JP3177673B2 - ATM network flow control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM network flow control method and, more particularly, to an ATM network flow control method capable of performing flow control even at an inexpensive terminal without lowering the transmission / reception efficiency of user information cells. About.

[0002]

2. Description of the Related Art Asynchronous transfer mode (Asynchronous transfer mode)
ous Transfer Mode (hereinafter referred to as ATM) is expected to be a future communication infrastructure, and has been actively researched recently. The ATM switching system is a system for transferring fixed-length packets called cells into a network. FIG. 1 shows a configuration example of an ATM network. In FIG.
Reference numerals 18 to 18 denote terminals, and 109 to 112 denote exchanges. Terminal 1
01 to 104 are connected to the exchange 109,
106 is connected to the exchange 112, and the terminals 107 to 108
Is connected to the switch 111, also exchange 109,11
1 and 112 are connected to the exchange 110. Terminal (1
01 to 108) are connected via exchanges (109 to 112).

In an ATM network, a logical connection called a virtual channel (hereinafter, referred to as VC) is set up in a transmitting / receiving terminal for communication, and a number called a VCI (virtual channel identifier) for specifying a VC is used for information transmission. Information is transmitted by describing it in the header of a cell as a unit. Further, the cell header section indicates whether the cell is a user information cell or a special cell (hereinafter referred to as a non-user information cell) for other contents (resource management, operation and maintenance (hereinafter, referred to as OAM)). ) Is indicated as PTI, which indicates whether or not the PTI is the same.
Shows an example of the cell structure. A cell is composed of a header section and a data section, and the header section includes the following GFC, VPI, VC
I, PTI, CLP, and HEC. GFC: Generic Flow Control (Procedure for preventing cell collision between terminals) VPI: Virtual Path Identifier (virtual path identification) VCI: Virtual Channel Identifier (virtual channel identification) PTI: Payload Type Identifier (information field or user information or control information) CLP: Cell Loss Priority (displays cells with low priority) HEC: Header Error Control (used for error detection of header part and cell synchronization)

In the ATM network, it is possible to increase the number of cells to be transmitted if the transfer information density is high, and to reduce the number of cells to be transmitted if the transfer information density is low.
Terminals with different speeds can be accommodated in the same switch, and a flexible network can be constructed.For example, if the originating terminal is high-speed and cells are sent from the originating terminal one after another, it will not be possible to transfer cells within the network. Cell may overflow. Thus, if an excessive amount of cells flows in compared to the amount of resources of the network, quality deterioration such as cell loss occurs. To prevent this, it is necessary to control the number of transmitted cells according to the reception situation, that is, perform flow control, while not contacting between the sending and receiving terminals, without sending out cells unnecessarily as the sending and receiving terminals. For this purpose, various flow control functions have been proposed in ATM networks. Many of these flow control functions send and receive non-user information cells that notify the congestion status and load status of the network and the receiving end on the VC, and the transmitting end adjusts the transmission amount of the cell amount accordingly. It was done. Usually, the transmitting / receiving end is a terminal, and the transmitting / receiving end of the non-user information cell is also a terminal. For flow control,
For example, edited by Shimada, Egawa, Sato, "Multimedia Network Series; Network Node Method", pp.1
17-118.

[0005]

SUMMARY OF THE INVENTION The conventional ATM described above.
The network flow control method has the following problems. a) By transmitting and receiving non-user information cells for flow control between terminals, the amount of non-user information cells increases,
The network resources are considerably consumed, and the transmission / reception efficiency of the user information cell deteriorates. b) Generally, inexpensive terminals do not have a flow control function and cannot transmit / receive control information or transmit according to control information.
Congestion occurs on the exchange to be relayed, quality deterioration such as cell loss occurs, and good communication cannot be performed. The present invention solves such a problem, and does not cause a decrease in the transmission / reception efficiency of the user information cell, and can perform flow control even at an inexpensive terminal having no flow control function. The purpose is to provide.

[0006]

In order to achieve the above object, the present invention provides an asynchronous transfer mode (ATM) network having a terminal and a switch, which connects between the two switches (flow control segment). V for transmitting and receiving flow control information for a bundle of flowing virtual channels (VC bundle)
C, and by transmitting and receiving flow control information on the VC by non-user information cells such as resource management cells and operation and maintenance (OAM) cells, flow control is performed not for each VC but for each VC bundle. It is characterized in that it is performed.

[0007]

According to the present invention, the flow control is performed not on the transmission / reception terminals of each VC but on the exchanges shared by the bundle of VCs. Since flow control is performed on the VC bundle in this manner, it is not necessary to transmit and receive non-user information cells for each VC, and these cells can reduce the consumption of network resources. Also, since good flow control works between exchanges, good communication can be provided even between terminals that do not have a flow control function.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows a state where the terminals 101 to 108 are communicating via the exchange in the configuration of the ATM network shown in FIG. For example, the terminal 101 is connected to the exchanges 109, 11
0 and 111, and communicates with the terminal 108.
2 is the terminal 107 via the exchanges 109, 110, 111
The terminal 103 communicates with the exchanges 109, 110, 1
The terminal 104 communicates with the terminal 106 via the switch 12, and the terminal 104 communicates with the terminal 105 via the exchanges 109, 110 and 112. A virtual channel VC is set between each of the plurality of communicating terminals.

[0009] Now, the terminal 101 sharing the originating and terminating exchange.
A VC connecting the terminal and the terminal 108 and a VC connecting the terminal 102 and the terminal 107 are considered as a “VC bundle” which is an object of the present invention, and a portion between the calling and terminating exchanges 109 and 111 is defined as a “flow control target segment”. The flow control target segments are not only between exchanges, but also exchanges, terminals,
Networks such as routers, bridges, and gateways
Although it is possible to define between any two entities (Network Entities), a typical case is between two exchanges described in the present embodiment. As described above, a new “flow control information VC” is set for the flow control target segment defined between the exchanges 109 and 111. The setting of the flow control information VC is performed by a method similar to the conventional VC setting between terminals. That is, in this case, if a cell for VC setting (specifying the destination terminal) is generated at the source terminal, the VPI / V is determined while determining whether network resources can be secured.
The CI is determined for each exchange, and a cell header exchange table is set on the exchange. In the VC bundle, if the amount of incoming cells becomes excessively large compared to the buffer amount in the exchanges 109, 110, and 111 or the output VC band, quality deterioration such as cell loss occurs. Therefore, exchanges 109 and 111
Between the non-user information cell (resource management cell and operation and maintenance (OA) by using the newly set “VC for flow control information” via the exchange 110.
M) cells, etc.) to transmit / receive congestion information and control information of the exchanges 110 and 111.

Next, an embodiment of the flow control operation in the exchange will be described. FIG. 4 is an operation flow of the exchange 109 on the transmission side. In FIG. 4A, the exchange 1 on the transmitting side is illustrated.
In step 09, when there is a transmission cell belonging to the VC bundle (step 1), if the transmission amount is larger than the threshold value, the transmission is temporarily suspended (step 7). If the transmission amount is within the threshold, the user cell is transmitted (step 3). The exchange has a device for storing a counter of the number of user information cells and a predetermined threshold value. The counter counts the user cells (step 4) and sends out a non-user information cell every time the threshold value is reached. The VC bundle transmission rate is notified, and the counter is reset (steps 5 and 6).

On the other hand, the exchanges 110 and 111 which have received the cell from the exchange 109 perform the operation shown in FIG. The exchanges 110 and 111 are performing the processing shown in FIG. That is, the number of cells in the buffer is measured (step 27), and if the measured value is equal to or smaller than the threshold value (step 28; N), the process returns to step 27 and the measurement of the number of cells in the buffer is continued. If the measured value is greater than the threshold (step 28; Y), the available band, ie,
A band that can be allocated to the same VC bundle among the VP bands is calculated, and the control information transfer required bit is set to “1” (step 29),
It returns to step 27 again.

The exchanges 110 and 111 first determine whether or not the cell is a non-user information cell (control information cell) based on a PTI (Payload Type Identifier) in the header of the cell received from the exchange 109 by the cell receiver. If it is an information cell (Step 21; N), the next NE
(Terminal) (step 26). Exchange 110,
Next, the control unit 111 determines whether the control information transmission required bit is "1" (step 22). If the control information transmission required bit is "1" (step 22; Y), the next At the time of receiving the user information cell, the calculated usable bandwidth is added or the unreceivable bit is written into the cell (step 23), and the control information transmission required bit is set to "0" (step 24) and returned to the exchange 109 (step 23). 25).
If the control information transmission necessary bit is not "1" (step 22; N), the control information is returned to the exchange 109 as it is (step 25). Instead of the "return to exchange 109" process in step 25, the cell may always be forwarded to exchanges 110 and 111 and returned to exchange 111, or may be returned only to the returning non-user information cell. The usable bandwidth and the like may be written.

In the exchange 109 on the transmitting side, the exchange 11
The cell returned from 0, 111 is received by the cell receiving unit (step 8), and it is determined whether or not the cell is control information based on the PTI in the header of the cell (step 9). If the result of the determination is that the information is control information (step 9; Y), its contents are read (step 10). The transmission rate of the user information cell of the VC bundle is controlled based on the reception availability information and the reception available rate information obtained as a result, and an appropriate amount is transmitted (step 11). Specifically, a queue of cells waiting to be transferred is configured in accordance with the VC bundle, and cells are taken out and transferred at a period according to the allocatable band provided by the cells each time a non-user information cell is received. I do. As a result, the V
The cell flow rate belonging to the bundle C can be controlled by reflecting the status of the exchanges 110 and 111. (In the prior art, flow control is performed by the same mechanism. However, in the prior art, since the unit of control is performed between terminals for each VC, non-users do not use a dedicated control information VC but use the same VC on the same VC as the user information cell. Control is transmitted and received by flowing information cells.)

FIG. 3 is a diagram showing a control range in the present invention. In the figure, a solid line with an arrow indicates a control range (flow control target segment) of “VC for flow control information” in the present embodiment, and a broken line with an arrow indicates each V
The control range for a part of C is shown (no control when the terminal does not have a flow control function). According to the conventional flow control method, individual VCs are controlled for each terminal. However, in the present invention, a common VC for flow control information is used between exchanges (flow control target segments) as shown in FIG. , And is individually controlled only between the transmission terminal and the exchange on the transmission side and only between the reception terminal and the exchange on the reception side.

[0015]

When the ATM network flow control method of the present invention is used, the amount of cells transmitted from the exchanges 109 to 110 can be controlled, so that no congestion occurs in the exchanges 110 and 111. Further, between the exchanges 109 to 111, the non-user information cell for control information may be transmitted and received for the VC bundle,
Congestion can be reduced as compared with the conventional method of performing flow control for each VC.

[Brief description of the drawings]

FIG. 1 is a general connection configuration example of a terminal and an exchange in the present invention and a conventional example.

FIG. 2 is a diagram for explaining a VC bundle according to the present invention.

FIG. 3 is a diagram showing a control range in the present invention.

FIG. 4 is an operation flow of the transmission-side exchange in the present invention.

FIG. 5 is an operation flow of the exchanges on the relay and reception sides according to the present invention.

FIG. 6 is a diagram illustrating a configuration example of a cell.

[Explanation of symbols]

 101 to 108: terminal, 109 to 112: exchange

Continuation of the front page (56) References IEICE Technical Report SS 92-102 (November 27, 1992) IEICE Technical Report CS 92-32 (June 24, 1992) Ueda Hiromi et al. , “Virtual path OAM technology”, NTT R & D, Vol. 42, No. 3, pp. 381-392, Telecommunications Association of Japan, March 10, 1993 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04L 12/28 H04L 12/56

Claims (1)

(57) [Claims] An AT having a plurality of terminals and a plurality of exchanges
Oite flow control method of M network, between two exchanges, setting the VC for flow control information transmission and reception with respect to a bundle of virtual channels that flows between the exchange (VC), the non-user information cells on the VC A which transmits and receives flow control information and performs flow control for each bundle of VCs.
TM network flow control method.