JP3202727B2 - Error verification method and system for short cell in ATM network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM (Asynchro
Nous Transfer Mode) and a method and system for verifying short cell errors in a network.

[0002]

2. Description of the Related Art In order to adapt multimedia information to ATM, interworking between an ATM network and an upper layer is required. An ATM adaptation layer (AA) having the function is provided between the ATM layer and the upper layer.
L: ATM Adaptation Layer) exists. by the way,
The above-mentioned AAL is provided by the standardization organization (ITU-T).
Four types of AAL types 1 to 4 are standardized according to the type of information to be handled. AAL type 2 specifies variable bit rate real-time communication.

[0003] In an ATM network system, a base station or a relay station receives information from a plurality of subscriber terminals, multiplexes the received information, and generates a cell conforming to the ATM adaptation layer type 2. Then, the AAL cell verification circuit performs ITU-T Recommendation I. 36
The cell is discarded in accordance with 3.2, and only normal cells are transmitted to the communication path. The AAL2 cell, as is well known,
TM header, start field (STF), short cell header (CPS-PH: Common Part Sublayer-)
Packet Header) and short cell payload. The STF is a 6-bit offset field (OS
F), a 1-bit sequence number (SN), and 1
It is composed of parity bits. OSF is
It shows the position of the first short cell header in the AAL2 cell (the number of octets that have crossed over cells that could not be packed into the previous AAL2 cell). The short cell header (CPS-PH) includes an 8-bit channel identifier (CID), 6-bit short cell length indication information (LI: Length Indication), and a 5-bit UUI.
(Common Part Sublayer-User to Use) instruction and 5-bit header error control (HEC: Header)
Error Control) is well known.

FIG. 7 shows that OSF is "0" (no cell crossing).
2 shows an example of reception error processing of the AAL2 cell format in the case of. In FIG. 7, when the OSF in the STF (C1) is “0”, the AAL2 cell verification circuit
It is determined that there is no cell straddling. In this case, the next to the STF (C1) is determined as the header (C2) of the short cell 1, and the cyclic redundancy coding check (CRC5) is executed. Since the result of CRC5 for the header (C2) of the short cell 1 is normal, the short cell 1 is transferred to the communication path. Next, from the LI in the short cell header (C2), the short cell 2
The position of the header (C3) is determined, and CRC5 is executed. CRC5 for header (C2) of short cell 2
Is an error, the short cell 2 is discarded. Further, since the LI in the header (C2) of the short cell 2 is not reliable, the position of the header (C4) of the short cell 3 cannot be determined. As a result, the short cell 3 is unconditionally discarded. In the figure, the symbol “〇” shown in each short cell indicates a normal CRC5, the symbol “X” indicates a CRC5 error, and the symbol “*” indicates a short cell that cannot be checked and is discarded.

FIG. 8 shows an example of the AAL2 cell format reception error process when the OSF is other than “0” (there is a crossover of cells). In FIG. 8, when the OSF in the STF (C1) is other than “0”, the AAL2 cell verification circuit determines that there is a cell crossing. If there is a cell straddling, the number of straddling octets (Expct) that could not be packed into the AAL2 cell before the corresponding AAL2 cell is accumulated, and the Expct and the OS of the corresponding AAL2 cell are stored.
Compared with F, if they match, short cell 1 is transmitted to the communication path, and if they do not match OSF, short cell 1 is discarded. Then, the header (C2) position of the short cell 2 is determined by the OSF, and the CRC5 is executed. here,
Since the result of the CRC5 for the header (C2) of the short cell 2 is normal, the short cell 2 is transferred to the communication path. Next, the position of the header (C3) of the short cell 3 is determined from the LI in the short cell header (C2), and the CR is determined.
C5 is executed. C for the header of short cell 3
Since the result of RC5 is an error, the short cell 3 is discarded. Further, since the LI in the short cell header (C3) is not reliable, the position of the header (C4) of the short cell 4 cannot be determined. Therefore, the short cell 4 is unconditionally discarded. Note that, in the drawing, a mark “△” indicates a short cell that has become inconsistent as a result of comparing the number of octets across the remaining cells of the previous AAL2 cell stored with the STF and OSF.
Other symbols are the same as in FIG.

[0006]

As described above, conventionally, if the previous short cell causes an error as a result of the CRC5 check, the LI in the header cannot be trusted, and the header position of the corresponding short cell cannot be determined. , And subsequent short cells must be discarded unconditionally. This results in poor reliability of discard processing due to a short cell detection error, wastes ATM network resources, and is undesirable in securing service quality such as high throughput and low latency. The present invention has been made in view of the above circumstances, and is described in ITU-T Recommendation I.T. 363.2 ATM
In AAL2 signal processing using signal transmission, CRC
5 if an error in one or more multiplexed short cells in the AAL2 cell is detected using AA5
By referring to the length indication information (LI) of the next-stage short cell added in advance to each short cell in the L2 cell, the reliability of discard processing due to a short cell error in the AAL2 cell is improved, and high throughput is achieved. An object of the present invention is to provide a short cell error verification method and system in an ATM network that can ensure service quality such as low latency.

[0007]

According to a first aspect of the present invention, there is provided a method for verifying a short cell error in an ATM network, comprising receiving information from a plurality of subscriber terminals, and receiving the received information. The cells are multiplexed to generate cells conforming to the ATM adaptation layer type 2, and for each of the cells generated, ITU-T Recommendation I.T. ATM that performs cell discard processing according to 363.2 and transmits only normal cells to the communication path
In the network system, the last stage of the generated short cell and the preceding stage short cell, the length display information of the next stage short cell is added to the end of each short cell excluding the short cell that is straddling the cell, In the cell discarding processing, the position of each short cell header is determined based on the contents of the intra-cell offset field and the length display information field in the cell header, a cyclic redundancy coding check is performed, and when an error is detected, the addition is performed. The cyclic redundancy coding check is performed by determining the position of the next-stage short cell header by referring to the obtained length display information, and the short cell is transmitted through the communication path or discarded according to the result. I do.

According to a second aspect of the present invention, there is provided an error verification method for a short cell in an ATM network, wherein 6 bits are added to the end of each short cell multiplexed in the cell. Is added to the length display information of the next-stage short cell and 1-bit parity corresponding to the information. An error verification method for a short cell in an ATM network according to claim 3 is the error verification method according to claim 1, wherein a 6-bit next stage is provided at the end of each short cell multiplexed in the cell. The length display information of the short cell is added, and two bits of a parity corresponding to an odd bit and a parity corresponding to an even bit of the length display information bit are further added.

According to a fourth aspect of the present invention, there is provided an error verification system for a short cell in an ATM network, wherein information received from a plurality of subscriber terminals is multiplexed to multiplex an ATM adaptation layer.
Generate a type 2 compliant cell, and for each generated cell,
TU-T Recommendation I. In an ATM communication system that performs cell discard processing in accordance with 363.2 and transmits only normal cells to a communication path, a short cell in the last stage of the generated short cell and a short cell in a stage preceding the short cell and a short circuit in which the cell is straddled. A base station or a relay device that adds the length display information of the next-stage short cell to the end of each short cell, excluding the cell, and each short cell header based on the contents of the offset display field within the cell and the length display information field in the cell header. Perform a cyclic redundancy coding check by determining the position of, and when the error is detected, determine the position of the next-stage short cell header by referring to the added length display information and perform a cyclic coding check, According to the result, discard processing or transmit the short cell via the communication path. And having a cell verification circuit.

[0010] Of the plurality of short cells multiplexed in the AAL2 cell, even if the short cell multiplexed before the corresponding short cell is discarded due to a CRC5 error and the LI in the short cell header cannot be trusted. By referring to the LI of the next-stage short cell added to the end of each short cell multiplexed in the AAL2 cell, the position of the header of the corresponding short cell can be accurately determined. As a result, even if one of the first stage or the multiplexed short cells is discarded due to an error of CRC5, the header position of the short cell thereafter can be accurately determined, and the cells after the short cell in which the error has occurred are obtained. Need not be discarded unconditionally. Further, among a plurality of short cells multiplexed in the AAL2 cell, a short cell multiplexed before the corresponding short cell is a CRC.
LI in the short cell header discarded due to the error of result 5
Is not reliable, the position of the header of the corresponding short cell can be accurately determined by referring to the LI of the next-stage short cell added to the end of each short cell multiplexed in the AAL2 cell. Thus, even if one of the initial stage or the multiplexed short cells is discarded due to an error of the CRC5, the CRC5 can be executed without unconditionally discarding the subsequent short cells. Can be counted accurately. This increases the reliability of detection error detection and eliminates unnecessary discard processing, so that service quality such as high throughput and low latency can be ensured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of a short cell error verification system in an ATM network according to the present invention. The error verification system of the present invention accommodates a plurality of subscriber terminals 1 to N and performs multiplexing on a base station / relay device 11 and an AA transmitted from the base station / relay device 11.
The AAL2 cell verification circuit 12 verifies the L2 cell according to the following procedure, and the communication path 13 receives the output of the AAL2 cell verification circuit 2 as an input. In FIG. 1, the base station / relay device 11 receives information from a plurality of subscriber terminals 1 to N. Then, this information is multiplexed to generate an AAL2 cell. AAL2 cell verification circuit 12 for each AAL2 cell
Based on the OSF in the STF in the AAL2 cell and the LI in the short cell header, ITU-T Recommendation I. 363.
The short cell discarding process according to No. 2 is performed, and only normal cells are transmitted to the communication path 13.

AAL generated by base station / relay device 11
The two cell format is shown in FIG. In FIG. 2, the AA2 cell format is, as shown in FIG. 2A, an ATM header, a start field (hereinafter abbreviated as STF), a short cell header, a short cell payload, and a length indication (length length) of the next-stage short cell. It is composed of fields. As shown in FIG. 2B, the STF has a 6-bit offset field (hereinafter referred to as O field).
SF), 1-bit sequence number (SN),
And one parity bit (P). OSF indicates the position of the first short cell header in the AAL2 cell (the number of octets crossing cells that could not be packed in the previous AAL2 cell). As shown in FIG. 2 (c), the short cell header
Channel identifier (CID) in bits, self-length indication (LI) in 6 bits, common part sublayer-user to user indication (UUI) in 5 bits, and header error control (HEC) in 5 bits ). LI indicates the length of the own short cell.

FIG. 3 is a diagram showing an embodiment of an AAL cell 2 format for realizing the short cell error verification method in the ATM network according to the present invention. FIG. 2A shows the AA2 cell format when the OSF in the STF is "0", and FIG. 2B shows the AA2 cell format when the OSF in the STF is other than "0", that is, when there is a short cell straddle. As is clear from the figure, each short cell is composed of 6 bits of the OSF in the STF and LI (6 bits) of the next-stage short cell added to the tail of each short cell multiplexed in the AAL2 cell + parity. It is composed of one bit. The format of the length indicating next-stage short cell length display section is shown in FIG. 3 (c). However, since the position of the first short cell header (short cell 1 and short cell 6 headers) of the AAL2 cell can be determined by the OSF, the ALF
The short cell (short cell 4 and short cell 9) at the last stage of the L2 cell, the short cell (short cell 3 and short cell 8) immediately before the L2 cell, and the short cell (short cell 5) that is straddling the cell are included. No LI is added.

FIG. 4 is a diagram showing another embodiment of the AAL cell 2 format for implementing the short cell error verification method in the ATM network according to the present invention. FIG. 4A shows an STF.
FIG. 4B shows the AA2 cell format when the OSF in the STF is other than "0", that is, when there is a short cell span. As is clear from the figure, each short cell is composed of 6 bits of the OSF in the STF and LI (6 bits) of the next-stage short cell added to the tail of each short cell multiplexed in the AAL2 cell + parity. It is composed of two bits. The reason that the parity is 2 bits will be described later. The format of the length display section of the next-stage short cell is shown in FIG. However, since the position of the first short cell header (short cell 1, short cell 6 header) of the AAL2 cell can be determined by the OSF, ALL2
The short cell (short cell 4 and short cell 9) at the last stage of the cell, the short cell immediately before that (short cell 3 and short cell 8), and the short cell (short cell 5) straddling the cell are LI. Is not added.

FIGS. 5 and 6 are views cited for explaining the operation of the embodiment of the present invention, and are AA when there is no short cell straddle and when there is a short cell straddle, respectively.
The L2 format and its operation procedure are shown.

Hereinafter, referring to FIGS. 5 and 6, FIG.
The operation of the embodiment of the present invention shown in FIG. 4 will be described in detail. First, the operation of the embodiment shown in FIG. 3 will be described. FIG. 5 shows the AAl2 cell verification circuit 1 when the OSF in the STF is “0” (when no cell crossing occurs).
2 is shown. AAL2 cell STF (C1)
The OSF in the parentheses indicates the number of octets straddling. If the OSF value is “0”, it is determined that there is no cell crossing in the previous AAL2 cell. Next, the position immediately after the STF is determined as the position of the short cell header (C2) of the short cell 1, and CRC5 is executed. Here, since the result of the CRC5 for the header (C2) of the short cell 1 is normal, the short cell 1 is transferred to the communication path 13 and the short cell 2 has its own cell octet number indicated by LI in the short cell header (C2). The position of the short cell header (C4) is determined, and CRC5 is executed. Since the result of CRC5 for short cell 2 is an error, short cell 2
Is discarded. Further, the LI in the short cell header (C4) becomes unreliable. In this case, the length display portion (C) of the next-stage short cell added to the short cell 1
See 3). As a result, the header (C) of the short cell 3 is determined by the LI stored therein (C3).
The position of 5) is determined, and CRC5 is executed. here,
Since the result of the CRC 5 for the short cell 3 is normal, the short cell 3 is transferred to the communication path 13. Conventionally, if a CRC5 error occurs in the short cell 2, the position of the header (C5) of the short cell 3 cannot be determined, and the short cell 3 is discarded unconditionally. However, even if a CRC5 error occurs in the short cell 2 according to the present invention, the position of the header (C5) of the short cell 3 can be determined, so that the short cell 3 is not discarded unconditionally.
The reliability of detection can be improved.

FIG. 5 shows the operation when the OSF in the STF is other than “0”, that is, when the cell crosses over. The OSF in the STF (C1) of the AAL2 cell indicates the number of octets straddling. OSF
If the value is other than "0", the number is compared with the number of remaining short cell octets in the previous AAL2 cell, and if they do not match, the short cell 1 (short cell causing cell crossing)
Discard. If they match, the message is transmitted to the communication path 13.
Whether the result is normal or error, STF
From the OSF in (C1) to the header (C
The position of 2) is determined, and CRC5 is executed. Here, since the result of CRC5 for the header (C2) of the short cell 1 is normal, the short cell 2 is transferred to the communication path 13, and
The position of the short cell header (C4) of the short cell 3 is determined based on the LI indicating its own cell octet number in the short cell header (C2), and CRC5 is executed. Here, since the result of the CRC 5 for the short cell 3 is an error, the short cell 3 is discarded. Further, the LI in the short cell header (C4) becomes unreliable. In that case, the length display portion (C3) of the next-stage short cell added to the short cell 2 is referred to. As a result, the position of the header (C5) of the short cell 4 can be determined from the LI stored therein (C3), and the CRC5 is executed. Here, since the result of the CRC 5 for the short cell 4 is normal, the short cell 4
To the call path 13. Conventionally, short cell 2 has C
When an error occurs in RC5, the header (C
Since the position of 5) cannot be determined, the short cell 4 has been discarded unconditionally. However, even if a CRC5 error occurs in the short cell 3 according to the present invention, the short cell 4
Since the position of the header (C5) can be determined, the header is not discarded unconditionally, the reliability of detection is improved, and unnecessary discard processing can be eliminated.

In the operation of the other embodiment shown in FIG. 4, similarly to the above, the header position of the short cell for a plurality of short cells is determined by the OSF and the LI of the next-stage short cell added to each short cell. it can. However, in the embodiment shown in FIG.
The parity bit for I is 2 bits. This is, for example, to add one bit as a parity bit for the odd-numbered bit of the LI of the next-stage short cell and add the other as a parity bit for the even-numbered bit of the LI of the next-stage short cell, and perform the parity check twice. This improves the reliability of the LI of the next-stage short cell added in step (1).

As described above, the present invention receives information from a plurality of subscriber terminals, multiplexes the received information, and
A cell conforming to TM adaptation layer type 2 is generated, and for each cell generated, ITU-T Recommendation I.T. 363.
In an ATM network system that performs cell discard processing in accordance with 2 and transmits only normal cells to the communication path, the short cell generated at the last stage of the generated short cell, the short cell at the preceding stage thereof, and the short cell that is crossing over the cell are generated. At the end of each short cell excluding, the length display information of the next-stage short cell is added, and in the cell discarding process, the short cell header of each short cell is determined based on the contents of the intra-cell offset field and the length display information field in the cell header. The cyclic redundancy coding check is performed by determining the position, and when an error is detected, the position of the next-stage short cell header is determined by referring to the added length display information to perform the cyclic redundancy coding check. , According to the result, discarding or transmitting the short cell via a communication path, Conventionally, when a header of a short cell other than the last stage multiplexed in an AAL2 cell is discarded due to an error due to the CRC5, the LI in the discarded short cell header cannot be relied on, and the short circuit after that cannot be performed. If the header position of the cell could not be determined, the header position of the subsequent short cell can be determined, so that the reliability of detection is improved without being discarded unconditionally.

[0020]

As described above, according to the present invention, AA
Even if the short cell multiplexed before the corresponding short cell among the plurality of short cells multiplexed in the L2 cell is discarded due to a CRC5 error and the LI in the short cell header cannot be trusted, the AAL2 cell By referring to the LI of the next-stage short cell added to the end of each short cell multiplexed into the short cell, the position of the header of the corresponding short cell can be accurately determined. As a result, even if one of the initial stage or the multiplexed short cells is discarded due to an error of the CRC5, the header position of the short cell thereafter can be accurately determined. Need not be discarded unconditionally.

Further, among the plurality of short cells multiplexed in the AAL2 cell, the short cell multiplexed in front of the corresponding short cell is discarded due to a CRC5 error, and the LI in the short cell header cannot be trusted. Even in this case, the position of the header of the corresponding short cell can be accurately determined by referring to the LI of the next-stage short cell added to the end of each short cell multiplexed in the AAL2 cell. Thus, even if one of the initial stage or the multiplexed short cells is discarded due to an error of the CRC5, the CRC5 can be executed without unconditionally discarding the subsequent short cells. Can be counted accurately. As a result, the reliability of discard processing due to a short cell error in the AAL2 cell can be improved, and service quality such as high throughput and low latency can be secured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a short cell error verification system in an ATM network according to the present invention.

FIG. 2 is a diagram illustrating an AAL2 cell format generated in a base station / relay device in FIG. 1;

FIG. 3 is a diagram illustrating an embodiment of an AAL2 format for realizing a short cell error verification method in an ATM network according to the present invention.

FIG. 4 is a diagram showing another embodiment of the AAL2 format for realizing the short cell error verification method in the ATM network according to the present invention.

FIG. 5 is a diagram showing an operation procedure when no short cell is crossed in the embodiment shown in FIGS. 3 and 4;

FIG. 6 is a diagram showing an operation procedure when a short cell is straddled in the embodiment shown in FIGS. 3 and 4;

FIG. 7 is a diagram illustrating a conventional AAL2 cell format and an operation procedure when there is no short cell generated by the base station / relay device.

FIG. 8 is a diagram showing a conventional AAL2 cell format and an operation procedure when there is a short cell span generated by a base station / relay device.

[Explanation of symbols]

 1 to N subscriber terminal 11 base station / relay device 12 AAL2 cell verification circuit 13 communication path

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04L 12/56 H04L 12/28

Claims (4)

(57) [Claims] 1. A method for receiving information from a plurality of subscriber terminals, multiplexing the received information to generate cells conforming to an ATM adaptation layer type 2, and for each of the generated cells,
ITU-T Recommendation I. In an ATM network system that performs cell discard processing in accordance with 363.2 and transmits only normal cells to a communication path, the short cell in the last stage of the generated short cell and the short cell in the preceding stage thereof, and a short circuit in which the cell is straddled. At the end of each short cell excluding the cell, the length indication information of the next-stage short cell is added, and in the discard processing of the cell, each of the short cell is determined based on the contents of the intra-cell offset field and the length indication information field in the cell header. The position of the short cell header is determined, a cyclic redundancy coding check is performed, and when an error is detected, the position of the next-stage short cell header is determined by referring to the added length display information to determine cyclic redundancy coding. Check and discard according to the result or send the short cell via the communication path. Error method of verifying a short cell in the ATM network to be. 2. A 6-bit short-cell length indication information of a next-stage short cell and 1-bit parity corresponding to the information are added to the end of each short cell multiplexed in the cell. 2. The method for verifying short cell errors in an ATM network according to claim 1, wherein: 3. A 6-bit short-cell length indication information of the next stage is added to the end of each short cell multiplexed in the cell, and further, an odd-numbered bit of the length indication information bit is added. 2. A method according to claim 1, wherein two bits of a corresponding parity and a parity corresponding to an even-numbered bit are added.
3. The method for verifying short cell errors in an ATM network according to claim 1. 4. A method for multiplexing information received from a plurality of subscriber terminals to generate cells conforming to the ATM adaptation layer type 2, and for each of the generated cells, an ITU-T Recommendation I.T. In an ATM communication system that performs cell discard processing in accordance with 363.2 and transmits only normal cells to a communication path, a short cell in the last stage of the generated short cell and a short cell in a stage preceding the short cell and a short circuit in which the cell is straddled. A base station or a relay device that adds the length indication information of the next-stage short cell to the end of each short cell, excluding the cell, and each short cell based on the contents of the length offset information field in the cell offset field and the cell header. A cyclic redundancy coding check is performed by determining the position of the cell header. When an error is detected, the position of the next-stage short cell header is determined by referring to the added length display information to check the cyclic coding. And a cell that transmits the short cell via a communication path according to the result. Error check system of the short cells in ATM network and having a testimony circuit.