Multiplex communications – Channel assignment techniques – Combining or distributing information via time channels...
Reexamination Certificate
1999-05-07
2002-08-13
Patel, Ajit (Department: 2662)
Multiplex communications
Channel assignment techniques
Combining or distributing information via time channels...
C370S468000
Reexamination Certificate
active
06434164
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multiple-access communication system, such as a bidirectional CATV network, a passive optical star network and so forth for a center station to dynamically assign upstream bandwidth to subscriber stations, and in particular relates to a method of guaranteeing quality of service in the upstream channel.
A communication system, such as a bidirectional CATV network or a passive optical star network, generally has a broadcasting downstream channel from a center station to subscriber stations, and a time-division multiple-access upstream channel from subscriber stations to the center station. In a communication system like this, the center station assigns one or more identifiers to the subscriber station when a subscriber station begins an operation, and then the subscriber station transmits data to the center station. Procedures of upstream bandwidth allocation are detailed below.
First, the center station transmits reservation-permit information to the subscriber stations, and then the subscriber stations having an upstream data to transmit send reservation information comprising an identifier and a requested upstream bandwidth to the center station. If reservation information sent from multiple subscriber stations collides in the upstream channel, the center and subscriber stations resolve the collision so that the center station eventually receives all the reservation information correctly.
Also, when a subscriber station holds next data to send at time of data transmission, it transmits the current data with appending reservation information for the next data. The center station makes upstream-bandwidth-grant information from this reservation information and send it to the subscriber station, and the subscriber station sends the upstream data to the center station in the allocated upstream bandwidth. If the subscriber stations do not particularly require a service quality, the center station performs above-mentioned upstream bandwidth allocation procedure equally to all subscriber stations for each upstream data transmission.
Accordingly, when the upstream channel is congested in a communication system like this, collision of reservation information among subscriber stations and retention of reservation information in the center station may increase, resulting in an increase in a delay time required for upstream bandwidth allocation.
On the other hand, when a required upstream service quality such as guaranteed bandwidth or upper limit of transmission delay is already known, the quality of services in the upstream channel must be guaranteed. Examples of such services are real-time audio and video packet transmission.
Conventionally, as a first method to guarantee a service quality in a multiple-access communication system like this, there is one in which a subscriber station informs the center station of a required service quality before sending an upstream reservation information, and the center station, allocates upstream bandwidth at a periodic basis. As a second method to guarantee a service quality in a multiple-access communication system like this, there is one in which the center station periodically sends reservation-permit information to the subscriber station to allocate upstream bandwidth on priority basis to the subscriber station. As an example of reports about the first method of the prior art, there is James E. Dail et al., “IEEE Communication Magazine,” pp. 104-112, March 1996. Also, as an example of reports about the second method of the prior art, Patent Application H10-18318 can be mentioned.
In case of the first method to guarantee service quality of the prior art, if a quantity of upstream data generated by a subscriber station temporarily exceeds an upstream bandwidth periodically allocated by the center station, the subscriber station may send reservation information in a normal procedure to request excess bandwidth and the center station receiving this allocates the excess upstream bandwidth if there is still some available.
Also, in case of the second method to guarantee service quality of the prior art, if a quantity of upstream data generated by a subscriber station temporarily exceeds the guaranteed upstream bandwidth, the subscriber station may request excess upstream bandwidth in response to the periodic reservation-permit information from the center station, and the center station receiving this allocates the excess upstream bandwidth if there is still some available.
Like this, in the method to guarantee service quality of the prior art in above-mentioned communication system, when the subscriber station attempts to send upstream data at a transmission rate higher than the guaranteed upstream rate, the center station has no means to defer upstream bandwidth allocation. Accordingly, if a certain subscriber station sends upstream data at a rate far above a guaranteed upstream rate, upstream bandwidth allocation to other subscriber stations is delayed due to the lack of limiting upstream bandwidth allocation to the guaranteed rate, resulting in a degradation of service quality supplied to other subscriber stations.
Further, in a method to guarantee service quality of the prior art, the time required for queuing-reservation information at the center station cannot be guaranteed. Particularly, when the center station periodically sends reservation-permit information to subscriber stations by the conventional method, the time between the reception of reservation information and the upstream bandwidth allocation at the center station is not bounded. Accordingly, there is a problem that the service quality cannot be guaranteed if queuing delay at the center station becomes long.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention, in a multiple-access communication system, such as a bidirectional CATV network, a passive optical star network and so forth where a center station dynamically allocates bandwidths of an upstream channel to subscriber stations, to measure and guarantee a service quality supplied for each service permitted to subscriber stations and prevent a degradation in service quality for other subscriber stations due to an influence of a subscriber station that sends data exceeding a previously contracted guaranteed value of a service quality.
Other objects of the present invention will become clear as the description proceeds.
A multiple-access communication system of a first invention wherein the center station has means for permitting the use of services of different qualities which it guarantees to subscriber stations; means for assigning identifiers corresponding to each service to the subscriber stations; means for transmitting reservation-permit information to the subscriber stations; means for receiving reservation information from the subscriber stations; means for measuring an upstream service quality being supplied with regard to a service corresponding to an identifier that is added to a reservation information when receiving the reservation information from a subscriber station; means for comparing the measured upstream service quality with a guaranteed value of a previously assigned service quality; means for immediately accepting the reservation information, if the measured value is below the guaranteed value, and assigning an upstream bandwidth; and means for accepting a reservation information of other subscriber stations prior to accepting the received reservation information, if the measured value is above the guaranteed-value, so as to prevent degradation of service quality to the other subscriber stations.
Also, wherein a subscriber station has means for requesting the use of services to the center station; means for receiving identifiers assigned by the center station according to each requested services; means for receiving a reservation-permit information from the center station; means for transmitting a reservation information to the center station in an upstream bandwidth designated by the reservation-permit information; mean
Matsunaga Yasuhiko
Momona Morihisa
NEC Corporation
Patel Ajit
Whitham Curtis & Christofferson, PC
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