JPH057205A - Packet transmission control system - Google Patents

Abstract

PURPOSE:To suitably limit the number of packet transmittable terminal devices, to lessen the generation frequency of the collision of data and to decrease the overhead by a back-off processing. CONSTITUTION:The system has a first timer 101 to inform of the start of the TC(Terminal Controller) cycle of a certain constant time, a counter 102 to increment or decrement by the detection or the non-detection of a carrier on transmission media, a second timer 104 to start to count the packet transmittable time by a self-edge station device, a random number generator 106 to generate each time the TC cycle of the first timer is started, a delaying control part 105 to a delay flag signal for a random time by the random number generating signal, and a transmitting receiving control part 109 to perform the packet transmission by the active of the flag signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet transmission control system, and more particularly to a CSMA / CD (Car) access system.
rier Sense Multiple Acces
s withCollision Detectio
The present invention relates to a packet transmission control method that reduces the frequency of collision of packets in a local area network using the n) method and reduces the overhead due to backoff processing.

[0002]

2. Description of the Related Art Conventionally, a packet transmission control system of this type has a transmission medium 209 of a general local area network shown in FIG. 2 and a plurality of terminal devices 2 connected thereto.
When the transmission medium 209 is empty like 01 to 208, all the terminal devices 2 which are always connected to the transmission medium
01-208 were allowed to send packets.
Next, a specific access procedure of the terminal devices 201 to 208 will be described.

A terminal which is going to transmit a packet carries out carrier detection (CS) on the transmission medium and checks whether or not the transmission medium is empty. Next, when the availability of the transmission medium is confirmed, the packet is sent out. A plurality of terminals each perform the above-mentioned confirmation and share one transmission medium. Now, when two or more terminals happen to simultaneously check the vacancy of the transmission medium and each send out a packet, the packets collide with each other on the transmission medium to cause interference. Therefore, collision detection (C
When the packet collision is detected in D), all the collided packets are invalidated and the transmission operation of each terminal device is started again. At this time, in order to reduce the probability of re-collision, each terminal has taken appropriate timing called back-off algorithm to prevent the collision.

[0004]

In the above-described conventional packet transmission control method, backoff processing is performed because collisions frequently occur when transmission media are crowded, but this backoff processing increases overhead. There are drawbacks. Therefore, each terminal device has a drawback that it is kept waiting for a long time or is judged to be out of order and transmission is stopped.

[0005]

A packet transmission control system of the present invention is a packet transmission control system of each terminal device connected to a transmission medium of a local area network using a CSMA / CD system as an access system. , TC (Terminal control) for a certain period of time
a first timer notifying the start of a cycle, incrementing if a carrier on the transmission medium is detected, decrementing if no carrier is detected,
Further, a counter that performs an operation in which the self terminal device sets all bits to 1 after transmitting a packet each time there is a TC cycle start notification of the first timer, and the start of the TC cycle is notified by the first timer. At the same time, the amount of time during which the own terminal device is allowed to transmit packets in this cycle is determined by the value of the counter, and a second timer that starts counting the time and the first timer Flag generator for generating a flag signal that becomes active when the timer of the first timer notifies the start of the TC cycle and becomes inactive when the second timer finishes counting, and a TC cycle start notification of the first timer. And a random number generator that generates a random number each time there is a value of the counter and the random number generator in one TC cycle. The random number delays the flag signal by a random time so that the pulse indicating the active state of the flag signal stays in this cycle as it is, and is delayed by the random delay time immediately after the start of this cycle. The delay control unit that controls the flag signal to be inactive, and that the flag signal delayed by the delay control unit is active are one of the conditions for the terminal device to perform packet transmission. And a transmission controller.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a terminal device that performs a packet transmission control method according to an embodiment of the present invention, and FIG. 3 is a timing chart for explaining the operation of the terminal device. In FIG. 1, 10
1 is TC (Terminal controller)
A timer A for notifying the start of the cycle, 102 is a 2-bit counter for measuring the congestion degree of the transmission medium 112, 103 is a flag set by the timer A 101 and reset by the timer B, 104 is within 1 TC cycle of the terminal device. A timer B, 105 for counting the packet transmission permission time, has a delay control unit for delaying the output signal of the flag 103 by a random time according to the random number generated by the random number generator 106 and the value of the counter 102, 106 is a random number generator, 107 Is a CPU, 108 is a transmission / reception buffer, 109
Is a transmission / reception control unit, 110 is an internal bus of the terminal device, and 111
Is a transceiver and 112 is a transmission medium.

Next, the operation of this embodiment will be described with reference to the timing chart of FIG. C0 to C in FIG.
Each of the 7 cycles represents 1 TC cycle. In this example, the counter 10 indicates the rate per 1 TC cycle in which the terminal device has the packet transmission permission time.
The value of 2 determines the ratio of the transmission permission time as shown in the explanatory diagram of FIG. TC of C1 by timer A in FIG.
When notified that the cycle has started, flag 10
3 is set to “1” (P1 in the figure), the random number generator 10
6 outputs the random number RN1. The counter 102 receives the information that the carrier exists on the transmission medium 112 from the transmission / reception control unit 109 and counts up the counter value from “2” to “3” as shown in FIG. The value "3" of the counter 102 determines how much time the terminal device is allowed to transmit packets within the TC cycle of C1 and starts counting the time. Then, the flag 103 is reset by the count end instruction of the timer B. During the TC cycle of C1, the delay control unit 105 determines how much the output signal P1 of the flag 103 is delayed by the random number RN1 output from the random number generator 106 and the value “3” of the counter 102, and the flag 103 A signal (hereinafter referred to as "transmit enable") D1 obtained by randomly delaying the output signal is output. At this time, the output signal of the flag 103 is delayed by the delay control unit 1 after the TC cycle of C0 is completed.
Since there is a vacant time corresponding to the delay time as shown by D1 in FIG. 3 until the output from 05, the transmit enable is controlled during this time. The delay time determined by the delay control unit 105 is the flag 1 generated in the TC cycle of C1.
The pulse P1 indicating the active state of 03 should be a delay time such that the pulse P1 appears as it is, without being transformed, in the TC cycle of C1 as a transmit enable. Since the pulse width of the pulse P1 depends on the value of the counter 102, in order to determine the delay time in the delay control unit 105, it is necessary to consider the value of the counter 102 in addition to the random number output from the random number generator 106. is there. Therefore, if the value of the counter 102 is "0" (C5, C
6 TC cycles), the delay time in the delay control unit 105 must be “0”. The transmit enable output from the delay control unit 105 is input to the transmission / reception control unit 109. The transmission / reception control unit 109 determines that a packet to be transmitted exists in the transmission / reception buffer 108,
Even if there is no carrier on the transmission medium 112,
Control is performed so that transmission is disabled unless the transmit enable is active, but the other packet transmission / reception procedures operate in exactly the same manner as the normal CSMA / CD method.

Thereafter, the random number generated by the random number generator 106 and the counter 10 are counted every TC cycle of C2, C3 and C4.
The above operation is repeated while changing the counter value of 2. The random number generated by the random number generator 106 is C
Random number R for each TC cycle of 0, C1, C2, C3 ...
N0, RN1, RN2, RN3, ...
The counter value of the counter 102 is incremented by "1" when the carrier is detected and "1" when the carrier is not detected each time the start of the TC cycle is notified by the timer A101.
Is only decremented. However, the counter value is "3"
When the carrier is detected in the state of, the counter value is maintained at "3", and when the carrier is not detected in the state of the counter value of "0", the counter value is maintained at "0".
Further, after the packet transmission of the own terminal device, in order to prevent one terminal device from monopolizing the transmission medium, the counter value is set to "3" like the TC cycle of C8 to shorten the packet transmission permission time of the own terminal device, After that, the counter value changes depending on the carrier detection state as described above.

[0009]

As described above, the present invention has a carrier counter for measuring the congestion degree of a transmission medium, and a transmitter for controlling the ratio of active time per unit time by this counter value. -By generating an enable signal and performing transmission control so that this transmit enable signal is one of the conditions under which this terminal device can transmit packets, the number of terminal devices that can transmit packets is appropriately limited, and It is possible to reduce the frequency of collisions of the data and reduce the overhead due to the backoff processing. Further, by temporarily shortening the active time of the transmit enable signal after the packet transmission of the own terminal device, it is possible to prevent one terminal device from monopolizing the transmission medium.

[Brief description of drawings]

FIG. 1 is a block diagram of a terminal device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a shape of a general local area network.

FIG. 3 is a timing chart of the present embodiment.

FIG. 4 is an explanatory diagram of the present embodiment.

[Explanation of symbols]

 101, 104 Timer 102 Counter 103 Flag 105 Delay Control Unit 106 Random Number Generator 107 CPU 108 Transmission / Reception Buffer 109 Transmission / Reception Control Unit 110 Internal Bus 111 Transceiver 112 Transmission Medium 201-208 Terminal Device (T) 209 Transmission Medium

Claims (1)

Claim: What is claimed is: 1. In a packet transmission control method of each terminal device connected to a transmission medium of a local area network using a CSMA / CD method as an access method, TC ( Terminal cont
first timer for notifying the start of a cycle, incrementing when a carrier on the transmission medium is detected, decrementing when a carrier is not detected, and the terminal device transmits all bits to all bits after packet transmission. 1
A counter for performing the operation of setting the TC cycle each time there is a TC cycle start notification of the first timer, and at the same time the start of the TC cycle is notified by the first timer Active by deciding how much time is allowed to be reached by the value of the counter and starting counting the time by the second timer and the first timer notifying the start of the TC cycle. A flag generator that generates a flag signal that becomes inactive when the second timer finishes counting, and the TC of the first timer.
A random number generator that generates a random number each time there is a cycle start notification, and in a certain 1TC cycle, a pulse indicating the active state of the flag signal according to the value of the counter and the random number generated by the random number generator remains unchanged in this cycle. A delay control unit that delays the flag signal by a random time so as to fit, and controls the delayed flag signal to become inactive by the amount of the random delay time immediately after the start of this cycle, A packet transmission control method comprising: a transmission control unit that makes one of the conditions for the terminal device to perform packet transmission that the flag signal delayed by the delay control unit is active.