KR20000041332A - Method for processing asynchronous transfer mode(atm) adaptive layer(aal)-5 for selective atm transmission in atm communication network - Google Patents

Abstract

PURPOSE: A method for processing an asynchronous transfer mode(ATM) adaptive layer(AAL)-5 for selective ATM transmission in an ATM communication network, is provided to selectively re-transmit only corresponding cells in an error of abandonment of a specific ATM cell, without changing a structure of the AAL-5. CONSTITUTION: An asynchronous transfer mode(ATM) adaptive layer(AAL)-5 has a segment and reassembly(SAR) sub-layer, a common part convergence(CPCS) sub-layer, and a specific service convergence(SSCS) sub-layer. A method for processing the AAL-5 for selective ATM transmission in an ATM communication network, comprises as follows. ATM cell identification information is inserted in a specific place of an ATM cell and transmitted, when a transmission terminal transmits a protocol data unit of the CPCS sub-layer. A receiving terminal interprets the ATM cell identification information, and demands re-transmission for an abandoned cell.

Description

AAL-5 for transmitting selective ATM cell of ATM communication networks

The present invention relates to an ATM Adaptation Layer (AAL) in an Asynchronous Transfer Mode (ATM) network. More specifically, it relates to AAL-5, which makes it possible to selectively request a cell to be retransmitted in case of ATM cell failure or discard.

The ATM communication method combines real-time signals with a wide bandwidth distribution from narrowband service (telephone, facsimile) to wideband service (video conferencing, high-speed data / video transmission) and aggregated data signals that can aggregate clustered data signals. It is proposed to implement the BISDN.

The protocol reference model of the BISDN is composed of a user plane 10, a control plane 11, and a management plane 13, as shown in FIG. 1. The user plane 10 provides a user information related function of the BISDN, and the control plane 11 provides various control functions for providing a service. The management plane 13 is divided into hierarchical management 14 and plane management 15, and provides a monitoring function of a communication network.

The user plane 10 and the control plane 11 are each composed of a physical layer 16, an ATM layer 17, an AAL 18 and an upper layer 19. The physical layer 16 provides a physical medium and a transmission function, and the ATM layer 17 provides a call forwarding function for all services. The AAL 18 provides service related functions for layers above the AAL. The upper layer 19-1 of the user plane provides functions related to processing of service information, and the upper layer 19-2 of the control plane provides functions related to call control and connection control.

In particular, the AAL, as defined in International Telecommunication Union-T (ITU-T) Recommendation I.362, matches user service information with the format of ATM cells, handles transmission errors, loss or handling of cells, And processing of error cells. In addition, the AAL also provides a flow control function to satisfy the quality of service required by the user and a time control function to recover the user signal.

Because these functions cannot be satisfied by one standard, depending on the application (for example, whether the constant bit rate, real-time, connectivity, etc. according to the service characteristics) AAL-1, AAL-2, AAL-3 / 4, and AAL-5.

The present invention relates to AAL-5, which is characterized by a simplified function of AAL-3 / 4. AAL-3 / 4 has a non-real time, variable bit rate and provides connected and unconnected data communication services. However, there are disadvantages in that it is not suitable for high speed data communication due to the complicated procedures. Therefore, among the features of AAL-3 / 4, the protocol is simplified to enable high-speed data communication.

As shown in FIG. 2, the AAL-5 is located above the ATM layer 24 and sequentially includes a segmentation and reassembly (SAR) sublayer 23 and a common part convergence (Common Part Convergence); CPCS) sublayer 22 and Specific Service Convergence (SSCS) sublayer 21.

In the transmission process, the SSCS sublayer 21 divides a user-service data unit (U-SDU) from an upper layer (not shown) and transmits the AAL-SDU (= SSCS-PDU paid). Load), and the SSCS-Protocol Data Unit (PDU) 25 is made by attaching the SSCS-PDU header part and the trailer part before and after the AAL-SDU.

The CPCS sublayer 22 divides the SSCS-PDU to obtain a CPCS-SDU, and attaches a CPCS-PDU trailer to the CPCS-SDU (= CPCS-PDU payload) to form a CPCS-PDU 26.

The SAR sublayer 23 receives a variable length CPCS-PDU, which is an integer multiple of 48 octets, to form a 48 octet SAR-PDU (= ATM SDU) 27.

The ATM layer 24 provides the ability to mark the end of the CPCS-PDU, so that the SAR sublayer 23 can be delivered without any protocol overhead. Thus, protocol processing is simplified. The ATM User to User Indication (AUU) parameter of the Payload Type (PT) section in the header of the ATM cell 28 indicates which part of the SAR-PDU is included. If the AUU value is '0', the SAR-PDU is the beginning or middle part of the CPCS-PDU. If the AUU value is '1', it indicates the end of the CPCS-PDU.

The conventional ACS-5 CPCS-PDU structure 30, as shown in Fig. 3, has no header portion and only an 8-byte CPCS-PDU trailer portion. The PAD section (0 to 47B) is the portion of the CPCS-PDU payload that is filled before the trailer starts so that the CPCS-PDU length is an integer multiple of 48 octets.

In the CPCS-PDU trailer 32, a user-to-user (CPCS-UU) 1B carries information between CPCS users, and the CPI 1B indicates whether the corresponding PDU is common. LI (2B) represents the length of the CPCS-PDU payload section, and the CRC section (4B) contains the Cyclic Redundancy Check CRC-32 calculation results for the payload, PAD, and the first four octets of the trailer. It is a section. At this time, the length of the CPCS-PDU payload is greater than 1 and less than or equal to 65,535 bytes.

According to the prior art implementation of AAL-5, the length of the payload is known only after the input of the AAL-5 payload data of one 8-bit frame is completely completed, and thus the length of the PAD to be padded can be known. After that, the CPCS-PDU of the AAL-5 is completed by calculating the payload and PAD data and the CRC for the first four octets of the trailer to complete the trailer's CRC section. The CPCS-PDUs are cut into 48 bytes each to make and transmit ATM cells.

For example, a 96B CPCS-PDU with a 10B padding and an 8B trailer for a 78B size data packet and a 15B padding and an 8B trailer for a 121B size data packet are created. The SAR sublayer 23 simply performs the function of cutting them to size 48B, and they immediately go down to the ATM layer 24 to become an ATM cell payload. At this time, the AUU bit in the PT section is set to '1' if the corresponding payload is the end of the original data packet.

However, according to the conventional ATM AAL-5, when the receiving end detects an error of a specific ATM cell or the specific ATM cell is discarded due to excessive load on the transmission network, the receiving end all data of all packets of the AAL-5. You have to ask for a retransmission. In fact, since the length of the CPCS-PDU payload is up to 64K bytes, the time required to retransmit the entire packet will not be ignored and there is a problem that causes more load on the network.

Accordingly, the present invention has been made to solve the above problems, and the selective cell transmission in the ATM communication network can be selectively retransmitted in case of a specific ATM cell failure or discard without changing the structure of the AAL-5. The purpose is to provide a method for treating AAL-5.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a BISDN protocol reference.

2 is a diagram showing a sublayer and a corresponding data structure of a conventional AAL-5.

3 is a diagram illustrating a CPCS-PDU structure of a conventional AAL-5.

4 is a first embodiment of an ATM cell data structure in accordance with the present invention.

5 is a second embodiment of an ATM cell data structure according to the present invention;

In order to achieve the above object, the present invention provides asynchronous transmission mode adaptation layer-5 (AAL) consisting of a segmentation and recombination (SAR) sublayer, a common subconvergence (CPCS) sublayer, and a specific service convergence (SSCS) sublayer in an ATM communication network. In the ATM cell transmission method through -5), when the transmitting end transmits the protocol data unit (CPCS-PDU) of the CPCS sublayer, the ATM cell identification information is inserted into a specific position on the ATM cell and transmitted. The ATM cell identification information is interpreted to request retransmission of the discarded cell.

In addition, the present invention for achieving the above object is an asynchronous transmission mode adaptation layer-5 consisting of a segmentation and recombination (SAR) sublayer, a common subconvergence (CPCS) sublayer and a specific service convergence (SSCS) sublayer in an ATM communication network In the ATM cell transmission method using (AAL-5), when a transmitting end transmits a protocol data unit (CPCS-PDU) of the CPCS sublayer, (a) inserts and transmits the ATM cell information at a specific position on an ATM cell. Doing; and (b) a receiver interpreting the ATM cell information to determine a discarded cell, interpreting the ATM cell payload protection information to determine an error cell, and requesting retransmission of the corresponding cell. do.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

4 is an ATM cell data structure diagram according to a first embodiment of the present invention, and FIG. 5 is an ATM cell data structure diagram according to a second embodiment of the present invention. First, the present invention is designed to change the payload of an ATM cell at the time of transmission without changing the structure of AAL-5.

In AAL-5, when creating an ATM cell from a CPCS-PDU payload of up to 65,535 bytes, 1,366 ATM cells are required. At this time, 48 bytes excluding the header in the ATM cell are filled with CPCS-PDU payload and trailer.

First, referring to FIG. 4, the transmitting ATM cell 40 according to the first embodiment includes a 5-byte cell header (including PT), a 46-byte ATM-SDU, and a 2-byte cell number (NUM). . The 46-byte ATM-SDU is filled with CPCS-PDU payloads and trailers. The 2-byte NUM (corresponding to the 47th and 48th bytes of the payload of the cell) is inserted with the cell number (from 0 to 1365) per packet.

The transmitter divides the CPCS-PDUs into 46 bytes each and attaches a cell header at the front end and a cell number (NUM) at the front to make a 53-byte ATM cell.

Then, the receiving end can immediately know the number of the ATM cell inputted by this NUM value, and can immediately know the number of the lost or discarded ATM cell. Thus, there is an advantage in that only the lost / deprecated ATM cells may be required to be retransmitted.

On the other hand, if the cell number is inserted in the cell payload section as shown in FIG. 4, if the length of the CPCS-PDU payload is the maximum value, the number of ATM cells to be transmitted is 1425, and thus the transmission bit of the corresponding channel. Speed may be reduced.

In a more preferred embodiment of the present invention, it is possible to further grant the protection function of the ATM cell payload as well as the identification function of the ATM cell.

Referring to FIG. 5, the transmission ATM cell 50 according to the second embodiment includes a 5-byte cell header (including PT), a 46-byte ATM-SDU, and 2-byte cell information INFO. The 46-byte ATM-PSU is filled with CPCS-PDU payloads and trailers. In addition, two bytes of INFO (corresponding to the last 47 and 48th bytes of the payload of the cell) contain information for checking whether the packet is normal and the number of the cell.

At the transmitter, the CPCS-PDU is divided into 46 bytes each to make an ATM-PSU. A 53-byte ATM cell is created by attaching a cell header and a cell information (INFO) at the front end. At this time, the cell information INFO is obtained by passing the ATM cell payload 46 bytes of data through a 16-bit CRC, and performing the exclusive logical sum operation with the sequence number NUM of the corresponding cell and the CRC value for the 46 bytes. It is contained in the first and 48th bytes.

The receiver passes the payloads of the input ATM cell through the same 16-bit CRC as the transmitter, and performs an exclusive logic operation on the CRC values up to 46 bytes with the received 47th and 48th byte values. The result of this operation corresponds to the cell number (NUM) of the corresponding ATM cell.

If the cell number currently received at the receiver (NUM _i ) is compared with the previously received cell number (NUM _i-1 ), the difference between the two values is +1 (NUM _i -NUM _i-1 = 1). Otherwise, it is determined that cells transmitted between the previous cell and the current cell are discarded.

In addition, in a further embodiment, if a 46-byte payload of one cell is CRC processed and the result is inputted by XORing with NUM of the last 2 bytes of the same cell, the current cell can be immediately checked.

If CRC processing the 46-byte payload of one cell and fill the result with 2 bytes at any position on the payload of the next cell, the CRC is passed through the currently input cell and the NUM and XOR values are next. After a cell is entered, it must be compared with the NUM information of that cell. In this case, the error of the current cell can be confirmed only after the input of the next cell. That is, whether the current cell is normal is determined according to whether the cells which are sequentially input next are normal. For example, when the receiving side receives a cell whose NUM value is the previous cell number 2 and the current cell number 4, the NUM information of the previously input cell is 2, and the 46-byte payload of the next input cell is CRC. The value XORed after 3 is different from the NUM information (assuming '4') of the current cell. In this case, the third cell is requested to be retransmitted, and the CRC is continuously calculated using the payload (46 bytes) of the cell having NUM information of 4.

Applying the second embodiment, it is possible to accurately determine the discarded cells and faulty cells, so that only the corresponding cells can be selectively retransmitted.

In the first and second embodiments, the last two bytes of the ATM cell are transmitted as cell number (NUM) / cell information (NUM), but the position of these two bytes does not necessarily have to be the last two bytes. It may be any other position. This is because the CRC may be calculated across cells.

In a further embodiment of the present invention, when the payload in the ATM cell is protected and transmitted using the CRC, the final CRC 32 bits of the CPCS-PDU trailer in the AAL-5 format are not necessary. This is because the accuracy of the payload can be recognized by calculating the CRC for the payload in the ATM cell.

Thus, the format of AAL-5 can be adjusted to be an integer multiple of 46 bytes by adjusting the PDU length of the AAL-5 CPCS-PDU, if possible, to remove and send the last 4 byte CRC of the CPCS-PDU. In fact, for example, the number of bits for sending the cell number of an ATM cell is given as 16 bits. If the number of bits is greater than or equal to 11 bits, any value may be used.

In another embodiment of the present invention, the number related information of the cell may be replaced with the time related information for sending the cell.

The present invention is not limited by the embodiments described above, and various changes and modifications can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

As described above, when the conventional ATM AAL-5 data packet is transmitted to the ATM cell due to an error or discard of the ATM cell, retransmission of the entire data packet is inevitable.

According to the present invention, an ATM cell number or cell information is loaded at a specific (arbitrary) location of a payload in an ATM cell, thereby detecting an error or a number of discarded cells and requesting retransmission of only that cell.

In addition, the proposed cell information can more accurately determine whether the cell is lost by adding CRC to the payload. As a result, it is possible to accurately determine at which position of the CPCS-PDU packet the ATM cell loss occurs, and the last 32-bit CRC of the CPCS-PDU may be removed.

Claims (10)

ATM cell transmission method through asynchronous transmission mode adaptation layer-5 (AAL-5), which is composed of segmentation and recombination (SAR) sublayer, common subconvergence (CPCS) sublayer and specific service convergence (SSCS) sublayer in ATM network To When the transmitting end transmits the protocol data unit (CPCS-PDU) of the CPCS sublayer, the ATM cell identification information is inserted and transmitted at a specific position on the ATM cell, AAL-5 for selective ATM cell transmission in an ATM communication network, characterized in that the receiver interprets the ATM cell identification information and requests retransmission for the discarded cell. 2. The AAL-5 according to claim 1, wherein the ATM cell identification information is an ATM cell number in a transmission unit packet. 2. The AAL-5 according to claim 1, wherein the ATM cell identification information is transmission time information. 2. The optional ATM cell of an ATM communication network according to claim 1, wherein the receiving end requests retransmission by detecting a cell identification number of a cell that has failed due to a cyclic redundancy check (CRC) of the CPCS-PDU trailer. AAL-5 for transmission. 2. The AAL-5 according to claim 1, wherein the bit size of the ATM cell identification information is 11 bits or more. ATM cell transmission method through asynchronous transmission mode adaptation layer-5 (AAL-5), which is composed of segmentation and recombination (SAR) sublayer, common subconvergence (CPCS) sublayer and specific service convergence (SSCS) sublayer in ATM network To When the transmitting end transmits the protocol data unit (CPCS-PDU) of the CPCS sublayer, (a) inserting and transmitting the ATM cell information at a specific location on an ATM cell; (b) receiving at the receiving end by analyzing the ATM cell information to determine the discarded cell and at the same time determining the cell in error, and requesting retransmission of the corresponding cell. AAL-5 for transmission. 7. The CPCS sublayer of claim 6, wherein the CPCS sublayer adjusts the padding length of the CPCS-PDU to provide the SAR sublayer with a variable length CPCS-PDU having an integer multiple of an ATM cell payload length. AAL-5 for Selective ATM Cell Transmission in ATM Networks. Where ATM cell payload length = 48 bytes-ATM cell sequence information length The method of claim 6, wherein step (a) (a1) calculating a cyclic redundancy check (CRC) for the length of the ATM cell payload; (a2) an exclusive logical sum operation of the CRC result value and the identification number of the corresponding cell, (a3) AAL-5 for selective ATM cell transmission in an ATM communication network using the result value (a2) as ATM cell information. The method of claim 8, wherein step (b) (b1) calculate the length of the received ATM cell payload by the redundant circulation test (CRC), (b2) an exclusive logical sum operation of the CRC result value and the received (a2) result value of the cell to obtain an identification number of the cell; (b3) AAL-5 for selective ATM cell transmission in an ATM communication network, characterized by detecting the identification number of the discarded cell by comparing the currently received cell identification number with the previously received cell identification number. 10. The AAL-5 according to claim 9, wherein the normality of the currently received cell is determined according to the normality of the next received cells.