JP2004186737A - Communication apparatus and communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a communication apparatus capable of efficiently retransmitting packets without affecting a communication apparatus exchanging data having real time performance by packet communication using RTP. <P>SOLUTION: At a receiving terminal of an RTP packet, a retransmission control apparatus 20 detects the sequence number included in a received packet to be used for predetermined streaming, detects packet disposal on the basis of this sequence number, and requests retransmission of the packet based on the detection of the packet disposal. At a transmitting terminal of the RTP packet, a retransmission control apparatus 30 accumulates packets to be used for the predetermined streaming out of the transmission packets, and upon receiving the retransmission of the packets, the apparatus 30 transmits the accumulated corresponding packet to the retransmission request source. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication device and a communication system that control packet retransmission.
[0002]
[Prior art]
In a packet communication method using UDP (User Datagram Protocol) and IP (Internet Protocol), a UDP port number is added to an IP packet, but data is transmitted using the IP packet almost as it is. At the IP layer level, packets may be discarded due to congestion or the like, but UDP does not take this countermeasure.
[0003]
RTP (Realtime Transport Protocol) is a protocol used on UDP and IP, and provides a function of detecting a packet discarded on a communication path. The packet discard detection function of the RTP will be described. FIG. 7 is a diagram showing a format of the RTP packet. FIG. 8 is a diagram showing the configuration of the RTP header shown in FIG. The IP header includes an IP address and the like, and the UDP header includes a port number and the like.
[0004]
In RTP, the sequence number in the RTP header in FIG. 8 is changed one by one for each packet. Then, the receiving side identifies the discarded packet by detecting the discontinuity of the sequence number. However, the RTP does not specify the handling of the discarded packet, and performs a discard countermeasure process using a higher-level protocol. The type (payload type) in Fig. 8 indicates which upper layer protocol the packet is processed (for example, in the case of H.263, type "34").
[0005]
Next, a retransmission function of TCP (Transmission Control Protocol) will be described. TCP is a protocol used over IP and widely used in the Internet. In TCP, a TCP header has fields of a sequence number and a reception confirmation sequence number. The transmitting side attaches a sequence number to each packet and transmits the packet. The receiving side inserts the sequence number (reception confirmation sequence number) confirmed by the reception of the packet into the reception confirmation sequence number field and transmits the packet to the transmission side. The transmission side confirms the delivery of the transmitted packet based on the reception confirmation sequence number. If the acknowledgment of the transmission of the transmitted packet is not performed within a certain timeout period, the transmitting side retransmits the unacknowledged packet. As a result, all packets are normally delivered, and the reliability of communication data is ensured.
Further, unlike the RTP, the TCP checks received data by CRC and performs rate control for avoiding congestion. Therefore, the processing load is generally higher than that using UDP / IP, and applications requiring real-time properties are required. Often does not apply.
[0006]
There is also an apparatus that controls retransmission using an ARQ (Automatic Repeat Request) method (for example, see Patent Document 1). In the ARQ scheme, retransmission control is performed by returning an acknowledgment (ACK) for a received packet, and returning a negative acknowledgment (NAK) for a packet that could not be received.
[0007]
[Patent Document 1]
JP-A-11-88466
[Problems to be solved by the invention]
However, as described above, the function of detecting packet discard is provided in RTP, but the function of retransmitting the discarded packet depends on the upper layer protocol. Therefore, when reliability of communication data is required, since RTP does not include a retransmission protocol, it is necessary to use another protocol having a retransmission function such as TCP. However, there are problems such as a decrease in performance and a limitation of connectable communication devices.
[0009]
Further, in the ARQ method, since an acknowledgment (ACK) is transmitted, there is a problem that the use efficiency of the bandwidth resource is reduced. Further, since retransmission control is performed for all packets to be transmitted and received, unnecessary packets are retransmitted, and communication efficiency deteriorates.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to efficiently perform packet retransmission without affecting a communication device that transmits and receives real-time data by packet communication using RTP. It is an object of the present invention to provide a communication device and a communication system that can perform well.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, a communication device according to claim 1 includes a receiving unit that receives a packet, an identifying unit that identifies a type of the packet received by the receiving unit, and a receiving unit that receives the packet. Detecting means for detecting a sequence number included in the packet when identifying the packet, determining means for determining packet discard based on the sequence number detected by the detecting means, when the packet is discarded by the determining means, Retransmission request means for requesting retransmission of the packet.
[0012]
The communication device according to claim 2, wherein a transmission protocol of the packet is RTP, and a retransmission request of the retransmission request unit is added to an RTCP APP packet.
[0013]
4. The communication apparatus according to claim 3, wherein the transmitting unit adds a type to the packet and transmits the packet, a storage unit that stores the packet transmitted by the transmitting unit, a receiving unit that receives the packet, and retransmits the packet by the receiving unit. When receiving the request packet, there is provided control means for reading out a packet corresponding to the retransmission request from the storage means and transmitting the packet from the transmission means.
[0014]
5. The communication device according to claim 4, wherein a transmission protocol of the packet is RTP, and the control unit deletes all data in the storage unit when the receiving unit receives an RTCP BYE packet. And
[0015]
The communication system according to claim 5, wherein the communication terminal transmits at least a video signal compressed according to the MPEG-4 system from a transmission terminal to a reception terminal using RTP, wherein the transmission terminal includes a header of an RTP packet to be transmitted. The transmitting terminal further includes a transmitting unit for transmitting by adding the type of the element stream, and the receiving terminal determines whether the type of the element stream added to the header of the RTP packet received from the transmitting terminal is a type requiring retransmission. Identification means for identification, detection means for detecting a sequence number included in the packet when the identification means identifies the type as requiring retransmission, and determination of packet discard based on the sequence number detected by the detection means Determining means for determining whether to discard a packet. Characterized in that a retransmission request means for requesting.
[0016]
The communication system according to claim 6, wherein the retransmission request of the retransmission request unit is added to an RTCP APP packet.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration example of a communication system using retransmission control devices 20 and 30 (communication devices) according to an embodiment of the present invention. The communication system shown in FIG. 1 includes an RTP reception terminal 10, an RTP retransmission control device 20 located at an RTP packet reception end, an RTP retransmission control device 30 located at an RTP packet transmission end, and an RTP transmission device 40. .
The RTP transmitting device 40 provides data to the RTP receiving terminal 10 by packet communication using RTP. The RTP transmitting device 40 and the RTP receiving terminal 10 mutually transmit and receive RTP packets.
[0018]
The RTP retransmission control device 20 is connected to a highly reliable local network to which the RTP receiving device 10 is connected, and to the Internet 50. The RTP retransmission control device 20 has a function of transferring an RTP packet received from the Internet 50 to a local network and a function of retransmitting the RTP packet. The RTP retransmission control device 20 at the receiving end receives the RTP packet from the Internet 50, detects an RTP packet requiring retransmission, and transmits a retransmission request to the RTP retransmission control device 30 at the transmitting end.
[0019]
The RTP retransmission control device 30 is connected to a highly reliable local network to which the RTP transmission device 40 is connected, and to the Internet 50. The RTP retransmission control device 30 has a function of transferring an RTP packet received from the RTP transmission device 40 via the local network to the Internet 50, and a function of retransmitting the RTP packet. The RTP retransmission control device 30 at the transmission end monitors the packet sequence, accumulates RTP packets requiring reliability, and stores the accumulated RTP packets when there is a retransmission request from the RTP retransmission control device 20 at the reception end. resend.
[0020]
FIG. 2 is a block diagram showing the configuration of the RTP retransmission control device 20 at the receiving end shown in FIG. In FIG. 2, the multiplexing / restoring unit 210 receives the packet sequence transmitted from the RTP retransmission control device 30 at the transmitting end via the Internet 50, decomposes the packet sequence, and outputs the packet sequence to the RTP analysis unit 220.
The RTP analysis unit 220 determines whether the received RTP packet is an RTP packet included in the stream to be retransmitted, and performs a discard detection process on only the RTP packet to be retransmitted. The determination as to whether the stream is included in the retransmission target stream is made based on the value of the type (payload type) of the RTP header in FIG.
[0021]
In the discard detection process, the RTP analysis unit 220 checks the sequence number included in the RTP packet to be retransmitted, and compares the sequence number with the sequence number to be received next. As a result of the comparison, if the sequence numbers are different, it is determined that the packet has been discarded, and the sequence number of the discarded RTP packet is notified to the retransmission control unit 240 to instruct retransmission. Further, the RTP packets of the corresponding stream arriving after the time when the packet discard is detected are accumulated.
[0022]
Upon receiving a retransmission instruction from RTP analysis section 220, retransmission control section 240 generates an APP-RTCP packet for retransmitting the RTP packet of the notified sequence number, and outputs the APP-RTCP packet to multiplexing section 260. The APP-RTCP packet indicates an RTCP application-defined packet.
The multiplexing / restoring unit 250 receives the packet sequence transmitted from the RTP receiving terminal 10 via the local network, decomposes the packet sequence, and outputs the packet sequence to the multiplexing unit 260.
The multiplexing unit 260 multiplexes the APP-RTCP packet input from the retransmission control unit 240 with the packet input from the multiplexing decompression unit 250 and transmits the multiplexed packet to the RTP retransmission control device 30 at the transmission end via the Internet 50. .
[0023]
When receiving the retransmission packet from the RTP retransmission control device 30 via the Internet 50, the RTP analysis unit 220 outputs the retransmission packet and the stored RTP packet of the corresponding stream to the multiplexing unit 230 in sequence number order. The multiplexing unit 230 multiplexes the input packet and transmits the multiplexed packet to the RTP receiving terminal 10 via the local network. As a result, the RTP packets arrive at the RTP receiving terminal 10 in the order of the sequence numbers.
[0024]
Note that the RTP packets received from the Internet 50 may be sequentially transmitted to the RTP receiving terminal 10, and the received retransmission packets may be transmitted to the RTP receiving terminal 10 as they are. However, in this case, the RTP receiving terminal 10 rearranges the received packets in the order of the sequence numbers.
[0025]
FIG. 3 is a block diagram showing a configuration of the RTP retransmission control device 30 at the transmitting end shown in FIG. In FIG. 3, the multiplex restoration unit 310 receives a packet sequence transmitted from the RTP transmitting device 40 via a local network, decomposes the packet sequence, and outputs the packet sequence to the RTP analysis unit 320.
RTP analysis section 320 determines whether or not the received RTP packet is a packet included in the stream to be retransmitted, and stores only the RTP packet to be retransmitted in data storage section 350. Further, RTP analysis section 320 outputs the packet input from multiplexing / decompression section 310 to multiplexing section 330.
[0026]
The demultiplexing unit 370 receives the packet sequence transmitted from the RTP retransmission control device 20 at the receiving end via the Internet 50, decomposes the packet sequence, and outputs it to the RTP analysis unit 380.
When detecting the APP-RTCP packet generated by the RTP retransmission control device 20 at the receiving end, the RTP analysis unit 380 extracts a sequence number to be retransmitted from the APP-RTCP packet, and instructs the retransmission control unit 360 to perform retransmission. I do. All other packets are output to the multiplexer 390.
The multiplexing unit 390 multiplexes the input packet and transmits the multiplexed packet to the RTP transmitting terminal 40 via the local network.
[0027]
Retransmission control section 360 reads out the RTP packet of the sequence number specified by RTP analysis section 380 from data storage section 350 and outputs it to multiplexing section 330.
The multiplexing unit 330 multiplexes the retransmission packet input from the retransmission control unit 360 and the packet input from the RTP analysis unit 320, and transmits the multiplexed packet to the RTP retransmission control device 20 at the receiving end via the Internet 50.
The data management unit 340 deletes unnecessary packets from the data storage unit 350 among the RTP packets stored in the data storage unit 350.
[0028]
Next, an Internet MPEG-4 distribution system will be described as an embodiment of a communication system using the above-described retransmission control devices 20 and 30 according to the present invention. FIG. 4 is a block diagram showing a configuration example of the Internet MPEG-4 distribution system. FIG. 5 is a block diagram showing a basic configuration related to data transmission of the Internet MPEG-4 distribution system shown in FIG.
The Internet MPEG-4 distribution system includes an MPEG-4 playback terminal 15, the RTP retransmission control device 20 of FIG. 2 located at the RTP packet receiving end, and the RTP retransmission control device 30 of FIG. 3 located at the RTP packet transmitting end. And an MPEG-4 video server 45.
[0029]
The MPEG-4 video server 45 stores video image data and scene description data that have been encoded in advance according to the MPEG-4 standard. The MPEG-4 video server 45 transmits the video image data and the scene description data to the RTP retransmission control device 30. The RTP retransmission control device 30 transfers the received video image data and scene description data to the RTP retransmission control device 20 via the Internet 50. The RTP retransmission control device 20 transmits the received video image data and scene description data to the MPEG-4 playback terminal 15. An independent element stream is used for the transmission format of the scene description data and the video image data. To distinguish this element stream, the payload type of the RTP header is used.
[0030]
In the Internet 50 shown in FIG. 4, when the communication channel is congested, the packet is discarded without discriminating whether a certain RTP packet contains video image data or scene description data. . The MPEG-4 scene description data includes characters and graphics in a scene and information on how to display a video image in the scene. For this reason, if scene description data is lost due to packet discarding, the adverse effect on communication quality is large, such as the worst case of not displaying the entire video. On the other hand, the elementary stream of video image data contains a lot of information, and even if one RTP packet is discarded, the image quality deteriorates in a part of one frame. Absent. Therefore, the elementary stream of the scene description data requires higher communication reliability than the stream of the video image data.
[0031]
Next, an operation related to retransmission control of the Internet MPEG-4 distribution system of FIG. 4 will be described. Hereinafter, portions corresponding to FIGS. 2 and 3 are denoted by the same reference numerals.
In the RTP retransmission control device 30 at the transmitting end, the multiplexing / restoring unit 310 decomposes the signal received from the MPEG-4 video server 45 into IP packets and outputs the IP packets to the RTP analyzing unit 320. The RTP analysis unit 320 extracts only the received RTP packet, but does not discard, replace, or rewrite the packet, and outputs the packet to the multiplexing unit 330 as it is. The RTP analysis unit 320 accumulates a packet whose payload type is a scene description stream among the received RTP packets in the data accumulation unit 350, and records information in a management table of the data management unit 340.
[0032]
In the RTP retransmission control device 20 at the receiving end, the demultiplexing unit 210 receives the packet sequence transmitted from the RTP retransmission control device 30 at the transmission end via the Internet 50, and decomposes the packet sequence into IP packets. Output to the RTP analysis unit 220. The RTP analysis unit 220 extracts a sequence number of a packet, which is an RTP packet and has a payload type of a scene description stream, from among the received IP packets. If the difference between this sequence number and the sequence number of the previously received RTP packet of the scene description stream is not 1, the RTP analysis unit 220 determines that packets between those sequence numbers have been discarded. Then, it notifies the retransmission control unit 240 of the sequence number determined to have been discarded.
[0033]
Upon receiving the sequence number from RTP analysis section 220, retransmission control section 240 creates an APP-RTCP packet to be transmitted to RTP retransmission control apparatus 30 at the transmitting end. FIG. 6 shows the configuration of the APP-RTCP packet.
[0034]
As shown in FIG. 6, "204" representing APP is used in the type field of the RTCP header for the APP-RTCP packet, and the value of the receiving terminal (MPEG-4 playback terminal 15) is used for the sender identifier. The RTCP payload includes a unique code of an application identifier, the number of sequence numbers that need to be retransmitted, and a sequence number sequence.
[0035]
Retransmission control section 240 outputs the created APP-RTCP packet to multiplexing section 260. The multiplexing unit 260 multiplexes the APP-RTCP packet and the RTCP packet returned by the MPEG-4 playback terminal 15 to the MPEG-4 video server 45, and transmits the RTP retransmission control device at the transmission end via the Internet 50. Send to 30.
[0036]
In the RTP retransmission control device 30 at the transmission end, the multiplexing / restoring unit 370 decomposes a packet sequence received via the Internet 50 into IP packets and outputs the IP packets to the RTP analyzing unit 380. The RTP analysis unit 380 extracts, from the received APP-RTCP packets, those generated by the RTP retransmission control device 20 at the receiving end, and multiplexes the other packets to the MPEG-4 video server 45 by the multiplexing unit 390. Send. RTP analysis section 380 notifies retransmission control section 360 of the sequence number of the retransmission request target included in the extracted APP-RTCP packet.
[0037]
Upon receiving the sequence number, retransmission control section 360 reads a packet having the sequence number from data storage section 350 and outputs the packet to multiplexing section 330. The multiplexing unit 330 multiplexes the retransmission packet and another RTP packet, and transmits the multiplexed packet to the RTP retransmission control device 20 at the receiving end via the Internet 50.
[0038]
The data management unit 340 deletes unnecessary packets from the data storage unit 350 among the RTP packets stored in the data storage unit 350. If the sequence number of the packet stored in the data storage unit 350 by the RTP analysis unit 320 is the same as the sequence number of the already stored packet, the data management unit 340 stores the already stored packet in the data storage unit. It is deleted from the section 350. Note that the sequence number is composed of 16 bits, and the value is cyclic. When the BYE-RTCP packet is received and the RTP analysis unit 320 detects that the RTP session has been completed, the data management unit 340 stores all the RTP packets of the RTP session from the data storage unit 350 by this detection. delete.
[0039]
In this embodiment, the communication device on the receiving side is composed of an RTP retransmission control device and an RTP receiving terminal (or MPEG-4 playback terminal) connected by a local area network, and the communication device on the transmission side is an RTP retransmission control device. And an RTP transmission terminal (or MPEG-4 video server) connected by a local area network, but may be configured to include all of the communication terminals without being connected by the local area network.
[0040]
As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiments, and includes a design change or the like without departing from the gist of the present invention.
[0041]
【The invention's effect】
As described above, according to the present invention, retransmission control is performed with only RTP packets used for predetermined streaming as retransmission targets, for example, which affects communication devices that exchange data by packet communication using RTP. Thus, the packet can be efficiently retransmitted. Thereby, in communication using, for example, RTP / UDP / IP, the reliability of important communication streams can be ensured without changing the transmission server and the receiving terminal.
[0042]
Further, among the transmission packets stored for retransmission, unnecessary packets are deleted, so that the packet storage efficiency is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a communication system using retransmission control devices 20 and 30 according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an RTP retransmission control device 20 at an RTP packet receiving end.
FIG. 3 is a block diagram illustrating a configuration of an RTP retransmission control device 30 at an RTP packet transmitting end.
FIG. 4 is a block diagram showing a configuration example of an Internet MPEG-4 distribution system using the retransmission control devices 20 and 30 according to the present invention.
5 is a block diagram showing a basic configuration related to data transmission of the Internet MPEG-4 distribution system shown in FIG.
FIG. 6 is a diagram showing a configuration of an APP-RTCP packet.
FIG. 7 is a diagram showing a format of an RTP packet.
FIG. 8 is a diagram showing a configuration of an RTP header.
[Explanation of symbols]
10 RTP receiving terminal, 15 MPEG-4 playback terminal, 20, 30 RTP retransmission control device, 40 RTP transmission device, 45 MPEG-4 video server, 50 Internet, 210, 250, 310, 370 multiplexing RTP analysis unit, 230, 260, 330, 390 Multiplexing unit, 240, 360 Retransmission control unit, 340 Data management unit, 350 Data storage unit

Claims (6)

Receiving means for receiving the packet;
Identifying means for identifying the type of packet received by the receiving means;
Detecting means for detecting a sequence number included in the packet when the identification means has identified a predetermined packet;
Determining means for determining packet discard based on the sequence number detected by the detecting means;
Retransmission request means for requesting retransmission of the packet when the packet is determined to be discarded by the determination means;
A communication device comprising: 2. The communication apparatus according to claim 1, wherein a transmission protocol of the packet is RTP, and a retransmission request of the retransmission request unit is added to an RTCP APP packet. Transmitting means for adding a type to the packet and transmitting the packet;
Storage means for storing the packet transmitted by the transmission means,
Receiving means for receiving the packet;
Control means for controlling when a packet of a retransmission request is received by the receiving means to read a packet corresponding to the retransmission request from the storage means and to transmit the packet from the transmission means;
A communication device comprising: 4. The communication apparatus according to claim 3, wherein a transmission protocol of the packet is RTP, and the control unit deletes all data in the storage unit when the reception unit receives an RTCP BYE packet. In a communication system for transmitting at least a video signal compressed by MPEG-4 from a transmitting terminal to a receiving terminal using RTP,
The transmitting terminal,
Transmission means for adding an element stream type to a header of an RTP packet to be transmitted and transmitting the element stream;
The receiving terminal,
Identification means for identifying whether or not the type of the element stream added to the header of the RTP packet received from the transmitting terminal is a type requiring retransmission;
Detecting means for detecting a sequence number included in the packet when the identification means identifies the type as requiring retransmission;
Determining means for determining packet discard based on the sequence number detected by the detecting means;
Retransmission request means for requesting retransmission of the packet when the packet is determined to be discarded by the determination means;
A communication system comprising: The communication system according to claim 5, wherein the retransmission request of the retransmission request unit is added to an RTCP APP packet.

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