Multiplex communications – Communication techniques for information carried in plural... – Assembly or disassembly of messages having address headers
Patent
1996-08-15
1998-07-14
Chin, Wellington
Multiplex communications
Communication techniques for information carried in plural...
Assembly or disassembly of messages having address headers
370235, 370395, 370471, H04J 324
Patent
active
057815542
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for communicating between nodes in a communications network, particularly, but not exclusively, an asynchronous transfer mode network for communicating delay sensitive low rate isochronous services such as voice data.
2. Related Art
In asynchronous transfer mode (ATM) networks a node on the network transmits data to another node in the network by loading the data into a cell which travels through the network. Taking, for example, a single telephone source or a number of telephone sources, the data will comprise regularly taken samples of the analogue voice information which is digitised. Once a buffer in the node has sufficient information to fill the cell the data block is transmitted to the other node. Subsequently further cells are filled in a similar manner and transmitted to the other node.
It will be appreciated that the voice information from one telephone conversation may be split up into samples which are transmitted in different cells and time delays which are perceivable by a telephone user can occur because of the need for each node to "gather" or receive enough information to fill a cell. The time delays manifest themselves as echoing, and although echo cancelling equipment is available which can alleviate this problem, such equipment is expensive and not always reliable. This has led to the belief that ATM is not a suitable technology to serve voice traffic or other delay sensitive low rate isochronous services.
The present invention arose from a realisation by the inventor that the currently perceived requirement to fill each cell with data does not need to be a rigid requirement. By only partially filling a cell with data, it would be possible to reduce the time delay introduced into the communications network by the buffering process used by each transmitting node. For example, it would be possible for a node to utilise one cell to transmit just one digitized sample from one telephone conversation. This would, of course, lead to an excessive load on the asynchronous transfer mode network because the other information that would have been carried by that cell would now have to be carried by other cells.
EP-A-0415843 discloses a data communication system for communicating data between nodes of the system. When a source node sends data to a destination node it splits the data into packets of, for example, 512 bytes each. In order to avoid congestion occurring in the system the maximum number of packets the source node can send at any given time, or the maximum rate at which it can send packets, is controlled in accordance with the round-trip delay between source and destination nodes. The maximum number or maximum rate is controlled to be higher for smaller delays and lower for larger delays.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of communicating data in blocks between first and second nodes in a communications network, the method comprising determining a time delay between transmission and reception of data blocks between the nodes and communicating the data in blocks the amount of data in each of which is controlled in accordance with the time delay thus determined, the amount of data in each block being controlled to be larger for smaller delays and smaller for larger delays, characterised in that the blocks are communicated within respective data cells which all have the same data-carrying capacity so that the fill factor of each cell is higher for smaller delays and lower for larger delays.
By determining the time delay between transmission and reception of data blocks between nodes and controlling the amount of data in each of the data blocks in accordance with the determined time delay it is possible to compromise between the load on the network and the time delay introduced by the node assembling the data into a data block prior to transmission.
For example, where the network has a low transmission path delay it may by to
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British Telecommunications public limited company
Chin Wellington
Hyun Soon-Dong
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