JPH1188301A - Low bit rate multimedia communication method - Google Patents

Abstract

(57) [Summary] The present invention relates to a low bit rate multimedia communication protocol, in which each AL-P transmitted in a divided manner is transmitted.
An object is to ensure that a DU can be reproduced in an AL-SDU on a receiving side. When an AL-SDU is divided and transmitted, a PM (packet marker), which is combined information of each divided AL-SDU (= AL payload field), is transmitted to the AL.
-An extension field is provided in the PDU and stored there, and even when retransmission occurs, the AL payload field and PM
(Packet marker) to be retransmitted in the set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ARQ (ARQ
The present invention relates to a low-bit-rate multimedia communication method that can reliably combine and reconstruct divided data on the receiving side when error correction is performed by utomatic Repeat reQuest).

[0002]

2. Description of the Related Art In recent years, low bit rate
Video encoding systems for multimedia services, multiplexing systems, and communication procedures have been officially recommended. Video communication terminal devices such as TV conference systems and video TV phones conforming to ITU-T recommendations from various companies. Has been released. Under these circumstances, H.324 (multimedia terminal for GSTN low bit rate videophone service) is H.223.
(Multiplexing protocol for low bit rate multimedia communication) is used as part of the communication method.

Conventionally, as a low bit rate multimedia communication method, a method as shown in FIGS. 5, 6, 8, and 9 is generally used, and will be described below with reference to these drawings.

FIG. 5 shows a conventional AL3-SDU (Adaptation Layer 3-Service Data Unit) divided into ALs.
FIG. 3 is a configuration diagram of a MUX-PDU when stored in a 3-PDU (Adaptation Layer 3-Protocol Data Unit). Here, the protocol data unit (PDU) is a unit of information exchanged between peer protocol layer entities, and includes a service data unit (SD).
U) is a logical unit of information that is completely transferred from one protocol layer entity to another. Generally, a service data unit is the minimum unit of data that can be reproduced by a decoder.

[0005] Audio is divided into audio data (AL2-SDU) of 30 [ms], which is the minimum unit that can be reproduced according to ITU-T Recommendation G.723, and is directly incorporated into AL2-PDU (audio). The image is transmitted by dividing video data (AL3-SDU) for one frame reproducible by ITU-T Recommendations H.261 and H.263 into a plurality of AL3-PDUs.

In FIG. 5, an AL3-SDU composed of video data is shown.
Is divided, converted into an AL3-PDU, and incorporated into the MUX-PDU. Here, the AL3-SDU is divided into three AL3 payload fields, each of which is added with an AL3 header and an AL3 CRC field, and converted into an AL3-PDU. In FIG. 5, reference numeral 12 denotes M located at the head of the MUX-PDU.
UX header. Reference numeral 17 denotes an AL3 payload field mainly assigned in the MUX-PDU for transmitting video data. 19 is the AL3 payload field, 20 is A
An L3 payload field, 21 is an AL3 payload field.

When a data unit (AL3-SDU) composed of data to be transmitted is divided and transmitted as shown in FIG. 5, each of the plurality of divided data units is stored in a separate MUX-PDU. And store the combined information of the divided data units in each MUX-PD
It is stored in the MUX header 12 of U.

FIG. 3 shows an AL3 header format.
As shown in FIG. 3, the AL3 header 16 includes an SN (sequence number field) and a PT (AL-PDU payload type). SN (sequence number field)
Indicates that the receiving side is missing the AL-PDU or the MUX-PDU
This is an order number used to detect that the layer has been erroneously delivered. The PT indicates the payload type of the AL-PDU. When the PT is “1”, it indicates that the AL-PDU payload field includes the AL-SDU. Also, when the PT is “0”, it indicates that the AL-PDU payload field includes a monitoring message used in the retransmission procedure.

The AL3 CRC field 18 is used to perform error detection over the entire AL-PDU including the AL3 header. The value of the CRC field is obtained by dividing the contents of the AL-PDU excluding the CRC field bits by a generator polynomial (modulo
2) The remainder.

[0010] When the AL3-SDU is divided into AL3 payload fields and converted into AL3-PDUs, data of different AL3-SDUs is not incorporated in one AL3 payload field. This is determined by H.223, and eliminates the need to separate the AL3-SDU on the receiving side. Conversely, the break of the video frame of AL3-SDU is the break of AL3-PDU. The audio data (AL2-SDU) is not divided. In FIG. 5, the MU is used for AL2-PDU and AL3-PDU.
An X-SDU is configured, and a MUX header is added to the MUX-SDU.

As shown in FIG. 6, the MUX header 12 is composed of MC (multiplex code field), HEC (header error control field), and PM (packet marker field). The MC (multiplexing code field) refers to the entry of the multiplexing table, and the MUX-PDU
Each octet of the information field (MUX-SDU) indicates which logical channel it belongs to. The receiving side can know which AL PDU is incorporated in the MUX-SDU by using the multiplexing code. The HEC (header error control field) is a 3-bit CRC and provides an error correction function for a multiplexed code field.

[0012] The MUX header 12 stores connection information of the divided AL3 payload fields. PM mentioned above
The (packet marker field) is used to mark the end of the MUX-SDU of the divisible logical channel. Specifically, PM (packet / packet) of the MUX header of the MUX-PDU in which the data of the AL3 payload field is written
Marker) is set to “0” indicating that the data of the previous MUX-PDU is not the data of the last octet. The PM of the MUX header of the MUX-PDU in which the data of the AL3 payload field is written is also set to “0” indicating that the data of the previous MUX-PDU is not the last octet data. On the receiving side, when the PM is "0", it is combined with the data of the AL3 payload field of the previous MUX-PDU.

On the contrary, the PM of the MUX-PDU of the MUX-PDU in which the data of the AL3 payload field is written is set to “1” indicating that the data of the previous MUX-PDU is the last octet data. You. On the receiving side, PM is "1"
Is not combined with the data of the previous MUX-PDU,
Processing is performed with the data of the AL3 payload field of the UX-PDU at the top. Multimedia data is multiplexed in the above data format.

FIG. 8 and FIG. 9 are sequence diagrams of procedures for retransmission when an error occurs in the AL3-PDU and reconfiguration of the AL3-SDU. Retransmission and A when an error occurs in AL3-PDU
The L3-SDU reconfiguration sequence will be described with reference to FIG. In FIG. 8, the left half is the transmitting side and the right half is the receiving side, and time flows from top to bottom. For each frame of video data to be transmitted here, the first frame is frame A, the next frame is frame B, and the next frame is frame C.

First, communication processing of frame A is performed.
On the transmitting side, the AL3-SDU of frame A is divided into three AL3 payloads (A-, A-, A-), stored in a MUX-PDU, and transmitted. MUX of MUX-PDU storing AL3 payload A-
“1” is stored in the PM of the header, which indicates that the MUX-PDU storing the AL3 payload A- stores the first octet of the frame A.

When the receiving side that has received the MUX-PDU storing the AL3 payload A- checks the AL3 CRC and confirms that there is no error, it is the beginning of a new frame because the PM of the MUX header is "1". Therefore, reconfiguration of a new AL3-SDU is started.

Next, the MUX-P storing the AL3 payload A-
DU is sent. In the PM of the MUX header of this MUX-PDU,
“0” is stored to indicate that the previous MUX-PDU has stored data of frame A. That is, AL3 payload A-
Indicates that the data from the middle of the frame A is stored in the MUX-PDU.

The receiving side that has received the MUX-PDU storing the AL3 payload A- checks the AL3 CRC. In FIG. 8, a communication error has occurred in the MUX-SDU storing the AL3 payload A-, and the CRC calculation result results in an error. However, in FIG. 8, no error has occurred in the MUX header.

[0019] The received MUX-SDU is discarded. Also MUX
MC (multiplexing code) and HEC among the contents of the header
(Header error control) is discarded because it has no meaning. However, PM is valid. Here, since PM = 0, it is recognized that the data stored in the previous MUX-PDU is not the last octet.

[0020] The PM of the MUX header of the MUX-PDU storing the AL3 payload A- sent next thereto stores "0" in the PM, which indicates that the MUX-PDU storing the AL3 payload A- is in the middle of the frame A. Indicates that the data from is stored. The receiving side that has received the MUX-PDU storing the AL3 payload A- checks the AL3CRC and confirms that there is no error. Since the PM of the MUX header is "0", the previous MUX-PDU is received.
Recognizes that it does not store the last octet of frame A, and tries to concatenate it with the AL3 payload of the previous packet.

However, since the immediately preceding AL3 payload has been discarded due to a CRC error, the AL3 header shown in FIG.
A discontinuity in the SN of the format is detected. For this reason,
A retransmission request is transmitted so that the AL3 payload of the SN assumed to be received is transmitted again. This SN is written in the retransmission request message sent to the transmission side. Note that the PM information in the MUX header of the MUX-PDU that stores the AL3 payload A- is meaningless and is discarded because it is information about the MUX-SDU immediately before that that could not be correctly received.

When the transmitting side receives the retransmission request message,
The SN packet and the AL3 payload A- included in this message are retransmitted. MUX-PDU sent earlier is AL3
The payload A- is stored, and since this is the end of frame A, even if it is retransmission, the retransmission data (AL3
PM of MUX header of MUX-PDU that stores payload A-)
Stores "1".

The receiving side that has received this retransmitted packet has the AL
3 Check the CRC and check for errors. After confirming that there is no AL3CRC error, the SN is checked next. If the SN matches the SN that issued the retransmission request, the packet is recognized as a retransmission response packet.

When the packet is recognized as a retransmission response packet, the connection process is performed according to the fact that the PM at the time when the AL3 CRC error occurred was "0" regardless of the PM of the MUX header in the packet. , And is concatenated with the AL3 payload (A-) that has completed reception up to that point. That is,
The content of PM received by the retransmission response packet is "1"
Is meaningless to the receiving side and is discarded.

When the retransmission of the AL3 payload A- is completed, the transmitting side also retransmits the next packet AL3 payload A-. The PM of the MUX header of the MUX-PDU storing the AL3 payload A- (retransmission packet) contains "0" to indicate that data from the middle of the frame A is stored as in the case described above. Is stored. The receiving side that has received the retransmission packet checks the AL3CRC and if there is no error, then checks the SN. If the continuity of the sequence numbers is confirmed, the connection processing is performed with the AL3 payload A- previously received because the PM received at this time is "0".

Next, communication processing of frame B is performed.
For the frame B, the transmitting side divides the AL3-SDU into two AL3 payloads (B-, B-), stores them in a MUX-PDU, and transmits them. MUX of MUX-PDU containing AL3 payload B-
"1" is stored in the PM of the header, which is the AL3 payload
The MUX-PDU storing B- indicates that the first octet of the frame B is stored.

When the receiving side that has received the MUX-PDU storing the AL3 payload B- confirms that there is no error, it determines that the start of a new frame has occurred since the PM of the MUX header is "1". Start reconstruction of a new AL3-SDU.
At the same time, it is determined that the previously received frame A has ended, and the processing of the AL3-SDU of the completed frame A is transferred to the video encoder 23 (decoding process) in FIG.

MU of MUX-PDU storing AL3 payload B-
“0” is stored in the PM of the X header, which indicates that the MUX-PDU storing the AL3 payload B- stores data from the middle of the frame B.

The receiving side that has received the MUX-PDU storing the AL3 payload B- checks the AL3CRC, and if there is no error, the SN next.
Find out. If the continuity of the sequence numbers is confirmed, the connection processing is performed with the previously received AL3 payload B- because the PM received at this time is "0".

Subsequently, communication processing of frame C is performed in the same procedure. On the transmitting side, the AL3-SDU of the frame C is divided into two AL3 payloads (C-, C-), stored in the MUX-PDU, and transmitted.

In such a flow, retransmission when an error occurs in the AL3-PDU and reconfiguration of the AL3-SDU are executed.

[0032]

Problems in such a conventional low bit rate video communication method will be described with reference to FIG.

When performing communication processing of frame A, even if a communication error occurs as shown in FIG.
Since no error has occurred in the header, PM (packet marker) is valid. However, in the example of FIG. 9, a communication error has occurred in the MUX-SDU storing the AL3 payload A-, and therefore, the CRC calculation result results in an error. Further, in FIG. 9, an error has occurred in the MUX header unfortunately, and PM = “0” is reversed to PM = “1”. At this time, among the contents of the MUX header, MC and HEC are discarded, but PM (packet marker) is valid.

Next, the transmitting side sends a MUX-PDU storing the AL3 payload A-, and the PM of the MUX header of the MUX-PDU is transmitted.
Stores "0" indicating that data from the middle of frame A is stored. Stored AL3 payload A-
When the receiving side that has received the MUX-PDU confirms that there is no error, since the PM of the MUX header is “0”, the receiving side attempts to connect to the AL3 payload of the previous packet.

However, since the previous AL3 payload has been discarded due to a CRC error, the AL3 header shown in FIG.
A discontinuity in the SN of the format is detected. AL
3 Send a retransmission request so that the payload is transmitted.
This SN is included in the retransmission request message. At this time
The PM information of the MUX-PDU that stores the AL3 payload A-
MUX-SDU just before that could not be received correctly
Is meaningless and is discarded.

The transmitting side receiving the retransmission request message,
The SN packet and the AL3 payload A- included in this message are retransmitted. Previous MUX-PDU is already AL3
Since the payload A- is stored and is the end of the frame A, “1” is stored in PM of the MUX header of the retransmission MUX-PDU storing the AL3 payload A-.

When the receiving side that has received the retransmission packet confirms that there is no error, it next checks the SN. SN
If this matches the SN that made the retransmission request, it recognizes that this packet is a retransmission response packet. But before
When an AL3CRC error occurs, since the PM of the MUX-PDU has become "1", it is determined that this is the start of a new frame, and reconfiguration of a new AL3-SDU is started. As described above, when the PM is received as “1” due to the error, the connection processing is not performed when the retransmission response packet is received thereafter.

When the retransmission of the AL3 payload A- is completed, the transmitting side retransmits the next packet AL3 payload A-. MUX of MUX-PDU storing this AL3 payload A-
“0” is stored in the PM (packet marker) of the header. The receiving side that has received the retransmission packet checks the SN next if there is no error. If the continuity of the sequence numbers is confirmed, the connection processing is performed with the AL3 payload A- previously received because the PM received at this time is "0".

As described above, since the PM has been inverted due to the occurrence of the error, one frame A is composed of the frame A composed of the AL3 payload A- and the frame A composed of the AL3 payload A-.
In addition, the frame is divided into two frames, that is, the frame A including the AL3 payload A-, and is processed on the receiving side. For this reason, the video encoder 23 cannot correctly decode the video.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to enable each receiving side to reliably reproduce each of the divided AL-PDUs in an AL-SDU.

[0041]

According to the present invention, in order to achieve the above object, when an AL-SDU is divided and transmitted,
An extended field is provided in an AL-PDU and a PM (packet marker), which is combined information of each divided AL-SDU (= AL payload field), is stored therein.

According to the present invention, each AL-PDU that is divided and transmitted can be reliably reproduced in the AL-SDU on the receiving side.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, when a data unit consisting of data to be transmitted is divided and transmitted, each data unit divided into a plurality of data units is transmitted.
Storing the unit in a payload field, storing a packet marker indicating combination information of the divided data units in an extension field in the payload field, storing error detection information in the payload field, and receiving On the side, a low bit rate multimedia communication method for reconstructing a data unit based on a packet marker stored in an extension field of the payload field, wherein each AL-PDU divided and transmitted is This has the effect that the data can be reliably reproduced in the AL-SDU on the receiving side.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 shows an AL according to an embodiment of the present invention.
FIG. 3 is a configuration diagram of a MUX-PDU when a 3-SDU is divided and stored in an AL3-PDU. FIG. 2 is a multiplexing block diagram of a multiplexing protocol for low bit rate multimedia communication, and FIG. 3 is an AL3 header format. FIG. 4 shows an extended format of the AL3-PDU. FIG. 7 shows a MUX- according to the embodiment of the present invention.
FIG. 13 is a sequence diagram of a procedure for retransmission and an AL3-SDU reconfiguration when an error occurs in a PDU.

FIG. 1 shows an AL3-SDU (Adaptation Layer 3-Service Data Unit) divided into AL3-PDUs.
1 shows a configuration of a MUX-PDU (multiplex-protocol data unit) when stored in an (adaptation layer 3-protocol data unit). In FIG. Is an AL2 payload field, 4 is an AL2 CRC field, 5 is an AL3 header, 6 is an AL3 payload field, 7 is an AL3 extension field, and 8 is an AL3 CRC field. The transmission data frame AL3-SDU is divided into a plurality of parts for transmission. 9 is A
L3 payload field, 10 is AL3 payload field, 11 is AL3 payload field,
Thus, the transmission data frame AL3-SDU is divided into three, and the divided subunits are stored in the above-described AL3-PDU.

FIG. 2 shows a multiplexing block diagram of a multiplexing protocol for low bit rate multimedia communication. As shown in FIG. 2, reference numeral 22 denotes a video input / output, 23 denotes a video encoder, and 24 denotes an adaptation layer 3 ( AL3), 25 is an audio input / output, 26 is an audio encoder, 27 is an adaptation layer 2 (AL2), 28 is an application, 29 is a data protocol, 30 is H.245 control,
31 is LAPM, 32 is adaptation layer 1 (AL
1) and 33 are multiplex layers, and 34 is a physical layer.

The video data output from the video input / output 22 as shown in FIG.
Output as 3-SDU. AL3-SDU is an adaptation
The data is converted into an AL3-PDU by the layer 3 (AL3) 24.

The audio data output from the audio input / output 25 is encoded by the audio encoder
Output as 2-SDU (Adaptation Layer 2-Service Data Unit). The AL2-SDU is converted into an AL2-PDU (Adaptation Layer 2-Protocol Data Unit) by an adaptation layer 2 (AL2) 27.

The user data output from the application 28 is converted by the data protocol 29 and
SDU (Adaptation Layer 1-Service Data
Unit). The AL1-SDU is converted by an adaptation layer 1 (AL1) 32 into an AL1-PDU (Adaptation Layer 1-Protocol Data Unit).

The control command output from the application 28 is converted into control data by the H.245 control 30 and output. The control data output from the H.245 control 30 is LAPM (L
Ink Access Procedure on the Modems (31), which is also output as AL1-SDU (Adaptation Layer 1-Service Data Unit), which is also converted into AL1-PDU in Adaptation Layer 1 (AL1) 32 You.

The multiplexing layer 33 includes an adaptation layer
The AL3-PDU from the layer 3 (AL3) 24, the AL2-PDU from the adaptation layer 2 (AL2) 27, and the AL1-PDU from the adaptation layer 1 (AL1) 32 are multiplexed, and M
Outputs UX-PDU. MU output from multiplexing layer 33
The X-PDU is converted into a physical signal in the physical layer 34.

The multimedia data is multiplexed through the above process, and FIG. 1 shows the data format. In FIG. 1, the AL3-SDU is divided and the AL3
-It is converted into a PDU and incorporated into the MUX-PDU. Here, the AL3-SDU is divided into three AL3 payload fields, each of which is added with an AL3 header, an AL3 extension field, and an AL3 CRC field, and is converted into an AL3-PDU.

The AL3 header comprises an SN (sequence number field) and a PT (AL-PDU payload type) as shown in FIG. The SN (sequence number field) is a sequence number used to detect that the AL-PDU is missing on the receiving side or that the AL-PDU is erroneously delivered in the MUX-PDU layer.

PT (AL-PDU payload type) is AL-PDU
When the PT is "1", it indicates that the AL-PDU payload field contains AL-SDU,
When the PT is "0", it indicates that the AL-PDU payload field contains a monitoring message used in the retransmission procedure.

In this embodiment, as shown in FIG.
A PM (packet marker) is also provided in the extension field. This PM is used to mark the end of the MUX-SDU of the splittable logical channel. As shown in FIG. 1, in the AL3 extension field of the AL3-PDU including the AL3 payload field, information on coupling with the AL3 payload field is stored.

That is, the AL3-PDU including the AL3 payload field and the AL3-PDU including the AL3 payload field
PM (packet marker) of the AL3 extension field of the PDU
Is set to "0" to indicate that the data of the AL3-PDU is not the data of the last octet. Conversely, the PM of the AL3 extension field of the AL3-PDU including the AL3 payload field is set to “1” to indicate that the data of the AL3-PDU is the last octet data. It should be noted here that the PM of the AL3 extension field does not necessarily indicate the binding information with the AL3 payload field included in the immediately preceding AL3-PDU, and the most recent AL3 including the AL-SDU does not necessarily indicate the binding information. -It indicates connection information with the AL3 payload field of the PDU.

The AL3CRC field contains an AL- header including an AL3 header.
Used to perform error detection across the PDU. The value of the CRC field is divided by the generator polynomial from the contents of the AL-PDU excluding the CRC field bits (modulo 2)
Is the remainder.

In H.223, when an AL3-SDU is divided into AL3 payload fields and converted into an AL3-PDU, different AL3-SDU data is not incorporated in one AL3 payload field, and This eliminates the need to separate AL3-SDU. Conversely, the break of the video frame of AL3-SDU is the break of AL3-PDU.

The AL2-SDU is the same as the AL3-SDU. However, since the delimiter of the audio data is 30 [ms] data, the AL2-SDU is divided into 22 bits or 26 bits. Since this data amount is sufficiently small for the communication packet, the AL2-SDU is not usually divided.

As shown in FIG. 5, MAL-PDU is used for AL2-PDU and AL3-PDU.
An SDU is configured, and a MUX header is added to the MUX-SDU to form a MUX-PDU. As shown in FIG. 6, the MUX header is composed of MC (multiplex code field), HEC (header error control field), and PM (packet marker field). As in the related art, the multiplex code field indicates which logical channel each octet of the MUX-PDU information field (MUX-SDU) belongs to by referring to the entry of the multiplex table.
The receiving side uses this multiplexing code to specify which AL to MUX-SDU.
Of PDUs are installed. The header error control field is a 3-bit CRC and provides an error correction function for the multiplexed code field.

The PM provided in the MUX header is used to mark the end of the MUX-SDU of the divisible logical channel as in the related art. That is, the PM of the MUX-PDU including the AL3 payload field and the PM of the MUX-PDU including the AL3 payload field in FIG.
(AL3 payload field) is set to "0" to indicate that it is not the last octet data. Conversely, MUX-P with AL3 payload field
PM of the MUX header of the DU is set to “1” to indicate that the data of the previous MUX-PDU is the data of the last octet. As described above, the PM of the MUX header contains the immediately preceding AL3
-Store binding information with the AL3 payload field included in the PDU. This is provided for consistency with existing systems, and the receiving side of the present invention uses the PM of the MUX header.
No information is used.

The multimedia data is multiplexed in the data format described above. Next, a sequence of retransmission and an AL3-SDU reconfiguration when an error occurs in the AL3-PDU will be described with reference to FIG. In FIG. 7, the left half is the transmitting side and the right half is the receiving side, and time flows from top to bottom.

First, communication processing of frame A is performed.
On the transmitting side, the AL3-SDU of frame A is divided into three AL3 payloads (A-, A-, A-), stored in a MUX-PDU, and transmitted. AL3 of AL3-PDU containing AL3 payload A-
The PM (packet marker) in the extension field indicates that the next AL3-PDU stores the data of frame A. "
0 "is stored. That is, M that stores AL3 payload A-
The UX-PDU indicates that it does not include the last octet of frame A. MUX that stores this AL3 payload A-
-PDU is a normal packet, not a retransmitted packet. AL
3 The receiving side that has received the MUX-PDU storing the payload A-
Check the AL3CRC and confirm that there is no error. Since the PM of the AL3 extension field is "0", the next A to be received
It determines that the AL3-SDU included in the L3 payload is to be combined with the current AL3-SDU and waits.

In the PM of the extension field of the AL3-PDU storing the AL3 payload A-, "0" indicating that the next AL3-PDU stores the data of the frame A is stored. That is, AL3
This indicates that the MUX-PDU storing the payload A- does not include the last octet of the frame A. The MUX-PDU storing the AL3 payload A- is a normal packet, not a retransmission packet. The receiving side that has received the MUX-PDU storing the AL3 payload A- checks the AL3 CRC.

In FIG. 7, a communication error has occurred in the MUX-SDU storing the AL3 payload A-, so that the CRC calculation result results in an error. MUX received for this
-SDU is discarded. At this time, MUX header, AL3 header, AL
The three payloads and the AL3 extension field are all discarded, and the PM at this time is not used.

MU of MUX-PDU storing AL3 payload A-
In the PM of the X header, “1” indicating that the next AL3-PDU stores the data of the next frame of the frame A is stored. That is, it indicates that the MUX-PDU storing the AL3 payload A- includes the last octet of the frame A. The MUX-PDU storing the AL3 payload A- is a normal packet, not a retransmission packet. AL3 payload A
When the receiving side that has received the MUX-PDU storing the-confirms that there is no error, since the PM of the AL3 extension field is "1", the current MUX-PDU stores the last octet of frame A. Recognize that

However, since the immediately preceding AL3 payload has been discarded due to a CRC error, the AL3 header shown in FIG.
A discontinuity in the SN (sequence number) of the format is detected. Therefore, a retransmission request is transmitted such that the AL3 payload of the SN assumed to be received is transmitted.

The SN is included in the retransmission request message. At this time, the PM information in the extension field of the AL3-PDU that stores the AL3 payload A- is meaningless and is discarded because it is information about the AL3-SDU immediately before that that could not be correctly received.

When the transmitting side receives the retransmission request message,
The SN packet and the AL3 payload A- included in this message are retransmitted. Since the current AL3-PDU stores the AL3 payload A- and this is not the end of frame A, the AL3-PDU storing this AL3 payload A-
"0" is stored in the PM of the extension field of. This AL3
The MUX-PDU storing the payload A- is a retransmission packet, not a normal packet.

When the receiving side receiving this retransmission packet confirms that there is no error, it then checks the SN. SN
Is the same as the SN that made the retransmission request, the packet is recognized as a retransmission response packet, and the PM of the AL3 extension field of the AL3 payload A- received before is "0". Perform connection processing with AL3 payload A-. Note that PM = "0" in the retransmission packet at this time indicates that the next AL3-SDU to be received will be connected thereafter.

When the retransmission of the AL3 payload A- is completed, the transmitting side retransmits the next packet AL3 payload A-. AL3 of the AL3-PDU that stores this AL3 payload A-
In the PM of the extension field, "1" indicating that this is the end of the frame A is stored.

If there is no error, the receiving side receiving the retransmission packet checks the SN next. If the continuity of the sequence numbers is confirmed, the connection processing with the AL3 payload A- is performed as it is. Also, since the PM of the extension field of the packet received at this time is “1”, it is determined that the frame A received so far has been terminated, and the
The processing of the AL3-SDU is transferred to the video encoder 23 (decoding processing) in FIG.

Next, communication processing of frame B is performed.
On the transmitting side, the AL3-SDU of frame B is divided into two AL3 payloads (B-, B-), stored in a MUX-PDU, and transmitted. In the PM of the AL3 extension field of the AL3-PDU storing the AL3 payload B-, “0” indicating that the next AL3-PDU stores the data of the frame B is stored. In other words, this indicates that the MUX-PDU storing the AL3 payload B- does not include the last octet of the frame B. The MUX-PDU storing the AL3 payload B- is a normal packet, not a retransmission packet.

The receiving side that has received the MUX-PDU storing the AL3 payload B- checks the AL3 CRC and confirms that there is no error. Since the PM of the MUX header is "0", the receiving side receives the MUX-PDU. The included AL3-SDU is the current AL3-SDU
And waits.

MU of MUX-PDU storing AL3 payload B-
In the PM of the X header, “1” indicating that the next AL3-PDU stores the data of the frame next to the frame B is stored. That is, it indicates that the MUX-PDU storing the AL3 payload B- includes the last octet of the frame A. The MUX-PDU storing the AL3 payload B- is a normal packet, not a retransmission packet.

The receiving side that has received the MUX-PDU storing the AL3 payload B- checks the AL3 CRC, and if there is no error, the next step is SN.
Find out. If the continuity of the sequence numbers is confirmed, since the PM received at this time is "1", it is determined that the frame B received so far is terminated, and the AL of the completed frame B is determined.
The processing of the 3-SDU is transferred to the video encoder 23 (decoding processing) in FIG.

Subsequently, a communication process for frame C is performed. On the transmitting side, the AL3-SDU of the frame C is divided into two AL3 payloads (C-, C-), stored in the MUX-PDU, and transmitted. “0” indicating that the next AL3-PDU stores the data of the frame C is stored in the PM of the MUX header of the MUX-PDU storing the AL3 payload C-. In other words, this indicates that the MUX-PDU storing the AL3 payload C- does not include the last octet of the frame C. This AL3 payload C
The MUX-PDU storing-is a normal packet. The receiving side that has received the MUX-PDU storing the AL3 payload C-
Check C and confirm that there are no errors.
Since M is “0”, it is determined that the AL3-SDU included in the AL3 payload to be received next is to be combined with the current AL3-SDU and waits.

In the manner described above, retransmission when an error occurs in the AL3-PDU and reconfiguration of the AL3-SDU are executed.

As described above, according to the low bit rate multimedia communication method of the present invention, each AL that is divided and transmitted is transmitted.
-The PDU can be reliably reproduced in the AL-SDU on the receiving side.

[0080]

As is apparent from the above description, according to the present invention, the PM, which is the combined information of the divided AL-SDUs (= AL payload field), is provided with an extension field in the AL-PDU. And store it there, even when retransmissions occur.
By making the AL payload field and PM (packet marker) retransmitted as a set, each AL-PDU that is transmitted separately can be reliably reproduced in the AL-SDU on the receiving side. Become.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a MUX-PDU when an AL3-SDU is divided and stored in an AL3-PDU according to an embodiment of the present invention.

FIG. 2 is a multiplexing block diagram of a multiplexing protocol for low bit rate multimedia communication according to the embodiment;

FIG. 3 is a diagram showing an AL3 header format according to the embodiment;

FIG. 4 is a diagram showing an extended format of an AL3-PDU in the embodiment.

FIG. 5 is a configuration diagram of a MUX-PDU when a conventional AL3-SDU is divided and stored in an AL3-PDU.

FIG. 6 is a diagram showing a header format of a MUX-PDU.

FIG. 7 is a sequence diagram of a retransmission procedure and an AL3-SDU reconfiguration procedure when an error occurs in a MUX-PDU according to the embodiment of the present invention.

FIG. 8: Retransmission and AL3 when an error occurs in AL3-PDU
-SDU reconfiguration procedure sequence diagram

FIG. 9 is a sequence diagram of a procedure of retransmission and AL3-SDU reconfiguration when an error occurs in a conventional MUX-PDU.

[Explanation of symbols]

 1 MUX header 3 AL2 payload field 4 AL2CRC field 6 AL3 payload field 7 AL3 extension field 8 AL3CRC field 9 AL3 payload field 10 AL3 payload field 11 AL3 payload field 22 Video input / output 23 Video encoder 24 Adaptation layer 3 (AL3) 31 LAPM 33 multiplexing layer

Claims (2)

[Claims] When a data unit composed of data to be transmitted is divided and transmitted, each of the plurality of divided data units is stored in a payload field,
A packet marker indicating the combined information of the divided data units is stored in an extension field of the payload field, and error detection information is stored in the payload field. A low bit rate multimedia communication method, comprising reconstructing a data unit based on a packet marker stored in an extension field. 2. A sub-unit obtained by dividing a data unit using a plurality of payload fields including an AL header, an AL payload field, an extension field, and an AL CRC field, and 2. The low bit rate multimedia communication device according to claim 1, wherein the communication is performed by storing the data in an AL payload field in the communication.