JPH04249448A - Congestion mitigation system for wide band isdn - Google Patents

Abstract

PURPOSE:To mitigate congestion by sending a request bit as '1' when the subscriber switch receives a request for mitigating congestion, and limiting up cells to be sent from subscribers. CONSTITUTION:Cell sent from another station via a relay line is multiplexed by FINF 26 at multiplexing section 23, is switched by ATM switch 24-2, is output from a distribution section 25-2 to each SINF 22, and is sent to each NT 20. On receiving a control information cell requesting for congestion moderation from another switch, the information is sent from FINF 26 to a congestion mitigation control section 27. The control section 27 discriminates the information, and sets the request bit at '1' at a predetermined ratio to SINF 22 relating to congestion moderation, whereby up cells to be sent from subscribers are limited, thereby being able to mitigate congestion.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a congestion mitigation system in a wideband ISDN in which information is transmitted by ATM cells and a home is connected from a network termination device to a bus based on the DQDB protocol. Broad-band ISDN
Integrated Services Digit
al Network) is currently being researched for practical use as an ISDN capable of wideband communication such as video. This broadband ISDN is currently
This is realized using a chronous transfer mode (asynchronous transfer mode). ATM is divided into short fixed-length packets called cells and transmitted.
Cells are exchanged/transmitted at M exchanges or nodes.

[0002] In ATM, a virtual line is set up and the necessary ATM cells are transmitted on that line, without leaving the line open, so that one transmission line can be connected to multiple virtual lines. share. A multiplexing method called statistical multiplexing is used for this multiplexing, and it is necessary to manage the information multiplexed onto one transmission path so that the total does not exceed the capacity of the transmission path. This creates a multiplexing effect and increases the efficiency of line usage, but research is underway on how to deal with congestion when it occurs. Subscribers who connect to such broadband ISDNs use a configuration in which multiple terminal devices in their homes are connected via a bus.
Ributed Queue Dual Bus) is considered to be the most likely option.

0003

2. Description of the Related Art FIG. 6 shows the system configuration of an ATM network, which is a broadband ISDN. In the figure, 60 is an ATM network;
Reference numeral 1 designates an ATM relay exchange (which may accommodate subscribers), 62 an ATM subscriber exchange, and 63 an in-home device. In-house equipment can be used by general subscribers, LAN or P
Some devices have a configuration that accommodates a large number of terminals such as BX (private branch exchange), but in this case, as in-home equipment, a certain number of terminals ( TE) 66 are connected in parallel via a bus 67. If the terminal (TE) 66 does not support ATM, the TE 66 is connected via a terminal adapter (TA) 65.

FIG. 7 shows the configuration of in-home equipment and cells of an ATM network. The in-home equipment of the ATM network is A. in FIG. As shown in the figure, a network termination device (
A plurality of terminals (TE) 66 or terminal adapters (TA) 65 are sequentially connected to the NT) 64 via a bus 67. The bus shown in the figure is based on the DQDB (Distribute Qu DB), which is considered to be a promising option for in-house ATMs.
An example of a configuration using the eue dual bus protocol is shown. The bus is connected to cells sent out from the NT64 (local exchange 62).
Downlink buses 67D and N
An uplink bus 67U is provided for inserting transmission information into empty cells generated from T64 at TA or TE and transmitting the information to NT64.

[0005] This DQDB protocol is an access contention control method, and the protocol is used for access contention control for the uplink bus. In the access contention control method using DQDB, B. A cell with the configuration shown in is used. In other words, the cell length is 53 bytes in total, consisting of 5 bytes for the header and 48 bytes for the information field proposed by CCITT, but the GFC field (General Flow Control: 4
2 bits are allocated as busy bits and request bits and used for contention control. This busy bit indicates whether the cell contains valid information or not, that is, whether the cell is already being used by another TA 65 (or TE 66, hereinafter simply referred to as TA 65), and the TA 65 transmits information to the cell. If inserted, insert busy bit = 1.

[0006] The request bit is used to notify the TA 65 of a transmission request (that there is information to be put in a cell) to the upstream side of the upstream bus by transmitting it to the downstream bus. The TA 65 inserts the request bit="1" to notify the transmission request. Each TA65 (TE) has a request counter (RC) and a down counter (
The request counter (RC) counts requests (transmission requests) on the downstream side of the upstream bus, and the down counter (DC) counts requests from other TAs (TEs) that have generated requests before itself. This is a counter that counts down to your turn in order to allocate cells first.

[0007] An overview of the access contention control method using DQDB will be explained using FIGS. 8 and 9. FIG. 8 is a state transition diagram in each TA or TE, and FIG. 9 is an explanatory diagram of the operation of the counter corresponding to the contention control procedure. As shown in FIG. 8, when it is initially in the idle state (80 in FIG. 8), when it becomes necessary to transmit a cell and a transmission request occurs, the request (Req) is sent down the bus 67D (80 in FIG. 7).
(see 81). This request corresponds to B. in Figure 7 above. Set the request bit of the cell to “1” as shown in
”

At this time, if the value of the request counter is not equal to 0, the value of the request counter is loaded into the down counter, the request counter is reset to "0", and a transition is made to the countdown state (83). If the request counter value = 0, Ready
(82). After transitioning to the countdown state, the busy bit of the cell on the upstream bus 67U (Figure 7
B. Each time "0" passes, the down counter is decremented by 1, and when it becomes "0", the state shifts to the ready state. When the state is ready, the busy bit is set to “0” on the upstream bus.
” cell arrives, transmits information on it and transmits it (ibid. 84).

The operation in each state shown in FIG. 8 will be explained with reference to FIG. A in FIG. represents the operation of the request counter from the idle state to request transmission, and the TA request counter counts down (-1) when a cell with busy bit = 0 passes on the upstream bus, and when a request bit = 1 passes on the downstream bus. Then count up (
+1). As a result, the number of request bits sent by the TA on the right side of itself is counted, and the number of unused cells that can be sent by the TA on the right side is counted down, so the request counter is currently Displays the number of cells that cannot be transmitted even after a transmission request is issued at the TA.

Next, B. of FIG. is the countdown state (83 in Figure 8) and ready state (82 in Figure 8) after transmitting the request bit, loading the value of the request counter to the down counter, and clearing the value of the request counter.
represents the operation of the request counter. In this state, the counting operation of the request counter is to know the number of the distributed queue after transmitting the cell. Therefore, when a cell with request bit = 1 passes on the downlink bus, it counts up (+1), but even if a cell with busy bit = 0 passes, it does not count down because it has not yet transmitted the cell itself.

The following C. in FIG. represents the operation of a down counter that transmits a request bit, loads the value of the request counter, and enters a countdown state (83 in FIG. 8). In this case, when busy bit = 0 passes,
The down counter counts down (-1) and becomes “0”.
”, the transmission is performed. By controlling in this way, contention control with small delay during access can be performed.

0012

[Problem to be Solved by the Invention] As mentioned above, a broadband ISDN that adopts the DQDB protocol in the premises
In communication, when congestion occurs on the network side, a method to alleviate congestion is to send ATM cells to the device where the congestion occurred (not only the ATM switch but also any processing device that processes ATM cells, etc.). One possible method is to limit cell transmission to certain subscribers. A conventional method for implementing this method is to send a request to limit the number of transmitted cells when congestion occurs to the subscriber transmitting to the device where the congestion occurred. Specifically, the busy bit of the cells generated from the upstream end of the upstream bus (the cell generator 64 of the network termination device NT in FIG. 6) is set to "1", and cells are transmitted at the requested rate. Which TA (
Even in TE), the cell is not used and becomes an invalid cell, and is discarded when it is received by a device such as an ATM switch. As a result, the number of cells transmitted to devices such as ATM switches that are congested is reduced, and congestion is alleviated.

[0013] The above system requires a function for transmitting empty cells to upstream terminals on the upstream bus, and requires a device to draw the upstream terminals on the upstream bus to the network terminal device NT. Furthermore, in order to draw in the upstream bus terminal to the network termination device NT, it is necessary to provide a cell-aware function in the network termination device NT. Additionally, a mechanism is provided in the subscriber exchange to notify the network termination device NT of cell restriction requests, and a mechanism is provided to the network termination device NT to receive the notification and to set the busy bit to “1” and send it in response to the request. The problem is that it is necessary to set up An object of the present invention is to provide a congestion alleviation method in a wideband ISDN that can alleviate congestion at ATM switches, nodes, etc. within the network without providing any new additional mechanisms to in-home equipment.

[0014]

[Means for Solving the Problems] FIG. 1 is a diagram showing the basic configuration of the present invention. In Figure 1, 1 is a terminal (or terminal adapter, hereinafter simply referred to as a terminal), 2 is a home bus using the DQDB protocol, 2D is a down bus, 2U is an up bus, 3 is a network termination unit (NT), and 4 is a subscriber line, 5
6 is a subscriber exchange (or node, processing device, etc.) of the broadband ISDN, 6 is a request generating means, 7 is a relaxation request determining means, and 8 is a transmitter. In the present invention, when an exchange in which congestion has occurred makes a mitigation request to the subscriber exchange that accommodates the subscriber line that transmits cells to that exchange, the subscriber exchange receives the maximum amount of mitigation requests from multiple exchanges. Determine the relaxation request and set a request bit in the cells transmitted to the downlink subscriber line at a rate corresponding to the request. This cell is directly sent from the home network terminal device to the home downlink bus 2D. Every time a request cell passes through each terminal,
By counting up the request counter, the number of cells to be transmitted is limited in accordance with the count value.

[0015]

[Operation] When congestion occurs in another exchange or the own exchange, the relaxation request determining means 7 of the subscriber exchange 5 receives a relaxation request corresponding to the congestion rate from the other exchange as a control signal (control cell). or input from a congestion management unit (not shown) within the local exchange. In this case, the mitigation request is sent along with a number representing the percentage by which the number of cells needs to be reduced from the current state to alleviate congestion. These ratios are compared in the relaxation request determining means 7, and the largest ratio is determined. This determination result is supplied to the request generating means 6. Request generation means 6
sets "1" to the request bit of the cell transmitted from the transmitter 8 at a frequency corresponding to the input ratio.

The NT3 logically sends the cells received via the downlink subscriber line to the downlink bus 2D in the home. When each terminal 1 identifies the cell passing through this downlink bus 2D and detects request bit = 1 in it,
Each request counter (not shown) is counted up (+1). This cell is received by any terminal within the house. When the request counter counts up, even if there is a terminal 1 that wants to send data to the NT 3 (and subscriber exchange 5), it will not be able to send data immediately because the request counter has counted more than a predetermined number. In that case, the rate at which information is sent to the subscriber exchange 5 and other exchanges is limited by the generation rate of cells with request bit = 1, and therefore congestion in the subscriber exchange 5 and other exchanges is alleviated. . The principles of this invention are applicable not only to restricting information transmission from subscriber exchanges to in-home equipment, but also to requests from congested exchanges to limit the amount of transmitted cells between exchanges. can.

[0017]

[Embodiment] FIG. 2 is a block diagram of an embodiment of an exchange, FIG. 3 is a block diagram of an embodiment of a subscriber line interface (SINF), and FIG. 4 is an operational flow diagram of the embodiment. is the operation flow of the entire system.B. is the processing flow in the subscriber exchange, and Figure 5 is the AT
FIG. 2 is a diagram illustrating a specific example of congestion occurring in an M network system. In Figure 2, 20 is an NT (network terminal equipment), 21 is an A
TM's subscriber exchange, 22 is a subscriber line interface (
SINF), 23-1, 23-2 are multiplex units (indicated by MUX), 24-1, 24-2 are ATM switches, 25-1
, 25-2 is a distribution unit (represented by DMUX), 26 is a trunk line interface (FINF), and 27 is a congestion control unit.

The FINF 26 is connected to other ATM exchanges via trunk lines, which are bidirectional transmission lines, and transmits and receives information cells and control signals between the exchanges. The information cells sent from NT20 are sent to SINF22 via the subscriber line.
is input to the FINF 26 (or SINF 22
) is output. Cells transmitted from other stations via the trunk line are multiplexed by the multiplexer 23-2 from the FINF 26 and sent to the ATM.
Switched by switch 24-2 and distributed to distribution section 25-2
is output from SINF22 to each N
Sent at T20.

When receiving a cell of control information requesting congestion alleviation from another exchange, the FINF 26 sends a cell to the congestion control unit 27.
The information will be sent to. The congestion control unit 27 controls each FINF
26 and performs control to set request bits to "1" at a predetermined ratio for the SINF 22 related to the occurrence of congestion. The NT 20 and a terminal or terminal adapter (not shown) have a configuration similar to the conventional one and perform a counting operation on cells with request bit=1, thereby limiting the cells to which information is transmitted.

The configuration of the SINF 22 shown in FIG. 3 is shown,
In the figure, 220 is a line terminal, 221 is a switch (S
W) Interface, 222 is request (REQ) 1
The cell sending unit 223 is a VPI/VCI conversion unit that converts the virtual path number and virtual channel number of the cell output from the ATM switch and transmitted to the subscriber. The SINF 22 in FIG. 2 receives instructions from the congestion control unit 27 for information cells output from the ATM switch 24-2 and distribution unit 25-2 in FIG. 2 and sent to the destination subscriber line. “1” is set in the request bit. That is, when an instruction to set the request bit sent from the congestion control unit 27 (FIG. 2) to “1” is input, the request 1 cell sending unit 222 sends the request bit to the distribution unit 25.
The second bit from the beginning of the header of the cell output from -2 is set to "1" and output to the switch interface 221.

The operational flow of the embodiment shown in FIG. 4 will be explained with reference to a specific example of the occurrence of congestion in the ATM network system shown in FIG. In FIG. 5, #1 to #3 are exchanges forming nodes, 53, 54 are subscriber exchanges, 52,
55 is an NT (network terminal equipment), 50 and 56 are TAs (terminal adapters) connected to each NT via a DQDB protocol bus, and 51 and 57 are TEs (terminals). A in FIG. In the operation flow of the entire system, when congestion first occurs at a node, the node where the congestion has occurred outputs a restriction request to the subscriber exchange that is transmitting the request to itself (40 in FIG. 4). To explain this using the example of FIG. ), node #1 requests a 30% limit, and subscriber exchange 53 requests a 10% limit.

The subscriber exchange 53 selects the largest restriction request (41). In the example of FIG. 5, the limit requests from each node #1, #2 and the own exchange are determined, and the maximum limit request, that is, 30%, is selected. In accordance with this maximum request, a cell with request bit=1 is transmitted to the designated subscriber line down bus (42). On the other hand, the NT52 (Fig. 5) transmits the cell contents as is to the in-home bus, and the TA52 connected to the in-home bus
In TE 51, the value of the request counter is counted up each time a cell with request bit=1 passes through as a DQDB operation (43), similarly to the description of the conventional example (see FIGS. 8 and 9).

[0023] Then, on the upstream bus, the cells with busy bit = 0 transmitted from the subscriber exchange 53 are transferred to the NT5.
0 to reach the subscriber exchange. Since the cell is an invalid cell without a destination, it is discarded by the local exchange 53 and is not transmitted to the destination (44). Therefore, the number of cells transmitted to all the nodes (nodes #1, #2) where congestion has occurred is limited to the requested number or more than the requested number, and the congestion can be alleviated (45). In this case, congestion in the subscriber exchange 53 itself is also alleviated.

[0024] Such congestion mitigation methods limit not only the nodes within the network, but also the transmission signals from the processing equipment (computer system) when communicating via the network. It can be implemented in a similar manner whenever desired (including in the subscriber exchange itself). Figure 4
B. is a processing flow in the subscriber exchange (53 in FIG. 5), in which the TA under management,
Limit the number of cells sent from the TE.

[0025]

[Effects of the Invention] According to the present invention, a DQDB bus is used in the home, and in broadband ISDN using ATM cells,
Even if congestion occurs within the network at subscriber exchanges, nodes, etc., cell transmission can be restricted and the congestion can be alleviated without adding any additional mechanism to the home equipment. Furthermore, by applying it between nodes (between exchanges) in a network, it is possible to restrict transmissions from other nodes when congestion occurs. This can improve the reliability of the broadband ISDN system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention.

FIG. 2 is an exemplary configuration diagram of an exchange.

FIG. 3 is an exemplary configuration diagram of a subscriber line interface (SINF).

FIG. 4 is an operational flow of the embodiment; is the operation flow of the entire system.B. is the processing flow in the subscriber exchange.

FIG. 5 is a diagram showing a specific example of congestion occurrence in an ATM network system.

FIG. 6 is a system configuration of an ATM network that is a broadband ISDN.

FIG. 7 shows the configuration of in-home equipment and cells of an ATM network.

FIG. 8 is a state transition diagram in each TA or TE.

FIG. 9 is an explanatory diagram of the operation of a counter corresponding to a contention control procedure.

[Explanation of symbols]

1 Terminal 2 In-home bus 2D using DQDB protocol Down bus 2U Up bus 3 Network terminal equipment (NT) 4
Subscriber line 5 Subscriber exchange (or node, processing device, etc.) 6 Request generating means 7
Mitigation request determination means 8 Transmitter

Claims (2)

[Claims] Claim 1: In a wideband ISDN in which information is transmitted by ATM cells and a home is connected to a network terminal device via a bus based on the DQDB protocol, in a processing device that relays nodes such as exchanges and cells that constitute the broadband ISDN network. When congestion occurs, a congestion mitigation request is notified to the subscriber exchange on the sending subscriber side of the cell, and upon receiving the notification, the subscriber exchange transmits the cell from the downlink subscriber line to the network termination equipment in the premises. A congestion mitigation method in wideband ISDN characterized by limiting uplink cells transmitted from subscribers by transmitting a request bit as "1". 2. In claim 1, when congestion occurs in nodes such as switching equipment in the broadband ISDN network and in each section of processing equipment that relays cells, a mitigation request including a rate to be restricted is sent to the sending subscriber side of the cell. Notify the subscriber exchange,
The subscriber exchange on the sending subscriber side of the cell accepts requests from the subscriber based on the maximum ratio among the multiple restriction ratios included in the mitigation request due to congestion that has occurred in the own exchange and in the mitigation request notified from each section. A congestion mitigation method in wideband ISDN characterized by limiting uplink cells to be transmitted.