Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1998-02-25
2001-03-13
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S253000, C370S395430, C370S444000, C370S449000
Reexamination Certificate
active
06201790
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of controlling access to an asynchronous transfer mode transmission network for messages contained in cells transmitted by data sources, said method comprising a first step of defining a transmission contract between each data source and said network and a second step of authorizing the access of the cells to the network.
For controlling the access to an asynchronous transfer mode transmission network for messages contained in cells transmitted by data sources, the invention also relates to a device for implementing said method and to a communication system comprising such a device.
BACKGROUND OF THE INVENTION
Traditional communication networks such as, for example, telephone or cable television are by nature intended each for a particular use and thus individually ill-adapted to executing the tasks which the other networks execute. Networks of a novel type have thus appeared and notably those operating in an Asynchronous Transfer Mode (ATM). According to this ATM, the transmission of a signal is effected in a digital data stream which is subdivided into fixed-size cells (53 octets). Each cell itself is formed by a header (5 octets) which contains the necessary information for the transfer of the cell, and a payload (48 octets), containing the useful information generated by a source. All the generated cells are then multiplexed via queues which are joined together to form an ATM network.
In the same ATM network, very different types of data may be present having specific constraints for each type. For example, the transmission of voice is to be effected in real time, but transmission errors are permitted within certain limits. Conversely, no real-time constraint affects a file transfer, but corrections of transmission errors are indispensable. When the transmitted data are video data according to the MPEG2 standard, a transmission in real time and having a smallest possible error rate is necessary.
For permitting data of such diverse nature to coexist in the network, a featuring of the traffic is basically ensured, by carrying out two operations called Connection Admission Control (CAC) and User Parameter Control (UPC). The operation of admission control, which the invention does not relate to, consists of verifying, when a user A wishes to communicate with a user B, whether the network has enough resources for effectively authorizing the connection of A and the corresponding data transfer to B, taking account of the connections already established across the network at that particular instant and of the necessity of not producing disturbances for these established connections.
For the network that establishes that a connection has been admitted between two users A and B, the operation of user parameter control (UPC) to which the present invention relates, consists of verifying that the sending user well respects the transmission contract which has been the object of the preceding admission control. Indeed, if this contract is violated either by accident (malfunctioning of the software) or voluntarily (fraudulent action), the additional resources which the network is to assign to these nonauthorized data transfers are taken from those that had already been assigned to the connections admitted by contract and respecting their transmission contract. Furthermore, an unforeseen data congestion may result from this violation of contract and corrupt wholly or in part the operation of the network. Indeed, the queues are always of limited length, and, finally, more and more data cells occur which are to be discarded.
A very frequently used method of implementing this user parameter control operation is described in patent application GB-2287854. Better known under its English name of leaky bucket algorithm, this method provides an authorization of access of a message, for example, an ATM cell, to a network only as a function of the residual level of a token reserve previously assigned as a function of a certain number of criteria notably linked with the featuring of the traffic. Initially, a time period T(UPC) is defined and a reserve of N tokens is formed for the duration of this period. A message, generated by a data source can then have access to a network only utilizing one of these tokens and it is thus a maximum of N messages that will be able to penetrate into the network during this period T(UPC). If the checking of the tokens, realized by a counter, shows that no token is available any longer for a new requested access, the message is rejected, or at any rate labeled to be transmitted only with a lower priority and on condition that it does not cause any problem for the operation of the network, even if the message is admitted.
This control method, however, has the following drawback. As only a maximum of N tokens can be disposed of at an arbitrary instant, no new token is created if no token has been used during the period T(UPC) that is completed (if certain tokens have been used, all the non-used tokens are lost). Therefore, in the situation where no token whatsoever has still been used and where suddenly a burst of N messages occurs, each of them uses a token and all messages access the network, but the token reserve is emptied and any new access is, however, forbidden for a rather long period of time (certain networks furthermore provide that the transmission contracts are not concluded when the messages thus occur as bursts, very irregularly running the risk of completely disturbing the network).
SUMMARY OF THE INVENTION
It is an object of the invention to propose an improved user parameter control method with which it is possible to adapt to whatever type of service or source of traffic.
For this purpose, the invention relates to a method as defined in the opening paragraph of the description and is furthermore characterized in that, for each source:
the first step comprises for the cells which occur in each time unit, a first operation of classification into n groups, depending on the larger or smaller value of the time interval between two successive cells, that is to say, depending on the instantaneous rate associated to each cell, and a second operation of distributing a global stock of tokens allocated to said time unit in proportion to the number of cells in each group;
the second step comprises for each cell which occurs at the input of the network a first operation of requesting authorization of access of this cell to the network, said access only occurring in the case of an available token for the group that corresponds to the instantaneous rate of this cell, followed, if access is refused, by one or various additional operations of requesting authorization to access the same cell by successively searching for an available token per group that has directly higher instantaneous rates, till an authorization of access for one of the groups encountered, or definitive refusal.
If only the method according to the state of the art is used, no distinction is made between the cells which have a high instantaneous rate and the cells which are slower. The cells arriving in bursts are indeed network disturbers because they will abruptly fill the input queues of the network access switches and thus very rapidly cause the following cells to be rejected. When adapting this method by introducing distinct priorities which depend on the type of cells which occur, these disturbances are avoided. The access control method thus proposed makes it possible to provide a much more flexible management than previously of the resources of the respective network.
In a particular embodiment of the invention, this method is further characterized in that, for implementing said second step, a cell rank verification operation occurs, either followed by an operation of acceptance of this cell by the network if this cell is the first cell to occur for the time interval concerned and the token reserve corresponding thereto, or, if this cell is not the first cell, by a first test operation testing whether a token is available in th
Hsu Alpus H.
Piotrowski Daniel J.
U.S. Philips Corporation
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