Electrical computers and digital processing systems: multicomput – Computer network managing
Reexamination Certificate
1999-02-08
2004-02-24
Banankhah, Majid A. (Department: 2127)
Electrical computers and digital processing systems: multicomput
Computer network managing
C709S241000, C709S241000, C709S200000, C709S201000, C709S226000
Reexamination Certificate
active
06697855
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns an adaptive hybrid method for access to a transmission channel.
A centralised network has a base station (also referred to as the “central station”) and mobile stations (also referred to as “peripheral stations”) which are supervised by the base stations, that is to say they can access the network only when the base station gives them authorisation to do so, by allocating to them individually or collectively a momentary access right or “token”, corresponding to an interval of time during which one or more stations are authorised to send.
Two principal access methods are known. The first, referred to as “polling”, consists of successively allocating individual access rights which authorise one of the mobile stations to access the network. The second, referred to as “contention”, consists of allocating a right of access simultaneously to all the mobile stations. In this second case, each mobile station is authorised to access the network at any moment, according to procedures which depend only on its internal functioning, and risks of collision arise.
Two performance criteria for the networks which are generally used are on the one hand the maximum total throughput of data circulating therein and on the other hand the mean latency, that is to say the mean period which elapses between the instant when a frame is ready to be sent and the correct and complete reception of this frame.
It will easily be understood that the polling method makes it possible to achieve a very high theoretical total throughput but entails a high latency, whereas the contention method affords low latency but does not allow a very high maximum throughput.
The polling method is in fact best suited to cases where the total throughput required for all transmissions of information between the stations is high, whereas the contention method is most suited to low throughputs relating to an available passband.
The document U.S. Pat. No. 4,071,908 (Bell Telephone Lab) describes a hybrid access method which uses the principle of a progressive subdivision of a group which initially contains all the stations, in making the division account being taken only of the criterion of the total transmission load on the channel. Each division takes place in groups, the composition of which is predetermined by the addresses of the stations, as long as a group replies to a token and includes at least two stations. Thus, in many cases, stations which have only a small requirement for access to the channel are allocated individual access rights, because of the proximity of their address to those of the stations which have a high requirement for access to the channel. Access to the channel is then poorly distributed between the stations.
The document WO 91/16775 presents a hybrid communication system which allocates individual access rights according to the number of collisions which is detected. The groups are, there too, defined by the addresses of the stations. This system has the same drawbacks as the one described in the document U.S. Pat. No. 4,071,908.
The present invention sets out to remedy these drawbacks. In particular, the invention is distinguished by the determination of the requirement of each station for access to the channel and then by the determination of groups according to these access requirements, and then by allocating access rights to the stations in each group, in succession.
It should be noted here that the access requirements are preferentially measured either in proportion to the distributed time intervals, or in proportion to the period of use of the shared channel.
To this end, the present invention relates, according to a first aspect, to a method for access to a transmission channel shared between several stations, characterised in that it includes iteratively:
an operation of estimating requirements of each of the said stations for access to the transmission channel,
an operation of determining groups of stations taking into account the estimated access requirement of the said stations, at least one of the said groups of stations being said to be “collective”,
an operation of allocating, to each of the said groups, access rights each corresponding to an interval of time during which the stations which do not form part of the said group are not authorised to access the transmission channel, and during which, if the said group is collective, each station which it includes gains access to the transmission channel according to a contention method.
It should be noted here that an estimation of the access requirement of a station amounts to defining an estimated access requirement which represents the true access requirement of the said station. For example, in order to make the said estimation, it is possible to take account of the number of accesses already effected by the said station, the number of collisions suffered by the data frames sent by the said station, the number of frames remaining to be sent by the said station or the quality of service required by the said station.
By virtue of these provisions, each station, whose access requirement is first estimated, is associated with a group according to this access requirement. The invention therefore makes it possible to allocate the access rights progressively according to the estimated access requirement of each station.
According to particular characteristics, during the operation of determining groups, at most only one group having more than one station is determined.
This group is referred to as “collective” in distinction to the groups which contain only one station and which are hereinafter called “individual”.
By virtue of these provisions, apart from the stations in the said collective group, all the other stations can receive individual rights of access to the transmission channel. In addition the presence of each station in any collective group depends only on their estimated access requirement. Finally, the stations in the said collective group can be allocated collective access rights. The type, individual or collective, of the access rights allocated to a station is then a function of the estimated access requirement of this station.
According to particular characteristics, the access method as briefly disclosed above:
includes an operation of defining a first so-called “stability” threshold applicable to the sum of the estimated access requirements of a group, and
during the group determination operation, each group is determined so that no collective group has a sum of access requirements of the stations which it includes which is greater than the said first stability threshold.
Preferentially, the determination of the said first stability threshold takes account of the contention method concerned.
By virtue of these provisions, when collective access rights are given to the stations in the said collective group, the stability of the network can be guaranteed, since the estimation of the access requirements is reliable.
According to particular characteristics, the group determination operation includes:
a so-called “stability” test during which it is determined whether the sum of the estimated access requirements of all the stations is greater than the said first stability threshold, and
in the affirmative, an operation of generating at least one individual group each including one and only one of the stations which have an estimated access requirement greater than or equal to the estimated access requirement of each other station.
By virtue of these provisions, when access by contention for all the stations would lead to saturation of the channel, at least two groups are determined, some of which, individual, each have a station amongst those whose estimated access requirement is the highest, and the last, generally collective, includes all the other stations. It is then possible to allocate to the first ones an individual access right and to the last one a collective access right.
According to particular characteristics, conjointly with the implementation of the said gen
Le Dantec Claude
Rousseau Pascal
Ali Syed J
Banankhah Majid A.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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