Multiplex communications – Wide area network – Packet switching
Patent
1993-11-24
1995-05-09
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 60, 370 859, 370 941, H04L 1256
Patent
active
054146984
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of communicating a digital broadband signal in the form of a series of cells, each cell being formed by m portions, between a transmitter and a receiver via a plurality, n, of narrow band communications paths, each path having an arbitrary propagation time, in which successive portions of the cells are propagated along the paths in a fixed cyclic order. When using this technique, it is necessary to establish the cyclic order of the paths used, so the receiver can order the received portions in the correct order. Further, the different paths may have arbitrary propagation times, and it therefore becomes necessary to determine what the relative delays are, in order to re-establish the proper sequence of the portions that are transmitted down the paths.
BACKGROUND OF THE INVENTION
One method of handling high data rate traffic (voice, computer or TV for example) is to have a communications ring (eg ORWELL) or a bus (eg a Distributed Queue Dual Bus DQDB) to provide a Local Area Network (LAN) or Wide Area Network (WAN) service. Such data is carried as packets through the network. With Asynchronous Transfer Mode (ATM) or DQDB configurations, the packets are designated as cells each of which can be considered to be made up of portions, for example 8-bit octets, for example a cell might be made up of 53, 8-bit octets.
One method of communicating a high data rate signal down several lower data rate paths is disclosed in PCT patent application WO 90/12467 published on 18th Oct. 1990, in which the differences in propagation time are compensated by transmitting a flag down each path, and by individually delaying the received signals in the receiver in response to the received flags, so that the broadband signal can be re-established from the portions by multiplexing.
Further, each flag is distinctive of each distinct path, so the receiver can identify the cyclic order of the paths from the flag information.
Standard ATM data formats, amongst other formats, for communication on a single high bandwidth path guarantees proper cell sequence order at a receiver. There is, therefore, no requirement for a mechanism identifying cells by any sequence identifier, for example a cell number, in standard ATM formats and so none is provided.
A disadvantage of above described multi-path communication method, if it were to be applied to present ATM communications standards, is that the flags would have to be added to the data stream, and their form and their content would need to be standardised if open communications are needed.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention a method of communicating a digital broadband signal according to the preamble of claim 1 is characterised in that: same in each idle cell and unique to the header, and in that the receiver determines the cyclic order from the order of arrival at the receiver of the first header portions of successive idle cells and the values of m and n.
According to a second aspect of the present invention, a method of communication according to the preamble of claim 2 is characterised in that: same in each idle cell and unique to the header, and in that the relative delays of the propagation times of the other paths relative to a given one of the paths is determined from the arrival times of the first header portions of the headers received from the paths.
These aspects of the present invention provide a method of determining the cyclic order of the paths and, if necessary, the relative delays of the paths during the initial set-up of a communications link from idle cells without recourse to adding special patterns into the information field of cells or transmitting additional path identifiers. This permits, for example, standard ATM data signals to be communicated down multi-path links transparently. That is, the originator of the signal need not have prior knowledge of the nature of the ATM link to be used --it could be a high data rate link or a multi-path link-- as no informatio
REFERENCES:
patent: 4577312 (1986-03-01), Nash
patent: 5293378 (1994-03-01), Shimizu
patent: 5303232 (1994-04-01), Proctor et al.
Patent Abstracts of Japan, Vo. 14, No. 336, Jul., 1990, JP A 21 13 747.
Blum Russell
British Telecommunications public limited company
Olms Douglas W.
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