JPH1065713A - Method for detecting atm system cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ATM system cell detecting method which is used for an asynchronous transmission mode(ATM) adaptive layer(AAL) to effectively detect a loss cell or an erroneous insertion cell and to enable the real time service of a message to be executed. SOLUTION: Plural data cells which are respectively consisting of present data cells and preceding data cells are successively received with a channel(S9), a preceding sequence number included in a header of the preceding data cell is detected, the preceding data cell is transmitted in an upper part layer (S10), a present sequence number included in the header of the present data cell is detected, state information of the preceding data cell which expresses whether the preceding data cell is normal, lost or erroneously inserted is decided (S12) and the state information is transmitted to the upper part layer (S13).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing sequence numbers in an asynchronous transfer mode (ATM) system, and more particularly to a method for processing a plurality of sequences used in an ATM adaptation layer (AAL) and included in data cells of the AAL. AT for detecting lost or misinserted cells based on number
The present invention relates to a cell detection method for an M system.

[0002]

2. Description of the Related Art A broadband service integrated digital network (B-
Within the range of high data rates from ISDN, there are various applications with many different data rates that need to be exchanged with each other.

[0003] ATM is a packet-based transmission mode in which a plurality of logical connection structures are multiplexed through a single physical interface. The information flow on each logical connection structure is configured as a fixed size packet, or cell, with no error control and no flow control between the links.

[0004] The logical connection structure in the ATM is called a virtual channel. In B-ISDN, each virtual channel is a basic unit of switching. A virtual channel is configured between two end users over a network. The data rate of the virtual channel can be changed, and the full duplex communication flow of cells having a certain size is exchanged through this logical connection structure.

ATM uses a plurality of fixed size cells, each of which consists of a 5 octet header and a 48 octet information field, as shown in FIG.

[0006] The use of cells of a fixed size, having a small size, has several advantages. First, higher priority cells may access resources before lower priority cells, so smaller cells may be used to reduce latency for higher priority cells, and
Smaller sized cells have smaller latencies than larger sized cells. Second, certain sized cells are switched more efficiently, which is very important in the high data rate of ATM.

FIG. 2 is a diagram showing a header format in an interface between a user network and a 4-bit general flow control (generic f).
low control (GFC), 8-bit virtual path identifier (virtual path identifier)
er; VPI), 16-bit virtual channel identifier (v
actual channel identity
r; VCI), 3-bit payload type (payl
load type (PT), 1-bit cell loss priority (CLP)
And 8-bit header error control (header e
error control (HEC). The general flow control (GFC) field is used for end-to-end flow control and may be used for several different types of data flows. The virtual path identifier (VPI) field represents a virtual path between the users or between the user and the network, the virtual channel identifier (VCI) field represents the virtual channel between the users or between the user and the network, and the payload type. The (PT) field indicates the form of information in the information field. The Cell Loss Priority (CLP) field is congestion
On) occurs and is used to provide guidance to the network. A "0" value represents a higher priority cell and will not be discarded unless there is another possible alternative, and a "1" value indicates a lower priority cell whose cell may be discarded in the network. It represents that.

[0008] The header error control (HEC) field is an 8-bit error code used to correct single bit errors in the header and detect double bit errors.

FIG. 3 is a schematic diagram showing a cell header format inside a network. In the figure, the general flow control field for performing end-to-end functions is not included. Instead, the virtual route identifier field is set to 8
It is expanded from bits to 12 bits. From now on, the number of virtual routes inside the network will be increased to have the necessary elements for supporting subscribers and managing the network.

When an ATM is used, an adaptation layer is required to support an information transmission protocol without being based on the ATM. Referring to FIG. 4, a hierarchical data structure in an ATM communication network is shown as an example to show how a message mode service is implemented by an ATM adaptation layer (AAL). Higher layer (HL)
Information block from (ie, user input data) (ie, user service data unit (U-SDU))
After passing through the AAL service access (AAL-SAP), the AAL first-in first-out buffer (AAL-FIF)
O) to AAL service data unit (AAL-SD)
U). Then, the convergence sublayer (CS)
Generate an S-protocol data unit (CS-PDU). This CS-PDU includes a header (H) and a CS-PDU.
It consists of protocol control information and padding for generating a PDU as an integer multiple of 32 bits, and a trailer (T), which is sent to the AAL segmentation and reassembly (AAL-SAR) sublayer. In AAL-SAR, CS-PDU
Is divided into one or more segments having 47 octets based on the message to be transmitted. Here, each segment is combined with a one-octet SAR header to generate a SAR-PDU, which is sent to the ATM layer through ATM-SAP. Each SAR-PD in ATM layer
U is combined with the 5 octet ATM cell header to form a 53 octet ATM cell so that the ATM cell can be transmitted to other terminals or ATM switches through one or more transmission paths of the physical layer. Transmitted.

The AAL associates information with a plurality of cells and divides and reassembles the cells. In the service area,
Four types of services are defined as shown in Table 1 below.

[0012]

[Table 1]

These four types are based on whether a time relationship should be maintained between the source and the destination, whether the bit rate is constant in the application, and whether the data transmission is based on the connection structure. Or not.

An example of a class A service is circuit emulation. In this case, a constant bit rate is used that requires a time relationship between the source and the destination,
Data transmission is performed based on the connection structure. Class B
For example, there is a variable bit rate video used for an electronic conference. In this case, the application is based on the connection structure and the time relationship is important, but the bit rate can be changed by the amount of activity in the scene. Classes C and D correspond to data transmission applications.
In these two cases, the bit rate is changed and no specific time relationship is required. The bit rate difference is adjusted by the termination system using each buffer. The transmission of data is one of a connection structure (class C) and a non-connection structure (class D).

To support these classes of services,
A set of AAL level protocols is defined. The AAL layer is composed of two logical sublayers, a convergent sublayer (CS) and a split and reassembly sublayer (SAR).
This convergence sublayer (CS) is used for service purposes,
L provides the required functions. The use of the AAL for services is through a service access point (SAP), which represents the address of the relevant application. Therefore, the SAR is changed depending on the service.

The split and reassembly (SAR) sublayer is C
It packs the information received from S into cells for transmission and serves to unpack the information at other terminals. That is, the SAR sublayer has to pack certain SAR header, trailer and CS information into 48 octet blocks. AAL protocol type 1 class A, type 2 class B
Type 3 supports class C and type 4 supports class D.

FIG. 5 shows a protocol data unit (P) at the SAR level for AAL protocol type 1.
FIG. 3 is a schematic diagram showing a format of DU). This PDU
Is composed of a 1-octet SAR-PDU header and a 47-octet SAR-PDU payload. In the SAR protocol, each bit is packed in a plurality of transmission cells, and only the function of unpacking is performed at the receiving end. Each block has a sequence number (SN), and each PDU with an error
Can be detected. Here, the sequence number is composed of a 1-bit convergent sublayer identifier (CSI) and a 3-bit sequence count (SC). Sequence number protection (SNP) with 3-bit cyclic redundancy detection code (CRC) and 1-bit parity (P)
The field is an error code for error detection on the sequence number field and error correction as much as possible.

However, in order to detect a lost cell or an erroneously inserted cell due to processing of a plurality of sequence numbers, the plurality of sequence numbers must be compared with each other. A large amount of memory is required. Therefore, there is an inconvenience that real-time service for the message becomes difficult.

[0019]

Accordingly, a primary object of the present invention is to provide an asynchronous transfer mode (ATM) adaptation layer (AAL).
And a cell detection method for an ATM system capable of real-time service for a message by effectively detecting a lost cell or an erroneously inserted cell based on a plurality of sequence numbers included in the AAL data cell. To provide.

[0020]

According to the present invention, there is provided, in accordance with the present invention, a sequence number for use in an asynchronous transmission mode (ATM) system, the sequence number indicating the transmission order of data cells transmitted over a selected channel. A cell detection method for an ATM system for detecting a lost cell or an erroneously inserted cell based on a sequence number in a data cell having a header having the following structure, wherein a plurality of data cells each including a current data cell and a previous data cell are detected. , A first step of sequentially receiving data through a channel, and a second step of detecting a previous sequence number included in the header in the previous data cell.
A third step of transmitting the previous data cell to an upper layer, a fourth step of detecting a current sequence number included in the header in the current data cell, a step of transmitting the previous sequence number and the current sequence number. A fifth step of determining state information of the previous data cell indicating whether the previous data cell is normal, lost or erroneously inserted based on the above, and a sixth step of transmitting the state information to the upper layer. A cell detection method for an ATM system is provided.

[0021]

Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 6 is a flow chart for explaining a cell detection method for an ATM system according to an embodiment of the present invention, wherein a lost cell or an inserted cell is determined based on each sequence number included in a data cell. To detect. Here, the data cell includes a header having a sequence number indicating a transmission order of the data cell transmitted through the selected channel. First, one cell (for example, the i-th cell) is input from the ATM hierarchy in step S9, and
Is transmitted to a higher layer. At this time, the i-th sequence number included in the SAR header of the i-th cell is stored again. Then, in step S11, the next cell having a 5-octet header and a 48-octet information field (ie, the (i + 1) th cell) is received, and the (i + 1) th sequence number is (i + 1) th.
Retrieved from the SAR header of the eye cell. continue,
In step S12, it is determined whether the i-th sequence number of the i-th cell is appropriate based on the (i + 1) -th sequence number. That is, it is determined whether the i-th cell is normal, lost or erroneously inserted based on the (i + 1) -th sequence number.

Referring to FIG. 7, there is shown a flowchart for explaining a detailed algorithm of the process step S12 in FIG. In step S1, the i-th sequence number SNi is compared with the expected number Exp_SNi for the i-th sequence number. Here, the expected number Exp_SNi for the i-th sequence number is
It is estimated using the previous sequence number determined to be appropriate. If it is determined in step S1 that the i-th sequence number matches the expected number Exp_SNi, it is determined that the i-th sequence number is correct, and step S2 is performed.
Then, the i-th normal information indicating that the i-th cell is normal is generated, Exp_SNi is increased by 1, and
The expected number Exp_SNi + 1 to be used in the process for the next sequence number SNi + 1 is assumed. Otherwise, in step S3, the next sequence number (ie, SNi + 1) is the expected number Exp_SNi for SNi.
Is compared to

In step S3, SNi + 1 becomes Exp_SNi.
When it is determined that the ith cell is erroneously inserted in step S4, ith erroneous insertion information indicating that the ith cell is erroneous is generated in step S4. , The expected number Exp_SNi + 1 for the processing of the next sequence number SNi + 1 is maintained in the same manner as Exp_SNi.
However, if it is determined in step S3 that SNi + 1 is different from Exp_SNi, it is determined that the original i-th cell has been lost, and in step S5, the value of the i-th cell before the i-th cell has been lost.
Generate i-th loss information indicating that one or more cells have been lost, replace the expected number Exp_SNi + 1 with SNi + 1, and determine the next sequence number SNi + 1 based on the current sequence number SNi. Expected number Exp_SNi predicted
The next sequence number SNi + 1 is processed using +1.

As shown in FIG. 6, in step S13, the ith normal information, erroneous insertion information or loss information is transmitted to a higher layer as ith state information for the ith cell. You. Subsequently, in step S14, i is set to 1
In step S15, i is compared with the last sequence number N. Steps S10 to S15 are repeated until the last cell corresponding to the last sequence number N is input. If i is N
, The ith cell (ie, the Nth cell) is transmitted to a higher layer and the process ends.

FIG. 8 shows an ATM according to another embodiment of the present invention.
It is a flowchart for demonstrating the cell detection method for systems. Here, after it is determined whether or not the i-th sequence number is correct based on the (i + 1) -th sequence number, the i-th cell is determined based on the determination result for the i-th sequence number. Is transmitted or discarded. More specifically, in step S20, the i-th cell is received in order from the ATM layer, and in step S21, the (i +
1) The (i + 1) th sequence number of the cell is AT
Received from the M layer. Then, in step S22, the i-th and (i + 1) -th sequence numbers are processed,
It is determined whether or not the i-th sequence number is correct by the method as shown in FIG. Subsequently, step S23
Then, based on the result of step S22, the i-th cell is transmitted or discarded. That is, if the i-th cell is normal, the i-th cell is transmitted to a higher layer; otherwise, the i-th cell is discarded. In step S24, the (i + 1) th cell of the (i + 1) th cell excluding the SAR header having the (i + 1) th sequence number
The (+1) th data is received from the ATM layer. Then, in step S25, i is increased by 1 and
At 26, i is compared with the last sequence number N, and the above steps S21 to S26 are repeated until the last cell having the last sequence number N is input.

While the preferred embodiment of the present invention has been described above, those skilled in the art will be able to make various modifications without departing from the scope of the present invention.

[0028]

Therefore, according to the present invention, based on the sequence number included in the data cell of the asynchronous transmission mode adaptation layer, a corrected cell, a lost cell or an erroneously inserted cell is effectively detected, and a message is more efficiently detected. More real-time services can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a data format of a conventional ATM cell.

FIG. 2 is a diagram showing a header format in a user network interface.

FIG. 3 is a diagram showing a cell header format inside a network.

FIG. 4 is a schematic diagram showing a hierarchical data structure in an ATM communication network.

FIG. 5 is a schematic diagram showing the format of a protocol data unit (PDU) at the SAR level for AAL protocol type 1.

FIG. 6 is a flowchart for explaining a cell detection method for an ATM system according to an embodiment of the present invention.

FIG. 7 is a flowchart for explaining a detailed algorithm of a process step S12 in FIG. 6;

FIG. 8 is a flowchart for explaining a cell detection method for an ATM system according to another embodiment of the present invention.

[Explanation of symbols]

 GFC 4-bit general flow control VPI 8-bit virtual path identifier VCI 16-bit virtual channel identifier PT 3-bit payload type CLP 1-bit cell loss order HEC 8-bit header error control U-SDU User service data unit AAL- FIFO AAL First-In-First-Out Buffer AAL-SAP AAL Service Access CS Convergence Sublayer CS-PDU CS Protocol Data Unit AAL-SAR AAL Split and Reassembly Sublayer H Header T Trailer

Claims (8)

[Claims] An asynchronous transmission mode (ATM) system, wherein a lost cell or an erroneous cell is detected based on a sequence number in a data cell having a header having a sequence number indicating a transmission order of data cells transmitted through a selected channel. A cell detection method for an ATM system for detecting an inserted cell, comprising: a first step of sequentially receiving a plurality of data cells each including a current data cell and a previous data cell via a channel; A second step of detecting a previous sequence number included in the header, a third step of transmitting the previous data cell to an upper layer, and detecting a current sequence number included in the header in the current data cell. A fourth step, based on the previous sequence number and the current sequence number, whether the previous data cell is normal, lost or Fifth process and the cell detection method for ATM systems; and a sixth step of transmitting the status information to the upper layer to determine the state information before data cell indicating whether inserted. 2. The method according to claim 1, wherein the fifth step is a step of comparing the previous sequence number with a predetermined expected number, and wherein the previous sequence number is equal to the expected number. Generating a normal status information indicating that it is appropriate as the status information, and if the previous sequence number is not equal to the expected number, comparing the current sequence number with the expected number; If the current sequence number is equal to the expected number, erroneous insertion state information indicating that the previous sequence number does not match is generated as the state information, and if the current sequence number is not equal to the expected number, the A fifth to third loss state information is generated as the state information, which indicates that one or more data cells before the data cell have been lost. 2. The method according to claim 1, wherein
3. The cell detection method for an ATM system according to claim 1. 3. The method of claim 2, wherein the expected number is determined based on a sequence number of a preceding data cell transmitted before the preceding data cell when each of the sequence numbers is deemed appropriate. ATM according to item 2
Cell detection method for system. 4. The method according to claim 2, wherein the number of lost cells is defined as a difference between the previous sequence number and the expected number. 5. A lost cell or erroneous cell based on a sequence number in a data cell used in an Asynchronous Transfer Mode (ATM) system and having a header having a sequence number indicating a transmission order of data cells transmitted through a selected channel. A cell detection method for an ATM system for detecting an inserted cell, comprising: a first step of sequentially receiving a plurality of data cells each including a current data cell and a previous data cell via a channel; A second step of detecting a previous sequence number included in the header; a third step of detecting a current sequence number included in the header in the current data cell; State information of the previous data cell indicating whether the previous data cell was normal, lost or erroneously inserted based on A fourth step of determining; transmitting the previous data cell to an upper layer if the status information of the previous data cell is normal; and transmitting the previous data cell if the status information of the previous data cell is not normal. A cell detection method for an ATM system, comprising: a fifth step of discarding a cell. 6. The fourth step is to compare the previous sequence number with a predetermined expected number. 4-1. If the previous sequence number is equal to the expected number, the fourth step is Generating a normal state information indicating that it is appropriate as the state information, and if the previous sequence number is not equal to the expected number, comparing the current sequence number with the expected number; If the current sequence number is equal to the expected number, erroneous insertion state information indicating that the previous sequence number does not match is generated as the state information, and if the current sequence number is not equal to the expected number, the 4-3. The fourth to third mode, wherein loss status information indicating that one or more data cells before the data cell have been lost is generated as the status information. 6. The method according to claim 5, wherein
3. The cell detection method for an ATM system according to claim 1. 7. The method as claimed in claim 7, wherein the expected number is determined based on a sequence number of a preceding data cell transmitted before the preceding data cell when each corresponding sequence number is considered to be proper. ATM according to item 6
Cell detection method for system. 8. The method according to claim 6, wherein the number of lost cells is defined as a difference between the previous sequence number and the expected number.