JP2012114774A - Transmission apparatuses and transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide transmission apparatuses of sending and receiving sides and a transmission system using them, capable of compensating data loss due to packet discard caused by the occurrence of one bit error, when packetizing TDM signals, sending them over a network, and outputting them as original TDM signals.SOLUTION: In transmission apparatuses and a transmission system, a packet format containing TDM signals is assumed to be a format in which already-transmitted data is stored in the payload together with data packetized in regular timing. A sending side transmission apparatus A1 copies the original data into two pieces of data as regular and delay data, and generates a packet containing the regular data and the delay data of passing over a certain period since the initial sending. A receiving side transmission apparatus Z2 retrieves regular data and delay data from a packet, and compensates lost data from the delay data when regular data is lost.

Description

  The present invention relates to a transmission apparatus and a transmission system, and more particularly to a transmission apparatus on a transmission side and a reception side that packetizes a TDM signal and sends it to a packet network, and outputs the received packetized TDM signal as an original TDM signal. The present invention also relates to a transmission system that transmits and receives a TDM signal via a packet network using these transmission devices.

  In recent years, packetization of networks has progressed, and in connection with this, conventionally, communication has been performed by always occupying a line or channel resource and transferring data by time division multiplexing (TDM) technology such as PDH and SDH. With regard to the carrier backbone (main line used by communication carriers), there is an increasing trend of using circuit emulation technology (CEP technology) to packetize a TDM signal to form a packet network.

  Generally, a trunk line that transmits a TDM signal has a characteristic that a 1-bit error generated in data transferred on the line is transferred as it is as a 1-bit error. On the other hand, when a 1-bit error occurs, the packet network, for example, determines that the MAC frame is an FCS error and discards the packet. For this reason, in the method of transferring the TDM signal through the packet network using the CEP technology, even if the packetized data has a 1-bit error, the packet is discarded. As a result, the error rate appears to be about 10 times worse than when the signal is transferred by the TDM network.

  For example, a technique disclosed in Non-Patent Document 1 or the like is known as a conventional technique capable of preventing the expansion of a data loss range due to a 1-bit error in the packet network as described above. According to this prior art, a packet carrying an error correction code is transmitted separately, and when the packet is lost due to the occurrence of a 1-bit error, the lost packet is restored to prevent data loss.

IETF RFC5109 (URL-> http://www.rfc-editor.org/rfc/rfc5109.txt)

  Since the above-described prior art requires an arithmetic circuit for generating an error correction code on the transmission side and an error correction code arithmetic circuit and an error correction circuit for checking on the reception side, the transmission apparatus Therefore, the circuit configuration becomes complicated and the apparatus cost increases.

  The object of the present invention is to solve the above-described problems of the prior art, packetize a TDM signal, send it to a packet network, and generate a 1-bit error when outputting the packetized TDM signal as the original TDM signal. Provided is a transmission device on the transmission side and reception side that can compensate for data loss due to packet discard that sometimes occurs, and a transmission system that enables transmission and reception of TDM signals via a packet network using those transmission devices. There is to do.

  According to the present invention, the object is to provide a transmission apparatus on the transmission side that packetizes the TDM signal and sends it to the packet network, and a transmission apparatus on the reception side that outputs the received packetized TDM signal as the original TDM signal. In the transmission system for transmitting and receiving a TDM signal, the transmission apparatus on the transmission side includes means for setting the data of the TDM signal as two data, one of the two data as normal data, and the two data The other of the data is held for a certain period to be delayed data, and the normal data and the delayed data that has been delayed for the certain period and already transmitted before the certain period are packetized. And the transmission device on the receiving side extracts normal data and delay data mounted in the packet. And means for reproducing normal data that should have been loaded in the lost packet by using delay data extracted from a packet received after a certain period when there is a packet that is lost due to an error in the data. This is achieved by comprising and configuring.

  According to the present invention, when a TDM signal is packetized and transmitted through a packet network, a circuit that compensates for packet loss due to a 1-bit error can be realized without causing a significant increase in cost.

It is a figure explaining the structural example of the transmission system by one Embodiment of this invention. FIG. 2 is a block diagram illustrating a functional configuration example of a transmission device on the transmission side illustrated in FIG. 1. It is a figure which shows the detailed structure of the packet sent on a packet network from the transmission apparatus of a transmission side. FIG. 2 is a block diagram illustrating a functional configuration example of a transmission device on the reception side illustrated in FIG. 1. 6 is a flowchart for explaining a processing operation for generating a next read pointer in the read pointer control function unit shown in FIG. 4. It is a figure explaining the data arrangement | positioning in the reception data buffer at the time of no data loss, and a data read-out order. It is a figure explaining the data arrangement | positioning in a received data buffer at the time of data missing, and a data reading order. It is a figure explaining the required capacity | capacitance of the reception data buffer in the transmission apparatus of the receiving side.

  Embodiments of a transmission apparatus and a transmission system according to the present invention will be described below in detail with reference to the drawings. In an embodiment of the present invention described below, when data of a TDM signal is packetized in a transmission system that transmits and receives a TDM signal via a packet network, data that has already been transmitted is stored in a surplus area within the packet. Data stored and compensated for lost data due to packet discard due to the occurrence of 1-bit error from the retransmit data stored in the surplus area in the later packet to prevent data loss is there.

  FIG. 1 is a diagram illustrating a configuration example of a transmission system according to an embodiment of the present invention. The transmission system shown in FIG. 1 packetizes a TDM signal on a TDM line and sends it to a packet network, and extracts the TDM signal in the packet from the packet network and sends it to the TDM line. A network system configured to include a transmission device on a receiving side. Although FIG. 1 shows a system that transmits a signal only in one direction, in general, signal transmission is performed in both directions and is not shown in the figure. A system for transmitting signals is provided.

  In the transmission system according to the embodiment of the present invention shown in FIG. 1, when the transmission apparatus A1 on the transmission side packetizes the TDM signal, the normal data and the delayed data that has already been transmitted as normal data are integrated into a packet. To the packet network, and when the receiving side transmission device Z2 on the opposite side detects a missing packet, the missing data is complemented using the delay data to recover the data string of the TDM signal. It is.

  That is, in the transmission system according to the embodiment of the present invention shown in FIG. 1, the TDM signal 6 received from the TDM interface 3 that is a TDM line is represented as packets 7, 8, and 9 that are TDM over Packet signals. The transmission device A1 having the function of encapsulating in shape and transmitting to the packet network 4 is opposed to the transmission device A1 via the packet network 4, and packets 7, 8, and 9 as TDM over Packet signals from the packet network 4 are transmitted. The transmission apparatus Z2 is configured to receive, extract a TDM signal from the received packet signal, and send the reconfigured TDM signal 10 to the TDM interface 5 which is a TDM line. Note that the transmission device Z2 requires a network synchronization clock to reproduce the TDM signal, and the external reference clock 11 is supplied from the clock supply device 12 as the network synchronization clock.

  The TDM signal 6 received by the transmission apparatus A1 from the TDM interface 3 has a time division multiplexing structure with a 125 μsec period as a unit. The transmission apparatus A1 illustrated in FIG. 1 receives data of the TDM signal 6 in order of a, b, c, d, and e. The transmission apparatus on the transmission side originally encapsulates only the data a, b, c, d, and e when packetizing the TDM signal 6, but the transmission side in the embodiment of the present invention. The transmission apparatus A1 encapsulates the original data and data that has already been transmitted several packets before in one packet. In the case of the example shown in FIG. 1, when the transmission device A1 packetizes the original data c, d, e as shown by the packet 7, the packet 8, and the packet 9, respectively, the data c, The packets a, b, and c that have already been transmitted are both packetized into packets in which d and e are mounted, and packets 7, packets 8, and 9 are encapsulated in the packet network 4. Sending out.

  The transmission device Z2 on the receiving side receives the packet 7, the packet 8, and the packet 9 transmitted via the packet network 4, extracts TDM data from these received packets, and supplies the external data supplied from the clock supply device 12 The TDM signal 10 synchronized with the reference clock 11 is reproduced and sent to the TDM interface 5. The transmission apparatus Z2 on the receiving side stores the already transmitted data of the last packet when any of the packet 7, the packet 8 and the packet 9 received via the packet network 4 is missing. The target data that should have been in the packet that was missing from the area in the packet is compensated, and the TDM signal 10 is reproduced without causing the loss of data.

  FIG. 2 is a block diagram illustrating a functional configuration example of the transmission apparatus A1 on the transmission side illustrated in FIG. Note that the example shown in FIG. 2 shows a configuration of a processing function that performs packetization of the TDM signal 6 into the packet 8.

  As described above, the transmission device A1 receives the TDM signal 6 from the TDM interface 3, and encapsulates the normal data d of the data of the TDM signal 6 and the already transmitted data b in the packet network 4. 8 is transmitted. Then, the transmission apparatus A1 receives and synchronizes the TDM signal 6 from the TDM interface 3 and copies the synchronized TDM signal 6 received from the TDM reception interface 101 to two TDM signals 6. , A normal write function unit 104 that receives one of the two TDM signals 6 from the copy function unit 102 and writes it to the transmission data buffer, and the other one of the two TDM signals 6 from the copy function unit 102 The delay write function unit 103 that writes data into the transmission data buffer after being delayed for a certain time, and the data from the normal data storage area 108 that holds the data from the normal write function unit 104 in the order of input and the data from the delay write function unit 103 Has a delayed data storage area 109 that holds data in the order of input Transmission data buffer 105, packet generation function unit 106 that reads out data stored from transmission data buffer 105 and generates a packet, and packet transmission that transmits the packet generated by packet generation function unit 106 onto packet network 4 And an interface 107.

  As described above, if the TDM reception interface 101 can distribute the synchronized TDM signal 6 to both the normal write function unit 104 and the delayed write function unit 103, the copy function unit 102 is unnecessary.

  The packet generation function unit 106 described above includes a payload unit generation function unit 111, an overhead unit generation function unit 112, and a packet assembly function unit (not shown). The packet generation function unit 106 is provided with a read timing clock generated by the read timing generation function unit 114 based on the clock signal generated by the free-running oscillator 113.

  In the transmission apparatus A1 configured as described above, the TDM reception interface 101 receives and synchronizes the TDM signal 6 that is time-division multiplexed and transmitted at a period of 125 μsec, and synchronizes the TDM signal 6 that is synchronized with the copy function unit 102. hand over. The copy function unit 102 copies the received TDM signal 6 and passes the TDM signal 6 to both the normal write function unit 104 and the delayed write function unit 103.

  The normal write function unit 104 writes the received synchronized TDM signal 6 in a free area having an address corresponding to the write time of the normal data storage area 108 in the transmission data buffer 105. The delayed write function unit 103 holds the received synchronized TDM signal 6 for a certain period of time, and responds to the writing time of the delayed data storage area 109 in the transmission data buffer 105 for the TDM signal 6 delayed after a predetermined holding time. Write to an empty area with the address to be. Then, by aligning the write timings of the normal write function unit 104 and the delayed write function unit 103, the data written immediately after reception at the same address in the normal data storage area 108 and the delayed data storage area 109 in the transmission data buffer The data written after a certain delay time is stored. In FIG. 2, a set of normal data and delayed data that are simultaneously written and read is shown as a simultaneous processing data unit 110.

  The payload part generation function unit 111 of the packet generation function part 106 configured to include the payload part generation function part 111 and the overhead part generation function part 112 is a read timing generation function based on the clock signal generated by the free-running oscillator 113. Data is read from the transmission data buffer 105 according to the read timing clock generated by the unit 114, and the payload portion of the packet to be generated is generated. At this time, the payload part generation function unit 111 reads the same address in both the normal data storage area 108 and the delayed data storage area 109 at the same time. Thereby, the simultaneous processing data unit 110 can be read collectively.

  The packet assembly function unit (not shown) included in the packet generation function unit 106 combines the payload unit generated by the payload unit generation function unit 111 and the packet overhead generated by the overhead unit generation function unit 112 to packetize the TDM signal. I do. The packet generation function unit 106 passes the generated packet to the packet transmission interface 107, and the packet transmission interface 107 transmits the received packet as the packet 8 to the packet network 4.

  FIG. 3 is a diagram showing a detailed configuration of a packet transmitted from the transmission apparatus A1 on the transmission side onto the packet network. In the embodiment of the present invention, MPLS is used as a packet protocol, and a frame called Martini in which labels are stacked in two stages is used as an MPLS frame. Then, for the MPLS packetization (frame formation) of the TDM signal, a standard defined in IETF RFC5086 is referred to.

  FIG. 3 shows a configuration of a packet 200 in which a TDM signal is converted into an MPLS frame. This packet includes a 14-byte MAC header 201, a 4-byte tunnel LSP shim header 202, a 4-byte VC LSP shim header 203, a 4-byte CESoPSN control word 204. , TDM payload (normal) 205, TDM payload (delay) 206, padding 207, and 4-byte FCS 208 are combined in this order.

  A packet based on an MPLS frame configured as described above is further accommodated in a MAC frame and has a nested structure. If the length of the MAC frame containing the MPLS frame is less than 64 bytes, if IETF RFC5086 is applied as it is (the present invention is not applied), dummy data of the same length is used instead of the TDM payload (delay) 206. Will be padded. The packet 200 in which the TDM signal in the embodiment of the present invention shown in FIG. 3 is converted into an MPLS frame is a packet of 8 frames of a TDM signal having a transmission rate of 64 kbit / sec (125 μsec × 8 = 1 msec packet). The TDM payload (ordinary) 205 and the TDM payload (delay) 206 are both 9 bytes, the padding 207 is 16 bytes, and the entire packet 200 is 64 bytes.

  The CESoPSN control word 204, the TDM payload (normal) 205, and the TDM payload (delay) 206 all have a structure defined in IETF RFC5086, and the CESoPSN control word 204 has a 10-bit control information 209 and a 6-bit frame length. It consists of information 210 and 16-bit sequence number 211. The TDM payload (normal) 205 and the TDM payload (delay) 206 when the framing period is 1 msec both have a frame area for 8 frames, and the 1st frame area 212, the 2nd frame area 213, the 3rd frame area 214 4th frame region 215, 5th frame region 216, 6th frame region 217, 7th frame region 218, 8th frame region 219, and signaling region 220.

  In the case of encapsulating a TDM signal having a transmission rate of 64 kbit / sec, the above-described 1st frame region 212 to 8th frame region 219 are 8 bit (1 byte) time slot compatible regions (TS # 1 (8 bits)) 221 respectively. The signaling area 220 includes SIG # 1 222 and 4-bit padding 223 which are nibbles for transferring 4-bit signaling information for TS # 1.

  When encapsulating a TDM signal having a transmission rate of 64 kbit / sec or more, the number of TSs, which is the number of time slots in the first frame region 212 to the 8th frame region 219, increases according to the signal rate. Further, the number of frame regions is increased or decreased according to the framing period. The field length of the padding 207 in the packet 200 is increased or decreased according to the signal speed and the framing period. In addition, when the data length excluding padding 207 exceeds 64 bytes, the packet 200 has a field length of 0 bytes, and when the data length excluding padding 207 is less than 64 bytes, the shortage is the field length of padding 207. It becomes. The field length of the padding 223 in the TDM payload (normal) 205 and the TDM payload (delay) 206 depends on the speed of the TDM signal, and the solution when the speed of the TDM signal is divided by 64 kbit / sec is an even number. The field length in this case is 0 bit, and the field length in the case of an odd number is 4 bits.

  As can be seen from the above, the packet 200 in which the TDM signal in the embodiment of the present invention is converted into an MPLS frame and the packet having the structure defined in IETF RFC5086 are the packet 200 according to the embodiment of the present invention, the TDM payload ( The only difference is that it has a (delay) 206.

  FIG. 4 is a block diagram illustrating a functional configuration example of the transmission apparatus Z2 on the reception side illustrated in FIG. The example shown in FIG. 4 shows a configuration of a processing function for restoring the packet signal 8 to the TDM signal 10.

  As described above, the transmission device Z2 receives the packet 8 from the packet network 4 and transmits the TDM signal 10 restored from the packet 8 to the TDM interface 5. Then, the transmission device Z2 performs a packet reception interface 301 that receives the packet 8 transmitted via the packet network 4, and a termination process of the packet data received from the packet reception interface 301, and performs normal processing in the packet payload. A packet termination function unit 302 that writes data and delay data to the reception data buffer, a reception data buffer 305 having a normal data storage area 306 and a delay data storage area 307, and sequence number information of packets received from the packet termination function unit 302 Originally, a packet loss detection function unit 309 that detects the presence or absence of a packet loss, and a read pointer that generates a read pointer from the reception data buffer based on the information on the presence or absence of packet loss received from the packet loss detection function unit 309. Data control function unit 310, an external reference clock reception function unit 314 that receives the external reference clock 11, a read timing generation function unit 312 that generates a read timing based on the external reference clock received from the external reference clock reception function unit 314, A receive data buffer read function unit 311 that reads information in the receive data buffer 305 based on the read control pointer information received from the read pointer control function unit 310 at the read timing generated by the read timing generation function unit 312; A TDM transmission interface 313 for transmitting data read by the reception data buffer reading function unit 311 to the TDM interface 5 is provided.

  In the transmission apparatus Z2 configured as described above, the packet reception interface 301 receives a packet (packet signal 8 in the illustrated example) from the packet network 4, and transfers the received packet data to the packet termination function unit 302. The packet reception interface 301 also checks the normality of the received packet. If a bit error has occurred in the transmission packet in the packet network 4, the error detection code FCS 208 added to the end of the MAC frame and the error detection code recalculated from the received packet are inconsistent, and the packet reception interface 301 Discards the corresponding packet.

  The packet termination function unit 302 includes an overhead unit termination function unit 303 and a reception buffer writing function unit 304. The packet termination function unit 302 divides the received packet data into an overhead part and a payload part, and the overhead part is a process required for communication with respect to the packet data received by the overhead part termination function unit 303. Termination processing is performed, and the reception buffer write function unit 304 writes the data in the TDM payload (normal) 205 and TDM payload (delay) 206 included in the payload portion into the reception data buffer 305. In the case of a general MAC frame, the MAC header 201 to the VC LSP shim header 203 is an overhead portion, and the CESoPSN control word 204 to the FCS 208 is a payload portion.

  As described above, the reception data buffer 305 includes the normal data storage area 306 and the delay data storage area 307. The reception buffer writing function unit 304 sets a set of normal data and delay data encapsulated in the packet 8 received from the packet network 4 as a simultaneous processing data unit 308, and a normal data storage area 306 and a delay data storage area 307, respectively. Write to the address corresponding to the same writing time. The overhead unit termination function unit 303 analyzes the data structure of the CESoPSN control word 204 included in the overhead unit, extracts the sequence number information 211, and transfers the sequence number information 211 to the packet loss detection function unit 309.

  The packet loss detection function unit 309 checks the sequence number information 211 and determines that there is no packet loss when the sequence number is the same as the last received sequence number, and that there is a packet loss when the sequence number is not the same as the last received sequence number. The determination is made and the determination result is passed to the read pointer control function unit 310. The read pointer control function unit 310 generates a read pointer based on the packet loss determination result, and passes the generated read pointer information to the reception data buffer read function unit 311.

  The reception data buffer read function unit 311 receives the read data from the read pointer control function unit 310 at the read timing generated by the read timing generation function unit 312 based on the external reference clock 11 received via the external reference clock reception function unit 314. Based on the read control pointer information, information in the received data buffer 305 is read. The reception data buffer reading function unit 311 passes the data read from the reception data buffer 305 to the TDM transmission interface 313, and the TDM transmission interface 313 reproduces the received data in the TDM data format and sends it to the TDM interface 5. Transmit as TDM signal 10.

  FIG. 5 is a flowchart for explaining the processing operation for generating the next read pointer in the read pointer control function unit 310 shown in FIG. 4, and this will be described next. It should be noted that the initial state at the start of the processing is that “next normal buffer pointer candidate value” 410 = normal buffer head address + x generated during the previous processing. Here, the variable x415 is an offset value from the normal buffer head address to the read position when reading the normal buffer in the previous process.

(1) The read pointer control function unit 310 is activated when a packet loss determination result is received from the packet loss detection function unit 309. First, as the next read pointer candidate value calculation process, Next normal buffer pointer candidate value 411 and next delay buffer pointer candidate value 412 are calculated based on “buffer pointer candidate value” 410. The next normal buffer pointer candidate value 411 is “next normal buffer pointer candidate value” 410 + 1 = normal buffer head address + (x + 1) at the previous processing, and the next delay buffer pointer candidate value 412 is the delay buffer head address and the previous processing time. The variable x of the “next normal buffer pointer candidate value” 410 plus the delay offset 414 = delay buffer head address + x + [delay offset] (step 401).

(2) Next, it is determined whether or not the sequence number is missing. If there is no missing sequence number, the next read pointer value 413 = next normal buffer pointer candidate value as the next read pointer setting process (normal) 411 is performed (steps 403 and 404).

(3) If it is determined in step 403 that the sequence number is missing, the next read pointer setting process (delay) is set to the next read pointer value 413 = the next delay buffer pointer candidate value 412, and further the next normal buffer pointer candidate As the value resetting process (normal), the next normal buffer pointer candidate value 411 is set to “next normal buffer pointer candidate value” 410 at the previous process (steps 405 and 406).

  FIG. 6 is a diagram for explaining the data arrangement in the reception data buffer 305 and the data reading order when there is no data loss, and FIG. 7 is for explaining the data arrangement and data reading order in the reception data buffer 305 when there is data loss. FIG. In the example shown in FIG. 7, it is assumed that normal data d and delay data b transferred by the packet 8 are missing. In the example shown in FIGS. 6 and 7, the delay offset is assumed to be a two-frame period time, and when the copy of the data stored in the normal data storage area 306 is not lost, the delay data storage area 307 It is stored in the address portion corresponding to two packetization cycle times, and when there is a packet loss, it is stored in the address portion corresponding to one frame generation cycle time. Note that the framing period needs to be an appropriate value in accordance with a request to the system.

  First, the case of no data loss shown in FIG. 6 will be described. Now, as shown in FIG. 6, offsets n 510, n + 1 511, n + 2 512, n + 3 513, n + 4 514, and n + 5 515 from the head of the normal data storage area 306 of the reception data buffer 305 include data c 533. , Data d 534, data e 535, data f 536, data g 537, and data h 538 are stored. In this case, the offsets n 510, n + 1 511, n + 2 512, n + 3 513, n + 4 514, and n + 5 515 from the beginning of the delayed data storage area 307 of the reception data buffer 305 include data a 531, data b 532, and data That is, c 533, data d 534, data e 535, and data f 536 are stored.

  Then, at each time from time t 550 to time t + 5 555, data is sequentially read from the corresponding area in the reception data buffer 305 as indicated by the long circle and the arrow line, and is the source data of the TDM signal A column 570 is generated. In the case of no data loss shown in FIG. 6, the data in the corresponding area is sequentially read from only the normal data storage area 306. In the example shown in FIG. 6, data from n 510 at time t 550, data from n + 1 511 at time t + 1 551, data from n + 2 512 at time t + 2 552, and n + 3 513 at time t + 3 553. Data from n + 4 514 at time t + 4 554 and data from n + 5 515 at time n + 5 555 are read out, and a data string 570 is generated.

  Next, the case where there is data loss shown in FIG. 7 will be described. In the example shown in FIG. 7, it is assumed that the normal data d and the delay data b transferred by the packet 8 are missing, so that the offsets n 510 and n + 1 511 from the head of the normal data storage area 306 of the reception data buffer 305 are assumed. , N + 2 512, n + 3 513, n + 4 514, and n + 5 515 store data c 533, data e 535, data f 536, data g 537, data h 538, and data i 539. In this case, the offsets n 510, n + 1 511, n + 2 512, n + 3 513, n + 4 514, and n + 5 515 from the beginning of the delayed data storage area 307 of the reception data buffer 305 include data a 531, data c 533, data d 534, data e 535, data f 536, and data g 537 are stored.

  Then, in the case where data is missing as shown in FIG. 7, the time t 550 and the time t + 2 552 to the time t + 5 555 correspond to the normal data storage area 306 and the time t + 1 551 corresponds to the delay data storage area 307. Data is sequentially read from the area to be processed. In the example shown in FIG. 7, data from n 510 in the normal data storage area 306 is read at time t 550, and data from n + 2 512 in the delay data storage area 307 is read at time t + 1 551. After that, at time t + 2 552, data from n + 1 511 in the normal data storage area 306, at time t + 3 553, data from n + 2 512 in the normal data storage area 306, and at time t + 4 554, n + 3 in the normal data storage area 306. At time n + 5 555, data from 513 is read out from n + 4 514 in the normal data storage area 306, and a data string 570 is generated.

  The time shown in FIGS. 6 and 7 is based on the framing cycle time. For example, when 8 frames are grouped together, 125 μsec × 8 = 1 msec is the framing cycle time. A value obtained by multiplying this is the processing time.

  FIG. 8 is a diagram for explaining a necessary capacity of the data buffer 305 in the transmission apparatus Z2 on the reception side. Next, referring to FIG. 8, absorption of packet transmission delay fluctuation and data loss in the transmission apparatus Z2 on the reception side A description will be given of the data arrival time difference absorption associated with the later arrival data reading, and the capacity of the data buffer 305 necessary for that purpose.

  FIG. 8 shows accumulated processing waiting data 601 in the delay data storage area and accumulated processing waiting data 602 in the normal data storage area. The number of data 603 of accumulated processing waiting data 601 and 602 in both storage areas is a lower limit on the lower side of the figure, and an upper limit on the upper side of the figure, that is, an upper limit value of the buffer amount. Further, in the example shown in FIG. 8, it is shown that the data in the upper part of the figure is the newly written data and the data is older in the lower part. In the example shown in FIG. 8, the data f is stored last in the accumulated processing wait data 601 in the delay data storage area, and the data h is written last in the cumulative process wait data 602 in the normal data storage area. The upper areas are an empty area 607 and an empty area 608, respectively, where data is not written. As described with reference to FIG. 4, the data is read at a constant cycle from the bottom of FIG. 8, that is, the oldest data, by the reception data buffer read function unit 311.

  Normally, packets loaded with TDM data are generated periodically, and the data read cycle by the received data buffer read function unit 311 coincides with the packet generation cycle, and the cumulative number of data up to the latest data Is expected to be in the vicinity of the intermediate value 606 of the total capacity value of the reception data buffer 305. However, the transmission delay may fluctuate due to competition between packets generated in the packet network in front of the transmission device Z2 in the network including the transmission device Z2.

  The transmission apparatus Z2 on the receiving side according to the present invention prepares a reception data buffer having a sufficient buffer amount with respect to the above-described transmission delay fluctuation so as not to cause packet loss due to transmission delay fluctuation. In the example shown in FIG. 8, a reception data buffer having a buffer amount indicated by a packet transmission delay fluctuation absorbing range 604 taking into account the maximum case and the minimum case of transmission delay fluctuation is prepared, and the transmission delay fluctuation is absorbed. It is shown that.

  If the transmission device Z2 on the receiving side continues to receive packets from the packet network 4 and the transmission delay of the received packets is decreasing, the received data buffer 305 has an intermediate value 606 of the accumulated processing waiting data count 603. In the upper part, the latest data is written and exists, and the free area 607 and the free area 608 are reduced. On the other hand, when the transmission delay of the received packet is in the increasing direction, the latest data is written in the received data buffer 305 below the intermediate value 606 of the accumulated processing wait data number 603, and the free space is present. 607 and free space 608 increase. If the reception data buffer 305 has a sufficient buffer amount with respect to delay fluctuations in both cases of an increase and a decrease in transmission delay, there is no shortage of free space, and data Data does not exist in the buffer, and data to be transmitted to the TDM data string is not interrupted.

  As described above, the reception data buffer 305 only needs to have a capacity necessary for absorbing the delay fluctuation of the packet in the network. However, as the capacity increases, the processing delay for the packet also increases accordingly. It is advisable to have the minimum capacity necessary to absorb.

  As described above, the transmission device Z2 on the reception side has a mechanism for absorbing transmission delay fluctuations of packets generated in the packet network. In other words, the function of absorbing the transmission delay fluctuation is delayed by delaying data received from the packet network by time conversion of the intermediate value 606 of the reception data buffer 305 and transmitting the delayed data to the TDM interface. It absorbs fluctuations.

  In the received data buffer having the delay fluctuation absorbing function shown in FIG. 8, the packet transmission delay fluctuation absorbing range 604 is further changed from normal data to delay data, which is a time difference for packetizing normal data and already transmitted delay data. When the capacity of the data buffer is expanded by the offset 605 between the two, it becomes possible to absorb the data arrival time difference associated with the later arrival data read due to data loss.

  In this case, the reception data buffer read function unit 311, when reading data from the accumulation processing waiting data 601 side in the delay data storage area, as usual, at the bottom of the reception data buffer 305 that is the buffer data read position 609 of the delay data When reading data from the accumulation processing waiting data 602 side in the normal data storage area, the normal buffer read position 610 that is newer than the bottom data by the offset 605 between the normal data and the delayed data is read. In other words, the upper data is read out.

  As described above, the transmission device Z2 on the receiving side can absorb the data arrival time difference associated with the later arrival data read due to the data loss with almost the same configuration as the mechanism for absorbing the transmission delay fluctuation in the packet network. .

  According to the above-described embodiment of the present invention, the function of buffer read pointer control can be achieved without mounting complicated circuits such as an error correction code arithmetic circuit and an error correction arithmetic circuit on both the transmission side and the reception side. By adding a simple function such as addition or expansion of a buffer for absorbing delay fluctuations, it becomes possible to compensate for packet loss due to bit errors occurring in the packet network.

  That is, according to the embodiment of the present invention, when a TDM signal is converted into CEP and transmitted using a packet network, a circuit that compensates for a 1-bit error can be realized without causing a significant increase in cost.

  In general, since the PDH signal is a low speed among TDM signals, for example, the data length when a 64 kbit / sec signal is packetized at a 1 msec period (125 μsec × 8 frames) is 8 bytes. Even if a 1-byte signaling data transfer area and a 4-byte CEP header are added to this, the data length is only 13 bytes, and in order to satisfy 64 bytes, which is the shortest data length of the MAC frame, dummy data is packed in the surplus area in the payload area. An operation called padding is performed.

  In the embodiment of the present invention described above, the area in the payload in which already transmitted data is mounted is this padding area, and the already transmitted data can be mounted in this padding area in the packet. A TDM signal can be packetized and transmitted via a packet network without causing a decrease in transfer efficiency.

1 Transmission equipment A
2 Transmission equipment Z
3, 5 TDM interface 4 packet network 6, 10 TDM signal 12 clock supply device 101 TDM reception interface 102 copy function unit 103 delayed write function unit 104 normal write function unit 105 transmission data buffer 106 packet generation function unit 107 packet transmission interface 108 normal Data storage area 109 Delayed data storage area 111 Payload part generation function part 112 Overhead part generation function part 113 Free-running oscillator 114 Read timing generation function part 301 Packet reception interface 302 Packet termination function part 303 Overhead part termination function 304 Reception buffer write function part 305 Reception data buffer 306 Normal data storage area 307 Delayed data storage area 309 Packet loss detection function unit 3 0 read pointer control function unit 311 receives the data buffer read function unit 312 read timing generation section 313 TDM transmit interface 314 external reference clock receiving unit

Claims (6)

In the transmission apparatus on the transmission side that packetizes the TDM signal and sends it to the packet network,
Means for making the data of the TDM signal into two data;
One of the two data is set as normal data, the other of the two data is held for a certain period as delay data, is delayed between the normal data and the certain period, and is constant. A transmission apparatus on the transmission side, comprising: means for transmitting the delay data, which is already transmitted before a cycle, in a packet. In the transmission apparatus on the receiving side that receives a packet from the packet network and outputs the packetized TDM signal as the original TDM signal,
Means for extracting normal data and delay data mounted in the packet;
A means for reproducing normal data that should have been loaded in the lost packet by using delayed data extracted from a packet received after a certain period when there is a packet lost due to an error in data. A transmission device on the receiving side. In the transmission apparatus on the transmission side that packetizes the TDM signal and sends it to the packet network,
A TDM receiving interface for receiving a TDM signal from the TDM interface;
A transmission data buffer having a normal data storage area and a delayed data storage area;
Normal writing means for writing data of the TDM signal received from the TDM receiving interface into a normal data storage area of the transmission data buffer;
The data of the TDM signal received from the TDM reception interface is held for a certain time which is a delay offset time, and then the delay data of the transmission data buffer is synchronized with the timing at which the normal data writing means writes data to the normal data storage area. A delayed writing means for writing to the storage area;
At the timing generated based on the external reference clock, data is read from the same address in the normal data storage area and the delay data storage area of the transmission data buffer, and the normal data and the delayed data that has been transmitted as normal data in the past are 1 A packet generation means that is mounted on one packet and packetized by assigning a sequence number;
A transmission apparatus on the transmission side, comprising: a packet transmission interface that transmits the packet generated by the packet generation means to a packet network. In a transmission apparatus on the receiving side that extracts data from a packet in which data of a TDM signal is packetized and outputs the data as a TDM signal,
A packet reception interface for receiving a packet in which normal data of a TDM signal and delayed data that has been transmitted as normal data in the past are packetized from the packet network;
A reception data buffer having a normal data storage area and a delayed data storage area;
Packet termination means for writing each of the normal data and the delayed data extracted from the received packet to the same address of the normal data storage area and the delayed data storage area of the reception data buffer, and extracting the sequence number from the received packet;
Receiving the sequence number and comparing it with the sequence number of the packet received last time, the lack of the sequence number, that is, the packet loss detection means for detecting the packet loss;
Based on the information on the presence or absence of detected packet loss, if there is no packet loss, determine the pointer to read data from the address next to the previous read address in the normal data storage area as a read pointer from the received data buffer, A read pointer control means for determining a pointer to read data from an address obtained by adding a delay offset time to the previous read address in the delay data storage area as a read pointer from the reception data buffer when there is a packet loss;
A reception data buffer reading means for reading data from an address in the reception data buffer indicated by the read pointer determined by the read pointer control means at a timing generated based on an external reference clock;
A reception-side transmission apparatus comprising: a TDM transmission interface that reproduces data read from the reception data buffer as a data string of TDM data and sends the data to a TDM interface. The transmission apparatus on the receiving side according to claim 4,
The reception data buffer has a buffer amount sufficient to absorb delay fluctuation that may occur in the packet network, and the transmission device on the transmission side packetizes the normal data and then packetizes the normal data as delay data. A transmission apparatus on the receiving side, which has a buffer capacity to which a buffer amount corresponding to the offset time up to is added. A transmission system for transmitting and receiving a TDM signal, comprising: a transmission device on the transmission side that packetizes the TDM signal and sends it to the packet network; and a transmission device on the reception side that outputs the received packetized TDM signal as the original TDM signal. In
The transmission device on the transmission side is:
Means for making the data of the TDM signal into two data;
One of the two data is set as normal data, the other of the two data is held for a certain period as delay data, is delayed between the normal data and the certain period, and is constant. Means for transmitting the delayed data, which is already transmitted data before the cycle, in a packet,
The transmission device on the receiving side is
Means for extracting normal data and delay data mounted in the packet;
Means that, when there is a packet that is missing due to a data error, normal data that should have been loaded in the missing packet is regenerated using delayed data extracted from the packet received after a certain period. A transmission system characterized by that.

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