KR0123225B1 - Detecting sar length error in aal type 3/4 of atm system - Google Patents

Abstract

There is provided an apparatus for detecting SAR length error in ATM telecommunication mode. The apparatus includes; 4-value comparator(12) for comparing a length(L1) data of SAR trailer as input with the value of 4; 8-value comparator(14) for comparing the length(L1) data with the value of 8; 44-value comparator(16) for comparing the length(L1) with the value of 44; and an error determining part(20) for determining whether or not the outputs of 4-value comparator(12), 8-value comparator(14), and 44-value comparator(16) deviate from an allowable value according to a segment type and thereby detecting a length error.

Description

SAR length error detection device of ATM communication system

1 is a view illustrating a detection apparatus in a SAR length according to the present invention.

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

(b) shows the SAR-PDU data format.

2 is a block diagram showing a SAR length error detection apparatus according to the present invention.

3 shows 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 (UNI).

* Explanation of symbols for main parts of the drawings

12: 4 Comparators 14: 8 Comparators

16: 44 Comparator 20: Length Error Determination Unit

According to the present invention, an ATM adaptation layer 3/4 (AAL 3) that connects an ATM layer and a higher user service layer to match user service information and ATM cell format and handles transmission errors in an asynchronous transfer mode (ATM) communication method. 4), and more particularly, to an apparatus for detecting SAR length errors by separating AAL3 / 4 SAR trailers from ATM cell data from the ATM layer.

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.

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 is based on the ATM cell as shown in (a) to (c) of FIG. 4, the user's long message is cut into the ATM cell and transmitted, the received ATM cells are again one Reassembled into messages and delivered to the parent user.

That is, as shown in (a) of FIG. 3, an ATM cell is divided into a header section of 5 bytes (or octets) and a user information section of 48 bytes, and the header of 5 bytes is represented by (b) and (Fig. 4). As shown in c), the header structure is divided into a header structure at the user network interface (UNI) and a header structure at the network node interface (NNI) and a header structure at the user network interface (UNI). The first byte consists of 4 bytes of General Flow Control (GFC) and the 4 bytes of Virtual Path Identifier (VPI), and the second byte consists of 4 bytes 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 identifies 4-bit virtual channel. Number (VCI), 3-bit payload type (PT) and 1-bit cell abandonment ranking (CLP) : Cell Loss Priority, 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) as shown in FIG. 3 (c), the general flow control (GFC) in the first byte of the user network interface (UNI) described above identifies the virtual path. It can be seen that it is the same as the header structure of the user interface (UNI) except that it is used as a number (VPI).

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 Ressembly sublayer, and Convergence Sublayer (CS) sublayer, and the physical layer is divided into physical medium (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 2 below.

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 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 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 as AAL1, AAL2, AAL3 / 4, AAL5 to efficiently process the service according to the type of service. It functions to deliver data of class C and class D service, and has message mode and stream mode, and transparently delivers service data unit (U-SDU) from service user, detects transmission error, identifies information and Variable length data received from Convergence Layer (CS) and Convergence Layer (CS), which performs buffer allocation function, is divided into ATM cells to make an ATM cell, transferred to ATM layer, ATM cell is received from ATM layer, reassembled by CS Subdivide the PDU into break and recombination sublayers (SAR).

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 Byung-ki and two others are described in detail in Broadband Information Communication (pp314 ~ 327).

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

Therefore, the present invention is to detect the SAR length of the ATM communication method implemented in hardware to implement the function of detecting the length error by receiving the AAL3 / 4 CPCS layer and SAR trailer in the ATM communication method in order to solve the conventional problems as described above. The purpose is to provide a device.

SAR length error detection apparatus of the present invention for achieving the above object is a four comparators 12 for inputting the length indication (LI) data of the SAR trailer 4 and fertilizer; An eight comparator 14 for inputting length indication (LI) data of the SAR trailer and comparing it with eight; 44 comparator 16 for inputting length indication (LI) data of the SAR trailer and comparing it with 44; And a length error determination unit 20 for detecting a length error by determining whether the deviation is outside the allowed value according to the segment type after inputting the comparison result of the 4,8,44 comparators.

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

First, in order to explain an embodiment of the present invention, as shown in (a) to (c) of FIG. 1, an AAL layer (an embodiment of the present invention relates to an AAL3 / 4 layer, where the AAL layer is AAL3 / 4). This is an overview of the data flow in the protocol layer.

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. The ATM layer receives 53 bytes of ATM cells (ATM-PDUs) through a physical transmission path such as an optical cable, processes 5 bytes of ATM headers, and then uses 48 bytes of ATM service data units (ATM-SDUs). Data Units are sent to the AAL SAR sublayer through ATM-SAP (ATM-SAP). 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 the AAL SAR sublayer, 48 bytes separate the 2-byte SAR header and 2-byte SAR trailer from the SAR-PDU to check for transmission errors, and 44 bytes of paid data are re-combined with each other according to the segment type. That is, it restores the CS-PDU and uploads it to the AAL CS sublayer, and the AAL CS sublayer processes the CPCS header and the CPCS trailer in the CS-PDU to check whether there is a transmission error or an error in the lower layer, SDU: In other words, CPCS paid load is sent to upper level sun workstation through AAL-SAP and I / O bus (SBUS).

(B) of FIG. 1 shows a data format of a SAR-PDU according to the AAL3 / 4 protocol, which is composed of a 2-byte SAR header, a 44-byte SAR payload, and a 2-byte SAR trailer. A 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).

In this case, the segment type (ST) is displayed by dividing the characteristics of each segment as shown in Table 4.

As shown in Table 4, if the segment type (ST) is '10', it can be seen that the 44-byte payload is data including the start of the message (that is, the CPCS header). If it is '01', it can be seen that the end of the message (that is, including the CPCS trailer), and if it is '11', it can be seen that the single segment is the message (CPCS header and CPCS trailer included in one segment).

In addition, in FIG. 1B, the sequence number SN is a serial number assigned to each segment in order to confirm whether there is an error during transmission when the message is divided into several segments. Used. Multiplexing Identification Number (MID) is an identifier used when multiplexing multiple CPCS connections through one ATM layer connection. Each segment has the same value in the same message, and the length indication (LI) indicates the SAR-PDU payload length. Is expressed in bytes. Cyclic redundancy check (CRC) is for error checking and correcting codes for the entire SAR-PDU, and 10 bits are allocated. to be.

2 is a block diagram illustrating a SAR length error detecting apparatus according to the present invention. The 4 comparator 12 which inputs length indication (LI) data of a SAR trailer and compares it with 4 ₁₀ and a length indication (LI) of a SAR trailer. 8) a comparator 14 for inputting data and comparing it with 8 ₁₀ ; A 44 comparator 16 for inputting length indication (LI) data of the SAR trailer and comparing it with 44 ₁₀ ; And an error determination unit 20 for detecting a length error by inputting the comparison result of the 4, 8, 44 comparators and determining whether the deviation is from the allowed value according to the segment type.

First, the combination of allowable lengths according to the segment type ST is summarized in the following Table 5.

As shown in Table 5, according to the segment type (ST), the BOM and COM are the front part cut when the message length is large, so the length of the SAR-PDU payload should be 44 bytes at all times, and the EOM is a CPCS trailer of at least 4 bytes. Must contain at least 4 bytes and not more than 44 bytes, and SSM must contain at least one segment with 4 bytes of CPCS header and 4 bytes of CPCS trailer.

Therefore, if the length indication (LI) data indicating the length of SAR payload in bytes is input and each result compared with 4,8,44 is out of the allowable length as shown in Table 5 according to the segment type, It generates and outputs a length error.

That is, when it is determined that the BOM and COM are the same as the output result 44 of the 44 comparator 16, if it is normal or larger or smaller than 44, a length error is generated, and the EOM is greater than the output 4 of the 4 comparator 12. If it is small, a length error is generated, and the SSM generates a length error if it is smaller than 8 as the output result of the 8 comparator 14.

On the other hand, when the length error detection circuit is implemented in the programmable array logic (RAL), it is represented in the hardware description language (HDL) as shown in Table 6.

In the embodiment of the present invention implemented by the HDL, the length indication (li [5..0]) data has LI_F [], LI_E [], LI_FF [] having a fixed size of 4, 8, 44, respectively. The result is compared and stored in (large_F, same_F), (large_E, same_E), large_FF, FF_same, respectively, and the stored values are judged whether the protocol is in an acceptable range and a length error is detected. On the other hand, if the upper six bits of the length indication L [15..0] of the CPCS, that is, the LI 15 to LI 10 are all 1 in the EOM segment, the user abort signal CPCS_U_Abort is generated.

As described above, the SAR length error detection apparatus according to the present invention implements the length error detection function of the AAL3 / 4 SAR layer with simple digital logic, thereby improving the length error detection speed and improving reliability.

Claims (1)

In receiving data according to AAL3 / 4 protocol of ATM communication method, it reads 48 bytes of ATM cell payload from ATM layer, extracts 2 bytes of SAR header and 2 bytes of SAR trailer, and detects length error of received SAR segment. An asynchronous transmission mode communication device, comprising: a four comparator (12) for inputting length indication (LI) data of the SAR trailer and comparing with "4"; An eight comparator 14 for inputting length indication (LI) data of the SAR trailer and comparing it with " 8 "; 44 fertilizer 16 comparing the length of the SAR trailer (LI) data and comparing it with " 4 " 4 and inputting a comparison result of the 4,8,44 comparators and then allowing the allowed values according to the segment type. SAR length error detection device characterized in that it comprises an error determination unit 20 for detecting the length error by determining whether the deviation.