JPH04249444A - System for constituting incoming/outgoing integrated bus in communication equipment - Google Patents

Abstract

PURPOSE:To eliminate the necessity of preparing a circuit for generating a vacant cell to be supplied from a network terminal to an incoming bus regarding an incoming/outgoing integrated bus constituting method for a communication apparatus using a DQDB protocol as an access integrated control system in which a plurality of slave units are connected to a master unit through incoming/outgoing bus. CONSTITUTION:A master unit 2 is connected successively to a plurality of slave units 3, and the tail of outgoing bus 4 is folded and connected to the top of incoming bus 5. Further, the top of the incoming bus 5 is connected to a slave unit at the upmost stream of incoming bus, and via successive connection with a plurality of slave units the tail of the incoming bus 5 is connected to master unit 2, thereby using a cell used in outgoing bus as a vacant cell for use in incoming bus.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for configuring an integrated uplink and downlink bus in a communication device in which a plurality of slave devices are connected to a master device via an uplink bus and a downlink bus, and the DQDB protocol is used as an access integrated control method. In recent years, broadband ISDN (Broad-band ISDN)
egrated ServicesDigital
Research is progressing toward practical use of ISDN, which enables broadband communications such as video. This broadband ISDN is based on ATM (Asynchronous
It is effective to use the ous Transfer Mode (asynchronous transfer mode). ATM is transmitted by being divided into short fixed-length packets called cells, and the cells are multiplexed and transmitted at an ATM switch or node.

[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. Subscribers who connect to such broadband ISDNs use a bus-coupled configuration for multiple terminal devices in their homes, and in this case, the bus format is D.
QDB (Distributed Queue Dua)
l Bus) is seen as a likely candidate. When a communication device using this DQDB bus performs bus competition control between a plurality of terminals, it is necessary to provide a mechanism for creating empty frames on the upstream bus, so improvements in this are desired.

0003

2. Description of the Related Art FIG. 3 is a system configuration diagram of a broadband ISDN (ATM network). In the figure, 30 is a wideband ISD
N (ATM network), 31 is an NT (network terminal device) provided inside the house, and 32 is a plurality of TAs (terminal adapters) provided inside the house. Note that it is assumed that a terminal (TE), not shown, is connected to each TA. 33, 34
are a down bus and an up bus connecting between the NT 31 and each TA 32. The bus configuration shown in Figure 3 is based on DQDB (Distributed
This is an example of a configuration using the Queue Dual Bus protocol. A cell frame generated from the frame generation unit 310 of the NT 31 is output to the uplink bus 34, and is supplied to the TA 32 at the farthest end of the NT 31, and the TA with the transmission right inputs information into an empty cell using contention control, which will be described later. and send. In addition, cells sent from the network 30 are transmitted to the downlink bus 33, and each TA receives cells from the downlink bus 33 whose destination is its own TA (a cell whose destination address matches its own TA's address). I do. The cell on the uplink bus 34 is sent to the network 30 by extracting the cell into which information has been inserted at the NT 31 .

FIG. 4 is a block diagram of a conventional NT. NT3
1 is connected to the network by an optical line, and on the downstream side, the optical signal sent from the network is connected to an optical-to-electrical converter (O/E) 315.
is converted into electricity, and after processing in the downstream processing unit 311, electricity
The signal is sent from the optical converter (E/O) 312 to the downlink bus 33. In addition, the frame (for cells) created by the frame generation unit 310 is sent from the electrical-to-optical converter (E/O) 314 to the uplink bus 34, and passes through each TA to the optical-to-electrical converter (O/E). ) 313, processed by an upstream processing unit 317, and then transmitted from an electrical/optical converter (E/O) 316 to the network as an optical signal.

The DQDB protocol using the bus configurations shown in FIGS. 3 and 4 is an access contention control method, and the protocol is used for access contention control for uplink buses. In the access contention control method using DQDB, a cell having a configuration as shown in FIG. 5 is used. In other words, the cell length is C
The header proposed by CITT is 5 bytes and the information field is 48 bytes, totaling 53 bytes, but the GFC field (General Flow
Control: 4 bits), 2 bits are allocated as busy bits and request bits and used for contention control. This busy bit indicates whether the relevant cell contains valid information or not. In the case of a downlink bus, a cell sent from the NT 31 to any TA 32 has a busy bit of 1, but when the cell is received by the destination TA 32, the busy bit is changed to 0. On the upstream bus, when each cell is an empty cell, the busy bit is set to 0, but if any TA32 obtains the transmission right through contention control and inputs information to an empty cell, the busy bit is set to 1 and sent to the NT31. Send. Therefore, each TA 32 can determine the busy bit of each cell to identify whether that cell is already being used (transmission information input) by another TA 32.

[0006] An overview of the access contention control method using DQDB will be explained using FIGS. 6 to 9. Each TA 32 is provided with a request (REQ) counter and a down (DOWN) counter, and is controlled by this counting operation. The request counter has a busy bit on the upstream bus = 0.
It monitors cells with request bit = 1 on the downlink bus, and counts the number of empty cells required by TAs located downstream of the uplink bus. FIG. 8 is an explanatory diagram of the countdown of the request counter. That is, when a cell with busy bit=0 passes on the upstream bus, the request counter of the TA is counted down (-1).

FIG. 9 is an explanatory diagram of counting up the request counter. This operation is executed when a cell with request bit=1 passes through the downlink bus, and the request counter is counted up (+1). As a result,
You can detect the number of requests on the upstream side of the downlink bus. FIG. 7 is an explanatory diagram of the count up of the request counter and the subsequent clearing state. This state is executed when the own TA wants to transmit information by cell, transmits the request bit=1, loads the value of the request counter into the down counter, and clears the request counter.

FIG. 6 is an explanatory diagram of the countdown of the down counter. In other words, after performing the operation shown in Figure 8, the TA counts down the down counter every time a cell with busy bit = 0 passes through the uplink bus, and when the down counter value reaches "0", an empty cell is detected. When the cell arrives at the upstream bus, the transmission information is input to that cell and sent to the upstream bus toward the TA. In this way, the request counter counts cells with request bit = 1 on the downstream side of the upstream bus, and the down counter allocates cells first to other TAs that have issued requests before itself. Count down the cells with busy bit = 0 until your turn. Such control makes it possible to perform contention control with small delay during access.

[0009]

In the above conventional system, empty cells must be sent to the upstream bus from the network terminal (NT) in advance. Therefore, a frame generating section 310 (FIGS. 3 and 4) for generating frames (sending empty cells) in the NT is required, which poses a problem in that the scale of the NT apparatus increases. SUMMARY OF THE INVENTION An object of the present invention is to provide a system for configuring an integrated uplink and downlink bus in a communication device that can eliminate the need for a circuit for generating empty cells to be supplied from a network termination device to an uplink bus.

0010

[Means for Solving the Problems] FIG. 1 is a diagram showing the basic configuration of the present invention. In Figure 1, 1 is a network, 2 is a network termination device (N
Master device such as T), 3 is a terminal adapter (TA)
4 is a down bus, 5 is an up bus, 6 is a cell on the down bus, and 7 is a cell on the up bus, and the master device 2 and slave device 3 are using DQDB or a similar protocol that performs contention control. It operates by In the present invention, the end of the downlink bus that is sequentially connected to multiple slave devices is connected back to the tip of the uplink bus, and the cell that transmitted the downlink bus is used as a free cell on the uplink bus, thereby allowing the master device to connect to the uplink bus. This eliminates the need for a configuration for generating empty cells.

[0011]

[Operation] Cells input from the network 1 to the master device 2 of the communication device are sent to the downlink bus 4. Each cell 6 is sequentially transmitted to a plurality of slave devices via the downlink bus 4, and when the cell is received by the slave device 3 corresponding to the destination included in the cell, it is also transmitted downstream. The slave device 3 that has received the data sets the busy bit in its cell 6 to 0. After that, when each cell 6 reaches the terminal end of the down bus 4, the down bus 4 is connected back to the end of the up bus 5, so it is directly inputted to the slave device 3 at the most upstream side of the up bus, and then in the following order. It is transmitted on the upstream bus according to the following.

[0012] Cell 7 of uplink bus 5 has already passed the information therein to one of the slave devices from cell 6 of downlink bus, so even if some information remains, it is unnecessary information. Therefore, on the upstream bus 5, that cell is used as a cell with busy bit = 0, and the above-mentioned conventional DQD
Similar to control method B, each slave device 3 uses this cell as an empty cell in contention control, and the slave device 3 that has the transmission right writes information to be transmitted into the cell and transmits it toward the master device 2. Can be done. In this way, it is no longer necessary to provide the master device 2 with a frame generation section for generating empty cells.

[0013]

Embodiment FIG. 2 is a block diagram of an embodiment of a network termination device. In FIG. 2, 2 is a network terminal device (NT: corresponds to the master device in FIG. 1), 20 is a downstream processing section, 21 is an upstream processing section, and 22
, 25 is an electrical/optical converter (E/0), 23, 24 is an optical/optical converter (E/0), and 23, 24 are optical/optical converters (E/0).
This is an electrical converter (O/E), and the other configurations are the same as in FIG. Although not shown, a plurality of terminal adapters TA corresponding to the slave device 3 of FIG. 1 are sequentially connected to the down bus 4 and up bus 5 as in FIG. 1. In the configuration of FIG. 2, cells from the network 1 are input to the optical-to-electrical converter 24 of the NT2, processed by the downstream processing section 20, and transmitted from the electrical-to-optical converter 22 to the downstream bus 4. After the busy bit of the cell transmitted on the downlink bus 4 and received by the destination TA (not shown) is rewritten to "0",
Information other than the busy bit in the cell is sent directly to the upstream bus 5.
appears upstream of After that, the cell into which transmission information has been input from the TA that has obtained the transmission right through bus contention control is input to the optical-to-electrical converter 23 of the NT2, and in the upstream processing unit 21, the cell with busy bit = 1 is The signal is sent from the optical converter 25 to the network 1 as an optical signal.

[0014] In FIGS. 1 and 2 above, an example of detecting a cell with "busy bit = 0" was explained as a method for identifying unnecessary cells, but there is also a method of detecting "VPI/VCI = all 0". There are other possible methods. However, with this method, after passing the information to the terminal adapter (TA) on the downlink bus, that terminal adapter
This method is disadvantageous compared to the method of detecting with busy bit=0 in that it is necessary to set all PI/VCI to 0, and a configuration for that purpose is added.

[0015]

According to the present invention, when using the DQDB contention control method, there is no need to send empty cells from the master device (network terminal device) to the uplink bus, so there is no need to provide a frame generation mechanism. The master device can be downsized.

[Brief explanation of the drawing]

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

FIG. 2 is a configuration diagram of an embodiment of a network termination device.

FIG. 3 is a system configuration diagram of a broadband ISDN (ATM network).

FIG. 4 is a configuration diagram of a conventional NT.

FIG. 5 is a configuration diagram of a cell used in an access contention control method using DQDB.

FIG. 6 is an explanatory diagram of a countdown of a down counter.

FIG. 7 is an explanatory diagram of the count up of a request counter and the subsequent clearing state.

FIG. 8 is an explanatory diagram of a countdown of a request counter.

FIG. 9 is an explanatory diagram of counting up a request counter.

[Explanation of symbols]

1 Net 2 Master device 3 Slave device 4 Downbound bus 5 Upbound bus 6 Cells on the downbound bus 7 Cells on the upbound bus

Claims (1)

[Claims] Claim 1: In a communication device in which a plurality of slave devices are connected to a master device by an uplink bus and a downlink bus, and the DQDB protocol is used as an integrated access control method, the master device is sequentially connected to the plurality of slave devices, and the master device The terminal end of the downlink bus that transmits the cells sent from the uplink bus is looped back and connected to the top end of the uplink bus, and the end of the uplink bus is connected to the most upstream slave device of the uplink bus, and the end is connected sequentially through a plurality of slave devices. A system for configuring an integrated uplink and downlink bus in a communication device that is connected to a master device and uses cells used on the downlink bus as vacant cells on the uplink bus.