporate means for frame boundary rate adaptation.
The arrangement facilitates inter-working between narrow band and broad band traffic in the public network. The most basic form of inter-working is for voice applications in which a POTS line or an ISDN B-Channel must be adapted to a Virtual Circuit using ATM Adaptation Layer 1 providing 64 kb/s con
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Brueckheimer Simon Daniel
Mauger Roy Harold
Northern Telecom Limited
Sam Phirin
Ton Dang
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