Multiplex communications – Channel assignment techniques – Polling
Reexamination Certificate
1997-11-26
2001-04-03
Olms, Douglas (Department: 2661)
Multiplex communications
Channel assignment techniques
Polling
C370S346000, C370S347000, C370S444000, C370S455000
Reexamination Certificate
active
06212196
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a multiple access communication system between a master station and slave stations and, more particularly, to the one for processing various kinds of data of different traffic characteristics.
Recently interactive multi-media networks such as CATV have been adapting bi-directional communication allowing for data transmission between a master station and slave stations interactively. Generally the data transmission from the master station to the slave station has been conducted on a broadcasting channel by which the same data are transmitted to all the slave stations concurrently. While the data transmission from the slave station to the master station has been conducted on a multiple access channel by which data are time division multiplexed for transmission therebetween. In a certain system, the master station designates a slave station which is expected to transmit the data by a polling signal. Responding to the receipt of the polling signal, the designated slave station transmits the data to the multiple access channel.
In case 3 slave stations are expected to transmit data sequentially, the master station designates the slave station one after another and transmits a polling signal. The length of data which can be sent by each slave station is designated by the polling signal output from the master station. The slave station transmits bandwidth request information containing the designated data length and data length required to be sent responding to the receipt of the next polling signal. Based on the bandwidth request information from the slave station, the master station determines the data length which will be designated in the next polling signal.
The time interval for transmitting the polling signal to the slave station is equal to the data length which is expected to be transmitted from each slave station. This intends to multiplex the respective data on the same channel most efficiently without leaving any gap therebetween. Each slave station starts transmitting the data immediately upon receiving the polling signal. The master station transmits the next polling signal without waiting for the data from slave unit.
Recently packet communication has also been increasingly adapted. In this communication, transmission data are divided into units of packets transmittable in a predetermined size. Asynchronous Transfer Mode (hereinafter referred to as ATM) system is especially suitable for transmitting and receiving sound and video information requiring strict punctuality. In the ATM communication system, all the information uses cells to transmit various data of traffic characteristics. For example, Constant Bit Rate (CBR) data service requires transmission of a predetermined length of data at a given time interval. Another service is a Variable Bit Rate (VBR) data service which allows for variation in transmission data length but requires keeping the average length of data transferred to a predetermined value or more. Also Available Bit Rate (ABR) data service allows for transmission of any data length.
In the above-described conventional multiple access communication system, the interval for polling signal transmission by the master station is defined by the length of data expected to be transmitted from the slave station. The length of data sent from the slave station varies with the bandwidth request information from the slave station. Supposing that cyclic polling is conducted to 3 slave stations, each cycle for a round of polling varies with the amount of data sent from the slave station. So in this system, the CBR data requiring constant cycle and data length cannot be transmitted. Furthermore, the conventional multiple access communication system is not designed to retain average length of data sent from the respective slave stations. This indicates that the VBR data requiring a constant average length of the data cannot be used. The prior art system has difficulty in transmitting the ATM mode communication data with adequate traffic characteristics where CBR, VBR and ABR are mixed therein.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a multiple access communication system which allows the transmission data with excellent traffic characteristics even if CBR, VBR and ABR data are mixed therein.
The above object of the present invention is achieved by a multiple access communication system for communicating various types of data with a polling method between a master station and a plurality of slave stations, wherein the master station comprising:
means for setting a periodic frame;
a bandwidth allocation means for allocating a certain amount of bandwidth transmittable within a the frame to each of the slave stations in order of priorities that is determined based on data types; and
an instruction means for transmitting an instruction to transmit data equivalent to a bandwidth allocated for each data by the bandwidth allocation means at every frame.
Furthermore, the above object of the present invention is achieved by a method for multiple access communication for communicating various types of data with a polling method between a master station and a plurality of slave stations, the method comprising steps of:
setting a periodic frame in the master station;
allocating a certain amount of bandwidth transmittable within a the frame to each of the slave stations in order of priorities that is determined based on data types in the master station;
transmitting an instruction to transmit a data equivalent to an allocated bandwidth to each slave station in the master station; and
transmitting a data equivalent to a bandwidth instructed by the master station in the slave station.
In the above described invention, the bandwidth within a frame is allocated to data from higher to lower priority orders. So the bandwidth will be allocated first to the data having highest priority for bandwidth allocation. Even though data of different priorities are mixed in the system, excellent traffic characteristics are obtained.
In the the present invention, the bandwidth allocation means comprises a reception means for receiving information containing data length required for the next transmission in order of priorities from each of the slave stations and allocates the respective bandwidth to data in order of priorities based on received information of the required data length.
According to the present invention, the bandwidth allocation is set in order of high priority given to data based on desired bandwidth received from the slave stations. As a result, excessive bandwidth is not allocated to the data with higher priority. The rest of the data are also allocated with appropriate bandwidth.
In the present invention, various kinds of data is transmitted including CBR data in which required bandwidth in the cycle is constant, VBR data in which bandwidth variation in the cycle is allowed but average bandwidth has to be kept to a predetermined value or larger and ABR data in which any bandwidth is available. The data are allocated with the respective bandwidth sequentially in order of CBR, VBR, and ABR from higher to lower priorities.
The present invention is capable of transferring the CBR, VBR and ABR data sequentially in this priority order which are mixed in the ATM communication.
The bandwidth allocation means of the present invention allocates constant bandwidth to the CBR data. The VBR data is allocated a bandwidth equivalent to the minimum value selected from: 1) the bandwidth required for keeping the average bandwidth to the predetermined value or more 2) the allowable maximum bandwidth; and 3) the bandwidth required by the slave station. The ABR data is allocated a bandwidth equivalent to the minimum value selected from the remaining bandwidth available in the frame resulting from the subtraction of bandwidth allocated to the CBR and VBR from the bandwidth required by slave station.
The present invention transfers CBR, VBR and ABR data. The CBR data are allocated with a constant bandwidth. The
Hom Shick
NEC Corporation
Olms Douglas
Ostrolenk Faber Gerb & Soffen, LLP
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