JPH07162431A - Method for separation processing of atm cell - Google Patents

Abstract

PURPOSE:To reduce a sequence number(SN) error processing time by comparing a sequence number(SN) of an asynchronous transfer mode ATM cell and its expected value SNR. CONSTITUTION:An SN discrimination circuit 7 compares an SN and an SNR in an AAL header decomposed by an ATM/ALL header separation circuit 3, and when they are coincident, data are stored in a cell decomposition buffer 9 according to a buffer address BA. An SN error count SNE of a cell decomposition control memory 5 is counted up when dissident, and when the count is 3, a cell abort signal is sent to a selector/cell abort circuit 8 to abort the data and the SNR is reset to the SN of a logic channel cell reached succeedingly. When not 3, the SN is compared with (SNR-1) and when coincident, an arrived cell abort signal is sent to the circuit 8. When dissident, a signal to write a dummy cell to the buffer is sent to the circuit 8 and the dummy cell is stored in the buffer 9 according to the address BA in the memory 5.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an ATM (Asynchronous
(Transfer Mode: Asynchronous transfer mode) Cell disassembly processing method, particularly ATM cell (hereinafter, also simply referred to as "cell")
Of the sequence number (hereinafter, also referred to as "SN") error, the ATM cell disassembling method is simplified.

[0002]

2. Description of the Related Art A fixed speed (CB
In order to realize R: Constant Bit Rate (R) communication, in general, in order to guarantee the order of cells that occur periodically on the transmission side, as shown in FIG.
N is added, and the cell receiving side verifies the sequence number SN of the received cell. Therefore, if it is determined that the sequence number SN is correct, the STM (Synchronization) of the cell is
ous Transfer Mode: Synchronous transfer mode) Performs data reproduction processing. However, in reality, when a cell is discarded in an ATM network or when a bit error in the network is caused, an ATM header error check (HEC) process or an AAL (ATM Adaptatat) process is performed.
Ion Layer) SNP (Sequence Number Pro) in the header
sequence number SN due to factors such as cell discard due to check processing, and erroneous delivery of cells in which information of other users interrupts due to missed HEC described above.
If the order of is not maintained (Hereafter, this is "SN error"
There is).

As a process expected for these SN errors, in the case of cell discard, it is necessary to insert a pseudo cell in order to guarantee the timing of CBR communication. Also,
In the case of an erroneously inserted cell, that cell needs to be discarded. In order to perform such processing, when an SN error occurs, it is necessary to determine what is the cause of the error. As a method, conventionally, for example, as shown in FIG. 3, when a cell of SN = 1 arrives next to SN = 1, it is determined whether the cell loss is due to cell loss or cell misdelivery. Sequence number SN of next arriving cell
A method of making a judgment by verifying was considered.
In this case, if SN = 2, it is determined that the cell is erroneously delivered, and SN
= 4, the cell loss is determined. In order to make such a determination, it is necessary to temporarily store the cell in which the SN error has occurred in the buffer and wait for the next cell.

Generally, when interconnecting an STM network and a packet (including ATM) network, the packet is transferred to the STM.
In reproducing the data, in order to absorb the delay fluctuation in the packet network, the cells are temporarily stored in the buffer, and after a certain period of time, the STM data is reproduced. Conventionally, in voice packet communication, it takes a long time to absorb fluctuations,
After accumulating a plurality of cells in the buffer, the reproducing process was performed. Therefore, in the determination of the error factor in the SN error processing, the appropriate processing is performed by accumulating the cell in which the error has occurred in the buffer and verifying the SN of the next cell. Note that, as this type of technology, for example, Japanese Patent Laid-Open No.
The technology disclosed in Japanese Patent Publication No. 37600 can be referred to.

[0005]

However, in the case of ATM communication, SDH (Synchronous Digital Hierarchy) is particularly important.
When cell assembling and disassembling processing is applied to a highly multiplexed STM line such as 156 Mb / s, the cell fluctuation absorption time is less than 1 cell time, error cells are accumulated like voice packet communication, and the SN of the next cell is verified. It was difficult to judge the cause of the SN error by doing so. As SN processing, in addition to the processing at the time of SN error as described above, SN
Even when is normal, it may be necessary to perform processing different from normal processing. This is because, for example, an SN when a buffer underflow occurs due to a cell arriving at the cell disassembly processing section later than expected.
Processing.

When a buffer underflow occurs, a pseudo cell is regenerated, and a cell arriving late must be discarded in order to guarantee the timing of CBR communication. Therefore, the SN of the cell that arrived late
(denoted as (a) ”) and compared with the SN of the next arriving cell (denoted as“ SN (b) ”), SN (b) = SN (a) +
If it is 1, a processing method of discarding the cell has been considered. As described above, conventionally, as the SN process in the ATM cell disassembling process, there is a problem that the SN error process and the process at the time of the buffer underflow are different algorithms, and moreover, in order to determine the cause of the SN error. It is necessary to hold the SN value for 2 cells,
There is also a problem that this is very difficult in terms of processing time. The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above-mentioned problems in the conventional technology, simplify the algorithm, and shorten the SN error processing time. It is to provide a decomposition treatment method.

[0007]

The above-mentioned object of the present invention is to
A TM data string is assembled into an ATM cell, a sequence number is added and transmitted, the ATM cell is received by a cell receiving section, and a cell fluctuation absorption buffer absorbs cell delay fluctuations and arrives cell sequence numbers. After verifying
A that periodically reproduces the ATM cells into an STM data string
A method for disassembling a TM cell, wherein an expected value (SNR) of a sequence number is set to 0 at the start of communication and incremented by 1 when an ATM cell having a normal sequence number arrives. When the ATM cell arrives at the cell reception processing unit, the sequence number of the ATM cell is compared with the expected value SNR, and if the two match, the ATM cell is regarded as normal and the STM data string is reproduced. This is accomplished by an ATM cell disassembling method characterized by performing processing, inserting pseudo cells when the two do not match, and updating the expected value SNR of the sequence number.

[0008]

In the ATM cell disassembly processing method according to the present invention, the sequence number SN of the cell arriving at the cell disassembly side.
As a method of verifying, the SNR that is the expected value of SN is held in the cell disassembly processing unit, and the verification is performed by comparing the SN and SNR of the arrived cell. If they match, it is regarded as normal, and STM playback processing is performed at the same time as S
Increment NR. Further, as processing when the arrival of cells at the disassembly side is delayed more than expected due to network congestion and the disassembly buffer underflows, the pseudo cell is regenerated and the SNR is incremented by one. As a result, the SN and SNR of the cell that arrives later do not match, and this is detected as an SN error. S like this
By performing the N processing, it becomes possible to incorporate the SN processing after the buffer underflow into the SN error processing algorithm.

This will be described in more detail below. The causes of SN error include cell loss and cell misdelivery, SNP check miss error, and cell disassembly buffer underflow processing. Cell loss occurs due to cell discard in the HEC or SNP check described above with respect to cell discard in the network and bit error on the transmission path. In addition, misdelivery of cells occurs when cells of other channels arrive due to missed HEC. Now, let's compare the probability that an error will occur due to each factor. In the case of voice communication, the probability that cells will be discarded in the network is specified to be less than about 10 ^-5 from the subjective voice quality. The probability of two consecutive cells being discarded can be considered as an event of the product of the probability of one cell discarding in the case of low speed such as voice communication, and is considered to be much smaller than one cell loss.

On the other hand, let us look at the probability of missing the HEC, which is the cause of erroneous cell delivery. Assuming a random error, the one-element error probability is set to p (p << 1), and the error detection probability of HEC is first obtained. The probability that an error of 3 bits or less occurs: P ₃ is

[Equation 1] In addition, the probability of an error of 4 bits or more: P ₄ is

[Equation 2] Becomes

Since p << ¹ , p ^k >> p ^{k + 1} ,
(1-p) ^k ≈1, the higher-order term of p approaches 0 without bound, and P ₃ >> P ₄ . Moreover, considering that an error of 4 bits or more can be detected with a considerable probability, it can be seen that the probability of occurrence of a missed error is much smaller.
Similarly, the probability that an SNP missed error will occur can be considered to be very small. Next, looking at the probability of a cell having a buffer underflow, this probability is equal to the probability of exceeding the delay fluctuation allowed in the network, which is less than the probability of cell discard in the network. Is designed. Therefore, the probability that a cell will undergo buffer underflow is approximately 10 ^-5 .

The basic idea of the present invention is to take into account the occurrence probabilities of these factors, cell misdelivery that can be determined to be small enough to be ignored, SNP check missed error,
The processing for discarding consecutive cells is not performed, but only the processing for discarding one cell and disassembling buffer underflow, which are highly likely to be factors of SN error, is performed. However, no matter how small the probability is, the probability of cell misdelivery or continuous cell discard does not become zero.
Therefore, when SN errors of a certain value or more occur continuously, a method of resetting the SN and setting the SN of the next arriving cell to the SNR and restarting the processing, or setting the SNR to 0
Is set, it is preferable to consider a processing flow in which all cells arriving up to the next cell with SN = 0 are discarded and normal processing can be restored from the cell with SN = 0. Note that this is the matter described in claim 2 described above.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 6 is a diagram showing a cell receiving apparatus according to an embodiment of the present invention. In the figure, 1 is an ATM cell input line, 2 is an ATM / AAL header separation circuit, 3 is an ATM header / AAL header separation circuit, 4 is VPI / VCI → logical CH number conversion table, 5 is a cell disassembly control memory, 6
Is a pseudo cell generation circuit, 7 is an SN determination circuit, 8 is a selector for selecting which of user data and pseudo cell is to be written in the buffer and a circuit for discarding cells, and 9 is a cell disassembly buffer. The outline of the operation of the cell receiving apparatus according to the present embodiment is as follows. Note that, here, an example will be described in which the SN is assigned by the Mojoro 8 on the transmitting side and the number of SN errors for the SN reset process is 3.

When an ATM cell is input to the cell receiving side from the ATM cell input line 1, the ATM / AAL header separating circuit 2 separates the ATM / AAL header and the user information portion, and further separates the ATM header / AAL header. Circuit 3
In, the ATM header and the AAL header are separated. Next, the VPI / VCI → logical CH number conversion table 4 is used to convert the VPI / VCI in the ATM header into a logical CH number, and the cell disassembly control memory 5 is accessed using this channel number as an address, and SNR is set. Read out.
On the other hand, the AAL header separated in the ATM header / AAL header separation circuit 3 compares the SN and SNR in the AAL header in the SN determination circuit 7, and if they match, according to the buffer address (BA). The data is stored in the cell disassembly buffer 9.

If the SN and SNR do not match, the SN error counter value in the cell disassembly control memory 5
(SNE) is counted up, and if SNE = 3, a signal for discarding the cell is sent to the selector and the circuit 8 for discarding the cell, data is discarded, and the same logical channel that arrives next is sent. The SNR is reset to the SN of the cell. When SNE = 3 is not satisfied, SN is further compared with SNR-1, and if SN matches SNR-1, the signal for discarding the arriving cell is selected and cell discard is performed. Send to circuit 8 to do, SN is SN
If it does not match R-1, the signal for writing the pseudo cell in the buffer is sent to the selector and the circuit 8 for discarding the cell, and the pseudo cell is set as the cell according to the buffer address (BA) in the cell disassembly control memory 5. Store in decomposition buffer 9.

The essential points of the above operation will be described below with reference to the operation flowchart shown in FIG. When the cell arrives (step 11), the SN of the arriving cell is compared with the SNR held in the cell receiving section (step 12). If they match, the cell is regarded as normal, and the cell is decomposed in the cell disassembly buffer 9
(Step 19). Then, the SNR is incremented by 1 (step 20). However, as shown in FIG. 4A, when one cell loss occurs in which a cell with SN = 2 is lost, when a cell with SN = 3 arrives next, SNR =
Since it is 2, an SN error occurs. Therefore, in order to continuously check whether or not the SN error is caused by the processing at the time of the decomposition buffer underflow, the SNR
-1 is compared with the SN of the arriving cell (step 15).

Here, since SNR-1 = 1 and SN = 3, they do not match. Therefore, SNR + 1 and SN
(Steps 17 and 12). Then, since there is a match here, one cell is regarded as one cell loss, one pseudo cell is inserted, the SN error counter is incremented by 1 (step 13), and the arrival cell is regenerated with SNR = 4.
(Step 19). Since the next arriving cell has SN = 4, the SN error counter is reset here, and thereafter,
Normal processing can be performed. Next, as shown in FIG. 4 (b), when the arrival of the cell with SN = 2 is delayed due to the cell fluctuation delay and a buffer underflow occurs, the pseudo cell reproduction processing is performed at that point, and the SNR is 1 Incremented (steps 16 and 17).

Therefore, if a cell with SN = 2 arrives with a delay, since SNR = 3, an SN error occurs. In this case, since SNR-1 and SN are compared and coincident with each other, it is determined that the SN error is due to the processing at the time of buffer underflow, and the arriving cell is discarded (steps 15 and 18). Next, as shown in FIG. 5 (a), in the case of mis-delivery of cells with a small occurrence rate, even if SN and SNR and SNR-1 are compared, they do not match, so an SN error occurs, and the SN error counter is incremented by 1 (step 12 and 13). Next, set the SNR to 1
Since they do not match when incremented and compared, the SN error counter is set to 2, and the SNR is also incremented by 1 (steps 13 and 17).

As a result, SNR = 3, but SN = 5.
Since they do not match, the SN error counter becomes 3, which is the specified value for SN reset, resulting in SN reset (steps 12 to 14 and 21, 22). In the SN reset process, the SNR is set to the SN (here, 2) of the next cell to arrive.
Set and return to normal processing. In addition, as shown in FIG. 5B, SN (=
4) is compared with SNR (= 2) and SNR-1 (= 1), respectively, but since they do not match, the SN error counter is incremented by 1 and the pseudo cell reproduction processing is performed.
(Steps 12-16).

Subsequently, the SNR is incremented by one, and the SN error counter is also incremented each time the pseudo cell is reproduced (steps 17 to 16). Here, when the SNR is incremented by 2, it matches SN = 4. At this time, since the SN error counter is 2, the SN is not reset and the normal processing is restored. In this way, even when a plurality of cell losses occur, the SN error specified value that is the SN reset process determines how many cells the cell loss is processed. If the cell loss is more than that, the SN reset process is performed. Becomes

According to the above embodiment, as a method for verifying the sequence number SN of the cell that has arrived on the cell disassembly side, S
The SNR that is the expected value of N is held in the cell disassembly processing unit, and verification is performed by comparing the SN and SNR of the arriving cell. If they match, it is regarded as normal, and the STM
And the SNR is incremented. Also, as a process when the arrival of cells at the disassembly side is delayed more than expected due to network congestion and the disassembly buffer underflows, the pseudo cell is regenerated and the SNR is
Is incremented by 1. As a result, the SN and SNR of the cell that arrives later do not match, and this is detected as an SN error. By performing such SN processing, it is possible to incorporate the SN processing after the buffer underflow into the SN error processing algorithm. It is needless to say that the above embodiment shows one example of the present invention, and the present invention should not be limited to this.

[0022]

As described above in detail, according to the present invention, it is possible to realize an ATM cell disassembling method in which the algorithm is simplified and the SN error processing time can be shortened. Is.

[Brief description of drawings]

FIG. 1 is an operation flowchart of an ATM cell disassembly processing method according to an embodiment of the present invention.

FIG. 2 is a diagram showing an ATM / AAL cell format.

FIG. 3 is a diagram showing an SN error determination method when an SN error occurs.

FIG. 4 is a sequence diagram (No. 1) showing processing on the receiving side for various SN errors.

FIG. 5 is a sequence diagram (No. 2) showing the processing on the receiving side for various SN errors.

FIG. 6 is a diagram showing a system configuration according to an embodiment.

[Explanation of symbols]

 1 ATM cell input line 2 ATM / AAL header separation circuit 3 ATM header / AAL header separation circuit 4 VPI / VCI to logical CH number conversion table 5 Cell disassembly control memory 6 Pseudo cell generation circuit 7 SN determination circuit 8 Selector and cell discard Circuit for performing 9 Cell disassembly buffer 10 Data readout circuit

Claims (3)

[Claims] 1. An STM data string is assembled into an ATM cell, a sequence number is added and transmitted, the ATM cell is received by a cell reception section, and a cell fluctuation absorption buffer absorbs and arrives cell delay fluctuations. An ATM cell disassembly processing method of periodically reproducing the ATM cell into an STM data string after verifying the sequence number of the cell, wherein an ATM cell having a normal sequence number is set to 0 at the start of communication. When the ATM cell arrives at the cell reception processing unit, the expected value (SNR) of the sequence number that is incremented by 1 is held in the cell reception processing unit, and when the ATM cell arrives at the cell reception processing unit, the sequence number of the ATM cell and its expected value SNR. And compare and if the two match, the ATM
The cell is regarded as normal and STM data string reproduction processing is performed.
A method for disassembling an ATM cell, characterized in that if the two do not match, a pseudo cell is inserted and then the expected value SNR of the sequence number is updated. 2. The sequence number and its expected value SNR
In the result of the comparison with the above, the number of times when the two do not match is counted, and when the counted number exceeds a predetermined value, the expected value SNR of the sequence number is set to a predetermined value. The AT according to claim 1,
Method for disassembling M cell. 3. When the buffer for absorbing cell fluctuations underflows, the pseudo cell is regenerated, the expected value SNR of the sequence number is incremented by 1, and the sequence number and the expected value SNR thereof match. The ATM cell according to claim 2, wherein when the sequence number is smaller than the expected value SNR by 1 in the case where the sequence number is not present, the expected cell SNR of the sequence number is not updated and the arriving cell is discarded. Cell disassembly method.