JPH06121001A - Retransmission control system for cellular communication error - Google Patents

Abstract

PURPOSE:To simplify procedures and to avoid retransmission of unnecessary cells with respect to retransmission control of AAL(ATM adaptation layer) in ATM(asynchronous transfer mode). CONSTITUTION:If it is found that a cell cannot be normally received, a reception-side AAL header trailer processing part 106 transmits a management cell, which indicates the stop of transmission of following cells, to the transmission side and reports the occurrence of cell reception error to a higher-order communication processing layer. Meanwhile, the transmission-side AAL receives the request of the stop of cell transmission to stop the cell transmission and abandons user information in a transmission buffer 101. Thus, a network is efficiently used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ATM (Asynchronous
Transfer Mode: Asynchronous communication mode) AAL (ATM Adaptation Layer) layer function in a communication method, and particularly relates to a retransmission control method when a cell communication error occurs.

[0002]

2. Description of the Related Art In the ATM communication system in which all the information to be transferred is divided into cells of fixed length packets and sent to the other party by using a high speed network, the data sent from the upper communication processing layer is divided into cells. Transfer to the network and also
A communication processing layer (hereinafter referred to as AAL .: ATMAda) that reconfigures cells arriving through the network into one piece of information.
ptation Layer).

In the AAL layer, the data sent from the upper communication layer is mapped to the communication processing layer (ATM layer) located below the AAL layer. Examples of services provided by this AAL layer are: Transfer error handling 2. 2. Processing for quantization by cell information field size Handling of lost and misinserted cells 4. Examples include flow control and timing control.

The function of the AAL layer can be logically divided into two. The first is the function of disassembling and assembling information from the upper layer into the ATM cell format (Segmentation and Reass
embly sublayer (SAR sublayer), the other is a function to provide AAL layer services to the upper layers (Converge
nce Sublayer: CS sublayer). The services provided by the AAL layer to upper layers can be classified as shown in FIG. In order to provide these four classes of service, there are three types of AAL protocol types that are composed of a combination of SAR and CS functions, but the details of the standardization are currently under discussion by the International Telegraph and Telephone Advisory Committee. There are many undecided parts that are under consideration at the meeting (CCITT). Hereinafter, for simplification of description, CS, SAR
It is assumed that the operation of the AAL layer is not the individual operation of the sub layer.

Next, an outline of the operation of the AAL layer will be briefly described with reference to FIG. At the AAL layer on the data transmission side, the user information sent from the upper layer is sent to the AAL-S.
Receive as DU. In order to send this user information to the ATM layer, it must be placed in the information field portion in the cell format in the ATM layer as shown in FIG. 4, so the user information is divided into 4 including header and trailer.
It is divided into blocks of 8 bytes (AAL-PDU). The 48-byte format is divided into four types as shown in FIG. 5 according to the above-mentioned protocol type. In this figure, SN is a sequence number. In addition,
The SN addition method of AAL types 3 and 4 is a free-run method for each AAL connection. SNP is sequence number protection, 3 bits (x ³ + x + 1) +1 bit (even parity), IT is information type (details to be determined), LI is effective information length in payload, and CRC is cyclic code. In addition, AA
The cyclic codes of L types 3 and 4 are G (x) = 1 + x + x ⁴ +
x ⁵ + x ⁹ + x ¹⁰ , ST is a segment type (cell division identifier), P is a priority field, MID is a multiplexing identifier, B is a byte, and b is a bit. Here, the sequence number (SN) is a number indicating the order of the divided blocks, and since it is composed of 4 bits, it is assigned to the AAL-PDU by repeating the number from 0 to 15. However, when the value of SN exceeds 15, it is again allocated in order from 0. The information type (IT) or segment type (cell division identifier) (ST) is divided into A
Whether the AL-PDU contains the beginning part of the original user information,
It indicates whether the information is at the end, the middle part, or one cell contains all of these pieces of information. LI, SNP,
FEC (Forward error correct)
Ion, forward error correction), CRC, etc. are prepared for error correction. The user information thus divided according to the cell format in the ATM layer is sequentially assigned the value of SN and sent to the ATM layer as an AAL-PDU, and then transmitted to the communication partner using the communication steps below the ATM layer. Transferred. On the other hand, the communication partner reconstructs the original user information from the cell sent from the ATM layer. Upon completion of reception of the cell indicating the end described above, the reconfiguration of the user information is completed, and the information is delivered to the upper layer.

Next, some failure occurs in the transmission line, and A
The operation when there is a bit error or a missing cell in the cell sent from the TM layer to the AAL layer will be described. Currently, CCI is used for control at the time of transmission error.
Although there is no standardization recommendation by TT, there are two types of methods that are considered to be used. In the first method, when a cell is normally received in the AAL layer without any error, 1 is added to the SN value of the cell that is normally received by that point and is received in advance, and the number and reception The cell SN is compared with the SN of the cell to check whether or not the cell has arrived. This system considers that the hardware is reduced as much as possible and the transmission speed is increased. Therefore, if cell loss is found, the receiving side notifies the upper communication processing layer that a cell reception error has occurred and information could not be reconstructed, or a notification to that effect. Not even done. Then, in the upper communication processing layer, in response to the error notification or no notification, the user information is retransmitted according to the retransmission procedure defined in the layer.

On the other hand, the second method is HDLC (High-
level Data Link Control Pr
procedure, high-level data link control procedure)
The method is similar to. This is because normally, the transmitting side continuously transmits a predetermined number of cells and waits for the arrival of a delivery confirmation from the receiving side, while the receiving side transmits the SN to the cells that can be normally received. It is sent to the transmission side as a delivery confirmation, and in response to this, the transmission side moves to transmission of the next cell. Then, if a cell arrival defect is found on the reception side, the reception side sends a retransmission request including the SN of the missing cell to the transmission side, and the transmission side retransmits the cell according to the retransmission request. It is something to do. Normally, cell-level retransmission is performed according to this procedure, but if normal reception is not possible even after the number of times specified in advance, a reception error is notified to the upper layer and retransmission processing is performed. Leave it to the upper layers.

[0008]

As described above,
The AAL layer in the ATM communication system performs mapping between the information from the upper layer and the ATM layer which is the lower layer, and further provides services such as transfer error processing to the upper layer. However, in the first retransmission method described above, when a reception error occurs, the reception side notifies the upper layer only of the occurrence of the error and does not notify the transmission side of anything. Therefore, the transmitting side continues to transmit cells after the reception error cell, and sends unnecessary cells to the network.

On the other hand, in the second method, even if the cell transmission is normally performed, a transmission confirmation cell is sent from the reception side to the transmission side every several cells, and thereby cell transmission is continued. However, since the communication path used in ATM is high-speed and the transmission error rate itself is very low, it is a processing overhead (the number of load calls) that the transmission confirmation is frequently exchanged, such as once every few cells. Routine work unrelated to) becomes large. However, even if an attempt is made to reduce the ratio of cells for transmission confirmation, the SN is 4 bits = 16, and the transmission interval for transmission confirmation is only once in 16 cells, which is not a great improvement.

In view of the above problems, the present invention simplifies the retransmission procedure when a cell error or cell drop occurs due to a transmission failure in the AAL layer, and at the same time, unnecessary cell transmission is performed. The purpose is to reduce

[0011]

In order to achieve the above object, in the invention of claim 1, the user information sent from the upper communication processing layer is divided into cells, and the cell is provided by the lower communication processing layer. Transfer to the other party of the communication using the function to, in the reception of the cell communication, reconfigure the cell sent from the lower communication processing layer in the form of the original user information,
In the cell communication method for delivering the reconfigured user information to the upper communication processing layer, when the cell communication from the transmitting side cannot be normally received, the upper communication processing layer is notified of the occurrence of the reception failure. At the same time as the step, the step of instructing the cell transmission side to stop the transmission of cells after the cell that cannot be normally received and is missing, and the cell transmission side from the receiving side of the cell communication When a cell transmission stop instruction is received, there is a step of stopping cell transmission, which is a retransmission control method at the time of cell communication error.

In the invention of claim 2, the user information sent from the upper communication processing layer is divided into cells, the lower communication processing layer transfers the cell to the other party of communication, and in the receiving side of the cell communication. Is a cell communication method that reconfigures a cell sent from a lower communication processing layer into the form of original user information and delivers the reconfigured user information to an upper communication processing layer, on the side that transmits user information. A step of allocating a sequence number to the cell when the user information is divided into cells and showing a sequence of cells to be transmitted, and a bit width necessary to represent the maximum value of the sequence number, which is allocated to the current cell. The sequence number added to the cell is used on the side that receives the user information after the step of storing the sequence number value. If the reception error of the cell is found in the step of counting the total number of cells normally received in succession and the step of checking the normal reception, The step of notifying the communication processing layer of the occurrence of the reception failure, and at the same time as the notification, in the transmitted user information indicated by the held normal reception cell total value to the other party of the communication. After considering the information of the cell retransmission position, if the number of times that it could not be normally received is within a predetermined number of times,
Resending instruction from the side receiving the user information, including a step of instructing retransmission of cells after the retransmission position and issuing an instruction to stop transmission of cells after the retransmission position when the predetermined number of times is exceeded. Or, on the side that sends user information based on the step of sending stop instruction,
When a retransmission instruction is received from the receiving side together with the retransmission position information, the cells after the retransmission position are retransmitted, and when a cell transmission stop instruction is received, a step of stopping transmission of cells after the retransmission position is performed. It has a retransmission control method when a cell communication error occurs.

According to the third aspect of the present invention, as a method of checking whether or not the cell on the side of receiving the user information is normally received by using the sequence number value added to the cell, the maximum of the sequence number value is set. Holding a total number of normally received cells sent from the lower communication processing layer, including the sequence number value, having a bit number equal to or larger than a bit width necessary for representing, When the sequence number of the cell arriving at is one greater than the sequence number value included in the held total number of received cells, it is determined that the cell has been normally received, and then is retained. The step of increasing the value of the existing sequence number by 1 and determining otherwise that the reception could not be normally performed is the retransmission control method at the time of cell communication error according to claim 2.

[0014]

With the above structure, in the invention of claim 1, when there is a cell that cannot be received normally when the cell is received, the occurrence of a reception failure is notified to the upper communication processing layer and the communication partner is notified. It gives an instruction to stop the cell transmission. According to the invention of claim 2, a value having a bit width equal to or larger than the bit width of the sequence number given to the cell in order to hold the sequence number of the cell which has been normally received on the reception side of the communication. To be able to hold. When the cell is normally received, if the sequence number of the received cell is 1 larger than the currently held value, the held value is also incremented by 1. Then, when the sequence number given to the cell exceeds the maximum value, it is repeated from 0 again. However, the holding value of the sequence number that operates on the receiving side has a bit width that is larger than the bit width necessary to represent the maximum sequence number value that the cell has, so that it may exceed the maximum sequence number value. Even in the case, the counting can be continued. And
Only when a reception error is found, information about cell reception confirmation is sent back to the transmission side. In that case, the sequence number of the cell which has been normally received is notified to the transmitting side, but the above-mentioned held value is sent back instead of the sequence number added to the cell.

According to a third aspect of the present invention, as a method for checking whether or not the cell on the side receiving the user information in the second aspect of the invention has been normally received by using the sequence number value added to the cell, the sequence Holds the total number of normally received cells sent from the lower communication processing layer, including the sequence number value, having a bit number equal to or larger than the bit width required to represent the maximum number value. However, when the sequence number of the newly arrived cell is one larger than the value of the sequence number included in the held total number of received cells, it is determined that the cell has been normally received, and The value of the held sequence number is incremented by 1, and if it is not, it is determined that the normal reception was not possible.

[0016]

EXAMPLES The present invention will be described below based on examples.
In carrying out the inventions of claims 1, 2 and 3, the main constituent elements (requirements) are common in carrying out the invention, and as a practical matter, the communication processing device in which the inventions of the claims are integrally incorporated is the most practical. The effects of the invention of each claim can be exerted. For this reason,
In the embodiments, description will be given at the same time as a communication processing device in which the inventions of the claims are integrally incorporated.

FIG. 1 shows the configuration of a communication device adopting the communication system according to the present invention. In the figure, 101 is a transmission buffer holding user information arriving from an upper communication processing layer, 102 is a transmission AAL-SAR header trailer processing unit, 103 is a transmission SN management unit, 104 is a transmission control unit, 1
Reference numeral 05 is a management information generation unit, 106 is a received AAL-SAR header trailer processing unit, 107 is an error processing control unit, and 108.
Is a reception SN management unit, 109 is a reconstruction buffer, and 110
Is a reception control unit. Next, the operation of each unit will be described. Here, for the sake of simplicity, a certain AAL-SA
The operation will be described focusing on the flow of user information arriving from P.

First, user information arriving from a certain AAL-SAP is stored in the transmission buffer 101. The transmission control unit 104 determines which service class of the AAL the user information from this AAL-SAP belongs to, and instructs the transmission buffer 101 how many bytes to read. Based on the instruction, the transmission buffer 101 fetches the user information in units of 44, 45, or 47 bytes in order from the beginning and sends it to the transmission AAL-SAR header trailer processing unit 102.

The transmission AAL-SAR header trailer processing unit 102 adds each header and trailer shown in FIG. 5 according to the AAL service class. First, the sequence number SN
Will be described. SNs such as 0, 1, 2, ... Are sequentially assigned to the information read from the transmission buffer 101 from the beginning. However, since SN is 4 bits, 0
The value ranges from 1 to 15. Therefore, SN is 1
When the number exceeds 5, the numbers are again assigned in order from 0. That is, it is managed by the remainder modulo 16. Currently, the assigned SN value is held in the sending SN management unit 103, and is incremented by 1 when the information is normally sent to the ATM layer.
IT and ST indicate the information type and segment type as described above. BO when the information read from the transmission buffer 101 is the beginning of the original user information
M, EOM at the end, C at the middle
OM, or SSM is assigned as an identifier when the user information fits in one read block. M
The ID is a multiplexing identifier and is used to distinguish user information from a plurality of AAL-SAPs when they are multiplexed on one ATM-SAP. In addition, various information for error checking is added to the ATM.
-Sent to the ATM layer as AAL-PDU through SAP.

Next, the operation on the receiving side will be described. A cell arriving from one ATM-SAP is a receiving AAL.
-Sent to the SAR header trailer processing unit 106. In the received AAL-SAR header part, it is checked whether or not there is a bit error by the error check header and trailer. If there is no bit error, it is further identified by MID or the like whether or not the data is for the AAL-SAP of interest. If the information is for the AAL-SAP of interest, the SN confirms the sequence number.
The confirmation of the number by this SN will be described.

The bit string managed by the reception SN management unit 108 has an 8-bit width, and the SN number of the cell that is normally received at the present time is the lower 4 bits of the 8 bits.
Hold on to a bit. (Note that when only the invention of claim 1 is adopted, only the lower 4 bits are managed and held.) And, as a whole of 8 bits, from the beginning to the present time, it is normal. It indicates the total number of cells received. In the reception AAL-SAR header trailer processing unit 106, the SN of the arrived cell is the reception S.
If the value is equal to the value of the lower 4 bits in the N management unit 108 plus 1, it is determined that the cell is normally received,
In addition to adding 1 to the value held in the reception SN management unit, the information included in the payload of the received cell is stored in the reconfiguration buffer 109.

The cells thus received are sequentially accumulated in the reconstruction buffer 109. And the receiving cell is EOM
If all the user information is received, the reception control unit 110 gives an instruction to end the reconfiguration to the reconfiguration buffer 109 and also outputs the reconfigured user information in the packet. Send to upper communication processing layer.

Now, in the receiving AAL-SAR header trailer processing unit 106, a bit error or S
The operation when an error is found in the N number will be described.
When the reception AAL-SAR header trailer processing unit finds some kind of error, it notifies the error processing control unit 107 of the SN of the cell in which the error is found. Error processing control unit 107
Counts the number of times the cell with that SN caused a reception error. If the number is less than or equal to a predetermined value, the retransmission request for the cells after that cell with that SN should be sent to the transmission side. Notify the transmission control unit 104. At this time, not just the 4-bit SN value added to the cell,
The value (for 8 bits) held by the reception SN management unit is also notified. Upon receiving this notification, the transmission control unit 104 gives an instruction to the management information generation unit 105 to send out a special management cell indicating a retransmission request.

The payload portion of the retransmission request cell includes the value notified from the reception SN management unit 108. This value does not simply indicate the SN value from 0 to 15 but is the bit width expanded by the reception SN management unit 108, so it can be said to be position information that can specify the position of the erroneous cell. In addition, the upper communication processing layer is notified that a user information reception failure has occurred. On the other hand, the user information normally received by that time and stored in the reconstruction buffer is retained as it is without being discarded.

If the cell having the SN cannot be normally received even after the retransmission request of the above-mentioned predetermined value or more, the error processing control unit 107 has some fundamental importance for the transmission itself. Then, the transmission control unit 104 is instructed to send a cell transmission stop request to the communication partner. In this case, as in the case of the first aspect of the invention, the upper communication processing layer is notified that the user information reception failure has occurred and the user information cannot be reconstructed. Then, the information normally received by that time and stored in the reconstruction buffer is discarded.

On the transmission side that receives such a management cell, the reconfiguration buffer 109 notifies the transmission control section 104 of the content of the management cell by the notification from the reception control section 110. If this is a cell transmission stop request, the transmission control unit 104 stops reading from the transmission buffer 101 and cell transmission, discards the user information in the transmission buffer, and discards unnecessary cells. Prevent the transmission from continuing. After that, removal of fundamentally important obstacles in transmission is considered. And, of course, it is transmitted after this is resolved.

On the other hand, when the content of the management cell is a retransmission request, the transmission control unit 104 determines the position of the retransmitted cell included in the payload portion of the management cell and notified from the receiving side. The position information of the cell which is correctly received by the other party in the entire user information is recognized by the number, and the user information of the portion necessary for retransmission is read from the transmission buffer 101. Then, the management information generation unit 10 creates a management cell that indicates the retransmission start display.
5 is notified and this cell is transmitted to the reception destination, and further to that cell, the cell transmission of the part of the user information that has not been correctly received by the other party is performed. (Note that
When only the invention of claim 1 is adopted, the reception AA
As error processing when the L-SAR header trailer processing unit finds some kind of error, a special management cell indicating information about the SN of the cell in which the error is found and a transmission stop request is sent to the transmission side. Further, the upper communication processing layer is notified that the user information cannot be reconstructed due to the reception failure of the user information. Then, the user information normally received by that time and stored in the reconstruction buffer is discarded. On the other hand, on the transmitting side which has received the management cell indicating this cell transmission stop request, the transmission buffer 101 after understanding the contents of the received management cell.
The reading from the cell and the cell transmission are stopped, and the user information in the transmission buffer is discarded. ) Then, on the receiving side, after receiving the management cell indicating the retransmission start indication, the same operation as that already described is performed, and the reconfiguration is performed together with the user information held in the reconfiguration buffer 109, Finally, the normally received and reconstructed user information is sent to the upper communication processing layer.

Although the present invention has been described based on the embodiment, one AAL-SAP is provided for simplification of the description.
The functional configuration and operation of the present invention have been described by focusing on the user information from. However, in practice, multiple AAL-SA
A lot of user information and cells arrive from P and ATM-SAP after being multiplexed. Therefore, the transmission SN management unit 10
It goes without saying that 3 and the reception SN management unit 108 are not in the form of a single unit but in the form of a table.

[0029]

The effects of the present invention will be described below. According to the conventional technique, when there is a cell reception error, at least all user information including the reception error cell is retransmitted. In the present invention, the reason why the cell is wasted despite being normally received is that a cell transmission stop request is sent from the reception side to the transmission side after the cell in which a reception error occurs, Only the cells that have been transmitted before the transmission is stopped. Especially for high-speed communication A
In TM, the time until the transmission stop request is confirmed is sufficiently short, and it is considered that the number of cells that are wastefully transmitted is not large, and thus the network can be used efficiently. In this way, high-speed processing is required by leaving the retransmission control at the time of a reception error to the upper layer and omitting the retransmission procedure in the lower layer as much as possible.
It can be easily adapted to TM.

In the inventions of claims 2 and 3, if the numerical values used in the embodiments are used, the bit width of the reception SN management section is set to 8 bits, and the bit width of the SN added to the cell is 4 bits. Making it big. 0 for 4 bits
Numerical values from 1 to 15 are repeatedly added as the SN value of the cell. That is, every 16th cell has the same SN value. However, since the bit width for counting the SN on the receiving side is made large, when the reception error occurs, it becomes easy to specify the position of the cell in which the reception error occurs. Considering, for example, the maximum packet length of 4500 bytes in FDDI as the maximum length of user information sent from the upper layer, this is divided into about 100 cells. Therefore, it is considered sufficient if the bit width of the reception SN management unit is 8 bits = 256. On the other hand, in the realization of this method using general-purpose components, the load increase due to the data management of the 4-bit width bit string and the 8-bit width data string is small. Therefore, it can be easily realized.

Further, on the transmitting side, the position of the cell where retransmission should be started can be easily specified, so that the cells after the cell having the reception error can be retransmitted, including the cell having the error. There is no need to resend all information packets. Therefore, the network can be used more efficiently than the invention of claim 1.

[Brief description of drawings]

FIG. 1 is a diagram showing a step configuration of the present invention.

FIG. 2 is a diagram showing classification of AAL service classes.

FIG. 3 is a diagram showing how user information is decomposed into cells by the AAL layer.

FIG. 4 is a diagram showing a structure of an ATM cell.

FIG. 5 is a diagram showing the structure of AAL-PDU.

[Explanation of symbols]

 101 transmission buffer 102 transmission AAL-SAR header trailer processing unit 103 transmission SN management unit 104 transmission control unit 105 management information generation unit 106 reception AAL-SAR header trailer processing unit 107 error processing control unit 108 reception SN management unit 109 reconstruction buffer 110 Reception controller

Claims (3)

[Claims] 1. The user information sent from an upper communication processing layer is divided into cells, the cells are transferred to a communication partner using a function provided by the lower communication processing layer, and in the receiving side of the cell communication. Is a cell communication method in which a cell transmitted from a lower communication processing layer is reconfigured in the form of original user information and the reconfigured user information is delivered to an upper communication processing layer. If the reception fails, the upper communication processing layer is notified of the occurrence of the reception failure, and at the same time as the step, the cells subsequent to the cell that cannot be normally received and are lost to the cell transmission side. The step of giving an instruction to stop the transmission of the cell, and the step of stopping the transmission of the cell when the cell transmitting side receives an instruction to stop the transmission of the cell from the receiving side of the cell communication. Retransmission control method when cell communication error is featured. 2. User information sent from an upper communication processing layer is divided into cells, the lower communication processing layer transfers the cells to a communication partner, and in the receiving side of the cell communication, the lower communication processing is performed. In the cell communication method that reconfigures the cell sent from the layer into the original user information and delivers the reconfigured user information to the upper communication processing layer, the user information is transmitted to the cell on the side that transmits the user information. When dividing, a step of allocating a sequence number for indicating the order of cells to be transmitted to cells, and having a bit width necessary to represent the maximum value of the sequence numbers, and the sequence number value currently allocated to the cell The step of holding the user information, on the side of receiving the user information based on the step of the side of transmitting the user information, the cell was normally received using the sequence number added to the cell. If a cell reception error is found by the step of checking whether or not the total number of cells that have been normally received in succession, and the step of checking the normal reception, if the reception error is detected in the upper communication processing layer. At the same time as notifying the occurrence of a failure, after considering the information of the cell retransmission position in the transmitted user information indicated by the held total number of normally received cells to the transmitting side at the same time as the notification. A step of instructing retransmission of cells after the retransmission position when the number of times of unsuccessful reception is within a predetermined number of times, and issuing an instruction of stopping transmission of cells after the retransmission position when exceeding the predetermined number of times From the receiving side, on the side that transmits the user information based on the step of the retransmission instruction or the transmission stop instruction from the side receiving the user information, When a retransmission instruction is received together with the retransmission position information, the cells after the retransmission position are retransmitted, and when a cell transmission stop instruction is received, the transmission of cells after the retransmission position is stopped. Retransmission control method when cell communication error is featured. 3. A method for checking whether or not a cell on the side of receiving user information has been normally received by using a sequence number value added to the cell, which is a bit required to represent the maximum of the sequence number value. A step of holding the total number of normally received cells sent from the lower communication processing layer including the sequence number value after having a bit number equal to or larger than the width, and the order of newly arrived cells When the number is one larger than the value of the sequence number included in the total number of received cells held, the value of the held sequence number is determined after determining that the received number is normal. 3. The retransmission control method at the time of cell communication error according to claim 2, further comprising the step of increasing the number by one and determining otherwise that the reception was not normally performed.