KR0123224B1 - Unit of receiving atm cells in aal type 5 sar layer - Google Patents

Abstract

The present invention relates to an ATM5 SAR receiving processing apparatus, comprising: a counter and a controller 20 for generating a FIFO control signal, a CRC enable signal, and a completion signal by counting 48 modules into a module when a start signal is input from an ATM layer; and An AUU processing unit 30 for inputting the AUU bit from the ATM layer to determine the end of the message; A length calculation unit 40 for calculating a length of a message received by the output of the AUU processing unit 30 and the output of the counter and the control unit 20; An assembly completion signal generator 50 generating an assembly completion signal (CPCS_invoke) signal according to an output of the counter and the controller 20 and an output of the AUU processor 30; A FIFO controller (10) for controlling the FIFOs (1, 3) to read data from an ATM FIFO (1) and write data to an AAL FIFO (3) in accordance with the FIFO control signal; And a CRC processing unit 60 which detects a CRC error of the received message according to the output of the counter and the control unit 20 to quickly process the AAL5 SAR receiver.

Description

ALL5 SAR receiver for ATM communication

1 is a view illustrating a SAR receiving processing apparatus according to the present invention.

(a) is a diagram illustrating a data flow structure of an AAL layer.

(b) shows a format of CPCS-PDU data.

(c) is a diagram showing the format of SAR-PDU data.

2 is a block diagram showing a SAR receiving processing apparatus according to the present invention.

3 shows the structure of a typical ATM cell.

(a) is a diagram showing the structure of the entire ATM cell.

(b) is a diagram illustrating an ATM cell header structure of a user network point of view (UNI).

(c) shows the ATM cell header structure of the network node interface (NNI).

* Explanation of symbols for main parts of the drawings

1,3: FIFO 2: SAR receiver

10: FIFO control unit 20: counter and control unit

30: AUU processing unit 40: length calculation unit

50: assembly completion signal generator 60: CRC processing unit

The present invention relates to an ATM Adaptation Layer (AAL) that matches user service information and ATM cell format in an Asynchronous Transfer Mode (ATM) communication scheme. In particular, the present invention relates to an ATM Adaptation Layer (AAL) protocol. Sagmentation and Reassembly Sublayer (SAR) Sub-layer reception processing plant reassembles a segment and sends it to the Convergence Sublayer (CS) sublayer.

Recently, as the means of communication is rapidly digitized and the development of optical communication enables the transmission of a wide band, a broadband ISDN (Broadband Intergrated Services Digital Network) has emerged to meet various user needs.

That is, B-ISDN is a video telephony service from narrowband services such as remote meter reading, data terminal, telephone, and facsimile, as described in broadband information communication (co-author Lee Byung-ki, Kang Min-ho, Jong-hee Lee; Kyohaksa; 1994; Seoul; p239 ~ 314). It is designed to handle and deliver broadband services such as video conferencing high-speed data transmission and video signal transmission in common, and is implemented based on an asynchronous transmission mode (ATM) communication method.

The ATM communication method is similar to the conventional packet communication method in that ATM cells are asynchronously transmitted by asynchronous time division multiplexing (ATDM) and are transmitted in cell units. It handles even signal of bit rate and is standardized by international standardization organization for use in local area network as well as huge public network.

This ATM communication method communicates based on ATM cells as shown in (a) to (c) of FIG. 4, and the user's long message is divided into ATM cells and transmitted, and the received ATM cells are again one message. Is reassembled and forwarded to the parent user.

That is, as shown in (a) of FIG. 3, an ATM cell is divided into a 5-byte header (H: Header) section and a 48-byte user information section, and the 5-byte header is divided into FIGS. As shown in (c), the header structure is divided into a header structure at a user network interface (UNI) and a header structure at a network node interface (NNI), and a header at a user network interface (UNI). The structure consists of 4 bytes of General Flow Control (GFC), 4 bytes of Virtual Path Identifier (VPI), and 2 bytes of 4 bytes of virtual path identification. It consists of a number (VPI) and a 4-bit virtual channel identifier (VCI), the third byte consists of an 8-bit virtual channel identifier (VCI), and the fourth byte is a 4-bit virtual channel. Identification number (VCI), 3-bit payload type (PT) and 1-bit cell abandonment ranking (CLP: Cel) Loss Priority (5), and the fifth byte consists of 8-bit header error control (HEC).

Here, the last bit of the 3-bit payload type (PL) is a user bit (AUU: ATM_USER to ATM_USER), which is useful in the AAL5 protocol.If the first bit is 1, the operation management load type (OAM: Operations, Administration, and Managent), and their meaning is summarized in Table 1 below.

Also, when looking at the header structure at the network node interface (NNI), the general flow control (GFC) in the first byte of the user network interface (UNI) described above is used as the virtual path identification number (VPI). It can be seen that the header structure of the user network interface (UNI) is the same.

This ATM communication method has a hierarchical structure as shown in Table 2 below, and has standardized standards for each layer.

As shown in Table 2, the ATM communication method is divided into vertical structures such as a physical layer, an ATM layer, an ATM adaptation layer (AAL), and a higher protocol layer. The AAL layer is a cut and recombination sublayer (SAR). Segmentation And Reassembly sublayer, and Convergence Sublayer (CS) sublayer, and the physical layer is divided into physical media (PM) and Transmission Convergence (TC) sublayer.

In addition, the services required by the user in the ATM communication method can be separated according to the characteristics of the source as shown in Table 3 below.

As shown in Table 3, the types of services in B-ISDN are classified into Classes A to D according to the nature of the source. The Class A services are real-time, identity bit rate, and connectivity services, and the Class B service is real-time, It is a variable bit rate, connectivity service, Class C service is a non-real time, variable bit rate, a non-connected service, Class D service is a non-real time, variable bit rate, a non-connected service. Representative examples of such services include identity rate video signals, variable rate video signals, connectivity data delivery, and connectionless data delivery.

On the other hand, AAL protocols corresponding to the above services are classified into AAL1 to AAL5 as shown in the following Table 4, but conventionally divided into AAL1 to AAL4, but AAL3 and AAL4 are similar to each other and have been combined into AAL3 / 4. AAL5 has been proposed to reduce the overhead.

As shown in Table 4, the AAL layer is divided horizontally as AAL1, AAL2, AAL3 / 4, AAL5 in order to efficiently process the service according to the type of service. It is suitable for high-speed data communication by reducing overhead of AAL3 / 4 layer that transmits data of class and class D service, and transparently deliver service data unit (U-SDU) from service user. ATM data is generated by dividing the variable-length data received from the convergence layer layer CS and the convergence layer layer CS, which detects transmission errors, and performs information identification and buffer allocation. The ATM cell is received from the layer and reassembled into subdivision and recombination sublayers (SARs) for recovering a converged sublayer protocol data unit (CS-PDU). In addition, the Convergence (CS) sublayer is a Common Part Convergence Sublayer (CPCS) that performs functions common to the connectivity and connectionless services, and a Service Specific Convergence Layer (SSCS) for providing specific AAL user services. : Service Specific Convergence Layer).

Details of this AAL layer have been proposed in ITU-T Recommendations 1.362 and 1.363, and by Gigabit Networking: Craig Partridge; 1994; Addison Wesley; pp (61-87) and Lee Byeong-gi It is described in detail in Broadband Information Communication (pp314 ~ 327).

Since the AAL5 cutting and assembly (SAR) sublayer as described above has been conventionally implemented as a software program, there is a problem that data transmission speed is slow and the computer is overloaded.

Accordingly, an object of the present invention is to provide an AAL5 SAR reception processing apparatus that implements a hardware reception function of an AAL5 truncation and reassembly (SAR) sublayer in an ATM communication scheme in order to solve the above problems.

The SAR receiving processing apparatus of the present invention for achieving the above object, the 48-byte ATM cell payload to the ATM layer to receive data according to the AAL5 protocol of the ATM communication method through the ATM FIFO to check the reception error In the asynchronous delivery mode receiving processing device to be delivered to the upper layer through the AAL FIFO, a counter for generating a FIFO control signal, a CRC enable signal, and a completion signal by counting 48 to the module when a start signal is input from the ATM layer; Control unit; And an AUU processing unit for determining the start and end of a message by inputting an AUU bit from an ATM layer. A length calculation unit calculating a length of a message received by the output of the AUU processing unit and the output of the counter and the control unit; An assembly completion signal generator configured to generate an assembly completion signal according to an output of the counter and the controller and an output of the AUU processor; A FIFO controller for controlling the FIFOs to read data from an ATM FIFO and write data to an ALL FIFO according to the FIFO control signal; And a CRC processing unit for detecting a CRC error of the received message according to the output of the counter and the controller.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, in order to facilitate understanding of the present invention, the data structure and flow in the AAL layer will be described with reference to FIGS.

(A) of FIG. 1 is a schematic diagram showing the data flow between layers according to the AAL5 protocol in the ATM communication method. The user service of the upper layer (hereinafter referred to as a sun workstation, hereinafter called a sun workstation) in the embodiment of the present invention. After the data unit (U-SDU) passes through the AAL Service Access Point (ALL-SAP), it is formed into AAL Service Data Units (AAL-SDU) and stored in the FIFO, and the AAL service data in the AAL5 CPCS layer. A CPCS trailer is added to the unit (ALL-SDU) to form a convergence protocol unit (AAL-SDU), which is then sent down the FIFO to the cut and recombine (SAR) layer. In the AAL SAR layer, a CPCS-PDU of variable length is divided into 48 bytes according to a message to be transmitted by a user, and then a truncation and reassembly protocol unit (SAR-PDU) is formed. The bytes are passed down to the ATM layer via the ATM-SAP.

The ATM layer attaches 1-byte header error control (HEC) to a 52-byte segment, forms a 52-byte ATM cell, and transmits another terminal or ATM switch through the optical transmission path of the physical layer.

That is, the AAL5 protocol simplifies the complex process of AAL3 / 4 for connected or disconnected data communication. Like AAL3 / 4, the AAL5 protocol has a sublayer of SAR, CPCS, and SSCS, and has a message mode and a strip mode. However, the AAL5 convergence layer adds only 8 bytes of trailer without headers and adds 0 to 48 bytes of pads to the last cell that contains the trailer so that the total message length is a multiple of 48. In the AAL5 SAR sublayer, 48 The CPCS-PDU, which is a multiple length of bytes, is divided into 48-byte SAR-PDU segments, and the AUU bit of the payload type (PL) of the ATM header of the last segment is set to 1 and transmitted. Therefore, overhead is reduced during data transmission according to the AAL5 protocol, and the procedure is simplified, and high speed transmission is possible.

(B) of FIG. 1 is a diagram showing the structure of a data format (CPCS-PDU) formed in the AAL5 CPCS layer. The variable length CPCS-PDU payload received from the upper layer and the total length of the CPCS-PDU are 48 bytes. The CPCS-PDU trailer is divided into a pad and an 8-byte CPCS-PDU trailer. The CPCS-PDU trailer has a 2-byte common part indicator (CPI) and a 2-byte length field (LI: Length field). ) And a 4-byte CRC. In addition, the 2-byte common identifier (CPI) may be further divided into one byte of a user-to-user indication field (UU) and one byte of a common identifier identifier (CPI). In the present invention, 2 bytes using the CPI, the contents of the CPI is input through the input and output bus (SBUS) from the sun workstation, which is the upper layer, the content of the length area (LI) is the size of the net pay load excluding the pad and trailer, The CRC is 32 bits with strong error detection and correction capability.

(C) of FIG. 1 shows the data format of a SAR-PDU according to the AAL5 protocol, and is formed by dividing a CPCS-PDU, which is a multiple of 48 bytes, into segments of 48 bytes, and (b) and (c) of FIGS. The AUU bit of the payload type (PL) of the same ATM header is set to 1 for the last segment including the trailer and reset to the remaining segment 0 and sent down to the ATM layer.

Next, a SAR reception processing apparatus according to the present invention will be described in detail with reference to FIG.

2 is a block diagram illustrating a SAR receiving processing apparatus according to the present invention. When a START signal is input from an ATM layer, the counter performs a 48 count modulo and generates a FIFO control signal, a CRC enable signal, and a completion signal. And a control unit 20; An AUU processing unit 30 for inputting the AUU bits from the ATM layer to determine the start and end of the message; A length calculation unit 40 for calculating a length of a message received by the output of the AUU processing unit 30 and the output of the counter and the control unit 20; An assembly completion signal generator 50 generating an assembly completion signal (CPCS_invoke) signal according to an output of the counter and the controller 20 and an output of the AUU processor 30; A FIFO controller (10) for controlling the FIFOs (1, 3) to read data from an ATM FIFO (1) and write data to an AAL FIFO (3) according to the FIFO control signal; And a CRC processing unit 60 for detecting a CRC error of the received message according to the output of the counter and the control unit 20.

That is, the ATM layer receives the cell data in the format according to the AAL5 protocol as described above, processes the ATM header, and then records 48 bytes of cell data in the ATM FIFO 1, and the payload type (PT) of the ATM header is stored. After the AUU bit is separated, the start signal and the AUU bit are applied to the SAR receiving apparatus 2 according to the present invention.

Then, the SAR reception processing apparatus 2 starts 48 counts modulo according to the START signal, reads the data received from the ATM FIFO 1 by 48 bytes, and writes the data to the AAL FIFO 3, which is then AUU. Repeat the segment from bit 0 to 1 to reassemble the segment in the transmission process and complete it as one message. Then, the assembly completion signal (CPCS_invoke) is generated to inform the CPCS sublayer. CRC_err) Detect occurrences.

The operation of the AAL5 SAR reception processing apparatus according to the present invention configured as described above will be described for each configuration block.

When the START signal is applied from the ATM layer, the counter and control unit 20 starts the module with 48 counts and sends the FIFO control signal for reading data from the ATM FIFO 1 and the read data to the AAL FIFO 3. A FIFO control signal for recording is generated, a signal for enabling the CRC processing unit 60 for detecting a CRC error of the received data is generated, and a completion signal is generated every 48 counts.

The AUU processing unit 30 inputs the AUU bit from the ATM layer, and if the AUU bit is 0, determines that it is a start segment or a continuous segment, and if it is 1, it determines that it is the last segment. That is, as described above, the AUU bit of the last segment including the CPCS trailer is set to 1 and the remaining segment is set to 0 at the time of transmission. Can be distinguished.

The length operation unit 40 calculates the length of the received message by multiplying the number of segments from the segment where the AUU bit is changed from 1 to 0 to the segment from 0 to 1 by 48, and then calculates the length of the assembly completion signal generator 50. According to the output, the length information len [15..0] of the message received in the CPCS layer is output. That is, since the data length of the SAR layer is a multiple of 48 by inserting a pad (PAD) in the CPCS layer at the time of transmission, it is possible to easily obtain the length of a message including the pad and the CPCS trailer by knowing only the number of received segments. In addition, if necessary, the length of the pad and the length of the payload to be transmitted to the upper layer may be calculated using the length information of the CPCS trailer.

The FIFO control unit 10 reads data from the ATM FIFO 1 according to the counter and the FIFO control signals of the control unit 20 (that is, fifo_start and fifo_end), writes data to the AAL FIFO 3, and assembles a message.

As described above, the CRC processing unit 60 detects a CRC error of the received message by analyzing a 32-bit CRC code of the transmitted CPCS trailer.

As described above, according to the present invention, the SAR reception apparatus has an effect of implementing the reception function of the AAL5 SAR layer with simple digital logic to improve data processing speed and improve reliability.

Claims (1)

In receiving data according to ATM communication method AAL5 protocol, 48-byte ATM cell payload is input to ATM layer through ATM FIFO (1), and after receiving error, it is transmitted to higher layer through AAL FIFO (3). An asynchronous delivery mode receiving processing apparatus comprising: a counter and a controller (20) for generating a FIFO control signal, a CRC enable signal, and a completion signal by counting a module 48 when a START signal is input from an ATM layer; An AUU processing unit 30 for inputting the AUU bits from the ATM layer to determine the start and end of the message; A length calculation unit 40 for calculating a length of a message received by the output of the AUU processing unit 30 and the output of the counter and the control unit 20; An assembly completion signal generator 50 generating an assembly completion signal (CPCS_invoke) signal according to the output of the counter and the control unit 20 and the output of the AUU processing unit 30; A FIFO control unit (10) for controlling the FIFOs (1, 3) to read data from the ATM FIFO (1) and write data to the ALL FIFO (3) according to the FIFO control signal; And a CRC processing unit (60) for detecting a CRC error of the received message according to the output of the counter and the control unit (20).