Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-09-22
2004-08-17
Ton, Dang (Department: 2666)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S235000, C370S230000
Reexamination Certificate
active
06778557
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a point-to-multipoint communication system in which communication is performed between a single master unit and a plurality of slave units along a transmission line, and more particularly to a point-to-multipoint communication system in which adequate communication can be achieved even when signals containing several megabytes of data are transmitted in bursts.
BACKGROUND ART
Point-to-multipoint communication systems such as LANs, CATV networks, satellite communication networks, and optical subscriber access networks are commonly configured such that a master unit and a plurality of slave units communicate by sharing, for example, transmission lines such as those used in coaxial communication, optical-fiber communication, and radio communication.
Here, an access protocol for allocating the use of a shared transmission line among slave units is important for ensuring smooth communication between the master unit and the slave units via this transmission line. There are various types of access protocols.
For example, the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol is one in which “carrier sense+multiaccess+collision detection” is the basic principle of operation, and the DAMA (Demand Assign Multiple Access) protocol is one in which “transmission start demand/end notification+transmission line sharing/release” is the basic principle of operation.
In such point-to-multipoint communication systems, burst traffic in which signals containing several megabytes of data are generated in bursts is rapidly becoming more widespread because of the increased popularity of personal computers, a larger number of Internet users, and the development of various multimedia services that blend communication and broadcasting.
Conventional access protocols, however, have the following drawbacks that make these protocols incapable of handling burst traffic containing several megabytes of data, which is expected to grow even more in the future.
When, for example, information signals generated in bursts of several megabytes are transmitted according to the CSMA/CD protocol, the information signals are separated into packets of about 64-1500 kB and repeatedly transmitted. Consequently, increased burst traffic results in a markedly lower throughput because of the higher frequency of retransmission due to packet collisions.
Probability calculations conducted under conditions corresponding to a collision of about 15 packets show a throughput of about 40%, and a period that is 1.5-2.5 times the normal time is needed for data transmission accompanied by collisions. As a result, the delay time increases and is not constant any longer.
On the other hand, transmitting information signals generated in bursts according to a TDMA protocol increases the time needed to complete the transmission when the information signals being transmitted contain several megabytes of data, so an increase in burst traffic sometimes makes a transmission-awaiting slave unit to miss its time slot and to fail to operate within the delay time allowed for data transmission. Thus, conventional access protocols for point-to-multipoint communication systems are disadvantageous in that an increase in burst traffic containing several megabytes of data results in a lower throughput and makes it impossible to comply with time requirements for downstream transmission.
DISCLOSURE OF THE INVENTION
With the foregoing in view, it is an object of the present invention to provide a point-to-multipoint communication system in which adequate communication can be achieved even when signals containing several megabytes of data are transmitted in bursts.
According to the access protocol for the point-to-multipoint communication system of the present invention, the main principle of operation is that “a report is issued regarding the information amount necessary for signal transmission+an instruction regarding transmission below a specific maximum value is issued on the basis of the information amount reported.”
First, slave units about to transmit signals issue reports on the information amount needed to transmit the signals in accordance with instructions from the master unit. The master unit, upon receipt of the reports from the slave units, issues instructions for the slave units to transmit the signals at no more than a specific maximum number of kilobits on the basis of the reported information amount.
Because such an arrangement allows slave units to transmit signals in accordance with instructions from the master unit, no signal collisions occur in the transmission line and a throughput reduction such as that observed in the case of CSMA/CD is avoided when signals containing several megabytes of data are transmitted in bursts.
Another feature is that because signal transmission instructions are issued dynamically and efficiently on the basis of the information amount reported by slave units, high throughput can be obtained even under complex conditions created by greater burst traffic or an increased number of slave units.
The aforementioned specific maximum number of kilobits is set such that the following relation is satisfied:
k
≦(
r×td
)÷(&agr;×
m
),
where m is the total number of slave units (m is an integer), &agr; is the proportion of currently active slave units (0<&agr;≦1.0), r (b/s) is the data transfer rate, and td (s) is the delay time allowed for data transmission and determined by the system.
A slave unit can therefore continuously transmit large signals because it has exclusive use of the upstream transmission line during the transmission of signals whose maximum size is measured in k (bits).
Another feature is that when the maximum value is determined on the basis of the above equation and signal transmission instructions are issued for the slave units, a time of td seconds is necessary for the transmission if all the slave units transmit kilobit signals, making it possible to secure an allowed delay time of td seconds for data transmission by all the slave units.
Fairness is also ensured because all the slave units can invariably transmit their signals within the allowed delay time of td seconds.
Yet another feature is that the master unit can instruct the slave units to issue information amount reports in a dynamic mode in accordance with changes in the transmission line load, the information amount reported, and the like.
In the case of low transmission line load, for example, variations in information amount can be identified by the master unit at a higher speed by reducing the interval between the instructions for information amount reporting.
The master unit can therefore be more flexible in issuing signal transmission instructions under conditions of varying information amount from slave units, making it possible to reduce the latency time elapsed before a slave unit transmits a signal and to lower the capacity of the buffer memory required by the slave unit to temporarily store the signal.
In the converse case of high transmission line load, the band that can be used to transmit signals along a transmission line by increasing the interval between the instructions for information amount reporting, making it possible to increase the throughput even further.
Instructions for a slave unit to report information amount can thus be given in a dynamic mode, making it possible to reduce the latency time elapsed before the slave unit can transmit a signal, to reduce the capacity of the buffer memory required for the slave unit to temporarily store signals, and to increase throughput.
Another feature is that when no instructions have been issued for a slave unit to transmit a signal, the same effect can be obtained by issuing instructions for reporting the information amount of the slave unit and performing a look-ahead procedure for the information amount of each slave unit.
Yet another feature of the present invention is that slave units about to transmit information signals temporarily store these information
Hatate Yoshio
Ibe Hiroyuki
Nakao Masatoshi
Yuki Yoshinori
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Ton Dang
Tran Phuc
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