WO2000042738A1

WO2000042738A1 - Apparatus and method for continuously checking atm cell

Info

Publication number: WO2000042738A1
Application number: PCT/JP1999/000096
Authority: WO
Inventors: Yoshihiro Uchida; Mikio Nakayama
Original assignee: Fujitsu Limited
Priority date: 1999-01-14
Filing date: 1999-01-14
Publication date: 2000-07-20

Abstract

An SC checking section (SCCHK) of an AAL1 receiving unit (RAAL1) recognizes the continuity of an ATM cell based on SAR-PDU validity/invalidity information from an SN checking section (SNCHK) and the value of an SC contained in an SAR-PDU header. An SC storage section (SCREG) is fed with the value of the SC of the SAR-PDU stored in a received SAR-PDU temporary storage section (ST) and the value of the SC of the SAR-PDU written in a latest re-assembly buffer (RBUF). Normally, a received ATM cell (including an SAR-PDU) is directly written in the RBUF. During a failure, the previously received SAR-PDU is stored in the ST, and the currently received SAR-PDU is stored in a currently received PDU buffer (CRBUF). Thus, since normally a SAR-PDU is directly written in the RB UF, no processing delay occurs; and since during a failure a SAR -PDU is temporarily stored in the ST, it is possible to insert dummy data in a position where data is to be inserted and to correctly discard a SAR-PDU to be discarded.

Description

Specification

Apparatus and method for checking continuity of ATM cells

The present invention relates to an inspection apparatus and method for inspecting continuity of ATM cells transmitted by a constant transmission rate service of an ATM network. Background art

Today, much research and development is being conducted to realize an information society with a global perspective. In such an information-oriented society, it is necessary to build an infrastructure that enables companies and ordinary people to easily access various multimedia information from audio to images. Networks that will become infrastructure in the multimedia information society must accommodate data with greatly different transmission volumes flexibly and provide various types of information to users. ATM is one such network.

(Asynchronous Transfer Mode) An ATM network using exchange techniques is regarded as promising and is being actively researched and developed.

ATM switching technology uses fixed-length packets (ATM cells) as unit data and transfers them over a high-speed packet switching network (ATM network with an ATM switch at the core) to provide various types of traffic. It was introduced with the aim of handling networks in a single network. However, when introducing an ATM network, it is necessary to gradually use an existing non-ATM network while effectively using the existing non-ATM network. Connect to The problem exists.

That is, how to take non-ATM traffic into the ATM network, transfer it efficiently, and reliably convert it to the original non-ATM traffic.

The traffic handled in ATM networks varies in nature depending on the services provided to users. In order to efficiently transfer these various types of traffic using the same structure of ATM cells, an ATM adaptation layer (hereinafter referred to as AAL) has been introduced. For AAL, user data is directly stored in the ATM cell payload (the area where ATM service users can store data, which is not allowed when processing ATM cells at the ATM Layer level). Instead, the AAL is set on top of the ATM Layer, and a SAL—PDU (Segmentation And Reassembly sublayer-Protocol Data Unit) is used as the AAL packet. The SAR—P DU payload Contains user data. The S AR—P DU header contains a protocol for efficient ATM cell transfer according to the traffic characteristics of each service (for example, end-to-end transfer error detection / data It contains the information necessary to implement the retransmission request. Several types of SAR-PDU formats are standardized according to the characteristics of the traffic to be handled, and AA LT ype 1 (hereinafter AAL 1) is one of them. There is power S.

The traffic handled by AA L1 is called CBR (Constant Bit Rate) service. For example, DS1 and DS1, which are used as standard for data transmission on existing non-ATM networks 3 and others. The characteristics of CBR traffic are that its bandwidth is always constant, and that it is sensitive to delays and delay variations added by being transmitted over the network. AR-PDUs have the necessary mechanisms to successfully transfer CBR traffic with the above characteristics in ATM networks where delay variation is essentially unavoidable. Figure 1 is a block diagram showing the configuration of an ATM network using AAL1.

In the network shown in Fig. 1, non-ATM terminals 1 and 2 are connected as end users and receive services by non-ATM traffic. The non-ATM traffic transmitted from the non-ATM terminal 1 is mapped to an ATM cell and transmitted to the ATM network 5. The ATM cells exchanged and transmitted in the ATM network 5 are converted into non-ATM traffic data format and converted to non-ATM terminal 2 _c non-ATM traffic to be converted to ATM cells (ie, Mapping non-ATM traffic to SAR-PDU payload, adding SAR-PDU header to generate SAR-PDU, and adding ATM header to generate ATM cells). The AAL1 transmitting unit (hereinafter referred to as S AAL 1) 3 is used, and the AAL1 receiving unit (hereinafter referred to as RAA L1) 4 reproduces non-ATM traffic from ATM cells.

FIG. 2A is a diagram showing the configuration of the ATM cell and the SAR-PDU. FIG. 2B is a table listing the meanings of the symbols in FIG. 2A.

Since the ATM cell header in FIG. 2A relates to the transfer function of the ATM layer, the description is omitted.

The S AR-P DU has a length of 48 octets that can fit in the ATM cell payload, and the first one octet is the S AR-P DU header. There are two fields in the SAR—PDU header: SN (Sequence Number) and SNP (SN Protection). 31 ^? Is inside. It has two subfields, 1¾〇 and P, and is used to detect and correct errors in the SN field by using CRC code and parity bit. On the other hand, for the SN field, there are two subfields, CSI (CS Indication) and SC (Sequence Count) .The usage of the CSI differs depending on the type of CBR service according to AAL1. Therefore, the description is omitted here. The SC subfield is a sequence number having a value of 0 to 7, and is assigned by SAAL 1 for each SAR-PDU. The SC attached to the ATM cell that stores continuous user data is set to increase by 1 (0 after 7).

That is, the SAAL1 decomposes the continuous non-ATM traffic transmitted from the non-ATM terminal and sequentially stores it in the SAR-PDU payload of the ATM cell as shown in FIG. 2A. The ATM cell configured in this manner carries continuous data of non-ATM traffic, and at this time, the non-traffic data stored in the SAR-P DU pay port is continuous. Serial numbers from 0 to 7 are set in the ATM cell SC. By examining the SC at the receiving end, it is possible to check whether the non-ATM traffic data is correctly transmitted by the ATM cell in the order transmitted from the transmitting end.

Note that GFC in Fig. 2A is an abbreviation of Generic Flow Control and is provided at the interface between the user and the network, so the VPI in this case is 8 bits. However, the GFC is not provided in the network interface, and is used as the VPI area. For a network-to-network interface, the VPI has a 12-bit area Assigned.

FIG. 3 is a block diagram showing the configuration of RAAL1.

R AAL 1 checks the contents of the SAR-PDU header of the SAR-PDU contained in the arriving ATM cell and, based on the detection result, re-assembles the SAR-PDU in a reassembly buffer (reassembly buffer). Buffers, hereafter RBUF), or whether to discard without capturing.

Header detection is a two-step process. First, the received ATM cell is input to SNHK in FIG. The SNCHK extracts only the SAR-PDU header from the ATM cells and checks the SAR-PDU header for normality. The SAR-PDU header health is determined by the presence or absence of a header error using the SNP field in the SAR-PDU header. If there is no header error, or if there is a header error but the error can be corrected by the CRC bit of the SAR-PDU header, it is determined to be "valid" and there is a header error and the If the error cannot be corrected, it is determined to be "invalid". The second is the continuity check of SC by SCC HK in Fig. 3. Normally, SC should be continuous in the direction of increasing by 1 in adjacent SAR-PDU, but ATM SC continuity will be lost if cells are dropped or duplicated during transfer in the network, or if unnecessary cells are mixed. The SC CHK uses the result of the SC continuity check and the “valid” and “invalid” information of the SAR-PDU, which is the result of the SNCHK, to decide whether to import or discard the SAR-PDU. Here, ATM cells are input to SC CHK, but when writing SAR—PDU to RBUF, adjust the timing so that the ATM cell header is not written to RBUF. And outputs the light naple signal WE to RB UF. As a result, the RBUF contains only the SAR—PDU of the ATM cells. Is written. The details of the capture / discard decision algorithm (hereinafter referred to as SNA) performed by this SC CHK are left to the actual implementation.

RBUF is a buffer for regenerating non-ATM traffic transmitted over ATM cells. For example, it stores SAR—PDUs that are determined to be captured and stores non-ATM traffic. Line rate

(For example, in the case of DS1, 1.554Mbps), the operation is such that only the SAR-PDU payload is read. At the same time, RBU F also absorbs the fluctuation of delay added to ATM cells during ATM network transfer. Therefore, the RBUF is usually configured as a FIF that has a capacity that does not cause overflow or underflow within the allowable range of the delay variation added in the ATM network. Note that the read control of the RBUF is performed by RBURCTL in FIG. R BURCT L supplies a read address and a read enable signal RE to RBU F, and sequentially reads out only the SAR-P DU ぺ of the SAR-P DU stored in RBUF. Control.

As described above, the RBU F should be able to keep the number of SAR-P DU payloads in the buffer almost constant when the ATM cells are normally transferred. When a drop occurs, the amount of data written decreases, and in the worst case, an underflow occurs. In order to prevent underflow, SC CHK detects cell loss and writes the number of dummy SAR-PDUs judged to have dropped to RBUF. On the other hand, when cells are duplicated and mixed on the ATM network, it is necessary to discard the duplicated cells and prevent the RBUF from overflowing. These dropped cells and duplicated mixed cells Is also a function of SCC HK.

Regarding SNA, it is not standardized, but two types are shown as reference information in ITU-TI.363.1 Appendix IE. These are the Robust SN algorithm (hereinafter referred to as RSNA) and the Fast SN algorithm (hereinafter referred to as FSNA). In an AAL1 processor, one of the two is usually applied. Often have.

FIG. 4 is a block diagram showing the hardware configuration of SCCHK using RSNA.

A feature of RSNA is that buffers for ST (SAR-PDU-time storage unit) and SAR-PDU- pieces are provided before the RBUF. The determination of writing to RBUF is based on the last SAR written to RBUF—SC of PDU (stored in SC ac of SCREG in the figure) and SAR in ST—SC of P DU (stored in SC st ), And then by checking the SC continuity of the arriving SAR-PDU. The continuity check section of S C is S EQ C in FIG.

The SC CHK receives the valid Z invalid information of the SAR-PDU from the SNC HK and the received SAR-PDU data from the ATM network. Actually, instead of SA R_PDU, the ATM cell containing this is input. SEQC is based on SAR-P DU valid / invalid information and SC ac and SC st stored in SC register (SC REG). SAR-P DU data (ATM Judge whether or not [Cell] is written to ST, and transmit the write enable signal WE st to ST. The WE st provides a timing for writing an ATM cell including SAR-PDU data input from the ATM network to the ST. SEQC is stored in ST If it is determined that an ATM cell should be written to the RBUF, a read enable signal RE st is given to the ST to output the ATM cell and output the AT [cell to the selector SEL. At the same time, a write control signal is given to 1¾81; F for 3 £ <3〇, and a write enable signal is output at a timing such that only the SAR-PDU portion of the ATM cell is written. If the SC included in the received ATM cell does not have continuity with the SC st or SC ac stored in the SC REG, it is determined that a cell has been inserted or dropped, and the ATM cell from the ST has been deleted. The output is stopped or the dummy data generated by the dummy PDU data generation unit DUMG EN is output from the SEL instead of the ATM cell that has been dropped. As described above, the ATM cell is actually stored in the ST, and control is performed such that only the SAR-PDU is written when writing to the RBUF. AR—The description is made assuming that the PDU itself is read and written to the ST.

FIG. 5 is a state transition diagram of RSNA performed by SEQUC of SCCHK in FIG.

In the case of RSNA, SEQUC detects cell loss duplication / contamination while transitioning between five states. Table 1 in Fig. 8 summarizes the symbolic expressions that appear in Fig. 5.

First, in the initial state, SEQC is in the STAR state. When an ATM cell including the SAR-P DU is input, it determines whether the SC of the SAR-P DU received this time is valid or invalid (invalid / valid). This judgment is made based on the SAR-PDU valid / invalid information given by SN CHK. SAR—If the header of the PDU contains an error and cannot be corrected, the SAR_PDU received this time is considered invalid. Then, the SAR—PDU (ATM cell) PDUr received this time is discarded. Then, it waits in the START state until the first valid SAR-PDU is input. When valid SAR-PDU is input, this SAR-PDU (PDUr) is stored in ST, and the state transits to OUT-OF-SYNC. In the OUT—OF—S YNC state, the SC of the received SAR—P DU is the force that is continuous with the SC value of the S AR—P stored in the ST, that is, SC r = SC st Judge whether it is +1 or not, and if not continuous, discard the SAR-PDU stored in ST and store the SAR-PDU received this time in ST. In this way, the state stays in the OUT-OF-S YNC state until a SAR-P DU having an SC continuous with the SAR-P DU stored in the ST is received. If an invalid SAR-P DU is received in the OUT-OF-S YNC state, the invalid SAR-P DU received this time is discarded, and the SAR-P stored in the ST is discarded. Discard the DU and return to the START state.

In the OUT—OF—S YNC state, the SC of the SAR—PDU received this time is continuous with the SC of the SAR—P DU stored in the ST, that is, SC r = SC st + 1. In this case, the SAR-PDU stored in the ST is written into the RBUF, and the SAR-PDU received this time is stored in the ST. Then, the state shifts to the SYNC state. In the S YNC state, it is determined whether the SC of the SAR-P DU received this time is a continuous SC with the SAR-P DU stored in the ST, and if it is determined that the SC is continuous. Writes the SAR-PDU stored in the ST into the RBU F and writes the SAR-PDU received this time into the ST. Then, if the SC of the received SAR-P DU is continuous with the SC of the SAR-P DU stored in the ST, the state changes to the SYNC state. Then, the operation of sequentially writing SAR-PDU to RBUF is performed.

In the SYNC state, if the SC of the SAR-PDU received this time is not continuous with the SC of the SAR-PDU stored in the ST, the SAR-PDU stored in the ST is replaced with the RBU. In addition to writing to F, the currently received SAR-PDU is written to S #, and the state transits to OUT-OF-SEQUUENCE state. If the SAR-PDU received this time is invalid, the state transits to the INVALID state. In the OU T — OF — S EQUE NCE state, if the SC of the SAR — PDU received this time is continuous with the SAR — P DU SC recently written to the RBU F, the S stored in the ST Discard the AR-PDU and store the received SAR-PDU in the ST and return to the SYNC state. If the SC of the received SAR-PDU is continuous with the SC of the SAR-PDU recorded in the ST, the dummy SAR-PDU is written to the RBUF, and then Write the SAR-PDU stored in the ST to the RBUF, store the SAR-PDU received this time in the ST, and return to the SYNC state. Alternatively, if the SC of the received SAR-P DU is the number obtained by adding "2" to the SC of the SAR-P DU recently written to the RBUF, the SAR-P DU stored in the ST Is written to RBU F, and the SAR-PDU received this time is written to ST, and returns to the SYNC state. In the OUT—OF—SE QUENCE state, if the received SAR—P DU is invalid, the SAR—P DU stored in the ST is discarded, and the SAR—P DU received this time is also discarded. To return to the ST ART state. The SAR received this time—the SAR that the PDU SC recently wrote to the RB UF—the one that added “1” to the SC of the PDU, the one that added “2”, or the SAR stored in the ST— To P DU SC If it is not one of the ones with "1" added, the SAR-PDU stored in the ST is discarded, the SAR-PDU received this time is stored in the ST, and the OUT-OF-SYNC state is entered. Move to

In the case of transition to the INVALID state, if the SAR-P DU received in this state is invalid, the SAR-P DU stored in the ST is discarded, and the SAR-P DU received this time is also discarded. To return to the STAR state. If the SC of the received SAR-P DU is the SC of the SAR-PDU recently written to RBUF plus "1", the SAR-P DU stored in the ST is discarded, The SAR-P DU received this time is stored in the ST and returns to the SYNC state. Also, this time you received 31 1? If the 3rd of 01; is the SAR—P DU SC that was recently written to RBUF plus “2”, then the SAR—P DU stored in ST is written to RBUF, and the S received this time AR—Stores P DU in ST and returns to SYNC state. In the INVALID state, the received SAR—P DU SC has recently written to the RBUF. SAR—P DU SC plus “1”. Then, the SAR_PDU stored in the ST is discarded, the SAR_PDU received this time is stored in the ST, and the state returns to the OUT-OF-SYNC state.

FIG. 6 is a block diagram showing the configuration of the SCCHK of the FSN.

The difference from the RSNA case is that there is no ST. (Since there is no ST, there is no SC st of SCREG. However, in the OUT-OF-SE QU E NC E state, the last valid SAR-P DU received. OUT— OF— SEQUENCE, in the INVALID state, which caused the transition from the SYNC state to these states, just before SAR— PDU There is an SC pr register that indicates the SC of the received SAR-P DU.) In the case of FSNA, the write decision is made by comparing the SC of the SAR-PDU that has just arrived with the SC (SCac) of the SAR-PDU recently written to the RBUF. If a cell loss is detected, it is necessary to write the dummy cell and the cell just received into the RBUF at once. Therefore, it is necessary to hold the cell just received until the dummy cell is written to the RBU F, and this is done by the C RBU F (Current Buffer).

First, SAR-PDU valid / invalid information is input to SEQC from SNCHK, and ATM cells (including SAR-PDU) are input to SEL from the ATM network. The S EQ C contains the SAR—P DU valid / invalid information and the S—A of the last received S—A PDU and the S—A of the recently written S—P—D DU stored in the SC REG. With reference to the value, it is determined whether or not the SAR-PDU of the ATM cell input to the SEL is to be written to the RBUF. Then, based on the FSNA, the SEQC sends a selection signal to the SEL to output the ATM cell, and also provides a write control signal to the RBUF to allow only the SAR-PDU portion of the ATM cell to be output. Control to write to RBUF. S EQC, when the ATM cell is missing is found from inspection of the SC, _c 7 for writing to RBU F a dummy datum generated by DUMG EN selected in SEL is the FSNA FIG. 9 is a state transition diagram of SEQC according to FIG.

The meaning of each symbol in the figure is as shown in the table of FIG. FS NA is similar to RSNA in that processing proceeds while transiting between the five states of START, OUT-OF-SYNC, SYNC, OUT-OF-SEQUENCE, and INVALID. S EQ C is initially in the START state. S In the TART state, if the received SAR-PDU is invalid, continue to discard the SAR-PDU, stay in the SART state, and wait until a valid SAR-PDU is input. I have. When a valid SAR—P DU is input, this valid SAR—P DU is discarded as a SAR—P DU for which continuity has not yet been confirmed, and the state is OUT—OF—S YN Move to the C state. In the OUT—OF—S YNC state, when a new SAR—P DU is received, whether the SC of this SAR—PDU and the SC (SC pr) of the immediately preceding SAR_P DU are continuous Then, if they are not consecutive, the newly received SAR-PDU is discarded and stays in OUT-OF-SYNC state. If the newly received SAR-PDU is invalid, discard the newly received SAR-PDU and return to the START state. If it is determined that the SC of the newly received SAR—P DU is continuous with the SC of the previously received SAR—P DU, the newly received S AR—P DU is stored in the RB UF. At the same time as writing, shift to the S YNC state. In the S YNC state, the SC of the newly received SAR-P DU is compared with the SC of the SAR-P DU written in the RB UF. Write SAR-P DU to RBUF. During this time, the state remains in the SYNC state. When an invalid SAR-PDU is received in the SYNC state, the SAR-PDU received this time is written to the RBUF and the state transits to the INVALID state. If it is determined that the newly received SAR—P DU SC is not continuous with the SAR—P DU SC written in RBU F, the newly received SAR—PDU is written in RB UF, OUT— OF— S £ 0 £ 1 ^. Move to £ state _(in OUT-OFSEQUENCE state, newly received S If the AR-P DU is invalid, discard the newly received S AR-P DU and return to the START state. The newly received SAR-PDU is valid, and the SC is connected to the SAR-PDU SC that was written to RBU F immediately before the SAR-PDU that was written to RBUF immediately before. In this case, the newly received SAR-PDU is discarded, and the state returns to the SYNC state. If the SC of the newly received SAR-P DU is "1" larger than the SC of the SAR-P DU previously written to the RB UF, it is determined that a cell has dropped out and the data Is written to the RBUF, and then the received SAR_PDU is written to the RBUF to return to the SYNC state. If the SC of the newly received SAR-P DU is "2" larger than the SC of the SAR-P DU written to the RBUF just before the SAR-P DU written to the RBU F immediately before Then, the newly received SAR-PDU is written to RBUF, and the state returns to the SYNC state. If it is determined that the SC of the newly received SAR-P DU does not satisfy any of the above conditions for returning to the S YNC state, the newly received S AR-P DU is discarded, OUT-◦ F- _c to move to S YNC state

If the newly received SAR-PDU is invalid in the I NVA LID state, the newly received SAR-PDU is discarded, and the state returns to the START state. If the newly received SAR—P DU is valid, and the SC is written to the RBUF immediately before the SAR—the SAR that was written to the RBUF immediately before the PDU—AR—is greater than the SC of the P DU by “1” Discards the newly received SAR-P DU and returns to the SYNC state ₍ the SC of the newly received SAR-P DU is immediately before the SAR-P DU written to the RBU F. If the SAR—PDU is larger than the SC by “2”, write the newly received SAR—P DU to RBUF and Return to YNC state. In the INVALID state, if none of the above conditions for returning to the SYNC state are satisfied, the newly received SAR-PDU is discarded, and the state shifts to the OUT-OF-SYNC state. .

R SNA and F SNA have the following advantages and disadvantages, respectively.

(1) Regarding the delay added by the processing, in the RS NA, the SAR-PDU arriving at RAA L 1 is always temporarily stored in the ST, and "accept" or "" after waiting for the next SAR-P DU to arrive. Because "discard" is determined, there is always a delay in writing to RBUF. This delay depends on when the next SAR-PDU arrives, and depends on the ATM cell generation interval determined by the bandwidth of the CBR traffic and the delay added during transmission within the ATM network. Become. On the other hand, in F SNA, the decision of “accept” or “discard” for the arriving SAR-PDU is made immediately, so there is no algorithm-specific delay caused by adopting F S NA. CBR traffic is a service that is sensitive to the amount of delay as described above, and it can be said that FSNA is superior from the viewpoint of delay.

(2) The detection capability of SC continuity abnormality is described using the following example.

(a) When it is determined that cells are duplicated and mixed

Received S AR — P DU SC: ·-1 2 3 4 4 5 6 7 0--· The second cell with SC = 4 is judged to be duplicated (mixed).

(b) When judging that a cell is dropped

Received S AR—SC of PDU: 1 2 3 4--3 4 5 6 7

Between SC-4 and 3, 6 cells (SN = 5, 6, 7, 0, 1, 2) It is judged that is dropped.

(c) When it is determined that the sequence is maintained

Receiving S AR — P DU SC: · · · 1 2 3 4 3 6 7 0 1-· · · Cells with SC = 3 sandwiched between SC-4 and 6 are judged to have SC = 5.

Both have the same capability for cell loss, and can detect up to six consecutive cell loss as shown in (b) above. However, when cell loss is found in the FS NA, the cell arriving immediately after the cell loss (the second SC = 3 cell in (b) above) has already been accepted by the RBUF, so the original cell A dummy cell cannot be inserted at the place where it was dropped. On the other hand, both algorithms are equivalent in terms of the detection capability regarding cell overlap (contamination) (one duplicated. Contamination is detected. See (a) to (c) above). There is a difference in discard ability. Explaining in (a) above, the cells considered to be mixed or duplicated in (a) above are those with the second SC = 4 (hereinafter referred to as cells to be discarded). In RS NA, when SC = 5 arrives at RAA L1, the cells to be discarded are temporarily stored in ST, so the cells to be discarded are not written by writing this to R BUF. can do. However, in the case of force S, FS NA, the cell with SC = 5 arrives at R AAL1, and the previous cell with SC = 4 (that is, the cell to be discarded) is an overlapped or mixed cell due to the algorithm. It turns out that the cells to be discarded have already been written to RBUF. However, since it was found that extra cells were mixed in, if the found (one) SAR-PDU was not discarded, the write bandwidth to the RBU F would be larger than specified, and in the worst case the RBUF Causes an overflow. Therefore, one Generally, in FSNA, the cell that arrives next to the cell to be discarded (SC = 5 in this example) is discarded to protect the band. The reason is that in order to discard cells with SC = 4 written in RBUF, the write address of RBUF (overwriting the next cell on top of the cell with SC = 4) or read This is because it is necessary to control the address (skipping cells with SC == 4), and a complicated memory write / read control circuit is required, which cannot be realized by simply operating the RBUF as a FIFO. . From the above, RSNA has a high ability to eliminate mixed cells, but has the characteristic of always causing delays due to algorithms.FSNA does not generate any algorithm-specific delay, but eliminates mixed cells themselves. The feature is that cells cannot be inserted.

Since the frequency of cell loss, duplication, and mixing is considered to be not so high under normal operating conditions, consider introducing an SC inspection algorithm from the viewpoint of protecting against infrequent events when such events occur. However, RSNA, which has a constant delay, is difficult to apply. In general, slower CBR services are more susceptible to delay, so sufficient consideration is needed for applying RSN A to slower services.

On the other hand, FSNA cannot discard cells that should be discarded when an abnormal event occurs, and discards cells that seem to be normal immediately after that. Even if a dummy cell is inserted, the correct position cannot be obtained. In particular, when mixed cells occur, the bandwidth of the CBR service is preserved, but reproduced non-ATM traffic is mixed with meaningless data and dropped out of meaningful data. There are concerns about the effects of the loss of data and loss of synchronization with services.

From the above, there is no delay due to the algorithm in the steady state, and An algorithm that can discard cells to be discarded (even if processing delays occur) is desirable. Disclosure of the invention

An object of the present invention is to provide a cell inspection apparatus and method which can correctly discard a cell to be discarded in an abnormal state without delay in a normal state. The checking device of the present invention checks the continuity of ATM cells received at a constant transmission rate from an ATM network, and accepts the user data to a reassembly buffer for reproducing user data contained in the ATM cells. A temporary storage means for storing received ATM cells, a sequence number of the ATM cells written in said temporary storage means, and a recently written in said reassembly buffer. Sequence number storage means for storing the sequence number of the ATM cell, and if the sequence number of the ATM cell received this time and the sequence number of the ATM cell recently received in the reassembly buffer have continuity, Write the received ATM cell directly to the reassembly buffer, and if the continuity is broken, write the ATM cell received this time to the temporary storage means, and then receive It was by examining the sequence number of the ATM cells, or writes the ATM cell Le stored in the temporary storage means to the reassembly buffer, and a controlling means for determining whether to discard.

The checking method of the present invention checks the continuity of ATM cells received at a constant transmission rate from an ATM network, and accepts or discards the user data in a reassembly buffer for reproducing user data contained in the ATM cell. A test method for determining whether or not the received ATM cell is stored; and (b) a method for storing the ATM cell stored in the step (a). A step of storing the sequence number of the ATM cell recently written in the reassembly buffer, and (c) the sequence number of the ATM cell received this time and the sequence of the ATM cell recently received in the reassembly buffer. If the sequence number has continuity, the ATM cell received this time is written directly into the reassembly buffer. If the continuity is broken, the ATM cell received this time is stored in step (a). Checking the sequence number of the next received ATM cell and determining whether to write or discard the ATM cell stored in step (a) into the reassembly buffer. .

According to the inspection apparatus or the inspection method of the present invention described above, in the normal state where continuity is maintained between ATM cells, the ATM cells are written directly to the reassembly buffer without temporarily storing the ATM cells. There is no processing delay like the conventional RSNA to store.

When the continuity of ATM cells is broken, the ATM cells are temporarily stored, and the sequence number of the next incoming ATM cell is checked to determine what kind of failure has occurred. After processing, the ATM cell to be discarded is written into the reassembly buffer unlike the conventional FSN, and the subsequent normal ATM cell is not discarded. ATM cells to be discarded can be discarded, and ATM cells to be written to the reassembly buffer can be correctly written. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram showing the configuration of an ATM network using AAL1.

FIG. 2A is a diagram showing a configuration of an ATM cell and a SAR-PDU. FIG. 2B is a table listing the meaning of each symbol in FIG. 2A.

FIG. 3 is a block diagram showing the configuration of RAAL1.

FIG. 6 is a block diagram showing the configuration of the FSCNA SCCHK.

FIG. 7 is a state transition diagram of SEQC in accordance with FSNA.

FIG. 8 is a table listing the meanings of the symbols used in the state transition diagrams of FIGS. 5 and 7.

FIG. 9 is a block diagram showing a hardware configuration of SCCHK for realizing ASNS according to an embodiment of the present invention.

FIG. 10 is a diagram showing a state transition diagram of an ASA according to an embodiment of the present invention.

FIG. 11 is a flowchart showing a process in the START state of the ASA according to an embodiment of the present invention.

FIG. 12 is a flowchart showing a process in the OUT-OF-SYNC state of ASNA according to an embodiment of the present invention.

FIG. 13 is a flowchart showing processing in the SYNC state of the ASNA according to an embodiment of the present invention.

FIG. 14 is a flowchart showing a first mode of processing in the OUT-OF-SEQUENCE state of the ASA according to an embodiment of the present invention.

FIG. 15 is a flowchart showing a second mode of the process in the OUT-OF-SE QUENCE state of ASNA according to one embodiment of the present invention. You.

FIG. 16 is a flowchart showing a process in the I NVALID state of the ASA according to an embodiment of the present invention.

FIG. 17 is a diagram showing an operating state of the ASA N according to an embodiment of the present invention in a normal state.

FIG. 18 is a diagram showing an operation state when cells of ASNS according to an embodiment of the present invention are mixed.

FIG. 19 is a diagram showing an operation state in a case where a cell is dropped out of the ASA and insertion of dummy data is performed according to an embodiment of the present invention.

FIG. 20 is a diagram illustrating an operation state when an error occurs in the SC of the ASN A according to the embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

An SNA that is an embodiment of the present invention is hereinafter referred to as an Adaptive Robust SN algorithm (hereinafter, referred to as an ASN A). FIG. 9 is a block diagram showing a hardware configuration of SCCHK for realizing ASNS which is one embodiment of the present invention.

In SCCHK that implements ASNA, the wiring that directly inputs the SAR-P DU (actually an ATM cell) input from the ATM network to the SEL, and the current wiring that stores the currently received SAR-P DU A reception PDU buffer CRBUF and a reception SAR-P DU-time storage unit ST for storing the SAR_P DU received immediately before the currently received SAR-P DU are provided.

SEQC obtains SAR-PDU valid Z invalid information. SEQC uses this SAR-P DU valid / invalid information and S stored in SCREG. By referring to the SAR SC of the PDU and the SC of the PDU written in the RBU F in the T, it is determined whether the ATM cell has been lost or duplicated, and which of the data input to the SEL is determined. Selector signal P DU— SEL is input to SEL to specify whether or not to send to RBUF. For SEL, SAR-PDU stored in ST, SAR-PDU stored in CRBUF, SAR-PDU directly input from ATM network, and dummy data generated by DUMGEN Is entered. The SEQU C determines which data should be written to the RBUF according to the ASNA described in detail below, and controls the SEL to write the appropriate data to the RBUF.

The SEQU C gives the ST a write enable signal WE st and a read enable signal RE st to write the SAR-P DU to the ST and the SAR-P from the ST. Controls DU reading.

In addition, in the case of ASNA, if a cell loss is detected, the dummy cell, the cell in the ST, and the cell just received are subjected to certain conditions after receiving a cell that has lost continuity or an invalid cell. When a cell that satisfies the condition is received, the cell in s T and the cell just received must be written to the RBUF at once.

Therefore, it is necessary to hold the cell just received until a dummy cell or a cell in the ST is written to the RBUF, and this is done by the C RBU F (Current Buffer Buffer) shown in Fig. 9. is there. C RBUF may be a buffer with the same structure as ST, but ST is to hold its contents until the next cell arrives, whereas CRBU F waits only for batch writing. However, C RB UF does not add a constant delay like ST in the case of RSNA. FIG. 10 is a diagram showing a state transition diagram of ASNA which is one embodiment of the present invention.

In the same figure, the meaning of each symbol in the figure is the same as in Table 1 in FIG.

Initially, S EQ C is initially in the START state. In the START state, when a valid cell arrives (a cell with an SN determined to be valid by S NCHK; the same applies hereafter), the cell is stored in ST and stored in the register SC st of SCREG. The SN of the cell is stored, and the state transits to the OUT-OF-SYNC state. If the arriving cell is not valid (invalid), the cell is discarded (not stored in the ST) and remains in the START state.

In the OUT-OF-SYNC state, a valid cell has been received, but the continuity of SC has not yet been detected. In the OUT—OF—S YNC state, a valid cell arrives and the SC of the arriving cell is larger than the value of the SC of the SAR—P DU stored in the ST by “1”, ie, SC st + 1. If there is, the cell in the ST and the valid cell just received are written to the RBU F, and the SC of the valid cell just received is stored in the register SC ac of SCREG. After that, it shifts to the SYNC state.

In the OUT—OF—S YNC state, when a valid cell arrives but its SC is a value other than SC st + 1, the ST and SC st are overwritten with the received valid cell, and OUT—OF—S YNC Stay in the state. That is, valid cells originally stored in the ST are discarded. Nothing is written to RBU F. If an invalid cell arrives in the OU T — OF — SYNC state, clear the ST and transit to the START state. The valid cells stored in the ST are discarded. The S YNC state is a state in which SC continuity is detected. In the SYNC state, if a valid cell is received and the SC is the value of the SC of the SAR-PDU recently written to the RBU F plus "1", that is, SC ac + 1 Then, the cell is written to the RB UF, SC ac is updated by the SC of the receiving cell, and the cell remains in the SYNC state. When a valid cell is received and the SC is a value other than SC ac + 1, the received cell is stored in ST, the SC of the received cell is stored in SC st, and the OUT—OF—SE QUENCE state is set. Transition to. When an invalid cell is received, the received cell is stored in the ST, and the state transits to the INVALID state.

In the I N V A L ID state, an invalid cell stored in ST

A decision is made to abandon the acceptance to the RBUF. If an invalid cell is received in the I NVAL ID state, ST is cleared and the state transits to the START state. Nothing is written to RBUF. When a valid cell is received and the SC is SC ac + 1, the invalid cell stored in the ST is determined to be a mixed cell, the ST is cleared, and the valid cell just received is set to RBUF. And the SC is stored in SC ac, and the state transits to the SYNC state. Invalid cells are discarded. If a valid cell is received and its SC is S C a c + 2, it is determined that the invalid cell stored in ST was originally a valid cell but could not be corrected.

(1) Writing valid cells stored in ST to RBUF

(2) Write the currently received valid cell to RBUF and store the SC of that cell in SCac.

To make a transition to the SYNC state.

In the INVALID state, if a valid cell is received and the SC is neither SC ac + 1 nor SC ac + 2, the continuity of SC is completely Judge as lost, overwrite ST and SC st with the contents of the valid cell just received, and transit to OUT-OF-SYNC state. Nothing is written to RBUF.

In the OUT—.OF—S EQUENC E state, the discontinuity of the SC is lost, and a decision is made to accept and discard the non-consecutive valid cells stored in the ST into the RBUF. When an invalid cell is received in the OUT-OF-SEQUENCE state, ST is cleared and the state transits to the START state. Nothing is written to RBUF. If a valid cell is received and the SC is SC ac + 1, the valid cell stored in ST is determined to be a mixed cell, ST is cleared, and the valid cell received just now is RBUF Then, the SC is stored in SC ac and the state transits to the SYNC state. The valid cell stored in ST will be discarded. When a valid cell is received and the SC is SC st + 1, the valid cell recently written in RBUF (the SC is represented by SC ac) and the valid cell stored in ST are It is determined that cell loss has occurred between

(1) Writing dummy cells to the RBUF for the number of cells determined to be missing, calculated from the difference between S C a c and S c st

(2) Write valid cells stored in ST to RB UF

(3) Write the valid cell just received to RBUF and store the SC of that cell in SCac

To change to the S YNC state.

When a valid cell is received and its SC is SC ac + 2, the valid cell stored in the ST has an abnormal value for some reason because it was originally a continuous SC. Judge that

(1) Write valid cells stored in ST to RBUF (2) Write the valid cell just received to RBUF and write the SC of that cell to SC ac.

And transit to the S YNC state.

If a valid cell is received and the SC is not one of SC ac + l, SC st + l, and SC ac + 2, it is determined that the continuity of the SC has been completely lost, and ST and Overwrites the contents of the valid cell just received to SC st and transits to OUT-OF-S YNC state. Nothing is written to RBUF. Each condition judgment indicated by the number in parentheses is performed in the order described. However, in the above condition determination, the relationship between the S C of the currently received valid cell (hereinafter referred to as S C r) and S C st, S C a c is

S C r = S C st + l = S C a c + l

Can also occur. In the above condition judgment, in the above description, the judgment of S Cr = S C a c + l is prioritized, but the judgment of S C r = S C st +1 may be prioritized. If the priority of S C r 2 S C s t +1 is given priority,

Receiving S AR—SC of P DU: ·-1 2 3 4 4 5 6 7 0-· · If SC = 4 and SC = 4 between the first SC = 4 and the second SC = 4 , 7, 0, 1, 2, and 3 are determined to have been dropped,

(1) Write 7 dummy cells to RBUF

(2) Writing valid cells stored in ST to RBUF

(3) Write valid cell just received

After that, the state transitions to the S YNC state. Therefore, even if SCs of the same sequence are received, by changing the priority of the judgment,

(a) One mixed cell

(b) 7 cells dropped A completely different decision is made.

In applying the actual algorithm, the priority is selected in consideration of which of (a) and (b) above is more likely to occur.

First, when the SEQUC is in the initial state, it is determined in a step S1 whether a SAR-PDU has been received. If the SAR-PDU has not been received, the process of step S1 is repeated to wait for the SAR-PDU to be received. In step S1, when SAR-PDU is received, in step S2, the SC of the currently received SAR-PDU (PDUr.SC) is set in SCr. Then, in step S3, it is determined whether SCr is valid or invalid based on the SAR—PDU valid / invalid information from the SNCHK. If it is determined in step S3 that the SC r is not valid, in step S5, the currently received SAR—P DU is discarded, and the process returns to step S1, where the next SAR—P DU is received. Wait for it to be done. If it is determined in step S3 that SC r is valid, in step S4, the currently received SAR—P DU is stored in the ST, and the SC r is stored in the ST—the SAR— Set to SC st that holds SC of PDU. Then, proceeding to step S6, the state transits to the OUT-OF-SYNC state.

In the OUT-OF-SYNC state, first, in step S10, it is determined whether or not a SAR-PDU has been received. If SAR-PDU has not been received, repeat step S1 and wait for SAR-PDU to be received. Step S10 confirms that the SAR—PDU has been received Then, in step SI1, SC of the received SAR-P DU (P DU r .SC) is set in SC r. Then, in step S12, it is determined whether the SC r force S is valid or invalid based on the SAR-PDU valid / invalid information from SNCHK. If the SC of the SAR-P DU received this time is not valid, the process proceeds to step S13, where the SAR-P DU stored in S # is discarded, and the SAR_P DU received this time is also deleted. Discard, step S 1

At 4, return to the START state.

If it is determined in step S12 that SCr is valid, it is determined in step S15 whether SCr = SCst + l. This is to determine whether the SC of the SAR_PDU received this time is continuous with the SC of the SAR-PDU stored in the ST. Steps

If the result of the determination in S15 is "NO", the flow proceeds to step S16, the SAR-PDU received this time is stored in ST, and the flow returns to step S10.

In step S 15, the S 8 1 received this time? 0 If 3 is stored in the 3 T, the S AR— If it is determined that it is continuous with the SC of the PDU, in step S 17, first, the S AR— Write the PDU to RBUF, and then write the SAR-PDU received this time to RBUF. Then, the process proceeds to step S18 to shift to the SYNC state. FIG. 13 is a flowchart showing a process in the SYNC state of the ASA according to an embodiment of the present invention.

In the SYNC state, S EQ.C determines whether or not the SAR-P DU has been received in step S20, and waits until the SAR-P DU has been received. If it is determined in step S20 that the SAR—P DU has been received, in step S21, the SAR—P which has been received this time by SC r Set the DU SC (P DU r. SC). Then, in step S22, it is determined whether SC r is valid or invalid based on the SAR_PDU validity / invalidity information from the SNCHK. If it is determined that the SC r is not valid, the process proceeds to step S23, where the received SAR-P DU is stored in the ST, and the SAR-P DU stored in the ST is stored. Set SC r to SC st where SC is set, and in step S24, transition to the INVALID state.

If it is determined in step S22 that SCr is valid, it is determined in step S25 whether or not SCr = SCac + 1. This is to determine whether the SC of the SAR-P DU received this time is continuous with the SC of the SAR-P DU recently written to the RBUF. Here, when numbers from "0" to "7" are used as SC, it is assumed that the number following "7" is "0". If it is determined in step S25 that the SC of the SAR—PDU received this time is continuous with the SC of the SAR—PDU recently written to the RBUF, the process proceeds to step S26. The currently received SAR-P DU is written to the RBU F, and SC r is set to the SC ac in which the SC of the SAR-P DU recently written to the RBU F is to be set. Then, the process returns to step S20, and waits for reception of the next SAR-PDU. In this way, if the SC of the received SAR—P DU is continuous with the SC of the SAR_P DU that has been recently written to the RBUF, that is, if the transfer is normally performed, step S 20 ~ Repeat the processing of step S26, and sequentially write the received SAR-PDU to RBUF.

In step S25, the SC of the SAR—P DU received this time is not continuous with the SC of the SAR—P DU that has recently been written to the RBUF. If it is determined that C r = SC ac +1 is not satisfied, the process proceeds to step S27, where the SAR—P DU received this time is written into ST, and the SC (of the SAR—P DU received this time) is written into SC st. SC r). Then, the flow advances to step S28 to shift to an OUT-OF-SEQUENCE state.

FIG. 14 is a flowchart showing a first mode of the process in the OUT-OF-SEQUEUNCE state of the ASA according to an embodiment of the present invention.

Upon entering the OUT-OF-SEQUENCE state, the SEQC determines in step S30 whether or not the SAR-PDU has been received. Then, the process of step S30 is repeated until SAR-PDU is received. If it is determined in step S30 that SAR—PDU has been received, in step S31, the SC (PDU.SC) of the received SAR—PDU is set to SCr, In step S32, it is determined whether SC r is valid. In the judgment of step S32, the SAR—PDU valid / invalid information notified from the SNCHK is used.

If it is determined in step S32 that SC r is not valid, the process proceeds to step S33, where the S AR—P DU stored in the ST is discarded, and the S AR received this time is discarded. — Discard the PDU. Then, in step S34, the state returns to the START state.

If it is determined in step S32 that SC r is valid, the flow advances to step S35 to determine whether or not SC r = SC ac +1. — It is determined whether the SC of the PDU is continuous with the SAR—PDU SC that has recently been written to the RBUF. If the determination in step S35 is "YES", in step S36, the SAR-PDU recorded in the ST is discarded, and the SAR-PDU received this time is discarded. Write to RBU F. Further, SC r is set in SC ac, and step S

4 Proceed to 3 to return to the S YNC state. This process is performed when one ATM cell is mixed and mixed.

If it is determined in step S35 that SCr = SCC + 1, it is determined in step S37 whether SCR = SCst + 1. That is, it is determined whether or not the SC of the SAR-P DU received this time is larger than the SC of the SAR-P DU stored in the ST by "1". this is,

5 By confirming the continuity between the SAR—P DU stored in T and the currently received SAR—P DU, the ATM cell (S AR—P DU) is placed before the S AR—PDU stored in the ST. ) Is detected. If the determination in step S37 is "YE S", the value of the function NoDUM (SCac, SCst) is set in NoDUM in step S38.

The function NoDUM (SCac, SCst) is a process for calculating the number of dropped ATM cells (SAR-PDU) when a drop is found. A program example of the function NoDUM (SCac, SCst) is shown below.

function NoDUM (SCac, SCst) {

if (SCst-SCac- 1≥ 0) {

return (SCst-SCac-1);

} else {

return (SCst-SCac + 7);

This program calculates the difference between SC (SC st) of SAR—P DU and SAR—P DU SC (SC ac) that has been written to RBUF recently. Calculate the lost ATM cell It estimates the number. For example, 3_Rei at _three "6", SC ac force S

In the case of "2", it means that three ATM cells "3", "4", and "5" have been dropped. Since the judgment formula in the above if statement is "true", SCst-SCac_l = 3 is calculated as the number of dropped cells. For example, in the case of SC st force S "2" and SC ac force S "6", three ATM cells of SC force S "7", "0, ...," "1" are missing. In this case, since the judgment formula of the above if statement is “false”, SCst_SCac + 7 = 3 is calculated as the number of dropped cells.

In this way, the calculated number of dropped cells is set in the variable NoDUM. Then, in step S38, only NoDUM dummy data is written to the RBU F, and then the SAR-P DU stored in the ST is written to the RBU F. Furthermore, the SAR-P DU received this time is also written into the RBUF, the SC (SC r) of the SAR-PDU received this time is set in SC ac, and the process proceeds to step S43 to shift to the S YNC state. .

If the result of the determination at step S37 is "N〇", it is determined at step S39 whether or not SCr = SCac + 2. This is because the SC (SC ac) of the SAR—P DU that was recently written to the RBU F and the SC (SC st) of the SAR—P DU currently written to the ST are not continuous. This is for determining whether or not the SC (SCr) of the received SAR-PDU is continuous with SCac. In the case of “YE S” in step S 39, the SC (SC st) of the S AR—P DU stored in the ST indicates that an error has occurred for some reason, but it is actually normal. SAR—Judges that this is a PDU. Therefore, in step S40, the SAR-PDU stored in the ST is written to the RBU F. Then, the SAR-PDU received this time is written to the RBUF, and the SCa SC r is set, and in step S43, the state transits to the S YNC state.

If the determination in step S39 is "NO", it is determined that two or more cells have been mixed, the SAR—PDU stored in the ST is discarded, and the SAR received this time is discarded. — Store the PDU in ST, set SCr in SC st, and move to OUT—OF—S YNC state in step S42. FIG. 15 is a diagram showing OUT—OF—SE of ASNA according to an embodiment of the present invention.

9 is a flowchart showing a second mode of the process in the QUENCE state.

In FIG. 15, the same steps as those in the flowchart of FIG. 14 are _{denoted by} the same step numbers, and the details of the same steps are omitted. _{C In} the second mode, the valid cell (valid S AR− After receiving the (P DU), in step S37 ', it is determined whether or not the SC of the currently received SAR—P DU and the SC of the SAR—P DU stored in the ST are continuous. Judge. If the result of the determination is “YE S”, in step S 38, the dummy data of the number equal to the number of cells determined to have been lost is written to the RBUF, and then the received SAR—P Write DU to RBU F. If "NO" is determined in the step S37 ', in the step S35', the SC of the SAR-PDU received this time is continuously connected with the SAR-SC of the PDU recently written to the RBUF. It is determined whether or not it is. If the result of the determination in step S35 'is "YES", the SAR-PDU in the ST is discarded, and the SAR-PDU received this time is written to the RBUF. If the determination in step S35 'is "NO", the processing from step S39 is performed. This process is similar to that described in FIG.

As described above, for example, the SC of the received SAR—PDU is “「 · 1 2 3 4 4 5 6 7 0 ··· I, and now SC ac = 4 (first Consider the case where "4"), SC st = 4 (the last "4 ,,)", and SC r = 5. In the first embodiment of FIG. Since the continuity between r and SC ac is observed, in the above example, the result of the determination is “YES.” Therefore, the process proceeds to step S36, and in the above example, SC is the last “4”. In contrast, in the second embodiment of FIG. 15, the continuity of SC r and SC st is determined in step S 37 in the second embodiment of FIG. Therefore, in this case, it is determined that there is continuity between SC r and SC s, and in step S38, SC corresponds to 0 to 7 between the first "4" and the last "4" in the above example. Assuming that the ATM cell is lost, eight dummy data are written.

As described above, any of the processing modes in the OUT-OF-S EQUENC E shown in FIGS. 14 and 15 can be implemented, and the priority of the determination in step S 35 and step S 37 ′ is given. The order should be appropriately determined by a person using this embodiment.

When the SEQUC transitions to the INVALID state, it determines in step S50 whether or not the SAR-PDU has been received, and repeats step S50 until the SAR-PDU is received. In step S50, when SAR-PDU is received, in step S51, the SC (PDU.SC) of the SAR-PDU received this time is set to SCr.

Proceeding to step S52, based on the SAR-PDU valid / invalid information from the SNCHK, it is determined whether the SC (SCr) of the SAR-PDU received this time is valid. If it is determined that SC r is not valid, the process proceeds to step S53, where the SAR—P DU stored in the ST is discarded, and The SAR-PDU received this time is also discarded, and in step S54, the state shifts to the START state.

If it is determined in step S52 that SC r is valid, the process proceeds to step S55 in which SC r is connected to the SC (SC ac) of the SAR—PDU that has recently written to RBUF. Is determined. If it is determined in step S55 that SCr is continuous with SCac, in step S56, the SAR_PDU stored in the ST is discarded and received this time. SAR — Write PDU to RBUF. Then, SCr is set to SAc, and in step S61, the state shifts to the SYNC state. If it is determined in step S55 that SCr is not continuous with SAc, the process proceeds to step S57 to determine whether SCr is larger than SAc by "2". If the decision result in the step S57 is "YES", the SAR-PDU stored in the ST is written to the RBU F, and the SAR-PDU received this time is written to the RBUF, and the SC r is set to SC ac, and in step S61, the state transits to the SYNC state. If the result of the determination is "NO" in step S57, the SAR-PDU stored in the ST is discarded in step S59, and the SAR-PDU received this time is discarded. Write to ST. Then, S Cr is set to S C st, and in step S 60, the state transits to the OUT—OF—SYNC state. FIG. 17 is a diagram showing an operating state of the ASA N according to an embodiment of the present invention in a normal state.

The normal state is when the SAR-PDU of the SC is successively input to the SC CHK. As shown in the upper part of FIG. 17, the SC force S “2”, “3 ,,”, “4, ′”, “5 ,,”, “6”, “7 ,,”, “0 ,,,” SAR-PDUs of 1, 2, and "2" are input to SC CHK in the above order. This place In this case, as shown in the lower part of FIG. 17, ASNA stays in the S YNC state. Also, there is no problem in SC continuity, so nothing is written in ST. Nothing is written to CRBUF, which writes the currently received SAR-PDU. Then, the input SAR-PDU is directly written to RBUF. That is, SAR-PDUs from SC "2" to the next "2" are sequentially written.

As shown in the upper part of FIG. 18, the SCCHK includes SC cards “2”, “3”, “4”, “4” (denoted as 4N), “5”,

SAR-PDU of "6" is input. In the AS NA, the SC is initially in the SYNC state and the SC writes 2 to 4 SAR-P DUs to the RBUF, but upon receiving a mixed cell, it shifts to the OUT-OF-S EQUE NCE state, The mixed cell is written to ST. Next, when the SAR-P DU with SC of "5" is input, the mixed cells in the ST are discarded and the state returns to the SYNC state. Write DU to R BU F. After that, the SAR—PDU after the SC “6” is written to the RBUF as in the normal case. In the case of FIG. 18, CRBUF is not used.

FIG. 19 is a diagram showing an operation state in a case where a cell of the ASAN according to an embodiment of the present invention is dropped and dummy data is inserted.

As shown in the upper part of FIG. 19, the SC CHK receives the SAR—P DU from the SC force S “2” to “4” and then inputs the SC force S “5”, The SAR-PDU of "7" is dropped, and then the SAR-PDU of SC force S "0 ,," and "2" are input. In such a case, the AS NA is initially in the S YNC state and processes the S AR-P DUs from SC cards "2" to "4" in the same way as normal, and writes them to the RBUF. When the SAR—P DU with SC “0” is input, the state of ASNA shifts to OUT—OF—SE QU ENC E state, and the ST receives the SAR with SC “0” this time. — PDU is written. Next, when the S AR—P DU of the SC power S “1” is input, since the SC powers “0” and “1” continue, the number of cells considered to be dropped is calculated. After writing the dummy data, the SAR-P DU with SC power S "0" written to ST is written to RBUF. Furthermore, the SC force "1 ,,, 381-? 0 丫 which was written to the CR BUF is also written to 1 811. Then, the state of the ASNA returns to the SYNC state, and it is the same as the normal state. Then, the SAR-PDU with SC power S "2" received later is written into the RBUF.

FIG. 20 is a diagram illustrating an operation state in a case where there is an error in the SC of the ASNA according to one embodiment of the present invention.

As shown in the upper part of FIG. 20, this case shows a case where two S AR-P DUs of S C force; “7” are successively input to S C C HK. In FIG. 20, the SAR—PDU that is first input to SC CHK among the SAR—PDUs of SC force S “7” at “7-1” and “7—2”, respectively, Shows the SAR-P DU input to SCC HK.

The ASNA is in the S YNC state while the SAR—PDU from SC “2” to “5” is being input, and each SAR—PDU is operated in the same way as normal. Writing to RBU F.

When a S AR—P DU with SC power S “5” is input and then a S SAR—PDU (represented by “7-1”) with SC power S “7” is input, AS NA becomes OUT— Moves to the OF—SE QU E NCE state and writes the received SAR—PDU of “7-1” to the ST. Next, when the SAR—P DU (represented by “7-2”) of the SC force S “7” is input, the SAR of the SC force S “5” that was recently written to the RBUF— Detected that the SC of PDU and the SAR of "7-2" were skipped by one, and the SC of "7-1" SAR-PDU was originally "6". Judge that the thing is "7" for some reason. Then, after receiving the SAR-P DU of "7-2" and performing the above determination, the SAR-P DU of "7-1" stored in the ST is written to the RBU F. Write the SAR-PDU of "7-2" written in C RBU F to RBUF and return to SYNC state.

Thereafter, in the SYNC state, the received SAR-PDUs are sequentially written to the RBUF as in the normal state.

As is clear from FIGS. 17 to 20, in the SYNC state, which is the highest in frequency, ASNA exhibits the same performance as FSNA, and no delay is added by the algorithm. Also, in the abnormal state, the cell to be discarded can be discarded since the next arrival cell is waited for using ST as in R SNA before accepting / discarding to RBUF. When returning from the other state to the SYNC state, if the contents of ST should be written to RBUF, they are written together with the received PDU, so the delay performance at this time is equivalent to that of FSNA.

From the above, AS NA is AS NA = FS NA> RS NA in terms of delay performance, and AS NA is two RS NA> FS NA in terms of discarding ability, which indicates that the overall performance is higher than RS NA and FS NA. You can play. Industrial applicability

According to the present invention, ATM traffic transmitted from an ATM network at a constant speed can be converted into non-ATM traffic and transferred to a non-ATM terminal. Therefore, even when the ATM network is introduced and the ATM network and the non-ATM network are mixed, it is possible to smoothly introduce the ATM network without lowering the service to the user.

Claims

The scope of the claims

1. A tester that checks the continuity of ATM cells received from the ATM network and determines whether to accept or discard the user data in a reassembly buffer for reproducing the user data contained in the ATM cell. A temporary storage means for storing the received ATM cells;

Sequence number storage means for storing the sequence number of the ATM cell written in the temporary storage means and the sequence number of the ATM cell recently written in the reassembly buffer;

If the sequence number of the ATM cell received this time and the sequence number of the ATM cell recently received in the reassembly buffer have continuity, the ATM cell received this time is written directly to the reassembly buffer, and the continuity is broken. In this case, the ATM cell received this time is written in the temporary storage means, the sequence number of the next received ATM cell is checked, and the ATM cell stored in the temporary storage means is stored in the reassembly buffer. Control means for deciding whether to write or discard;

An inspection apparatus comprising:

2-Determine whether the received ATM cell is valid / invalid based on information indicating whether or not the sequence number of the received ATM cell contains an error, and determine whether or not to write to the reassembly buffer. The inspection device according to claim 1, wherein the inspection device is an element.

3. The control means, if the continuity of the ATM cell is broken, the sequence number of the next received ATM cell and the latest reassembly buffer. The ATM cell stored in the temporary storage means is determined to be a cell to be discarded when continuity is found between the ATM cell and the sequence number of the ATM cell written to the ATM cell. Inspection equipment.

4. The control means, if no continuity is found between the sequence number of the next received ATM cell and the sequence number of the ATM cell recently written to the reassembly buffer, If there is continuity between the first sequence number of the ATM cell obtained and the second sequence number of the ATM cell stored in the temporary storage means, the ATM cell recently written to the reassembly buffer and the temporary storage means 3. The method according to claim 3, wherein it is determined that an ATM cell loss corresponding to a difference between the first sequence number and the second sequence number between the stored ATM cell and the ATM cell has occurred. The inspection device according to the item.

5. The system according to claim 4, further comprising: dummy data generating means for generating dummy data, wherein the same number of dummy data as the number of ATM cells determined to have been dropped is written to said reassembly buffer. The inspection described in section

6. The control unit, if continuity is not found between the sequence number of the next received ATM cell and the sequence number of the ATM cell stored in the temporary storage unit, If it is considered that the sequence number of the ATM cell and the sequence number of the ATM cell recently written in the reassembly buffer have continuity, the ATM cell stored in the temporary storage means has inherent continuity. Judge as an ATM cell The inspection device according to claim 1, wherein

7. The inspection apparatus according to claim 1, wherein the service of the constant transmission rate ATM network is a CBR service.

8. The inspection apparatus according to claim 7, wherein the service of the ATM network is a service provided by AAL1 using SAR-PDU.

9. selecting means for selecting one of the ATM cell received next to the ATM cell, the ATM cell stored in the temporary storage means, and the dummy data generated by the dummy data generating means;

6. The inspection apparatus according to claim 5, wherein writing to the reassembly buffer or discarding is performed by switching an output of the selection unit.

10. The selecting means sequentially switches between the next received ATM cell, the ATM cell stored in the temporary storage means, and the required number of dummy data, and performs the reassembly. 10. The inspection device according to claim 9, wherein writing is performed to a buffer.

1 1. further comprising a current cell storage means for storing the next received ATM cell;

ATM cells stored in the temporary storage means, dummy data generated by the dummy data generation means, and the next received AT 10. The writing method according to claim 9, wherein when writing all the M cells to the reassembly buffer, the timing of writing the ATM cells stored in the current cell storage means to the reassembly buffer is adjusted. Inspection equipment.

1 2. A test method that checks the continuity of ATM cells received from the ATM network and determines whether to accept or discard the user data in the reassembly buffer for reproducing the user data contained in the ATM cell. So,

(a) storing the received ATM cells;

(b) storing the sequence number of the ATM cell stored in step (a) and the sequence number of the ATM cell recently written in the reassembly buffer;

(c) If the sequence number of the ATM cell received this time and the sequence number of the ATM cell recently received by the reassembly buffer have continuity, write the ATM cell received this time directly into the reassembly buffer, and If the cell is violated, the currently received ATM cell is stored in step (a), the sequence number of the next received ATM cell is checked, and the ATM cell stored in step (a) is stored. Deciding whether to write or discard the reassembly buffer;

An inspection method, comprising:

1 3. Determine whether the received ATM cell is valid / invalid based on information indicating whether or not the sequence number of the received ATM cell contains an error, and determine whether or not to write to the reassembly buffer. The inspection method according to claim 12, characterized in that the inspection method is used as a judgment factor.

1 4. If the continuity of the ATM cell is broken in step (c), the sequence number of the next received ATM cell and the sequence number of the ATM cell recently written in the reassembly buffer are used. 13. The detection method according to claim 12, wherein when continuity is found in the cell, the ATM cell stored in the step (a) is determined to be a cell to be discarded.

1 5. In the step (c), if no continuity is found between the sequence number of the ATM cell received next and the sequence number of the ATM cell recently written in the reassembly buffer, If there is continuity between the first sequence number of the received ATM cell and the second sequence number of the ATM cell stored in the step (a), the ATM cell which has been recently written to the reassembly buffer and the step And determining that an ATM cell loss corresponding to the difference between the first sequence number and the second sequence number has occurred between the ATM cell and the ATM cell stored in (a). Inspection method according to item 14 of the scope.

1 6. The method further comprises the step of generating dummy data,

16. The inspection method according to claim 15, wherein the same number of dummy data as the number of ATM cells determined to be dropped are written to the reassembly buffer.

1 7. In the above step (c), if continuity is not found between the sequence number of the next received ATM cell and the sequence number of the ATM cell stored in step (a), A received next If it is considered that the sequence number of the TM cell and the sequence number of the ATM cell recently written in the reassembly buffer have continuity, the ATM cell stored in step (a) has continuity by nature. The inspection method according to claim 12, wherein the inspection method is determined to be an ATM cell.

18. The inspection method according to claim 12, wherein the service of the ATM network having the constant transmission rate is a CBR service.

19. The inspection method according to claim 18, wherein the service of the ATM network is a service provided by AAL1 using SAR-PDU.

20. A step of selecting any of the next received ATM cell, the ATM cell stored in the step (a), and the dummy data generated in the dummy data generation step.

17. The inspection method according to claim 16, wherein writing to the reassembly buffer or discarding is performed by switching an output of the selection step.

2 1. The selecting step sequentially switches between the next received ATM cell, the ATM cell stored in step (a), and the required number of dummy data to switch the reassembly buffer. 20. The inspection method according to claim 20, wherein the information is written in a file.

2 2. (d) storing the next received ATM cell,

When writing the ATM cell stored in the step (a), the dummy data generated in the dummy data generating step, and the next received AδΤΜ cell to the reassembly buffer, inspection method according to the second 0 term claims, characterized in that adjusting the tie Mi ing to write ATM cells stored in said step (d) in the reassembly buffer ₍