KR0123222B1 - Unit for reading fifo of aal 3/4 in atm system - Google Patents

Abstract

The FIFO reading circuit of an ATM adaptation layer 3/4 transmitting end includes a multiplexor(10) for inputting a message segment signal(st) from the outside to select one of '44', '40' or ' the remaining length indication(LI)', a down counter(12) set by an output vale of the multiplexor(10) and operated by means of a start signal from the outside to output a FIFO end signal at a final step, and a FIFO reading part(14) activated by the input of the external start signal and sequentially reading the data stored in an AAL FIFO(16) until the FIFO end signal of the down counter(12) is inputted.

Description

Asynchronous transfer mode adaptive system (AAL) 3/4 transmitter FIFO read circuit

1 is a block diagram showing a FIFO read circuit of an AAL 3/4 transmitter in accordance with the present invention.

2 is a diagram illustrating an AAL transmission processing apparatus according to the present invention.

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

(b) is a diagram showing the data format of a Common Convergence Sublayer (CPCS) packet data unit (PDU).

(c) illustrates the format of a Cut and Recombine Layer (SAR) Packet Data Unit (PDU).

3 shows a structure of a general 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 interface (UNI).

(c) is a diagram illustrating an ATM cell header structure of a network node interface (UNI).

* Explanation of symbols for main parts of the drawings

10: multiplexer 12: down counter

14: FIFO lead section 16: ALL FIFO

In the Asynchronous Transfer Mode (ATM) communication method of the present invention, an ATM adaptation layer (AAL) that connects an ATM layer and a higher user service layer, matches user service information with an ATM cell format, and handles transmission errors. In particular, it integrates the Asynchronous Adaptation Layer, which is divided into the Common Convergence Convergence Layer (CPCS) and the Truncation and Combination (SAR) Sublayer, to integrate a predetermined header and trailer into the data input to the upper service layer. In the asynchronous cell adaptation layer transmitting apparatus to send down to the ATM layer, the transmission FIFO of the asynchronous delivery mode adaptive layer (AAL) 3/4 which reads the data loaded in the AAL FIFO. It relates to the reading circuit.

In recent years, as the transmission means is rapidly digitized and the development of optical communication enables transmission of a wide band, a broadband ISDN (Broadband Intergrated Services Digital Network) has emerged to meet various user needs. In addition, this B-ISDN is designed to handle and deliver a wide range of services from narrowband services such as remote metering, data terminals, telephones, and facsimile to broadband services such as video telephony, video conferencing, high speed data transmission, and video signal transmission. It is implemented based on the communication method.

Here, the ATM communication method is similar to the conventional packet communication method in that ATM cells are asynchronously transmitted by asynchronous time division multiplexing (ATM) and transmitted in cell units. Is a communication method standardized by the International Organization for Standardization to handle signals of real time and identity rate and to be used in local area networks as well as huge public networks.

This ATM communication method is based on the ATM cells as shown in (a) to (c) of FIG. 3, and the user's long message is cut into ATM cells and transmitted. Reassembled into messages and delivered to the parent user.

That is, as shown in (a) of FIG. 3, the ATM cell is divided into a header section of 5 bytes and a usage information section of 48 bytes, and the header of 5 bytes is shown in (b) and (c) of FIG. As shown, the header structure in the user network interface (UNI) and the header structure in the network node interface (NNI) are divided into header structures. The header structure in the user network interface (UNI) is the first byte. 4 bytes of Generic Flow Control (GFC), 4 bytes of Virtual Path Identifier (VPI), and 2 bytes of 4 bytes of Virtual Path Identifier (VPI) It consists of a virtual channel identifier (VCI) of bits, the third byte consists of 8-bit virtual channel identification number (VCI), the fourth byte is a 4-bit virtual channel identification number (VCI) and 3-bit Payload Type (PT) and 1-bit Cell Loss Priority (CLP) The fifth byte is composed of 8-bit header error control (HEC).

Also, when looking at the header structure of the network node interface (NNI), except that 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 same as the header structure of the network interface (UNI).

This ATM communication method has a hierarchical structure as shown in Table 1 below, and has standardized standards for each layer.

That is, as shown in Table 1, 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, and the AAL layer is a cut and recombination sublayer ( It is divided into Segmentation And Reassembly sublayer (SAR) and Convergence Sublayer (CS) sublayer, and the physical layer is divided into Physical Media (PM) and Transmission Convergence (TC) sublayer.

In addition, according to the service of the user, that is, the characteristics of the source in the ATM communication method can be separated as shown in Table 2.

As shown in Table 2, the types of services in the B-ISDN are classified into Classes A to D according to the characteristics of the source. The Class A services are real-time, identity bit rate, and connectivity services. 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 transmission, and connectionless data transmission.

On the other hand, AAL protocols corresponding to the above services are classified into AAL1 to AAL5 as shown in Table 3 below. Conventionally, AAL1 to AAL4 are classified into AAL1 to AAL4. However, AAL3 and AAL4 are similar to each other. To reduce the overhead, AAL5 has been proposed.

As shown in Table 3 above, 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 functions to transfer the data of this variable class C and D service, and is divided into message mode and stream mode, and transparently delivers service data unit (U-SDU) from service user and detects transmission error. It cuts the data of convergence (CS) sublayer that performs information identification and buffer allocation function and variable length data received from this convergence (CS) sublayer, makes ATM cell, transfers it to ATM layer, and transfers ATM cell from ATM layer. Receive and reassemble to receive the CS-PDU to be broken down into the sub-layer to cut and recombination (SAR) sub-formula.

In particular, in the transmission of AAL 3/4, the data format for transferring data received from the upper layer to the lower layer and their relationship is as shown in (a) of FIG. 2, and the user service data unit of the upper layer ( U-SDU) is formed as AAL-SDU in AAL SSCS layer via AAL Service Access Point (AAL-SAP), and CS-PDU is formed by adding CPCS header and CPCS trailer to AAL-SDU in AAL CPCS layer. After the CS-PDU is cut by 44 bytes in the AAL SAR layer, a 2-byte header and a 2-byte trailer are attached to form a 48-byte SAR-PDU, which is transferred to the ATM layer via an ATM access point (ATM-SAP). Becomes an ATM-SDU. In the ATM layer, a 53-byte ATM cell (ATM-PDU) is formed by attaching a 5-byte header to a 48-byte ATM-SDU, and then transmits to another terminal or exchange using an optical transmission means in the physical layer.

Here, the data format (CPCS-PDU) DML structure formed in the AAL 3/4 CPCS layer has a payload (4 bytes of headers and 4 bytes in PayLoad) received from the user, as shown in FIG. In this case, the 4-byte header is composed of 1-byte Common Part Indicator (CPI), 1-byte Begin Tag (Btag), and 2-byte buffer allocation size (BAsize). Buffer Allocation Size; 4-byte trailer consists of 1 byte of alignment (AL), 1 byte of end tag, and 2 bytes of length indicator. .

In addition, the common part indication (CPI) indicates whether the corresponding CPCS-PDU is a common part, and is currently '0'. The start / end tags (Btag and Etag) receive the same number for the header and trailer of the same CPCS-PDU. This tag is used to detect errors at the same time. The buffer size (BAsize) indicates the size of the buffer allocation that the receiver should have up to 64K bytes, and the alignment (AL) fills the 32-bit trailer of the CPCS-PDU. The note is a pad, and the length indicator LI indicates the length of the pure CPCS-PDU excluding the pad PAD. The length indication LI is always smaller than or equal to the buffer size BAsize, and there is a pad PAD filling the length of the payload to be a multiple of 32 bits between the CPCS-PDU payload and the trailer.

On the other hand, the structure of the data format (SAR-PDU) formed in the AAL 3/4 SAR layer is received after cutting the CPCS-PDU of the CPCS layer into 44 bytes of data, as shown in (b) of FIG. A two-byte header and a two-byte trailer are added to the cut payload. Here, the two-byte header consists of a 2-bit segment type (ST), a 4-bit sequence number (SN), and a 10-bit multiplexing identification (MID); The two-byte trailer consists of a 6-bit Length Indication (LI) and a 10-bit Cyclic Redundancy Check (CRC).

At this time, the section shape (ST) is displayed separately to the characteristics of each section as shown in Table 4.

As shown in Table 4, when ST is '10', the 44-byte payload is the data including the beginning of the message. If it is '00', the middle part of the message is known. If it is '11', it can be seen that the message is a single segment.

In addition, the sequence number (SN) represents a serial number for a message, the multiplexing identification (MID) is an identifier used when multiplexing multiple CPCS connections through one ATM layer connection, and the length indication (LI) is a SAR. -PDU payload length in bytes. CRC is error checking and correction code for the entire SAR-PDU.

However, in the case of transmitting data in the AAL 3/4 method as described above, since each sublayer separates and implements functions, there is a problem in that a circuit element is consumed and bulky when implemented as a circuit.

Therefore, this nickname is AAL 3/4 transmission processing apparatus in which AAL 3/4 transmission function can be integrated and processed simultaneously in one structure without separating CPCS sublayer and SAR layer in ATM communication system. It is an object of the present invention to provide a transmission FIFO read circuit of the asynchronous transfer mode adaptive layer 3/4 which reads and outputs data loaded in a FIFO by a predetermined length.

The apparatus of the present invention for achieving the above object is the asynchronous transfer mode (ATM) adaptive layer (AAL 3/4) is divided into common part converging part layer (CPCS) and cutting and recombination part layer (SAR) is the common In the CPCS, a header and a trailer are added to a message input from an upper layer, and in the cut and recombine sublayer, the message in which the header and the trailer are added is divided into fragments having a predetermined size. In the asynchronous transfer mode communication apparatus for outputting to the lower layer, the message received from the upper layer is stored in the AAL FIFO, and the type of section is divided into the sectioning time signal. A multiplexer configured to receive and input any one of '44', '40' or 'rest length LI'; A down counter set to an output value of the multiplexer and configured to start down counting from the setting value by an external FIFO START signal and finally output a FIFO END signal; And a FIFO lead unit configured to receive and activate the external start signal and sequentially read and output data loaded in the AAL FIFO until the FIFO END signal of the down counter is input. It is done.

The present invention configured as described above simply controls the FIFO lead unit by inputting only the fragment type (ST) signal, the FIFO start signal, and the remaining length signal without the need to adjust the FIFO lead unit at the control counter of the AAL 3/4 transmission processing apparatus. The effect is to make the whole circuit simpler.

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

As shown in FIG. 1, the FIFO reading circuit according to the nickname receives an external message fragment type (ST) signal and selects one of '44', '40' or 'rest length (LI)' and outputs it. It is set to the output value of the multiplexer 10 and the multiplexer 10 to be operated by an external start signal to be activated by receiving the down counter 12 and the external start signal to output the FIFO end signal at last Until the FIFO signal of the down counter 12 is input, the FIFO lead unit 14 is configured to read and output data loaded in the AAL FIFO 16 sequentially.

Herein, the multiplexer 10 selects and outputs one of '44', '40' or 'rest length LI' according to the intercept type ST signal of a message input from the outside each time a message is generated. . That is, in the present invention, in order to simultaneously process the functions of the CPCS layer and the SAR layer, the CPCS header and the trailer should be simultaneously cut and attached to the payload (message) received from the upper layer and stored in the AAL FIFO 16. For this purpose, when the intercept type signal is '10' (BOM), the multiplexer 10 extracts 40 payloads from the effective load stored in the AAL FIFO 16 and attaches the 4 bytes of CPCS header to the '20' (BOM). (40) ', and in the case of the intercept type signal' 00 '(COM), the multiplexer 10 selects' 2C (44)' to extract an effective load of 44 bytes stored in the AAL FIFO 16. Let's choose. In other cases (ie, the EOM and the SSM), the multiplexer 10 outputs the input 'rest length LI' which is calculated from the outside.

In addition, the down counter 12 is set to an initial value by a value output from the multiplexer 10, and starts a down counter by a FIFO START signal input from an external source. The (FIFO END) signal is output to the FIFO lead section 14. At this time, the down counter operation proceeds in synchronization with the system clock, and one byte of FIFO data is read every clock. Therefore, whenever the down counter 12 goes down by the set initial value, the AAL FIFO 16 outputs the length of the effective load on which the actual data is loaded when forming the ATM cell.

The FIFO lead unit 14 is activated by an external start signal (FIFO START), and reads and outputs the data loaded in the AAL FIFO 16 by 1 byte according to the system clock to fill the payload when the ATM cell is formed. do. When the FIFO END signal is input from the down counter 12, all the payloads required by one ATM cell are output. Therefore, the FIFO lead unit 14 stops the temporary operation and restarts the FIFO. When the START) signal is input, the effective load required to form the next ATM cell is output.

In the present invention configured as described above, the multiplexer 10 selects and outputs a predetermined value corresponding to the size of the payload required to form an ATM cell according to the fragment type (ST) signal of an externally input message, and the down counter 12 After the initial value is set to the value output by the multiplexer 10, a down counter is performed. At this time, the down counter 12 starts down counting by the start (FIFO START) signal recorded from the outside, and at the same time, the FIFO lead unit 14 activated by the start (FIFO START) signal is the AAL FIFO 16. The data is read one byte from the data into the lower layer, and the down counter 12 completes the counting operation and outputs a FIFO END signal, thereby stopping the read operation.

As described above, the AAL 3/4 transmission apparatus to which the present invention is applied implements the CPCS sublayer and the SAR sublayer as a single digital logic in processing the AAL 3/4 transmission function. By reading the payload loaded on the AAL FIFO by a predetermined length by the circuit, it is possible to simply control the output of the FIFO data by simply inputting the message fragment type signal without burdening an external control counter. .

Claims (1)

Asynchronous transfer mode (ATM) adaptive layer (AAL 3/4) is divided into common part convergence part layer (CPCS) and cut and recombination part layer (SAR). The header and the trailer are added to the message, and the cut and recombination sublayer (SAR) divides the message to which the header and the trailer are added into fragments of a predetermined size, and outputs the message to the lower layer, but received from the upper layer. In the asynchronous transmission mode communication device in which the message is stored in the AAL FIFO (16) and is divided into a segment type (ST) signal of a section type, the signal of the segment type (ST) is received and received '44 ₁₀ ', '40. A multiplexer 10 configured to select and output one of ' ₁₀ ' or 'rest length LI'; A down count 12 which is set to an output value of the multiplexer 10 and starts down counting from the setting value by an external FIFO START signal to finally output a FIFO END signal; And sequentially reads and outputs the data loaded in the AAL FIFO 16 until the FIFO END signal of the down counter 12 is input by being activated by receiving the external FIFO START signal. A FIFO read circuit of an AAL 3/4 transmitter, comprising an FIFO lead section (14).