JPH02222243A - Digital exchange system - Google Patents

Abstract

PURPOSE:To accommodate existing terminal equipments into an ATM network and to enhance the throughput at communication by providing a terminal in- network procedure coupling function section converting a procedure of a terminal equipment and a procedure in the network mutually. CONSTITUTION:When an analog signal is outputted from a telephone set terminal equipment 3, an exchange 2 generates a cell with a sequence number written therein and sends the cell to an ATM network 1 and an analog signal is generated when the cell is supplied from the ATM network 1 while referencing the sequence number written in the cell and fed to the telephone set terminal equipment 3. The exchange 2 is provided with a terminal procedure termination function section 4, a terminal in-network procedure coupling function section 5, an in-network procedure termination function section 6 and a cell transfer function section 7 and the terminal in-network procedure coupling function section 5 converts the procedure of the terminal equipment and the procedure in the network mutually. Thus, existing terminal equipments are accommodated in the ATM network and the throughput at communication is enhanced.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to realizing a functional configuration for accommodating terminals in an ATM network that performs communication using cells, which are fixed-length packets. and a digital switching system accommodating terminals requiring high throughput.

(Prior art) Currently, l5DN services that integrate voice and data are being started on subscriber lines, and
ATV technology is beginning to attract attention as the next generation of 5DN.

Since ATM technology assumes a high-quality transmission path, it is possible to simplify protocols that were previously created assuming a low-quality transmission path, and it is also possible to fix the packet length. This reduces the processing required for switching, making it possible to perform processing that was previously performed using software using hardware.

By applying ATV technology to networks, high throughput can be achieved, which makes it possible to provide image communications, especially moving images.

(Problems to be Solved by the Invention) However, the current ATM technology described above has the following problems.

That is, in order to establish ATM technology, research into hardware-based switching technology or simplified protocols is currently underway.

However, with the methods proposed to date, existing terminals cannot be terminated to networks to which ATM technology is applied.

For this reason, there is a strong desire to develop a technology for accommodating existing terminals in a network using ATM technology, but no practical technology has yet been proposed.

In addition, as a simplified protocol, JP-A-62-85
A technique such as No. 532 has been proposed, which supports only error detection between exchanges in a network and does not perform retransmission control, thereby simplifying the protocol.

However, in this method, the error detection function is implemented within the network, so there is a delay due to error detection processing.
There is a problem in that the throughput during communication cannot be increased.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a digital switching system that can accommodate existing terminals in an ATM network and increase communication throughput.

[Structure of the invention]

(Means for solving the problem) Claims 1 to 3 according to the present invention to achieve the above object
In the digital switching method described in , in which the switching operation is realized using fixed-length cells,
A terminal procedure termination function unit that terminates procedures held by the terminal; an intra-network procedure termination function unit that terminates procedures within the network; and a terminal that performs mutual conversion between the procedures held by the terminal and the procedures within the network. It is characterized by having an intra-network procedure coupling function section and an ATM transmission function section having a cell transfer function.

Further, in the digital switching system according to claim 4, in the digital switching system that accommodates terminals that do not perform logical multiplexing and performs transmission on a cell-based basis, a subscriber line accommodating section that accommodates subscriber lines; The subscriber line accommodation section has a function of detecting frames output by a terminal, a function of outputting frames to the terminal, and a function of inputting frames between the frame/cell conversion function section. The frame/cell conversion unit has a function of inputting and outputting frames to and from the subscriber line accommodation unit, a function of identifying the subscriber line accommodation unit that outputs the frame, and a function of identifying the subscriber line accommodation unit that outputs the frame, and A function to generate cell headers for the line accommodation section, a function to allocate frames to cells, a function to output cells to the line, a function to input cells from the line, a function to restore frames from cells, and a function to extract cell headers from cells. It is characterized by having a detection function, a function of recognizing a subscriber line accommodation section to which a frame should be output from a cell header, and a function of outputting a frame to the subscriber line accommodation section.

(Function) In the above configuration, in the digital switching system according to claims 1 to 3, the terminal procedure termination function section terminates the terminal, and the intra-network procedure termination function section terminates the intra-network procedure. The terminal/intra-network procedure coupling function section performs mutual conversion between the procedures possessed by the terminal and the procedures within the network, and the ATM transmission function section performs a cell transfer function.

Further, in the digital switching system according to claim 4, the subscriber line accommodating section accommodates the subscriber line, and the frame/cell converting section generates cells from the frames input to the subscriber line accommodating section. on the line, or reproduce frames from cells received via this line and output them to the subscriber line via the corresponding subscriber accommodation section.

(Example) First, prior to detailed description of the present invention, an outline of a first example of the present invention will be explained.

In the ATM technology to which the digital switching system according to the present invention is applied, information transmission is realized by a cell transfer function. Although the cell transfer function is a function unique to ATM technology,
Similar to existing packet switching, header information added to the beginning of each piece of information is used to determine the route to which the cell should be output.

Unlike existing packet networks, ATM technology has fixed cell lengths, eliminates complicated procedures, and allows the above-mentioned route determination process to be performed in hardware. The delay time is shortened.

However, since ATM technology basically has characteristics similar to existing packet switching, the delay time within the network is related to the situation within the network, specifically the cell accumulation situation in the buffer.
Due to changes in network conditions, the network delay time differs for each cell even in the same connection.

Therefore, when cells are transmitted at regular intervals, the time intervals are not maintained when they are received, resulting in so-called fluctuation. If a cell with this fluctuation is directly converted into a signal on the terminal side, the signal will not be correct.

Therefore, in the present invention, the time stamp function using sequence numbers is used to write the time of each cell at the time of transmission, and the sequence number of each cell is referenced at the time of reception to compensate for cell fluctuations.

FIG. 1 is a block diagram showing an example of an exchange system to which the first embodiment of the present invention having the above-mentioned fluctuation compensation function is applied.

The switching system shown in this figure includes an exchange 2 connected to an ATM network 1 and a telephone terminal 3 connected to this exchange 2. When an analog signal is output from the telephone terminal 3, the exchange 2 A cell in which the sequence number is written is generated and sent to the ATM network 1 main 1.
When cells on the M network 1 main 1 are supplied, analog signals are generated and supplied to the telephone terminal 3 while referring to the sequence numbers written in these cells.

The exchange 2 includes a terminal procedure termination function section 4, a terminal/network procedure combination function section 5, an intranetwork procedure termination function section 6, and a cell transfer function section 7, and functions as described below.

(When an analog signal is output from the terminal 3) The terminal procedure termination function section 4 has the function of accommodating an analog line, and when an analog signal is output from the telephone terminal 3, it is taken in and connected to the terminal and network procedures. It is supplied to the functional unit 5.

The terminal/network procedure coupling function section 5 converts the analog signal supplied from the terminal procedure termination function section 4 into a digital signal using a coding method such as a PCM encoding method, an ADPCM encoding method, or an APC encoding method. At the same time, these digital signals are divided into sections of a certain length to generate blocks (audio blocks).

In this case, the length of each voice block is the length excluding the overhead necessary to implement the procedure from the cell information manager in order to simplify the processing in the intra-network procedure termination function unit 6.
For example, if the information length of the cell is "32" bytes and the required overhead is "1# byte," it is set to "31° byte." Also, each audio block is 64KPCM
3.8 when converting to a digital signal using an encoding method
Generated every 751m5 (31(B)/8(KB/S)).

If this voice block has a sound, it is supplied to the intra-network procedure termination function unit 6, and if it is silent, it is discarded.

The intra-network procedure termination function unit 6 has a sequence number VS1 spurt instruction bit ■■ and a consecutive missing number VL as internal variables, and receives “31” from the terminal/intra-network procedure coupling function unit 5.
When a digital signal is supplied in byte units, a cell information part is generated by adding a sequence number VS and a spurt instruction bit Vl necessary for the timestamp control function to this digital signal using each of the variables mentioned above, and this is supplied to the cell transfer function section 7.

In this case, the process shown in FIG. 2, for example, is used as the process to generate the cell information part.

In this process, when the connection is first set (the call has not started yet), each variable VS, Vl
is set to 0'' (step 5TI).

After this, when a "31" byte voice block is input from the terminal/network procedure coupling function unit 5, the content of the sequence number vS1 spurt instruction bit Vl is added to this voice block as shown in FIG. After generating the cell information part 8 of "32° byte" (step 5T2), the content of the consecutive missing number VL is set to '0' (step 5T3), and then the sequence number VS is incremented to the value "12".
8” (step 5T4).

After this, start the timer (step 5T5),
Wait for the next audio block (step 5T6).

Then, before this timer times up (for example, 3
．． If a voice block is supplied from the terminal/network procedure coupling function unit 5 at a time slightly longer than 875■S, the timer is stopped (step 5T7), and the sequence number VS and spurt instruction are sent to this voice block. The contents of bit Vl are added to generate cell information section 8 (step 5T8).

Thereafter, the above-described operation is repeated to generate the cell information part 8 corresponding to the audio block each time the audio block is supplied.

If the timer times up before the next audio block is supplied (step 5T6), the telephone terminal 3
It is determined that a sound analog signal is no longer being outputted, and the value of the consecutive missing number VL is incremented (step 5T9), and after this, whether the value of the consecutive missing number VL is greater than or equal to the preset value α■L? (Step 5TIO).

Then, if VL≦αVL, the process returns to the above-described operation of incrementing the sequence number vS, and repeats the above-described operation.

Here, if the supply of the next audio block is started before the timer expires while the condition vL≦αVL is satisfied, the generation operation of the cell information section 8 corresponding to this audio block is restarted. be done. In this case,
Since the sequence number VS of each cell information section 8 is incremented at regular intervals regardless of whether or not voice blocks are supplied, the value of the sequence number VS of the cell information section 8 obtained after the supply of voice blocks is resumed is The voice block becomes discontinuous with the sequence number VS of the cell information part 8 obtained before the supply was interrupted.

In addition, the state in which audio blocks are not supplied continues, and VL
> aVL (step 5TIO), the network procedure termination function unit 6 considers that the spurt has ended, inverts the spurt instruction bit VlO value, and resets the value of the sequence number VS to "0". return.

Then, the intra-network procedure termination function section 6 supplies each cell information section 8 generated according to the above-described procedure to the cell transfer function section 7.

Every time the cell information section 8 is supplied from the intra-network procedure termination section 6, the cell transfer function section 7 adds a header to each cell information section 8 to generate cells, and transfers these cells to the ATM network 1. Send the main 1st order.

In this case, the header has a connection identifier that indicates the connection to which the cell is to be transferred, and the cell sent to the main 1 of the ATM network 1 is transferred within the ATM network 1 based on this connection identifier to the communication destination. transferred to the exchange.

When a cell is supplied from the CATM network 1), when the cell transfer function section 7 receives the cell, it removes the header of the cell and supplies the cell information part 8 to the intra-network procedure termination function section 6.

When the intra-network procedure termination function section 6 receives the cell information section 8 from the cell transfer function section 7, it processes it according to the procedure described below.

In this process, as shown in the flowchart of FIG. 4, first, the previous reception spurt instruction bit Bl is set to "1", and the previous reception sequence number BS is set to "0" (step 5T15).

Thereafter, it is checked whether the value of the spurt instruction bit Vl of the cell information section 8 supplied this time matches the value of the previously received spurt instruction bit Bl (step 5).
T16.5T17).

If these do not match, it is assumed that the cell information section 8 supplied this time is the beginning of the spurt, and the audio block portion of this cell information section 8 is stored in a buffer (not shown). The value of the sequence number vS of the cell information section 8 is assigned to the previously received sequence number BS, after which a timer for fluctuation compensation is set, and the value of the previous spurt instruction bit Bl is assigned to the spurt instruction bit vI (step ST 18).

After this, each time the cell information section 8 is supplied, the value of the spurt instruction bit Vl of this cell information section 8 is compared with the value of the previously received spurt instruction bit Bl, and the above-mentioned operation is performed until they match. Execute repeatedly.

Then, the cell information section 8 supplied from the cell transfer function section 7
If the value of the spurt instruction bit Vt matches the value of the previously received spurt instruction bit Bl, it is determined whether the value of the sequence number vS of this cell information section 8 is within a predetermined range from the current previously received sequence number BS. If the value of the sequence number VS of the cell information section 8 supplied this time is not within a predetermined range from the current value of the previously received sequence number BS, this cell information is discarded (step 5T19). 5T20).

In addition, the sequence number V of the cell information section 8 supplied this time
If the value of the chain of S is within a predetermined range from the current value of the previous received sequence number BS, the value obtained by adding "1" to the value of the previous received sequence number BS and the sequence of the cell information part 8 supplied this time It is checked whether the value of the number VS matches the value of the number VS (step 5T21).

If these six values do not match, after storing silence information as an audio block in the buffer (step 5T22), the value of the previously received sequence number BS is incremented, and the value of the previously received sequence number BS is
Take the modulo of the value of “128” (step 5T23
).

Thereafter, this process is repeatedly executed until the value of the previously received sequence number BS and the value of the sequence number VS of the cell information section 8 supplied this time match.

Then, when the value of the previously received sequence number BS and the value of the sequence number VS of the cell information section 8 supplied this time match, the step of storing the audio block of the cell tn information section 8 supplied this time in the buffer is performed. 5T24), restarts the audio block extraction process described above.

In parallel with this processing, the intra-network procedure termination function unit 6 starts a timer for measuring a predetermined time when the timer for fluctuation compensation times up, and restarts this timer every time the timer times up. , the audio blocks (or silence information) stored in the buffer are sequentially retrieved from the beginning and sent to the terminal.
It is supplied to the intra-network procedure coupling function unit 5.

Every time a voice block (or silence information) is supplied from the network procedure termination function section 6, the terminal/network procedure coupling function section 5 converts it into an analog signal and supplies it to the terminal procedure termination function section 4. do.

Every time an analog signal is supplied from the terminal/network procedure coupling function section 5, the terminal procedure termination function section 4 takes in the analog signal and supplies it to the telephone terminal 3.

As described above, in this embodiment, when outputting the cell on the ATM network 1, the sequence number vS and the spurt instruction bit V! The exchange that receives this cell waits until the fluctuation compensation timer times up from the time it receives the first cell, and then converts this cell to an analog signal at predetermined intervals based on its sequence number vS. Therefore, the signal of the existing telephone terminal 3 and the signal of the ATM network 1 can be efficiently matched.

FIG. 5 is a block diagram showing an example of a switching system to which a second embodiment of the digital switching system according to the present invention is applied.

The exchange system shown in this figure includes an exchange 11 connected to an ATM network 10 and a plurality of HDLC terminals 12 connected to this exchange 11.
When a call setup request is received from the
2 to transmit information.

Each HDLC terminal 12 is a terminal that does not perform logical multiplexing and has an error detection function and a retransmission control function, and first issues a call setup request during communication.

After the call is set up, an HDLC frame is generated and supplied to the exchange 11.

The exchange 11 includes a plurality of subscriber line accommodating sections 13 accommodating each HDLC terminal 12, and a frame/cell converting section 14 connecting each of these subscriber line accommodating sections 13 and the ATM network 10. functions as described in .

(When a frame is output from the terminal 12) The subscriber line accommodation unit 13 receives the HDLC output from each HDLC terminal 12.
Frame flag pattern (for example, “ottttt
It has a function to detect a pattern called too.
If an HDLC frame 15 in the format shown in FIG. 6 is output from the HDLC terminal 12 that is the transmission source for which a call has been set among the HDLC terminals 12 accommodated, this is detected and this HDLC frame 15 is output. The data is captured and supplied to the frame/cell converter 14.

As shown in FIG. 7, the frame/cell conversion section 14 includes a subscriber line identification section 16, an address/cell header conversion section 17,
It is equipped with a frame division/restoration unit 18 and a cell transfer function unit 19, and when an HDLC frame 15 is supplied from the subscriber line accommodation unit 13, it generates a cell corresponding to this HDLC frame 15 and sends it to the ATM network. 0 on the net.

When an HDLC frame 15 is supplied from any of the subscriber line accommodation units 13, the subscriber line identification unit 16 identifies this HDLC frame 15.
The subscriber line accommodation unit 13 that outputs the DLC frame 15 is identified, an address indicating the subscriber line accommodation unit 13 that received the HDLC frame 15 is generated, and this is added to the HDLC frame 15 to perform address/cell header conversion. Part 17
supply to.

In this case, a method for identifying the subscriber line accommodation section 13 that has received the HDLC frame 15 is to transfer data between the subscriber line accommodation section 13 and the frame/cell conversion section 14 using DMA.
Data transfer is performed by identifying the subscriber line accommodation unit 13 from the number of the module that has performed the DMA interrupt, or by having the frame/cell conversion unit 14 poll the subscriber line accommodation unit 13. , a method of identifying the subscriber line accommodation unit 13 depending on which module is polled is used.

The address/cell header conversion section 17 is provided with a cell header table for converting the address obtained by the subscriber line identification section 16 into a cell header and converting the cell header into an address of the subscriber line accommodation section 13. The address supplied together with the HDLC frame 15 from the public line identification unit 16 is converted into a cell header, and this is sent to the HDLC frame 15.
It is supplied to the frame division/restoration unit 18 together with the LC frame 15.

When the frame division/restoration unit 18 receives the cell header and the I (DLC frame 15) from the address/cell header conversion unit 17, it processes them according to the procedure shown in FIG. 8 to generate cells.

In this process, first, it is checked whether the length of the HDLC frame 15 is longer than a certain length (step 5T30).

Then, if it is longer than a certain length, the section from the beginning to the certain length is cut off (Step 5T31), a cell header corresponding to this HDLC frame 15 is added to the cut piece to form a cell, and this is sent to the cell transfer function section. 19 (step 5T32).

After this, the remaining HDLC frame 15 with the beginning cut off
is regarded as a new HDLC frame 15. Step 5T
33) The above-described process is repeated for this HDLC frame 15, and the cells obtained thereby are sequentially supplied to the cell transfer function section 19.

If the length of the remaining HDLC frame 15 becomes less than a certain length, dummy data (for example, bit "0" string) is added to the end of this I (DLC frame 15) to make it a certain length, and The cell header supplied from the address/cell header converter N17 is added and supplied to the cell transfer function unit 19 (step 5T34).

Every time a cell is supplied from the frame division/restoration section 18, the cell transfer function section 19 takes in the cell and transfers it to the ATM network 1.
0 on the net.

In this case, the cells are transferred on the ATM network 1 in the order in which they are supplied from the frame division/restoration unit 18, so the cell at the beginning of the HDLC frame 15 is sent first, and the cell at the end of the HDLC frame 15 The cell corresponding to is sent out last.

Since the ATM network 10 determines which route this cell should be output to based on the information in the cell header, if the contents of the cell header are the same, the route will be the same and no overtaking of the cell will occur.

Therefore, the cells sent from the cell transfer function unit 19 to the ATM network 10 are sent to the other party in the order in which they were sent, that is, the cell at the beginning of the HDLC frame 15 goes first, and the cell at the end of the HDLC frame 15 goes last. It is carried to the exchange 11 on the side.

When cells are supplied from the CATMIO network) When the cell transfer function section 19 receives cells from the ATM network 10, it takes in the cells and supplies them to the frame division/restoration section 18.

Every time a cell is supplied from the cell transfer function section 19, the frame division/restoration section 18 identifies which connection this cell belongs to based on the cell header of this cell, and then based on this identification result. A portion of the cell excluding the cell header (hereinafter, this portion will be referred to as an information portion) is stored in a buffer of a connection corresponding to the cell in a write-once manner.

Also, at this time, the cell header of the cell is held in a portion corresponding to the buffer.

Then, each information part stored in the buffer is processed according to the procedure shown in FIG. 9 to reproduce the HDLC frame 15.

In this process, it is first checked whether there is a flag pattern at the beginning of the first information section stored in the buffer (step 5T35).

If there is no flag pattern at the beginning of this information section, it is discarded (step 5T36).

Also, if there is a flag pattern at the beginning of the information section,
Check whether there is a flag pattern other than the beginning of this information field (step 5T37). If there is a flag pattern other than the beginning, remove the part after the latter flag pattern in the information field. The HDLC frame 15 is supplied to the address/cell header converter 17, and the cell header is held in a portion corresponding to the buffer and converted into the address/cell header converter 1.
7 (step 5T38).

Also, if there is no flag pattern other than the first one, check whether the next information section includes a flag pattern or not in steps 5T39.5T40. ), if this information section does not contain a flag pattern, this information section is combined with the previous information section (step 5T41).

Thereafter, this operation is repeated until the flag pattern appears in the next information section to sequentially combine these information sections.

If there is a flag pattern in the next information section, the data after this flag pattern is removed and combined with the previous information section (step 5T42), and the information section sequence obtained thereby is converted into HDLC. While supplying the frame 15 to the address/cell header converter 17,
Supplying the cell header held in the portion corresponding to the buffer to the address/cell header converter 17 (
Step 5T43).

The address/cell header converter 17 performs the frame division/cell header conversion section 17.
When the HDLC frame 15 and cell header are supplied from the restoration unit 18, the address of the subscriber line accommodation unit 13 corresponding to this cell header is calculated while referring to the cell header table, and this address and the HDLC frame 15 are transferred to the subscriber line accommodation unit 13. The signal is supplied to the line identification section 16.

When the subscriber line identifying section 16 receives the address and the HDLC frame 15 from the address/cell header converting section 17, it supplies the HDLC frame 15 to the subscriber line accommodating section 13 designated by the address.

The subscriber line accommodating section 13 receives the HD from the subscriber line identifying section 16.
When the LC frame 15 is supplied, it is taken in and supplied as is to the HDLC terminal 12.

In this way, in this embodiment, HD
Generate cells from LC frame 15, or create HD from cells.
Since the HDLC terminal 12 is made to generate the LC frame 15 and perform control such as error control and retransmission control, the existing HDLC terminal 12 can be connected to the ATM network 10 efficiently and at a high throughput. .

Further, in this second embodiment, the HDLC frame 15
However, it is possible to process this HDLC frame 15 with the flag pattern removed (hereinafter referred to as the - hour frame) to generate a cell, or to generate a temporary frame from this cell. However, the original HDLC frame 15 may be generated from this -time frame.

In this case, since the temporary frame from which the flag pattern has been deleted is used, the beginning and end of the temporary frame cannot be detected using the flag pattern as described above. Therefore, in this embodiment, in order to indicate the beginning and end of the -time frame, two bits, the B bit and the F bit, are added to each data block obtained by dividing the temporary frame as shown in FIG. Information (effective length data) indicating the effective data length of the temporary frame is provided, and the beginning and end of the temporary frame are identified based on these bits and the effective length data.

Below, a procedure for generating cells from HDLC frame r5 using such a method will be explained.

First, when the HDLC frame 15 is output from the HDLC terminal 12, the subscriber accommodation unit 13 removes the flag φ pattern from the HDLC frame 15 to generate a temporary frame, and then this - hour frame is converted into an address/cell header. 17. Here, a cell header indicating the address of the subscriber accommodating unit 13 corresponding to the HDLC terminal 12 is generated by the same process as in the second embodiment described above, and this is added to the - hour frame to divide/restore the frame. 18.

When the frame division/restoration section 18 is supplied with a temporary frame to which a cell header has been added from the address/cell header conversion section 17, it processes it to generate cells in the procedure shown in FIG.

In this process, the frame division/restoration unit 18 first sets "1#" as the B bit and "0" as the F bit (step 5T50).

Then, if the - time frame is longer than a certain length (step 5T51), cut a certain length part from the beginning (step 5T52), and add B to the cut piece (data block).
After describing the bit and F bit and adding length information indicating the fixed length as effective length data, the cell header supplied from the address/cell header converter 17 is added to this to form a cell. , and supplies this to the cell transfer function unit 19 (step 5T53).

Next, after setting the B bit to "02", the remaining temporary frame whose beginning has been cut off is not regarded as a new temporary frame (step 5T54), and the above-mentioned process is repeated for this - hour frame, thereby obtaining the The cells are sequentially supplied to the cell transfer function unit 19 (Jl-).

If the length of the remaining temporary frame becomes less than a certain length (step 5T51), the F bit is set to '1' and the length indicating the length of the remaining temporary frame is set as effective length data. After adding the B bit, F bit, and effective length data to the frame, the cell header supplied from the address/cell header conversion unit 17 is added to the frame to form a cell, and this is supplied to the cell transfer function unit 19. do(
Step 5T55). In this case, if the length of this - hour frame is less than the preset length,
Fill in the missing data with dummy data (for example, bit “0” string)
Make up for it.

The cells thus generated are sent out onto the ATM network 10 via the cell transfer function section 19.

Further, when such a cell is supplied from the ATM network 10, a temporary frame is generated from this cell in the following procedure, and then an HDLC frame 15 is generated from this temporary frame.

First, when a cell is supplied from the ATM network 10, the cell transfer function section 19 takes it in and sends it to the frame division/restoration section 1.
Supply to 8.

The frame division/restoration section 18 includes the cell transfer function section 19.
Each time a cell is supplied from a cell, it is identified to which connection this cell belongs based on the cell header of the cell, and then the length of the cell is stored in the buffer to which this connection is allocated based on the identification result. Effective part indicated by the information (hereinafter, this part is referred to as the information part)
is stored in an append format. Also, at this time, the cell header of the cell is held in a portion corresponding to the buffer.

Then, each information section stored in the buffer is processed according to the procedure shown in FIG. 12 to reproduce a temporary frame.

In this process, it is first checked whether the B bit of the information field stored at the head of this buffer is "1" (step 5T60).

Then, if this day's pI is not "1", this information section is discarded (step 5T61).

Also, if the B bit of the prefectural information section is “1”, the F
Check whether the bit is "1" (step 5T62).

If this F bit is 1°, data (valid data) of the length indicated by the effective length data of the information section is extracted, and this is supplied to the address/cell header converter 17 as a - hour frame ( Step ST6g).

Further, if the F bit of this information section is "0", the valid data of this information section is saved, and then the next information section in the buffer is fetched (step 5T63), and the F bit of this information section is stored. is "1#" (step 5T64), and if it is not "1", the valid data of this information part is combined with the valid data of the previously processed information part (step 5T65).

Thereafter, this operation is repeated until an information section whose F bit is "1" appears, and the valid data of the remaining information sections are sequentially combined.

When an information section whose F bit is "1'" appears, the data (valid data) indicated by the effective length data is extracted from this information section and is added to the effective length of the information section that has been combined up to that point. Step 5T66 to join to data string
), this is supplied to the address/cell header converter 17 as a -time frame, and the cell header held in the portion corresponding to the buffer is supplied to the address/cell header converter 17.

Thereafter, the same process as in the second embodiment described above is executed to determine the subscriber accommodation unit 13 based on the cell header. Then, the subscriber accommodating section 13 adds a flag pattern to the - hour frame, reproduces the HDLC frame 15, and supplies the HDLC frame 15 to the corresponding HDLC terminal 12.

In this way, in this embodiment, two bits and effective length data are used, so that frames without flag patterns can be processed.

〔Effect of the invention〕

As explained above, according to the present invention, an existing terminal can be
It can be accommodated in the M network, and the throughput during communication can be increased.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a switching system to which the first embodiment of the digital switching system according to the present invention is applied;
The figure is a flowchart showing an example of the cell generation process procedure in the first embodiment, FIG. 3 is a schematic diagram showing an example of the format of the cell information section used in the first embodiment, and FIG. FIG. 5 is a block diagram showing an example of a switching system to which the second embodiment of the digital switching method according to the present invention is applied; FIG. 6 is a flowchart showing an example of a restoration processing procedure; FIG. FIG. 7 is a detailed block diagram of the exchange used in the second embodiment; FIG. 8 is a flowchart showing an example of the frame division processing procedure in the second embodiment;
The figure is a flowchart showing an example of a frame restoration process procedure in the second embodiment, FIG. 10 is a schematic diagram showing an example of the format of the information section used in the third embodiment, and FIG. 11 is a temporary frame division in the third embodiment. Flowchart showing an example of a processing procedure. FIG. 12 is a flowchart showing an example of a temporary frame restoration processing procedure in the third embodiment. 1... Network (ATM network) 3... Terminal (telephone terminal) 4... Terminal procedure termination function section 5... Terminal/intra-network procedure combination function section 6... Intra-network procedure termination function section 7 ...ATM transmission transmission function transfer function section) 10...
- Line (ATM network) 12... Terminal that does not perform logical multiplexing (HDLC terminal) 13... Subscriber line accommodation section 14... Frame/cell conversion section

Claims (4)

[Claims] (1) In a digital switching system that realizes switching operations using fixed-length cells, a terminal procedure termination function section that terminates procedures held by the terminal, an intra-network procedure termination function section that terminates procedures within the network, and the above-mentioned A terminal/network procedure combination function unit that performs mutual conversion between the procedures of the terminal and the procedures within the network, and an AT that has a cell transfer function.
A digital switching system characterized by having an M transmission function section and the following. (2) The terminal procedure termination function section has a function of terminating the physical interface of an analog line, and the intra-network procedure termination function section has a fluctuation compensation function and a cell information section allocation function, 2. The digital switching system according to claim 1, wherein the combining function section has an encoding processing function. (3) The digital switching system according to claim 2, wherein the fluctuation compensation function of the intra-network procedure termination function unit is realized by a time stamp. (4) A digital switching system that accommodates terminals that do not perform logical multiplexing and performs cell-based transmission, which has a subscriber line accommodation section that accommodates subscriber lines and a frame/cell conversion section, The subscriber line accommodation unit has a function of detecting frames output by a terminal, a function of outputting frames to the terminal, and a function of inputting and outputting frames between the frame/cell conversion function unit, and the frame/cell The conversion unit has a function of inputting and outputting frames to and from the subscriber line accommodation unit, a function of identifying the subscriber line accommodation unit that outputs the frame, and a function of generating a cell header for the identified subscriber line accommodation unit. , a function to allocate frames to cells, a function to output cells to a line,
A function to input cells from the line, a function to restore frames from cells, a function to detect cell headers from cells,
A digital switching system characterized by having a function of recognizing a subscriber line accommodation section from which a frame should be output from a cell header, and a function of outputting a frame to the subscriber line accommodation section.