JPH08195751A - Traffic shaper - Google Patents

Abstract

PURPOSE: To improve the efficiency of a network by setting a new TAT just before an ideal transmission time TAT through a prescribed arithmetic operation so as to send cells close to an ideal state. CONSTITUTION: A shaper algorithm 101 uses a TATb of other cell sent just before and a transmission line speed (a) to obtain a TAT corresponding to TATb+1/a. When a buffer memory at a location of a ring memory corresponding to the time is idle, a write pointer 102 is used to write the cell thereto. When not idle, the cell is written in an idle buffer memory at a time just before the write time. The processing is repeated to avoid a transmission time from being apart from an ideal time thereby sending a cell to a time closest to the ideal transmission time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is installed at an interface point between a communication network that handles an asynchronous transfer mode, in particular, a packet switching communication network and a device outside the communication network, and attempts to send the data. The present invention relates to a traffic shaper that determines the transmission time of a cell by using the transmission time of another cell transmitted immediately before and the transmission path speed and performs congestion control of the traffic generated in a communication network.

[0002]

2. Description of the Related Art In ATM, a traffic shaper is effective for preventing network congestion and improving network utilization efficiency. Traffic shaper is installed at the entrance of the net,
(Article 1) Pierre E. Boyer et al. IEEE Network 1
992 September paper “Spacing cells protects
For cells arriving at the shaper as suggested in “and enhances utilization of ATM network links”,
This is a kind of delay circuit that controls the transmission of cells by determining the time TAT to be transmitted by adding an appropriate delay time. This TAT is ideally 1 / a from the time TATb at which the immediately preceding cell should be transmitted to the cell arriving at the shaper when the transmission rate is a as proposed in paper 1, for example. Delayed, ie TATb + 1 /
TATb + at the time of a or delayed by 1 / a or more
It is decided at a time later than 1 / a. At this time, in order to fulfill the original purpose of the shaper, it is necessary to send at the ideal sending time, that is, at a time close to TATb + 1 / a. It should be noted that this TAT is the ideal time to be sent, not the time at which it was actually sent.

In this system, in a cell synchronization system, that is, in a system in which a cell transmission cycle is constant, dummy cells are transmitted even when there is no cell to be transmitted, and cell transmission is performed at a constant timing anyway, When 1 / a is a decimal, there is a problem that TAT = TATb + 1 / a becomes a decimal. Further, if another cell to be transmitted has already been scheduled at the time of TAT, there is a problem that the cell cannot be transmitted.

In the above paper 1, the smallest integer value not smaller than TAT is set as a new TAT, and if another cell to be transmitted already exists at the time of the new TAT, another cell to be transmitted as the new TAT. Smallest quantized TAT without
It is stated to be a value.

[0005]

In this conventional method, the new TAT is the original ideal transmission time TAT when many other cells are scheduled at the TAT transmission time of the cell and the time after that. There is a problem that they are far apart.

An object of the present invention is to solve the above problems and provide a traffic shaper capable of providing a new TAT so that the new TAT is as close as possible to the original ideal transmission time TAT.

[0007]

A traffic shaper of the present invention is installed at an interface point between a communication network handling an asynchronous transfer mode and a device outside the communication network, and determines a transmission time TAT of the cell. Using the transmission time TATb of the other cell transmitted immediately before and the transmission line speed a, the following equation TAT = TATb + 1 / a is calculated, and the calculation result is quantized per unit time to determine the actual cell transmission time. In the traffic shaper, when the result of the above formula is a decimal number, an ideal transmission that determines an integer value that is an integer value smaller than the result of the above formula and is the ideal transmission time of the cell It has a time determination means.

Further, if the ideal transmission time determined as the ideal transmission time of the cell has already been determined as the transmission time of another cell, the ideal transmission time determining means transmits the other cell. It is preferable to determine the largest integer value that is the transmission time not determined as the time as the ideal transmission time of the cell.

[0009]

Consider a case in which another cell is already scheduled to be transmitted at and after the ideal transmission time TAT, and another cell is not scheduled to be transmitted immediately before the ideal transmission time. The traffic shaper of the present invention can avoid the problem that the sending time is far from the ideal time by searching after TAT as in the conventional method, and the new TA is set just before TAT.
Since T can be set, cells can be transmitted at a time as close as possible to the ideal transmission time.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the traffic shaper of the present invention. FIG. 2 is a diagram showing an algorithm of the traffic shaper of the embodiment of FIG. The ideal transmission time calculation algorithm 101 determines the ideal transmission time TAT for the arrived cell (ideal transmission time TAT
When determining, the algorithm shown in Reference 1 is used. Note that TAT is referred to as TRT in Reference 1.) The ring memory 104 is a buffer memory for accumulating cells and is logically ring-shaped. Therefore, in the following description, when reading or writing, the physical head or the physical end of the ring memory 104 is used. It is not necessary to be aware of. Here, for the sake of convenience, the position pointed by the read pointer (that is, the point where the reading is being performed) is set as the head of the buffer memory.
Therefore, the head of the buffer memory can be physically changed.

A cell is input / output to / from the ring memory 104 by a write pointer 102 and a read pointer 103 which operate independently. In particular, the read pointer operates sequentially and reads the buffer memory sequentially so as to send cells to the network without interruption. At this time, even if there are no cells in the buffer memory (the buffer memory is empty), the read operation is performed, and as a result, an empty cell is sent to the network. Therefore, once the buffer memory location is determined (writing to the buffer memory), the time at which the buffer memory is read is also determined by calculation from the buffer memory location.
The write pointer, on the other hand, is a pointer for writing a cell to an appropriate buffer memory location, which is determined according to the time to be read, ie the ideal delivery time. As for this ideal sending time, the ideal sending time TAT is calculated by using the algorithm shown in Reference 1.
To decide.

In cell writing, an algorithm 200 as shown in FIG. 2 is applied to calculate the ideal transmission time TAT determined by the shaper algorithm 101 (S1). If the buffer memory at the position corresponding to the time corresponding to the ideal transmission time TAT is free, the cell is written there (S2). If the position is not empty, that is, another cell has already been written, the position of the time immediately before the time when writing is attempted is checked, and if it is empty, the buffer memory position is written. If it is not empty, this operation is repeated (S3). When reaching the head position of the buffer memory, it may be possible to switch to the conventional method because it is impossible to find a writing place any more.

[0013]

As described above, according to the present invention, in order to avoid the problem that the sending time is far from the ideal time by searching after the TAT, the ideal sending time is set by setting the new TAT immediately before the TAT. It is possible to achieve the original purpose of the shaper, which is to send out cells at a time as close as possible. As a result, there is an effect that the utilization efficiency of the network is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the architecture of one embodiment of the traffic shaper of the present invention.

FIG. 2 is a diagram showing an ideal transmission time determination algorithm in the embodiment of FIG.

[Explanation of symbols]

 101 Shaper Algorithm 102 Write Pointer 103 Read Pointer 104 Ring Memory

Claims (2)

[Claims] 1. A transmission network which handles an asynchronous transfer mode and a transmission time TATb of another cell which is installed at an interface point between a device outside the communication network and which has transmitted the transmission time TAT of the cell immediately before. In the traffic shaper that calculates the following formula using the transmission path speed a, TAT = TATb + 1 / a, and quantizes the calculation result in unit time to determine the actual cell transmission time, the result of the above formula is a decimal number. In this case, the traffic shape is characterized by having an ideal transmission time determining means for determining the largest integer value smaller than the result of the above equation as the ideal transmission time of the cell. Pa. 2. The ideal transmission time determination means, when the ideal transmission time determined as the ideal transmission time of the cell has already been determined as the transmission time of another cell,
The traffic shaper according to claim 1, wherein a transmission time that has not been determined as a transmission time of another cell, and the largest integer value is determined as an ideal transmission time of the cell.