JPH04282936A - Conversion/inverse conversion system for stm signal and atm signal - Google Patents

Abstract

PURPOSE:To convert an STM signal into an ATM signal and to convert inversely the ATM signal into the STM signal. CONSTITUTION:When a virtual container of an STM signal is converted into a cell of an ATM signal, a sequence number (SN) representing the sequence of the cell, a virtual container size (SS) representing the kind of the cell and information (VCS) representing a top position of the virtual container are contained in the cell. When the ATM signal is inversely converted into the STM signal, the position of the virtual container in the frame of the STM signal reproduced from the cell is decided by using VPI and VCI inserted to the cell header. Moreover, CRC calculation is implemented to the virtual container in the cell and the result is contained in the cell.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention is directed to ATM (Asynchronous
Synchronous Transfer Mode) network and STM (Synchronous Transfer Mode)
Mode) is related to interconnection with the network, especially S
The present invention relates to a method of transmitting TM signals over an ATM network.

0002

2. Description of the Related Art An STM network is a synchronous network in which the entire network operates using a synchronous clock. In an STM network, information signals are collected into units called virtual containers, incorporated into frames, and transmitted within the network. STM
A virtual container used in the network is a standardized multiplexing unit for multiplexing signals of various speeds, including existing low-speed signals. The virtual container is composed of a path overhead POH that accommodates line management information and a container that accommodates information signals. There are four types of virtual containers: VC-11, VC-2, VC-3, and VC-4, depending on the size of the container, that is, the amount of information it accommodates.
classified into types. The amount of information accommodated per frame is equivalent to 4 times that of VC-11 for VC-2, 7 times that of VC-2 for VC-3, and 3 times that of VC-3 for VC-4.

[0003] Virtual containers are transmitted as data streams within the STM network. Therefore, information within the STM network is transmitted in the form of a tributary unit in which each virtual container is appended with a pointer indicating the position of the first byte of the path overhead POH of this virtual container. The first byte of the path overhead POH is V5 for VC-11 and VC-2, and V5 for VC-3.
, is called J1 in VC-4.

On the other hand, in an ATM network, information signals are divided into units called cells and transferred within the network. A cell consists of a header comprising the first 5 bytes and a 48-byte information field following the header, for a total of 53 bytes. The header includes a virtual channel identifier VCI and a virtual path identifier VPI. The virtual path identifier VPI is used to identify the receiving end station of the cell, and the virtual channel identifier VCI is used to identify the receiving subscriber.

[0005] STM networks have already been introduced, and ATM networks are about to be introduced. When two types of networks coexist, STM signals are converted to ATM signals and A
It becomes necessary to transfer the ATM signal within the TM network, and further convert the ATM signal back into an STM signal and transfer it within the STM network. Therefore, converting the virtual container's data stream into cells,
It will be necessary to transform the cells back into virtual container data streams.

[0006]

[Problem to be solved by the invention] As mentioned above, STM
The signal is a Constant signal followed by constant bit rate data.
This is a Bit-Rate signal, and the ATM signal is a signal divided into 53-byte cells. When mutually converting signals having completely different structures as described above, the following points must be considered. (1) Pass overhead POH, container, virtual container, tributary unit, etc., many staircase S
How to efficiently convert TM signals into cells that are ATM signals. (2) Handling of information necessary to restore a virtual container from a cell when converting an STM signal to an ATM signal. (3) Types of virtual containers (VC-11 to VC-
4) Distinction. (4) Guarantee against data errors.

[0007] The present invention takes these points into consideration and provides S
STM, which made it possible to transmit TM signals over ATM networks
The purpose of this invention is to provide a method for converting/inverting signals and ATM signals.

[0008]

[Means for solving the problem] Points (1) to (3) above
In consideration of the above, the present invention provides information indicating the type of virtual container when converting an STM signal to an ATM signal in a conversion/inverse conversion method for STM signals and ATM signals;
Information indicating the starting position of the virtual container within the cell is now stored in the cell. Then, the ATM signal is converted into STM
When converting back to a signal, the position in the frame of the STM signal of the virtual container reproduced from the cell is determined using the virtual channel identifier and virtual path identifier of the cell.

Furthermore, in consideration of the above point (4), the present invention performs a CRC operation on a virtual container within a cell, and stores the result in the cell.

0010

[Operation] According to the present invention, the STM signal and the A
Since the TM signal conversion/inverse conversion method has been configured, when converting an STM signal to an ATM signal, information indicating the type of virtual container and information indicating the starting position of the virtual container within the cell are stored in the cell. , when inversely converting an ATM signal into an STM signal, the position of the virtual container reproduced from the cell in the frame of the STM signal is determined using the cell's virtual channel identifier and virtual path identifier.

Further, according to the present invention, as described above, ST
Since the M signal and ATM signal conversion/inverse conversion method has been configured, data errors in the virtual container are checked using the CRC bit inserted into the cell.

0012

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an S according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a method of converting a TM signal into a cell. First, we will consider each of the tributary unit and virtual container as STM signals to be converted into cells.

When trying to convert a tributary unit into a cell, when converting this cell back to an STM signal, in order to specify the position of J1 or V5, first determine the position of the pointer from the cell, and then It is necessary to determine the position of J1 or V5 from the pointer. On the other hand, when converting a virtual container to a cell,
It is sufficient to indicate only the position of J1 or V5. Therefore, in this embodiment, a case will be described in which a virtual container is converted into a cell.

FIG. 1 shows an example of a virtual container VC-
A method for converting 11 into a cell will be explained. VC-11 is
It consists of 104 bytes including the first byte V5 of the path overhead. This VC-11 is 4 from the first byte.
Divide into 4-byte units and store in the information field of the cell. As understood from FIG. 1, 44 bytes from the beginning of virtual container VC-11A are cell C.
Then, the next 44 bytes are stored in cell D. Finally, the remaining 16 bytes of virtual container VC-11A,
Virtual container VC- of the next frame of the STM signal
The first 28 bytes of 11B are stored in cell E.

That is, the virtual containers of successive frames are divided into 44-byte units and sequentially stored in the information field of the cell. The configuration of the cell thus converted will be explained using FIG. 2. As mentioned above, a cell consists of a 5-byte header and a 48-byte information field. 44 bytes of the 48-byte information field are reserved for storing a portion of the virtual container. Further, the remaining part of the information field is reserved for storing information for restoring the virtual container converted into a cell.

Information for restoring the virtual container includes sequence number SN, sequence number protection bit SNP, virtual container size SS, virtual container start position information VCS, and check bit CR.
C, there is a reserve R. This will be explained below. (1) Sequence number SN: Codes from 0 to 15 are periodically repeated in the order in which 4-bit cells occur. Guarantees cell order and guarantees against cell loss. (2) Sequence number protection bit SNP: Has the function of detecting and correcting errors in the 4-bit sequence number SN. (3) Virtual container size SS: Indicates the type of virtual container accommodated in the 2-bit cell. By referring to this, VC-11, VC-2, VC-
3. Four types of virtual containers of VC-4 can be distinguished from each other. (4) Virtual container head position information VCS: 6 bits Indicates the position of the head byte of the virtual container, ie, V1 or V5. (5) CRC: Has a function to perform data error checking by inserting the result of CRC operation on information field data excluding 10-bit SN and SNP. (6) Reserve: Insert “1” into the remaining 6 bits in the 6-bit cell.

Now, referring to FIG. 1 again, the process of converting a virtual container into a cell will be explained. Note that SNP, SS, CRS, and R are omitted here. In FIG. 1, the first occurring cell C is given SN=0. In this cell C, the virtual container VC
-11A V5 is stored at the beginning of 44 bytes stored in the cell. Virtual container head position information V
CS is a value indicating how far V5 is accommodated from the beginning of the 44-byte information, and therefore, in the case of cell C, VCS=0 is given.

[0018] Furthermore, in the next generated cell D, SN=1
is given. This cell D does not accommodate V5. In this case, a specific pattern other than 0 to 43 is given to the VCS. Furthermore, in the next generated cell E, SN=
2 is given. This cell E also stores the virtual container VC-11B of the next frame of the STM signal. At this time, V5 of the virtual container VC-11B is accommodated at a location 16 bytes away from the beginning of the 44-byte information. Therefore, in this case, VCS=16 is given.

Furthermore, in the cell F that occurs next, V
5 is not accommodated. Therefore, in this cell F as well, a specific pattern is given to the VCS. At this time, the specific pattern given to cell D and the specific pattern given to cell F are made different. The case of converting a cell back into a virtual container will be explained below. The order of each cell is guaranteed by the sequence number SN. Further, by using the sequence number protection bit SNP together, it is possible to detect and correct errors in the sequence number SN. Various methods can be applied to this error detection and correction, such as performing a parity check on SN and SNP, or setting SN and SNP in a complementary relationship.

Furthermore, on the receiving side, the 44 bytes of information stored in the cell, the virtual container size SS, the virtual container head position information VCS, and the CRC of the reserve R
The calculation is performed and the result is compared with the transmitted CRC. If the results of this comparison match, it means that the information has been transmitted correctly; if they do not match, it means that some kind of failure has occurred during transmission. In this case, the maintainer is notified of this comparison discrepancy. The maintenance person who receives this notification can take appropriate measures such as disabling the corresponding path.

[0021] Once the cell order and information content are guaranteed by SN, SNP, and CRC, this cell is inversely converted into an STM signal. In this case, first, the virtual container size SS is referred to and the type of virtual container to be restored is known. Next, the storage position of V5 is specified by referring to the value of VCS. The virtual container is restored by starting with this V5 and arranging subsequent information until the size of the virtual container to be restored is reached.

[0022] The thus restored virtual container is again incorporated into the STM signal frame. At this time, necessary information such as the time slot, highway information, sender ID, and receiver ID to be incorporated into the frame is transmitted by the VCI and VPI included in the cell header, so this information is used. If a lost cell is detected during cell reception, a fixed pattern is inserted into the virtual container to replace the lost cell. In addition, it is necessary to perform similar processing when cells are discarded, etc., so as not to affect the frame transmission of the STM signal.

[0023] As described above, VC-1 is used as a virtual container.
1 has been explained as an example, but there are three other sizes of virtual containers. For example, VC-3 has a container size of VC-11 per frame.
This is 28 times that of the previous year. To convert this VC-3 to a cell,
765 bytes (VC-3 size)/44 bytes (cell information amount)=18 cells are required. In this case, the specific patterns given to the VCS of the second and subsequent cells are all the same. Then, a specific pattern different from this is given to each cell into which the virtual container of the next frame is converted. In this way, a specific pattern that is different for each frame of the virtual container is given to the VCS given to the cell that does not accommodate the first byte of the path overhead POH. As a result, even if, for example, cells for one SN period are lost for some reason and the SN cannot detect the loss of cells, it is possible to prevent information from a virtual container from another frame from being incorporated.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0025]

As described above in detail, the present invention provides the following effects. (1) Since information regarding the type of virtual container and its starting position is placed in the cell, any type of virtual container can be converted into a cell. (2) Since the virtual containers are packed into the cells without any gaps, the cell accommodating efficiency is increased.

(3) Since the VCS (information indicating the starting position of the virtual container) is present in every cell, information indicating the existence of the VCS is unnecessary. Furthermore, when there is no head of a virtual container within a cell, VCS has a specific pattern that can be used to guarantee the order of cells. Furthermore, V
CS can also indicate the starting bit position of the frame of the synchronization signal, so any Constant Bit-Ra
It is also applicable to converting te signals into cells.

(4) If the head of the tributary unit is indicated by the VCS, it can also be applied to conversion/inverse conversion of the tributary unit to a cell.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for converting/inverting an STM signal into cells according to an embodiment of the present invention.

FIG. 2 is a block diagram of a cell converted from an STM signal according to an embodiment of the present invention.

[Explanation of symbols] A, B Virtual container C~F Cell

Claims (5)

[Claims] [Claim 1] The virtual container of the STM signal is A
STM signal and AT that convert into TM signal cells and inversely convert ATM signal cells into STM signal virtual containers.
In the M signal conversion/inverse conversion method, (a) the STM
When converting the signal into the ATM signal, information indicating the type of the virtual container and information indicating the leading position of the virtual container within the cell are stored in the cell, and (b) converting the ATM signal into the STM signal. STM signals and ATM signals characterized in that, when inversely converting into signals, the position in the frame of the STM signal of the virtual container reproduced from the cell is determined using the virtual channel identifier and virtual path identifier of the cell. Conversion/inverse conversion method. [Claim 2] A sequence number indicating the order of cells into which the virtual container has been converted, a sequence number protection bit for correcting errors in the sequence number, information indicating the type of virtual container, and information indicating the existence of the first byte of the virtual container. The ST according to claim 1, wherein the virtual container is accommodated in a cell using phase information indicating presence/absence and position and error information for data error detection, and the virtual container is reproduced from the cell.
Conversion/inverse conversion method between M signal and ATM signal. 3. The method for converting/inversely converting STM signals and ATM signals according to claim 2, wherein an interval between a first byte and the phase information is used as the phase information. 4. In a cell in which a first byte is not accommodated, a specific pattern is inserted into the phase information bits, and the sequence number and the specific pattern are used to indicate the order of the cells. 3. Conversion/inverse conversion method for STM signals and ATM signals. 5. The S according to claim 2, 3, or 4, wherein a result of a CRC operation is inserted into the error information.
TM signal and ATM signal conversion/inverse conversion method.