Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Patent
1994-08-02
1996-05-28
Chin, Stephen
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
370 99, 370118, H04B 166
Patent
active
055219403
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The field of the invention is that of data compression systems and, more specifically, that of structured transmission systems wherein the communications between two terminals are achieved by exchanges between protocol data units or PDUs.
The invention can be applied notably to packet transmission systems (systems implementing a layer 3 procedure according to the seven-layer OSI standardization model), but also to frame transmission systems (layer 2) or systems using transport protocol data units (layer 4). More generally, the invention can be applied to any type of transmission system, whatever the layer (according to the terminology of the OSI standards) of the communications protocol associated with the system considered.
One particular field of application of the invention is that of data exchange systems working according to the X25 protocol standardized by the CCITT. On French territory, the invention can be applied therefore to communications made through the public TRANSPAC (registered mark) network.
The invention relates more particularly to the optimization of communications, i.e. notably the reduction of costs through the reduction of volumes of data transmitted and/or of communication times.
It is indeed known that, especially when a public communications network needs to be used, the costs generally depend inter alia on the number of protocol data units (or subsets of these units) transmitted and on the communication times.
A known way of reducing the volume of the data transmitted is to compress the data to be transmitted.
Many data compression techniques are indeed known, notably for point-to-point links. Thus for example an adaptive compression algorithm called the Ziv-Lempel algorithm has been chosen in the CCITT recommendation V42a for asynchronous modems.
However, in the case of systems working by exchanges of protocol data units, for example according to the x25 standard, several difficulties are generally encountered.
Thus, there is a known system, called DATAMISER (registered mark), that methodically carries out the byte-by-byte compression of the entire flow of data delivered by a terminal. When this flow of data is organized in protocol data units, each comprising zones descriptive of the exchange (header fields) and data zones (data fields), a compression system such as this does not comply with this form of structuring. In other words, it neither recognizes nor keeps the headers. It therefore cannot be used for an exchange going through a packet-switched network.
In order to overcome this drawback, the selective compression of the data zones might be considered. In this case, the headers are preserved integrally, and the quantity of information elements to be transmitted is substantially reduced. In other words, with a source protocol data unit, there is associated a compressed protocol data unit whose header is identical to that of the source protocol data unit.
In practice, it turns out that the efficiency of this technique is not optimal. Indeed, the number of packets (or PDUs) transmitted remains by definition the same. The gain is therefore minimal since partially empty packets are transmitted.
The invention is notably aimed at overcoming these various drawbacks of the prior art.
More specifically, an aim of the invention is to provide a method to optimize the efficiency of communications made on a data exchange network, reducing the number of protocol data units or subsets of units transmitted.
Another aim of the invention is to provide a method such as this that relates to the structure of the protocol data units transmitted. In other words, an aim of the invention is to provide a method such as this that is transparent from the viewpoint of the terminals as well as from that of the transmission network.
More generally, the invention is aimed at providing a method such as this that enables the reduction of at least one of the following parameters: and/or bytes) without losing any element of the information transmitted.
Another aim of the inventi
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Ernault Jean-Marc
Lane Thao
Thepault Bernard
Chin Stephen
Ghebretinsae T.
Ouest Standard Telematique SA
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