JP2685082B2 - STM signal and ATM signal conversion / inverse conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ATM (Asynch).
ronus Transfer Mode) network and ST
M (Synchronous Transfer Mo)
de) related to interconnection with networks, especially STM
The present invention relates to a method of transmitting a signal on an ATM network.

[0002]

2. Description of the Related Art The STM network is a synchronous network in which the entire network operates with a synchronous clock. In the STM network, information signals are collected in a unit called a virtual container, incorporated into a frame, and transmitted in the network. STM
A virtual container used in a 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 containing the line management information and a container containing the information signal. Virtual containers are classified into four types, VC-11, VC-2, VC-3, and VC-4, according to the size of the container, that is, the amount of information to be stored. The amount of information that can be accommodated per frame is four times as large as VC-11 for VC-2 and 7 for VC-3 as for VC-3.
Times, VC-4 is equivalent to 3 times VC-3.

The virtual container is transmitted as a data stream in the STM network. Therefore, the information in the STM network is transmitted in the form of a tributary unit in which a pointer indicating the position of the first byte of the path overhead POH of this virtual container is added to each virtual container. The first byte of the path overhead POH is V-5 for VC-11 and VC-2, and VC-3 for VC-3.
, VC-4 called J1.

On the other hand, in the ATM network, information signals are divided into units called cells and transferred in the network. The cell is composed of a header which constitutes the first 5 bytes and a total of 53 bytes of a 48-byte information field following the header. The header contains the virtual channel identifier VCI and the virtual path identifier VPI. The virtual path identifier VPI is used to identify the receiving terminal of the cell, and the virtual channel identifier VCI is used to identify the receiving subscriber.

The STM network has already been introduced, and the ATM network is about to be introduced. When two types of networks coexist, STM signals are converted into ATM signals and A
It is necessary to transfer the data in the TM network, further convert the ATM signal back to the STM signal and transfer it in the STM network. So, convert the virtual container data stream to a cell,
It is necessary to convert the cells back into a virtual container data stream.

[0006]

SUMMARY OF THE INVENTION As described above, the STM
Signal is Constant, followed by constant bit rate data
It is a Bit-Rate signal, and the ATM signal is a signal divided into 53-byte cells. The following points must be taken into consideration when mutually converting signals having completely different structures. (1) Path overhead POH, container, virtual container, tributary unit, etc.
How to efficiently convert TM signals into cells that are ATM signals. (2) Handling of information necessary for restoring a virtual container from a cell when converting an STM signal into an ATM signal. (3) Types of virtual containers (VC-11 to VC-
4) distinction. (4) Guarantee against data errors.

In consideration of these points, the present invention makes S
STM that enables transmission of TM signals via ATM network
It is an object of the present invention to provide a signal / ATM signal conversion / inversion method.

[0008]

[Means for Solving the Problems] The above points (1) to (3)
In consideration of the above, according to the present invention, when converting an STM signal into an ATM signal in a conversion / inverse conversion method of an STM signal and an ATM signal, a sequence number indicating the order of cells in which a virtual container is converted, and this sequence number. Sequence number protection bit for error correction, information indicating the type of virtual container, presence / absence of the first byte of the virtual container, phase information indicating the position from this first byte and interval, and error for data error detection A virtual container is accommodated in a cell using information, and in a cell in which the first byte is not accommodated, a specific pattern is inserted in the bits of the phase information, and the sequence number and the specific pattern are used to indicate the cell order. I chose When the ATM signal is converted back to the STM signal, the position of the virtual container reproduced from the cell in the frame of the STM signal is determined by using the virtual channel identifier and the virtual path identifier of the cell.

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

[0010]

According to the present invention, the STM signal and A
Since the TM signal conversion / inverse conversion method is configured, when converting an STM signal into an ATM signal, at least information indicating the type of the virtual container and information indicating the start position of the virtual container in the cell are stored in the cell. When accommodating and converting the ATM signal back into the STM 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 the virtual path identifier of the cell.

Further, according to the present invention, ST
Since the conversion / inversion method of the M signal and the ATM signal is configured, the data error of the virtual container is checked by the CRC bit inserted in the cell.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows S according to an embodiment of the present invention.
It is explanatory drawing of the conversion system of a TM signal to a cell. First, each of the tributary unit and the virtual container will be considered as STM signals to be converted into cells.

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

FIG. 1 shows an example of a virtual container VC-
A method of converting 11 into cells will be described. VC-11 is
It is composed of 104 bytes including the first byte V5 of the path overhead. This VC-11 is 4 from the first byte
It is divided into 4 bytes and stored in the information field of the cell. As can be seen from FIG. 1, 44 bytes from the beginning of the virtual container VC-11A is the cell C.
Then, the next 44 bytes are stored in cell D. Finally, with the remaining 16 bytes of the virtual container VC-11A,
Virtual container VC of the next frame of the STM signal-
28 bytes from the beginning of 11B are stored in the cell E.

That is, a virtual container of continuous frames is divided into 44 bytes and stored in the information field of cells in sequence. The structure of the cell thus converted will be described with reference to FIG. As described above, the cell is composed of a 5-byte header and a 48-byte information field. 44 bytes of the 48-byte information field are reserved to store a part of the virtual container. Further, the remaining part of the information field is reserved for storing information for restoring the virtual container converted into the cell.

As information for restoring the virtual container, a sequence number SN, a sequence number protection bit SNP, a virtual container size SS, a virtual container head position information VCS, a check bit CR
There are C and reserve R. This will be described below. (1) Sequence number SN: 4 bits Codes 0 to 15 are periodically repeated in the order of cell occurrence. Guarantee cell order and cell loss. (2) Sequence number protection bit SNP: 4 bits It has a function of error detection and correction of the sequence number SN. (3) Virtual container size SS: 2 bits Indicates the type of virtual container contained in the cell. By referring to this, VC-11, VC-
It is possible to distinguish each of the four types of virtual containers 2, 2, VC-3, and VC-4. (4) Virtual container start position information VCS: 6 bits Indicates the start byte of the virtual container, that is, the position of V1 or V5. (5) CRC: 10 bits It has a function of inserting the result of CRC operation on the data of the information field excluding SN and SNP and performing a data error check. (6) Reserve: 6 bits Insert "1" into the remaining 6 bits of the cell.

The process of converting a virtual container into a cell will be described with reference to FIG. 1 again. Note that SNP, SS, CRS, and R are omitted here. In FIG. 1, SN = 0 is given to the cell C that occurs first. In this cell C, the virtual container VC
V5 of -11A is stored at the beginning of the 44 bytes stored in the cell. Virtual container start position information V
CS is a value indicating how far away V5 is contained from the beginning of the 44-byte information, and therefore for cell C, VCS = 0 is given.

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

In the cell F generated next, V
5 is not housed. Therefore, also in this cell F, a specific pattern is given to the VCS. At this time, the specific pattern given to the cell D and the specific pattern given to the cell F are different. The case where a cell is converted back into a virtual container will be described 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 the error of the sequence number SN. This error detection and correction is performed, for example, with SN and SNP.
Various methods can be applied, such as performing a parity check with and setting SN and SNP in a complementary relationship.

Further, 44 bytes of information stored in the cell on the receiving side, virtual container size SS, virtual container head position information VCS, and CRC of 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 was transmitted correctly, and if they do not match, some failure has occurred during transmission. In this case, the discrepancy in this comparison is notified to the maintainer. Upon receiving this notification, the maintenance person can take appropriate measures such as disabling the corresponding path.

When the cell order and information content are guaranteed by SN, SNP, and CRC, this cell is converted back to an STM signal. In this case, first, the virtual container size SS is referred to know the type of virtual container to be restored. Next, the accommodation position of V5 is specified by referring to the value of VCS. Starting from this V5, the subsequent information is arranged until the size of the virtual container to be restored is reached, and the virtual container is restored.

The virtual container thus restored is incorporated into the frame of the STM signal again. At this time, necessary information such as the time slot to be incorporated in the frame, highway information, sender ID, receiver ID, etc. is transmitted by the VCI and VPI included in the cell header, so this information is used. The frame of STM rope, for example, the frame called STM-1 has three VC-
3 is multiplexed. Each VC-3 has 7 VCs
-2, or 28 VC-11 are multiplexed.
That is, 84 VC-11 are multiplexed in the STM-1. So, a certain VC-11 is ATM
After the transmission through the rope, when accommodating again in the STM-1, the accommodating position of these 84 VC-11 is VP.
It is determined by the information in I and VCI. VPI / VCI
The relationship between the value of ST and the position accommodated in STM-1 is ST
It is decided by the agreement between the M class and the ATM class. In other words, it is predetermined when connecting two ropes, S
The exchange / reverse conversion between the TM class and the ATM class operates according to the agreement. If cell loss 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 the same processing even when the cell is discarded so as not to affect the frame transmission of the STM signal.

As described above, VC-1 is used as a virtual container.
1 has been described as an example, other virtual containers of three sizes exist. For example, VC-3 is VC-11 per frame as the size of the container.
It is 28 times. To convert this VC-3 into cells,
765 bytes (VC-3 size) / 44 bytes (cell information amount) ≈18 cells are required. In this case, the specific patterns given to the VCSs of the second and subsequent cells are all the same. Then, a specific pattern different from this is given to each cell obtained by converting the virtual container of the next frame. In this way, the VCS given to the cell that does not contain the first byte of the path overhead POH is given a specific pattern different for each frame of the virtual container. Thereby, even if the cell for one cycle of the SN is lost for some reason and the cell loss cannot be detected by the SN, it is possible to prevent the information of the virtual container of another frame from being incorporated.

The present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, which are not excluded from the scope of the present invention.

[0025]

As described above, according to the present invention, the following effects can be obtained. (1) Since the type of virtual container and the information about its head position are placed in the cell, any type of virtual container can be converted into a cell. (2) Since the cells can be filled with virtual containers without any gaps, the cell storage efficiency is improved.

(3) Since the VCS (information indicating the start position of the virtual container) is present in every cell, the information indicating the existence of the VCS is unnecessary. In addition, when there is no head of the virtual container in the cell, the VCS has a specific pattern and can be used to guarantee the order of cells. Furthermore, V
Since CS can also indicate the start bit position of the frame of the synchronization signal, which Constant Bit-Rat
It is also applicable to the conversion of e signals into cells.

(4) If the head of the tributary unit is indicated by the VCS, it can be applied to the conversion / reverse conversion of the tributary unit into cells.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an STM signal conversion / inverse conversion method 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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-98943 (JP, A) JP-A-4-100347 (JP, A) JP-A-4-138744 (JP, A) JP-A-4- 249447 (JP, A) Proceedings of IEICE Spring National Convention (3rd volume), B-707 (1991-3-15)

Claims (2)

(57) [Claims] 1. AT for virtual container of STM signal
STM signal and ATM for converting cells of M signal to inverse conversion of cells of ATM signal to virtual container of STM signal
In the signal conversion / inverse conversion method, (a) when converting the STM signal to the ATM signal, indicate the order of cells in which the virtual container is converted.
Sequence number and error correction of the sequence number
Sequence number protection bit and virtual controller
Information indicating the type of tena and the top bar of the virtual container
Indicates the presence or absence of a byte and the position from the first byte and the interval.
Uses phase information and error information for data error detection
The virtual container in the cell and
For cells that do not contain the head byte, the phase information bit
Insert a specific pattern into the
A fixed pattern is used to indicate the order of cells. (B) When the ATM signal is converted back to the STM signal, the ST of the virtual container reproduced from the cell
A conversion / inverse conversion method for an STM signal and an ATM signal, characterized in that the position of the M signal in the frame is determined by using the virtual channel identifier and the virtual path identifier of the cell. Wherein the error information according to claim 1, wherein the inserting the result of the CRC calculation STM signal and AT
M signal conversion / inverse conversion method.