KR20020093604A - Selective packet retransmission with timing control at the transmitter end - Google Patents

Abstract

PURPOSE: A transmission system, a terminal, a server, a packet transmission method executed in the transmission system, and a program executed in the packet transmission system are provided to check at a transmitter whether a retransmitted packet will be received by a receiver in a time to be processed and retransmit packets. CONSTITUTION: A transmission system has a transmitter(10) and a receiver(30). The transmitter(10) has a transmitting device(TX1) for transmitting packets that contain the indication of a packet processing time, and a receiving device(RX1) for receiving retransmission requests relating to a packet to be retransmitted. The receiver(30) has a receiving device(RX3) for receiving packets, a processing device(DEC)(302) for processing the received packets, and a transmitting device(TX3) for transmitting retransmission requests relating to a packet to be retransmitted. The retransmission requests contain recovery data allowing the recovery of the processing time indication of the packet being processed at the moment that the retransmission request is transmitted. The transmitter(10) has a microprocessor assembly(E1) for recovering a processing time indication from recovery data contained in a received retransmission request. The microprocessor assembly(E1) compares the recovered processing time indication with the processing time indication of the packet to be retransmitted, so as to authorize or block the retransmission of the packet to be retransmitted.

Description

A transmission system, a terminal, a server, a packet transmission method executed in the transmission system, and a program executed in the packet transmission method {Selective packet retransmission with timing control at the transmitter end}

The invention comprises at least a transmitter and a receiver, the transmitter comprising means for transmitting packets comprising an indication of packet processing time, and means for receiving a retransmission request for the packet to be retransmitted, wherein the receiver receives the packets. Means for receiving, means for processing received packets, and means for transmitting a retransmission request for a packet to be retransmitted.

The invention also relates to a terminal comprising means for receiving packets comprising an indication of the packet processing time, means for processing the received packets, and means for transmitting a retransmission request for the packets.

The invention also provides a retransmission request for a packet to be retransmitted, sent by a terminal having means for transmitting packets comprising an indication of the packet processing time, and means for receiving the packets and means for processing the received packets. It also relates to a server comprising means for receiving.

The invention also relates to a retransmission method intended to be employed in this kind of transmission system, and a program comprising program code instructions for executing this kind of retransmission method when executed by a processor.

The present application applies in a general manner to any packet transmission across an unreliable circuit. This applies in particular to the transmission of video data to mobile wireless communication terminals via the Internet.

Akihiro Miyazaki, Fukushima, Koichi Hata, Thomas Biikke, Rolf Hackenberg, Karsten Burmeister, published November 14, 2000 by the IETF, referring to "draft-ieft-avt-selret-00.txt" The document "RTP Payload Formatto Enable Multiple Selective Retransmission" by Norichito Tokatori and Seiji Okumura describes a system for transmitting packets between a server and a mobile terminal, Mechanisms for selectively transmitting them are described. This mechanism consists in taking into account the transmission delay in the network at the terminal, in particular in order to decide whether or not to transmit a retransmission request for the packet. This mechanism makes it possible to avoid the situation where the mobile terminal sends a retransmission request even when it is certain that the retransmitted packet cannot be received early enough to be available at the terminal.

This mechanism reduces the number of retransmission requests that pass through the network, thus saving bandwidth.

One object of the present invention is to propose a mechanism for selective retransmission that is secondary to what is described in this document.

For this purpose, a transmission system according to the invention and also described in the opening paragraph, wherein at least some of the retransmission requests can be processed at the moment when the retransmission request is sent for recovery of the processing time indication of the packet. Recovery data for recovering the indication of the processing time from the recovery data included in the received retransmission request, and for recovering the data to allow or block the retransmission of the packet to be retransmitted. Means for comparing the time indication with the processing time indication of the packet to be retransmitted.

Thus, the present invention proposes a control mechanism at the transmitter in order to avoid retransmission of the packet when it is certain that the retransmitted packet will not be received by the receiver at a time suitable for processing.

This kind of mechanism usefully supplements the mechanisms disclosed in the prior art. In fact, when prior art mechanisms are used, the receiver transmits a retransmission request for the packet when the receiver determines that the retransmission packet can be received at a time suitable for processing, taking into account the normal transmission delay on the network. . However, congestion may occur on the transmission network to such an extent that retransmission requests arrive late at the transmitter. Thanks to the present invention, when the retransmission request arrives late enough that it is no longer possible for the retransmitted packet to be received in time by the receiver, the packet to be retransmitted is not retransmitted by the transmitter.

In the first embodiment of the present invention, the repair data is an indication of the processing time of the packet being processed at the moment when the retransmission request is transmitted. This embodiment is advantageously used when the processing time indication included in a packet is specific to that packet, ie when two different packets cannot contain the same processing time indication.

In a second embodiment of the present invention, the packets include a sequence number, the repair data is an indication of the processing time of the packet being transmitted at the moment the retransmission request is sent, and the transmitter allows retransmission of the packet to be retransmitted. Or to block, when the recovered processing time indication is identical to the processing time indication of the packet to be resent, means for comparing the sequence number included in the retransmission request with the sequence number of the packet to be resent.

This embodiment is advantageously used when several packets contain the same processing time indication. If the packet being processed and the packet to be retransmitted at the instant of the retransmission request have the same processing time indication, it is possible to determine whether or not it is useful to retransmit the packet to be retransmitted by comparing their sequence numbers.

Another object of the present invention is to limit the number of data that must be stored at the transmitter to allow for possible retransmission of packets.

For this purpose, in an advantageous embodiment of the invention, the transmitter is adapted to at least store data relating to at least some packet, in particular a memory for storing the sequence number of the packet, and when retransmission of the packet to be retransmitted is blocked. Means for deleting data relating to at least some of the packets having a sequence number less than or equal to the sequence number of the packet to be retransmitted from the memory.

These and other features of the present invention will be apparent from the non-limiting examples, with reference to the examples described below.

1 is a functional diagram of an example of a transmission system according to the present invention.

2 is a representation of the steps of the first embodiment of the transmission method according to the invention.

3 is a representation of the steps of the second embodiment of a transmission method according to the invention.

Description of the main symbols in the drawings

10: server 20: transmission network

30: terminal 40: link

50: wireless link

1 shows an example of a transmission system according to the invention, comprising a server 10 performing the function of a transmitter according to the invention, and a terminal 30 performing the function of a receiver according to the invention.

The transmit network is, for example, a cellular network such as a GPRS network or a UMTS network. The server 10 is connected to the transmission network 20 by a link 40 such as a link that accesses a packet type network such as the Internet. The terminal 30 is connected to the cellular network by a radio link 50.

The server 10 includes a data source D-IN indicated by block 101, a memory storing data MEM indicated by block 102, a transceiver TX1 / RX1 indicated by block 103, and a block ( And includes a microprocessor assembly E1, indicated by 104 and comprising a dynamic memory WM1, a program memory PM1, and a processor C1. TX3 / RX3, the processing unit DEC represented by block 302, and block 303, and includes dynamic memory WM3, program memory PM3, and processor C3. PM1 and PM3 each contain a program memory or a group of programs G1 and G3, including program code instructions for implementing the retransmission method according to the present invention as will be explained according to Figs.

In a general manner, the present invention may be applied when packets sent by a server include a processing time indication intended to be used by a terminal to process received packets. The processing time indication is an indication from which the time from which the packet should be processed by the receiver can be recovered. When the transmitter and receiver do not have a common time reference, the processing time indication sent in the packet is advantageously a period. The receiver then recovers processing time from this period and its own time reference.

For example, data supplied by the data source D-IN is data encoded in MPEG-4 format. In this case, the processing device DEC is an MPEG-4 type decoder. And the processing time indication is an indication of the decoding time (DTS) as defined in section 7.3.4 of the standard MPEG-4 standard (Document ISO / IEC 14496-1).

The transmission between the server 10 and the terminal 30 is advantageously done by using a transport protocol of the RTP type. The RTP transport protocol is described in document RFC 1889 published by the IETF.

RTP type packets contain a field of the name "Timestamp". This "Timestamp" field is advantageously used to send an indication of the processing time of the packet.

The RTP packet also contains a field named "Sequence Number" which will be mentioned in the rest of this description. The sequence number SN included in this field is incremented by one each time an RTP packet is transmitted. This is intended to be used by the receiver to detect the loss of one or more packets in a packet sequence.

RTP packets also include a "Payload" field containing useful data such as data encoded in MPEG-4 format.

As emphasized in the foregoing prior art, the transmitted packets do not necessarily have to be of equal importance to the receiver. In order to avoid overloading the network, it is advantageous to limit the possibility of retransmission for the most important packets. In the following description, these packets will be referred to as retransmittable packets. In order to enable retransmission of the packets, some data related to the retransmitable packets must be stored in the server 10. These data are stored, for example, in a table TBL recorded in the data memory MEM.

2 is a diagram showing the steps in the first embodiment of the retransmission method according to the present invention. This embodiment is advantageously used when the processing time indication contained in a packet belongs to that packet, ie when two different packets cannot contain the same processing time indication. When the transmitted data is data encoded in MPFG-4 format, this condition is satisfied if the image is small enough to be transmitted in a single RPT packet.

In this first embodiment, the server stores useful data contained in the sequence number SN, the processing time indication T, and the "payload" in the table TBL for each resendable packet.

The retransmission method shown in FIG. 2 includes the following steps:

Step S1 for transmitting, by the terminal 30, a retransmission request RR relating to the lost packet Q _L. This request RR includes a processing time indication T _T of the packet Q _T processed at the terminal 30 when the terminal 30 transmits the retransmission request RR. The request also includes the sequence number SN _L of the packet Q _{L to} be retransmitted. This kind of request is sent in an RTCP packet, for example as described in paragraph 6 of RFC1889. In this case, the processing time indication T _T and the sequence number SN _L of the packet Q _{L to} be retransmitted are transmitted in the "profile-specific extensions" field of the RTCP packet.

Receiving step S2 of the retransmission request RR by the server 10.

Recovering the processing time indication T _T contained in the received retransmission request (S3).

Step S4 for retrieving the sequence number SN _L of the packet Q _{L to} be retransmitted from the table TBL. If the sequence number SN _L is not shown in the table TBL, this means that the packet to be resent cannot be resent.

Recovering the processing time indication T _L of the packet Q _{L to} be resent from the table TBL (S5).

Step S6 for the comparison of the processing time indication T _T with T _L , wherein the result of the comparison is used to allow or block transmission of the packet Q _{L to} be retransmitted. For example, this step S6 includes checking whether the difference δ between the processing time indications Q _T and Q _L is greater than half the estimate θ of the round trip transmission time on the transmission network. If T _L -T _T? ½θ (arrow A1), retransmission is made in step S7. If T _L -T _T <½θ (arrow A2), retransmission is blocked.

3 is a diagram showing the steps of the second embodiment of the retransmission method according to the present invention. This embodiment is advantageously used when several packets contain the same processing time indication. In this case, the packet being processed can be retransmitted when the retransmission request is sent with the same processing time indication. The sequence number of the two packets is then advantageously compared to determine if the receiver still needs to retransmit the packet. In this second embodiment, the server 10 must store useful data contained in the sequence number SN, processing time indication T and the "Payload" field in the table TBL for all transmitted packets.

The retransmission method shown in FIG. 3 includes the following steps:

Step S1 ′ for transmitting, by the terminal 30, a retransmission request RR relating to the lost packet Q _L. This request RR includes sequence number processing SN _T of the packet Q _T processed by the terminal 30 when the terminal 30 transmits the retransmission request RR. This sequence number SN _T is a type of recovery data for recovering the processing time indication T _T from the packet. The retransmission request RR also includes the sequence number SN _L of the packet to be retransmitted. If a retransmission request (RR) is sent in an RTCP packet, the sequence numbers SN _T and SN _L are sent in the "profile-specific extensions" field of the RTCP packet, respectively.

Receiving a retransmission request (RR) by the server 10 (S2 ').

The processing time indication T _T of the packet Q _T being processed at the moment when the retransmission request RR is transmitted, and the table TBL from the recovery data SN _T included in the received retransmission request. Using the step S3 'to recover from it.

Step S4 'for retrieving the sequence number SN _L of the packet to be retransmitted from the table TBL.

Recovering the processing time indication T _L of the packet Q _{L to} be retransmitted from the table TBL (S5 ′).

Step S6 'for comparison of the processing time indication T _T with T _L.

The step S6 'includes the following steps:

Check that T _L = T _T

If T _L = T _T (arrow A3), the sequence numbers SN _L and SN _T are compared.

If SN _L &lt; SN _T (arrow A4), retransmission is blocked.

If SN _L &gt; SN _T (arrow A5), transmission is performed in step S7 '.

If T _L ? T _T (arrow A6), check whether T _L -T _T ?

If T _L -T _T <θ½ (arrow A7), retransmission is blocked.

If T _L -T _T? Θ½ (arrow A8), retransmission is performed in step S7 '.

As an advantage, the method according to the invention comprises the further step shown in dashed lines in FIGS. 2 and 3 and with the member symbols S8 and S8 '. This additional step consists in erasing data that is no longer useful from the table TBL. As shown in Figs. 2 and 3, when retransmission of the packet Q _L to be retransmitted is blocked (arrows A2, A4 and A7), the sequence is less than or equal to the sequence number SN _L of the packet Q _{L to} be resent. Data relating to packets with the number SN is deleted from the table TBL, this embodiment makes it possible to avoid the situation in which the table TBL is overinflated.

Decision thresholds different from those described above may be used. In step S6 ', for example, a minimum difference may be given between the sequences SN _L and SN _T such that retransmission of the packet Q _L is allowed.

The present invention is not limited to the transmission of data encoded in the MPEG-4 format, nor is it limited to the use of protocol RTP. The invention applies in a general manner to the transmission of any data in which real time and sequence problems arise, from the moment a processing time indication for the data is transmitted with the data.

The present invention is applicable to a mechanism for retransmitting packets, including checking at the transmitter whether the retransmitted packet is to be received by the receiver in time to be processed.

Claims (12)

A transmission system comprising at least a transmitter 10 and a receiver 20, The transmitter receiving means (TX1) for transmitting packets comprising an indication of the packet processing time (T _T , T _L ), and the retransmission requests (RR) for the packet (Q _L ) to be retransmitted. Means RX1, The receiver comprising means (RX3) for receiving packets, means (DEC) for processing the received packets, and means (TX3) for transmitting retransmission requests relating to the packet to be retransmitted. At least some of the retransmission requests are for the recovery data to allow recovery of the processing time indication (T _T ) of the packet (Q _T ) to be processed at the moment the retransmission request (RR) is sent. (SN _T , T _T ), The transmitter means for recovering a processing time indication T _T from the recovery data SN _T , T _T included in the received retransmission request, and to allow or block retransmission of the packet to be resent, Means (E1) for comparing the recovered processing time indication with the processing time indication of the packet to be retransmitted. 2. The apparatus according to claim 1, wherein said packets comprise a sequence number (SN), said transmitter comprising at least data relating to particular packets, in particular a memory (TBL) for storing the sequence numbers of said packets, and said packet to be retransmitted. Means for deleting from the memory data relating to at least some of the packets having a sequence number less than or equal to the sequence number of the packet to be retransmitted when the retransmission of the &quot; The transmission system according to claim 1, wherein the recovery data is an indication of a processing time of a packet processed at the moment when the retransmission request is transmitted. 2. The apparatus of claim 1, wherein the packets comprise a sequence number, the repair data is a sequence number of a packet that is processed at the time the retransmission request is sent, and the transmitter is configured to allow or block retransmission of the packet to be retransmitted. And means for comparing the sequence number included in the retransmission request with the sequence number of the packet to be retransmitted when the recovered processing time indication and the processing time indication of the packet to be retransmitted are the same. Terminal 30 comprising means RX3 for receiving packets comprising an indication of the packet processing time T, means DEC for processing the received packets, and means TX3 for transmitting a retransmission request for the packet. ), At least some of the retransmission requests may include recovery data that allows recovery of the processing time indication T _T of the packet Q _T to be processed at the moment the retransmission request RR is sent. SN _T , T _T ), characterized in that the terminal. 6. The terminal according to claim 5, wherein the recovery data is an indication of a processing time of a packet processed at the moment when the retransmission request is transmitted. 6. The terminal of claim 5, wherein the packets include sequence numbers, and the repair data is a sequence number of a packet processed when the retransmission request is transmitted. 6. A terminal according to claim 5, wherein the transceiver device is a wireless device. Transmission by terminal 30 having means TX1 for transmitting packets comprising an indication of the packet processing time T, and means RX3 for receiving packets and means TX3 for processing the received packets. In the server 10 comprising means RX1 for receiving a retransmission request RR for a packet Q _L to be retransmitted, At least some of the retransmission requests include recovery data (SN _T , T _T ) that allows recovery of the processing time indication (T _T ) of the packet to be processed at the moment the retransmission request is sent, wherein the server Means (E1) for recovering a processing time indication (T _T ) from the recovery data included in the received retransmission request, and for allowing or blocking retransmission of the packet to be resent, the recovered processing time indication and the packet to be resent Means (E1) for comparing an indication of the processing time of the server. 8. The system of claim 7, wherein the packets comprise a sequence number, the server further comprising at least a memory (TBL) for storing data relating to particular packets, in particular the sequence numbers of the packets, and retransmission of the packet to be retransmitted. And when blocked, means for deleting data relating to at least some of the packets having a sequence number less than or equal to the sequence number of the packet to be retransmitted. A packet retransmission method intended to be executed in a transmission system comprising a transmitter 10 intended to transmit packets comprising an indication of packet processing time, and a receiver intended to receive packets and process received packets, the packet retransmission method being provided. Transmitting a retransmission request (RR) relating to a step (S1; S1 '), and receiving the retransmission request by the transmitter (S2; S2'). The retransmission request includes data SN _T ; T _T for restoring the processing time indication T _T of the packet processed at the moment the packet retransmission request is sent, The method, Restoring a processing time indication from the recovery data included in the received retransmission request (S3; S3 '), and Comparing the recovered processing time indication with the processing time indication of the packet to be resent (S6; S6 ') to allow (A1; A5; A8) or block (A2; A4; A7) to allow retransmission of the packet to be resent Characterized in that it comprises a, packet retransmission method. A program comprising instructions for executing a packet retransmission method as claimed in claim 11 when executed by a processor.