KR0123232B1 - A circuit for processing cpcs trailer in aal type 3/4 of atm - Google Patents

Abstract

The common part convergence sublayer CPCS trailer processing unit in accordance with an AAL 3/4 protocol of an asynchronous transfer mode ATM communication method is provided with an alignment error detecting unit (10) latching alignment AL data among CPCS trailer data to search an alignment error; a tag error detecting unit (20) latching end tag data Etag among CPCS trailer data CPCS to compare it with a begin tag Btag, thereby detecting tag error; a length error detecting unit (30) latching length identification LI data among CPCS trailer data to compare it with buffer assignment size BAsize data, thereby detecting length error; and a selector (40) selecting one of the alignment error detecting unit (10), tag error detecting unit (20) and length error detecting unit (30) according to a count bit after being enabled by a trailer select c_t signal, and divides the alignment of 1 byte, Etag of 1 bytes and LI of 2 bytes after respectively reading CPCS trailer of 4 bytes, thereby to detect the trailer being generated.

Description

CPCS Trailer Processing System of ATM Communication System

1 is a view illustrating a CPCS trailer processing apparatus according to the present invention.

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

(b) shows a CPCS-PDU data format.

2 is a block diagram showing a CPCS trailer processing apparatus according to the present invention.

3 is a detailed block diagram of the length error detection unit shown in FIG.

4 illustrates a structure of a general ATM cell.

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

(b) illustrates 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 (NNI).

* Explanation of symbols for main parts of the drawings

10: alignment error detection unit 20: tag error detection unit

30: length error detector 32: subtractor

34: Comparator 36: 4 Comparator

38,45: Oagate 40: Selector

The present invention connects an ATM in an asynchronous transfer mode (ATM) communication method with an upper user service layer to match user service information with an ATM cell format and handles an ATM error (AAL: ATM Adaptation Layer). In particular, it receives a message from the segment and reassembly (SAR) sublayer of the AAL and separates the common part convergence sublayer (CPCS) header and the CPCS trailer to detect CPCS trailer errors. It relates to a CPCS trailer processing apparatus for detecting.

Recently, with the rapid digitalization of communication means and the development of optical communication, wide band transmission is possible, Broadband Integrated Services Digital Network (BDN) has emerged to meet various service needs of users. , B-ISDN is a video telephony and video conferencing service from narrowband services such as remote meter reading, data terminal, telephone, and facsimile, as described in Broadband Telecommunications (co-author Lee Byung-ki, Kang Min-ho, Jong-hee Lee; It is designed to handle and deliver broadband services such as high-speed data transmission and video signal transmission in common. It is implemented based on the asynchronous transmission mode (ATM) communication method.

Here, the ATM communication method is similar to the conventional packet communication method in that an ATM cell is transmitted by cell unit by Asynchronous Time Division Multiplexing (ATDM). It handles real time and even bit rate signals and is standardized by the International Organization for Standardization as well as for local networks.

This ATM communication method is based on the ATM cells as shown in (a) to (c) of FIG. 4, and the user's long message is divided into ATM cells and transmitted. Reassembled into messages and delivered to the parent user.

That is, as shown in (a) of FIG. 4, 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 the user network interface (UNI). The structure consists of 4 bits of Generic Flow Control (GFC) and 4 bits of Virtual Path Identifier (VPI), and the 2nd byte of 4 bits of Virtual Path Identifier ( VPI) and 4-bit Virtual Channel Identifier (VCI), the third byte consists of 8-bit Virtual Channel Identifier (VCI), and the fourth byte is a 4-bit Virtual Channel Identifier (VCI). (VCI), 3-bit Payload Type (PT) and 1-bit Cell Loss Prison (CLP: Cell Loss Pri) ori), and 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.

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. The AAL layer is a cut and recombination sublayer (SAR). Segmentation And Reassembly sublayer) and Convergence Sublayer (CS) sublayers are divided into physical layers (PM) and Transmission Convergence (TC) sublayers.

In addition, according to the service of the user, that is, the characteristics of the source in the ATM communication method can be divided 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-connection 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 the following Table 3, but conventionally divided into AAL1 to AAL4, but AAL3 and AAL4 are similar to each other. AAL5 has been proposed to reduce the overhead.

As shown in Table 3, the AAL layer is divided horizontally, such as AAL1, AAL2, AAL3 / 4, and AAL5 to efficiently process the service according to the type of service.

Here, the AAL3 / 4 layer functions to transfer data of Class C and D services having variable bit rates, and has a message mode and a stream mode. In addition, the AAL3 / 4 layer transparently delivers a User-Service Data Unit (U-SDU) from the service user, detects transmission errors, and performs a function of identifying and buffering information. ) And the variable-length data received from the convergence sublayer (CS) to create an ATM cell, deliver it to the ATM layer, receive and reassemble the ATM cell from the ATM layer, and converge the sublayer protocol data unit (CS-PDU: CS). Subdivided into truncation and recombination sublayers (SAR) to recover the Portocol Data Unit. In addition, the convergence (CS) sublayer includes a common part convergence sublayer (CPCS) that performs functions common to the connected and disconnected services, and a service-specific convergence sublayer (CPCS) for providing a specific AAL user service. SSCS: Service Specific Convergence Layer).

Details of this AAL layer have been proposed in the ITU-T Recommendations, 1.362 and 1.363, and by Gigabit Networking (Craig Partridge; 1994; Addison Wesley; pp61-87) and Lee Byung-ki 2 It is described in detail in Broadband Information Communication (pp314 ~ 327).

As described above, the AAL3 / 4 layer has a problem that the processing speed of the CPCS trailer is slow because it is conventionally implemented as a software program.

Accordingly, an object of the present invention is to provide a CPCS trailer processing apparatus that implements a trailer processing function of AAL3 / 4 common part convergence layer (CPCS) in hardware in an ATM communication scheme.

CPCS trailer processing apparatus of the present invention for achieving the above object, the alignment error detection unit for latching the alignment (AL) data of the CPCS trailer data to search for alignment errors; A tag error detection unit which latches the end tag data among CPCS trailer data and detects a tag error by comparing with a start tag Btag; A length error detection unit which latches the length indication (LI) data among the CPCS trailer data and detects the length error by comparing with the buffer allocation data; And a selector for selecting one of the alignment error detection unit, the tag error detection unit, and the length error detection unit according to the count bits after being enabled by the trailer selection (c_t) signal. Check if a trailer error has occurred by dividing into an alignment, 1 byte of Etag, and 2 bytes of LI.

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 (a) and (b) of FIG.

FIG. 1 (a) is a schematic diagram schematically illustrating a data format changing in a process of being transmitted in accordance with an ATM communication scheme. Referring to (a) of FIG. 1, when the ATM layer receives 53-byte ATM cells (ATM-PDUs) through a physical transmission path such as an optical cable, the ATM layer processes a 5-byte ATM header and then processes a 48-byte ATM service. The ATM-SDU (ATM-SDU) is sent to the AAL SAR sublayer through an ATM-SAP (ATM-Service Access Point). As such, when the ATM-SDU reaches the AAL SAR sublayer through the service access point, it is called a SAR protocol data unit (SAR-PDU: SAR-Preotocol Data Unit or Segment).

In (a) of FIG. 1, the AAL SAR sublayer separates two-byte SAR headers and two-byte SAR trailers from 48-byte SAR-PDUs and checks for transmission errors. Recombine the related segments and restore one message, that is, the CS-PDU and upload it to the AAL Convergence Sublayer (CS). It checks whether there is an error and uploads user service data (AAL-SDU: CPCS paid load) to the upper level line workstation through AAL-SAP and I / O bus (SBUS).

(B) of FIG. 1 shows the structure of a data format (CPCS-PDU) received through a FIFO from an AAL3 / 4 SAR layer, where a CPCS-PDU has a 4-byte header for a payload of variable length. The 4-byte header has a common part indicator (CPI), a start tag (Btag) and a byte of 1 byte. It consists of a buffer allocation size (BAsize: Buffer Allcocation Size), and the 4-byte trailer is composed of 1-byte alignment (AL: alignment), 1-byte end tag (Etag: end tag), and 2-byte length. It consists of a display (LI: Length Indicator).

This CPCS header and CPCS trailer are created at the time of transmission and transmitted with the data.

Here, the common part mark (CPI) indicates whether the corresponding PDU is a common part, but is '0' at present, and the start / end tags (Btag and Etag) are tags that keep the same number for the header and trailer of the same CPCS-PDU. The buffer allocation size (BAsize) indicates the maximum buffer allocation size up to 64K bytes, and the alignment (AL) is pad that fills the trailer of the CPCS-PDU with 32 bits. The length indication LI represents the length of the pure CPCS-PDU excluding the pad. In addition, there is a pad (PAD) that fills the CPCS-PDU payload so that the length of the CPCS-PDU payload is a multiple of 32 bits.

Next, the CPCS trailer processing apparatus according to the present invention will be described in detail with reference to FIG.

CPCS trailer processing apparatus according to the present invention comprises an alignment error detection unit 10 for latching the alignment (AL) data of the CPCS trailer data to search for alignment errors; A tag error detection unit 20 for latching end tag data among CPCS trailer data to detect a tag error by comparing with a start tag Btag; A length error detection unit 30 for latching the length indication LI data of the CPCS trailer data and detecting the length EL by comparing with the buffer allocation data; And a selector 40 for selecting one of the alignment error detection unit 10, the tag error detection unit 20, or the length error detection unit 30 according to the count bit after being enabled by the trailer selection (c_t) signal. After reading each 4-byte CPCS trailer, it checks whether a trailer error has occurred by dividing it into 1-byte alignment, 1-byte Etag, and 2-byte LI. In addition, the CPCS trailer processing apparatus generates an trailer error (st_err) by ORing the output of the alignment error detector 10, the output of the tag error detector 20, and the output of the length error detector 30. (45) is further provided.

That is, the selector 40 according to the present invention selects the block according to the count value count [1..0] and the trailer selection signal c_t input from the counter (not shown) as shown in Table 4 below.

When the trailer selection signal c_t is 1 as shown in Table 4, the selector 40 according to the present invention is enabled according to the values of the count bits 1 (count [1]) and bit 0 (count [0]). Of the four bytes of CPCS trailer data, as shown in Fig. 1B, alignment AL, end tag Etag, and length indication LI are sequentially selected. At this time, it is assumed that the count value input from the counter not shown is counted down from 11 to 0.

The alignment error detection unit 10 checks whether the alignment (AL) data conforms to the protocol. In the embodiment of the present invention, since the AL is fixed to 0, the alignment error detection unit 10 checks whether the input AL data is 0 and detects an error.

In addition, the tag error detection unit 20 checks an error by latching the end tag Etag and comparing it with the start tag Btag input from the head processing circuit (not shown). That is, since the start tag and the end tag must have the same value in the same message, it can be seen that an error occurs when the comparison result is different.

In addition, the length error detection unit 30 according to the present invention is also indicated by the buffer allocation (BAsize [15..0]) data and the length display (LI: cpcs_length [15..0] below) as shown in FIG. A subtractor 32 for subtracting data; A comparator 34 for comparing the size of the buffer allocation data (BAsize) with the size of the length indication (cpcs_length); A four comparator 36 for comparing the output of the subtractor 32 with four; The comparator 34 and the comparator 36 are configured by an OR gate 38 for outputting a length error signal LI_err by ORing the outputs of the comparator 36. The subtractor 32 displays the length from the buffer allocation data. The length of the pad PAD is obtained by subtracting (cpcs_length). The 4 comparator 36 generates an error signal err1 when the output of the subtractor 36 is 4 or more, and the comparator 34 buffer allocation (BAsize). The size of the data is compared with the length display (cpcs_length) data, and if the length display data is larger than the size of the buffer allocation BA data, an error signal err2 is generated.

That is, the buffer size (BAsize) data is equal to the length of the CPCS-PDU payload plus the byte length of the pad (PAD), so it is always greater than or equal to the length indication (cpcs_length), and the pad is the length of the CPCS payload. Is a multiple of 32 bits, so it can have a length of 0 to 3 bytes. Therefore, subtracting the length indication (cpcs_length) from the buffer allocation (BAsize) results in the pad length (Pad_le [1..0]), and compares whether the pad length exceeds 4 to detect the length error.

As such, the buffer size (BAsize) data is a value obtained by adding a pad (PAD) to the CPCS-PDU payload, and therefore is always greater than or equal to the length indication (cpcs_length) value, and the start tag and the end tag are the same. Since it must be the same in the message, it checks whether the end tag (Etag) and the start tag (Btag) match, and compares whether the buffer allocation (BAsize) is equal to or greater than the length indication (LI) to detect a trailer error.

As described above, the CPCS trailer processing apparatus according to the present invention implements the trailer processing function of the AAL3 / 4 convergence (CS) sublayer with simple digital logic, thereby improving data processing speed and improving reliability.

Claims (3)

When receiving data according to AAL 3/4 protocol of ATM communication method, CPCS-PDU data assembled from ATM SAR receiving layer is inputted, and buffer allocation (BAsize) and start of CPCS trailer and CPCS header from CPCS-PDU data. An asynchronous transfer mode communication device for extracting a tag and detecting that an error has occurred in a received CPCS-PDU, comprising: an alignment error for latching alignment (AL) data in the CPCS trailer to search for an alignment error A detection unit 10; A tag error detection unit 20 for latching an end tag data of the CPCS trailer to detect a tag error by comparing with the start tag Btag; A length error detector (30) for latching length indication (LI) data in the CPCS trailer and detecting a length error by comparing the buffer allocation data with the BAsize data; And a selector 40 for selecting one of the alignment error detector 10, the tag error detector 20, or the length error detector 30 according to the count bit after being enabled by the trailer selection (c_t) signal. A CPCS trailer processing apparatus according to ATM communication method characterized by detecting whether a trailer error has occurred by reading a 4-byte CPCS trailer and dividing it into 1 byte alignment, 1 byte Etag, and 2 bytes LI. The CPCS trailer processing apparatus of claim 1, wherein the CPCS trailer processing apparatus combines the output of the alignment error detection unit 10, the output of the tag error detection unit 20, and the output of the length error detection unit 30 to detect a trailer error st_err. CPCS trailer processing apparatus of the ATM communication system characterized in that it further comprises an oragate (45) generated. 2. The apparatus of claim 1, wherein the length error detection unit (30) comprises: a subtractor (32) for subtracting buffer allocation data (BAsize) data and length indication (cpcs_length) data; A comparator 34 for comparing the size of the buffer allocation data (BAsize) with the size of the length indication (cpcs_length); A four comparator 36 for comparing the output of the subtractor 32 with " 4 "; And an OR gate (38) for outputting a length error signal (LI_err) by ORing the outputs of the comparator (34) and the four comparators (36).