JPH04291545A - Interface device - Google Patents

Abstract

PURPOSE:To prevent step-out of a frame in a private line network even when abort of an ATM cell takes place in an ATM network with respect to the interface device connecting to the ATM network and the private line network, revising data construction and implementing data transmission. CONSTITUTION:Abort of an ATM cell fed from an ATM network caused in an ATM network 1 is detected depending whether or not a signal including frame information is in existence and when the loss of the cell is detected, a frame insert means 3 outputs frame information to be synchronized to a private line network 4. The private line network 4 maintains the frame synchronization by outputting the frame information and step-out of the system cell abort is prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission system, and more particularly to an interface device for connecting different communication networks.

0002

[Prior Art] The ATM switching equipment currently being developed is AT
Switching operations are performed in units of cells called M cells. This AT
The M cell has a 5-byte header and consists of a total of 53 bytes. The ATM switch performs cell switching in units of ATM cells and transfers data.

On the other hand, dedicated line networks established before the development of ATM exchanges transmit data using frames consisting of 192 bits, each consisting of a pair of frame information and data. For example, PCM24B etc. is 1.544 M
Frame information and data are transmitted sequentially at a transfer rate of b/sec. Figure 4 shows an ATM network 11 and a leased line network 10.
FIG. 2 is an explanatory diagram of a system connecting the two. Leased line network 10 and A
An interface device 12 is provided between the TM networks 11. This interface device mutually converts data transfer in units of frames and data transfer in units of cells as described above.

FIG. 5 is an explanatory diagram of signal conversion. Signal A is a frame signal input from or output to the leased line network 10, and signal B is an ATM cell signal input from or output to the ATM network 11. The interface device 12, as shown in FIG.
This is a device that converts information in units of frames into units of cells, and information in units of cells into units of frames. For example, when signal A is input from the dedicated line network 10, its frame information and data are carried on ATM cells. In other words, create an ATM cell header (5 bytes), then a sequence number (1 byte), and then 47 x 8 bits (
47 bytes) of information is generated from the input frame. That is, the frame from signal A is divided into units of 47 bytes, stored in a data area within a cell, and transmitted. Also,
The reverse is true from the ATM network 11 to the dedicated line network 10.

[0005]

Problem to be Solved by the Invention In the ATM network 11, cell discard may occur due to cell collision. For example, if a large number of data transfer requests are made to a specific node within the ATM network 11, and the node exceeds its capacity, the received cells will be discarded. A
The TM network 11 takes this discard into consideration, and
No problems occur within the network 11. However, when the aforementioned dedicated line network 10 and ATM network 11 are connected via an interface device, when the ATM cell SX in signal B in FIG. 5 is discarded due to cell collision, for example, two frames are discarded. The frame bit F was lost, which caused a communication quality problem. Particularly in PCM-24B, if frame synchronization is lost, frame synchronization must be reestablished from multiple frames, and ATM
Discarding one cell would affect multiple frames.

The present invention resides in an interface device that stabilizes synchronization without losing frame synchronization even in the event of such cell discard, and ensures communication.

[0007]

[Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the present invention. The frame synchronization means 2 monitors frame information multiplexed on the signal from the ATM network 1. For example, the frame synchronization means 2 uses an ATM signal containing frame information.
In network 1, it is detected that an ATM cell is lost due to discarding.

[0008] The frame inserting means 3 inserts the frame information generated by the frame synchronizing means 2 when the frame synchronizing means detects that a signal including frame information is lost due to the discarding of ATM cells in the ATM network. It is output to the dedicated line network 4 as a signal.

[0009]

[Operation] An interface device provided between an ATM network and a dedicated line network detects whether an ATM cell added from the ATM network is discarded in the ATM network based on whether or not a signal containing frame information exists. , when detecting that this cell is lost, the frame inserting means 3 outputs frame information to be synchronized to the dedicated line network.

[0010] By outputting this frame information, the leased line network can maintain a frame synchronized state, and it is possible to prevent the system from becoming out of synchronization due to cell discard.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings. FIG. 2 is a block diagram of the first embodiment of the present invention. ATM
A signal smoothing circuit 21 is connected to the network. The signal smoothing circuit 21 is a circuit that converts cell-based information added from the ATM network into frame information. The frame converted by the signal smoothing circuit 21 is output to the dedicated line network via the frame pattern insertion circuit 22. Further, the output of the signal smoothing circuit 21 is also applied to the frame synchronization circuit 23. The frame synchronization circuit 23 is a circuit that detects frame bits from the frame information output from the signal smoothing circuit 21. If no frame bit is detected, i.e. ATM
When a cell is discarded in the network and a target cell is not received, the frame synchronization circuit 23 instructs the frame pattern insertion circuit 22 to generate a frame pattern provided for the lost cell, that is, the discarded cell. The frame pattern insertion circuit 22 forcibly inserts a frame pattern in response to the frame synchronization signal output from the frame synchronization circuit 23 in response to this insertion instruction. Note that this insertion is forced only during backward protection to prevent false synchronization on the leased line side. That is, the frame pattern insertion circuit 22 inserts a frame when frame synchronization is lost due to cell discard. For example, if a frame bit is inserted when the frame is out of synchronization from the beginning, it will become even more difficult to achieve synchronization, so in this case, the frame bit is not forcibly inserted.

FIG. 3 is a block diagram of a second embodiment of the present invention. In the first embodiment described above, the frame synchronization circuit 2
In the second embodiment of the present invention, frame omissions are extracted in the signal smoothing circuit 31. Naturally, a number checking circuit 32 for checking the frame number is provided in the signal smoothing circuit 31.
When the frame number is not detected by the number check circuit 32, the frame synchronization circuit 33 is notified that there is no frame. In response to the signal, the frame synchronization circuit 33 outputs a synchronization signal and an instruction signal for generating a frame pattern to the frame pattern insertion circuit 34. The frame pattern insertion circuit 34 inserts frame information at a target position based on the synchronization signal and instruction signal.

As mentioned above, the signal smoothing circuit 31 is an ATM
A leased line network frame is obtained from ATM cells input from the network. At this time, we also check the frame number, so
If the received and converted frame number is not the next frame number, it is determined that the cell is discarded and outputs to that effect. This function is necessary to smooth the signal, and by using this function, it is only necessary to perform frame synchronization and frame insertion.

As described above, according to the present invention, in the interface device between the ATM network and the leased line network, the ATM
Frame loss caused by cell discard within the M network can be continued without losing frame synchronization. It should be noted that the present invention is not limited to ATM networks and leased line networks, but can be similarly applied as long as the relationship between cells and frames is converted.

[0015]

[Effects of the Invention] As described above, according to the present invention, the AT
Even if frames are lost due to cell discard in M network etc., communication can be performed without losing frame synchronization.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the principle of the present invention.

FIG. 2 is a configuration diagram of a first embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a system explanatory diagram.

FIG. 5 is an explanatory diagram of signal conversion.

[Explanation of symbols]

1 ATM network 2 Frame synchronization means 3 Frame insertion means 4 Dedicated line network

Claims (3)

[Claims] 1. Frame synchronization means (2) for monitoring frame information of a signal containing multiplexed frame information from an ATM network (1);
When the frame synchronization means (2) detects that frame information and data are lost due to the discarding of ATM cells in the ATM network, the frame information generated by the frame synchronization means 2 is used as a signal to transmit the frame information and data to the leased line network (4). 2.) An interface device characterized by comprising: a frame insertion means (3) for outputting to a frame. 2. The frame information insertion means (3) comprises:
2. The interface device according to claim 1, wherein insertion of frame information is stopped when frame synchronization is lost. [Claim 3] Connected to the ATM network, the ATM
a signal smoothing means for checking frame reception and absorbing frame fluctuation; a frame synchronization means for synchronizing frames output from the signal smoothing means;
An interface device comprising frame inserting means for generating a frame corresponding to a lost cell when M cell discard is detected.