FR2965432A1 - METHOD FOR DISPATCHING IN A MULTI-HOP ACCESS NETWORK - Google Patents

Abstract

Forwarding method executed by a node of a multi-hop access network, said node comprising a plurality of outgoing interfaces, the forwarding method comprising: - a step of receiving a data packet from a multimedia stream, - a step of processing said data packet by a scheduler, and - after said processing step, a step of determining at least one output interface among said plurality of output interfaces, towards which to transmit said data packet, by consulting a dispatch database, characterized in that it comprises, before said processing step, a step of associating, with the data packet, at least one output interface and a prime number representative of a transmission quality with which the multimedia stream must be transmitted to said output interface, said forwarding database comprising a record per output interface of said plurality of output interfaces tie, each record containing an aggregation identity (IDag) representing a product of prime numbers, each of said prime numbers representing a transmission quality with which a multimedia stream must be transmitted to the output interface of said record, said determining step comprising, for each record of said shipping database: - a step (F72) of testing a condition representing the divisibility of the product represented by the aggregation identity of the record by said at least one prime number associated with said data packet during the association step, and - when said condition is verified, a step (F74) of transmitting said data packet to the output interface of said record.

Description

BACKGROUND OF THE INVENTION The invention relates to the general field of telecommunications. In particular, the invention relates to the multicasting of multimedia data streams in a multi-hop network. The WiMAX Relay technology, standardized by the WiMAX Forum and the IEEE, is presented in the document "IEEE Std 802.16jrM-2009 Part 16: Air Interface for Fixed and Mobile Broadband Wire / ess Access Systems, Mu / t / hop Re / ay Specification ", IEEE, 13 May 2009. According to this technology, communication between an MR-BS base station (for" Mu / tihop Re / ay-Base Station ") and a mobile terminal passes through at least one intermediate relay and an RS access relay (for "Relay Station").

A relay can work in transparent mode or in non-transparent mode. In a known manner, the non-transparent relays make it possible to widen the coverage area of a cell and improve the performance of the access network. In this case, to transmit data from the MR-BS base station to an RS access relay, the aforementioned document proposes to establish a tunnel that represents the entire path between the MR-BS base station and a relay. RS access. The MR-BS base station may allow a data broadcast service to several mobile terminals connected to different access relays, for example data from a multimedia stream (MBS). In this case, a tunnel is established to each access relay and a copy of the data is sent in each tunnel, even if the different tunnels pass through a same intermediary relay. This involves significant consumption of network resources, including available bandwidth and relay and base station processing capabilities. To improve the use of network resources while respecting quality of service (QoS) constraints, Chengxuan He, Oliver Yang and GuoQiang Wang, "Performance Evaluation of Multicast Routing Protocol and MBS Service Architecture in WiMAX Mu / Ti- Hop Re / ay Environment, "Future Networks: Cross-Layer Design, April 22-24, 2008, Ottawa, Ontario, Canada, proposes an architecture in which a tunnel represents the link between the MR-BS base station and an adjacent relay or between two adjacent relays. The proposed architecture aims to send a single copy of the broadcast data to a downstream relay, which saves the available bandwidth and relay processing capabilities. However, this document does not detail the mechanisms implemented in a relay to allow an efficient operation of this relay. It is known in particular that a relay uses a scheduler to prioritize the data packets and, at the output of the scheduler, a dispatch table 2 (also called a routing table or "forwarding table" in the English terminology) at the level of the MAC layer which determines to which output interface a received data packet is to be transmitted. Thus, in known manner, a dispatch table contains, for each identifier of a broadcast stream, a line per output interface to which the packets must be transmitted. The size of the shipping table can become important in case of transmission to different adjacent relays. However, to determine the output interface (s) to which to transmit a packet, a relay must traverse its entire shipping table. The shipping time, that is the time between the output of the scheduler and the transmission of a package, therefore increases with the size of the shipping table.

In addition, a multimedia data stream can be encoded according to different formats and different qualities. For example, the same audiovisual stream can be encoded in HD quality (for High Definition), SD quality (for Standard Definition), Web-TV quality (for viewing on a PC) or quality. Mobile-TV (intended for viewing on a mobile phone). Currently, telecommunications operators separately send different copies of an audiovisual stream coded according to different qualities. This also increases the use of network resources.

OBJECT AND SUMMARY OF THE INVENTION The object of the invention is to provide a forwarding method which enables the transmission of data to be broadcast in a multi-hop wireless network in an efficient manner. For this purpose, the invention proposes a forwarding method executed by a node of a multi-hop access network, said node comprising a plurality of output interfaces, the dispatching method comprising: a step of receiving a data packet from a multimedia stream, - a step of processing said data packet by a scheduler, and - after said processing step, a step of determining at least one of said plurality of output interface of output interfaces, to which to transmit said data packet, by consulting a dispatch database, characterized in that it comprises, before said processing step, an association step, with the data packet , at least one output interface and a prime number representative of a transmission quality with which the multimedia stream is to be transmitted to said output interface, said dispatch database comprising an output interface recording of said plurality of output interfaces, each record containing an aggregation identity representing a product of prime numbers, each of said prime numbers representing a transmission quality with which a multimedia stream is to be transmitted to the output interface of said record, said determining step comprising, for each record of said shipping database: a step of testing a condition representing the divisibility of the product represented by the aggregation identity of the recording by said at least one prime number associated with said data packet during the association step, and - when said condition is satisfied, a step of transmitting said data packet to the output interface of said record. The node that implements this shipping method may be a base station or an intermediate relay. The dispatch database composed of an output interface record is for example a dispatch table composed of one line per output interface. Since the node's shipping table contains only one line per output interface, the node can browse it quickly to determine which output interfaces to transmit the data packet to. The shipping process carried out by the intermediary relay is therefore efficient and fast. Thus, the invention makes it possible to reduce the time of dispatch of the packets at the output of the scheduler. The dispatching method may comprise, when said condition is verified and before said transmission step: a step of comparing a prime number representing the transmission quality of the received data packet with said at least one prime number associated with said packet of data during the association step, and - if said prime numbers are different, a step of recoding said data packet according to a transmission quality corresponding to the prime number associated with said data packet during the association step . In this case, when a multimedia stream is requested by several users according to several different transmission qualities, it is sufficient to transmit a copy of the stream with the highest transmission quality on the common part of the paths to the users. The shipping method implemented by the node thus saves network resources. According to an embodiment in which the shipping method is implemented by an intermediate relay, the shipping method comprises: a step of receiving a message containing shipping information, a step of setting a transition table day according to said shipping information, said transition table containing a plurality of lines, each line comprising an identifier of a multimedia stream, a prime number representing a transmission quality for said multimedia stream, and an identifier of one of said output interfaces for said multimedia stream, - a step of updating said dispatch table by aggregating said transition table, each aggregation identity of the dispatch table being calculated according to said prime numbers of the transition table. 4 Aggregation provides the reduced shipping table. The invention also relates to a computer program comprising instructions for the execution of the steps of the shipping method when said program is executed by a computer.

This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other form desirable shape. The invention also relates to a recording medium or information carrier readable by a computer, and comprising instructions of a computer program as mentioned above. The recording media mentioned above can be any entity or device capable of storing the program. For example, the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording medium, for example a floppy disk or a disk. hard. On the other hand, the recording media may correspond to a transmissible medium such as an electrical or optical signal that can be conveyed via an electrical or optical cable, by radio or by other means. The program according to the invention can be downloaded in particular on an Internet type network.

Alternatively, the recording media may correspond to an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question. The invention also proposes a node intended for a multi-hop access network, said node comprising a plurality of output interfaces and: means for receiving a data packet from a multimedia stream; processing said data packet by a scheduler, and - means for determining at least one output interface out of said plurality of output interfaces, to which to transmit said data packet, by consulting an expedition database , characterized in that it comprises means for associating, with the data packet, at least one output interface and a prime number representative of a transmission quality with which the multimedia stream must be transmitted to said output interface, said dispatch database including an output interface record of said plurality of output interfaces, each record containing an aggregation identity representing a product of prime numbers, each of said prime numbers representing a transmission quality with which a media stream is to be transmitted to the output interface of said record, the determining means comprising, for each record of said database, dispatch: means for testing a condition representing the divisibility of the product represented by the aggregation identity of the record by said at least one prime number associated with said packet of 5 given by the association means, and transmission means, activated when said condition is verified, of said data packet to the output interface of said record. The advantages and features discussed above with reference to the shipping method according to the invention correspondingly relate to the node according to the invention. The invention also relates to a multi-hop access network comprising a base station and at least one intermediate relay comprising a node according to the invention, said base station comprising: means for receiving a request for a multimedia stream, means for updating a broadcast table indicating, for each hop of a path on which said multimedia stream must be transmitted, a quality of transmission, and means of sending, to said intermediate relay, a message containing shipping information according to said broadcast table. In other words, the base station performs centralized processing of the multimedia stream requests to determine the transmission qualities on each hop. With these characteristics, the base station can choose to transmit only one copy of a multimedia stream, with the highest quality, when a stream is requested by several users according to several different transmission qualities.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will become apparent from the description given below, with reference to the accompanying drawings which illustrate an embodiment thereof devoid of any limiting character. In the figures: FIG. 1 is a diagram of an example of a WiMAX network in which a dispatch method according to one embodiment of the invention is implemented; FIG. 2 schematically represents a base station or a relay; according to one embodiment of the invention, FIGS. 3 and 4 represent steps of a control method executed by the base station of the network of FIG. 1, and FIGS. 5 to 7 represent steps of a method FIG. 1 shows a cell 1 of a multi-hop WiMAX network. FIG. Cell 1 comprises a base station 2, designated MR-BS in FIG. 1 for "Multlhop Relay-Base Station", two intermediate relays 3, respectively designated RS1 and RS2, three 3 'access relays, respectively designated RS3 to RS5, and four terminals designated U1 to U4. Hereinafter, the term "ncode" of the cell 1: the base station 2, one of the intermediate relays 3 or one of the access relays 3 '. The tree structure of cell 1 is shown in FIG. 1. More precisely, base station 2 is connected to intermediate relays RS1 and RS2 by wireless links corresponding to tunnels MT-CID1 and MT-CID2. The intermediate relay RS1 is connected to the RS3 and RS4 access relays by wireless links corresponding to tunnels MT-CID3 and MTCID4. The intermediate relay RS2 is connected to the access relay RS5 by a wireless link corresponding to an MT-CID5 tunnel. The terminals U1 and U2 are connected to the access relay RS3 by wireless links and the terminals U3 and U4 are connected to the access relay RS4 by wireless links.

The tunnels MT-CID1 and MT-CID2 constitute output interfaces of the base station 2 within the meaning of the present invention. Correspondingly, the MT-CID3 and MTCID4 tunnels constitute output interfaces of the intermediate relay RS1 and the MT-CID5 tunnel constitutes an output interface of the intermediate relay RS2. Of course, the cell 1 may comprise more or fewer relays and more or fewer terminals than in the example shown. FIG. 2 diagrammatically represents a communication device 4 which may be one of the nodes of the cell 1, that is to say the base station 2, an intermediate relay 3 or an access relay 3 '. The communication device 4 presents the hardware architecture of a computer and comprises in particular a processor 5, a read-only memory 6, a random access memory 7 and a communication interface 8. The processor 5 allows the execution of a program of communication. a computer stored in the read-only memory 6, using the RAM 7. The communication interface 8 makes it possible to communicate with the other nodes of the cell 1 (base station 2, intermediate relay 3, access relay 3 ') or with the terminals U1 to U4. The base station 2 is connected to a multimedia server (not shown) for providing a plurality of multimedia streams, for example a plurality of television channels. As a function of the requests sent by the terminals U1 to U4, the base station 2 broadcasts one or more multimedia streams in the cell 1. Hereinafter, on the one hand, the processing of the requests carried out by the base station 2 and on the other hand the shipping mechanism performed by the intermediate relays 3, to allow this diffusion. Figures 3 and 4 show steps of a control method performed by the base station 2. The steps of Figures 3 and 4 are for example implemented by a computer program executed by the base station 2.

The base station 2 performs central processing to establish paths to the RS3, RS4 and RS5 access relays. Thus, in step E10, the base station MR-BS 2 initiates a process of discovering the topology of the cell 1. Such a discovery process is described in the IEEE document mentioned above. The base station 2 stores the identified paths in a path table (Table I). The following path table shows the paths identified and stored for the example of cell 1. In the path table, for each row, the first column contains an identifier of a Path-ID path and the second column contains the list of relays 3 and 3 'composing the path. Path-ID Relay Path-ID1 RS1, RS3 Path-ID2 RS1, RS4 Path-ID3 RS2, RS5 Path Table (Table I) As previously explained, in Cell 1, each link between base station 2 and an intermediate relay 3 or between an intermediate relay 3 and an access relay 3 'corresponds to a tunnel. Thus, in step E20, the base station MR-BS 2 creates a tunnel table (Table II) which indicates the correspondences between the tunnels and the paths identified in step E10. In the tunnel table below, for each line, the first column contains the identifier of an MT-CID tunnel and the second column contains the list of paths using this tunnel. MT-CID Path-ID MT-CID1 Path-ID1, Path-ID2 MT-CID2 Path-ID3 MT-CID3 Path-ID1 MT-CID4 Path-ID2 MT-CID5 Path-ID3 Tunnel Table (Table II) Steps E10 and E20 are periodically executed to update the path table and the tunnel table, for example to account for the addition or disappearance of a relay 3 or 3 '. FIG. 4 represents the steps performed by the base station 2 in response to receiving a request from a multimedia stream by one of the terminals U1 to U4. When a terminal wishes to receive a multimedia stream, it sends a request to the base station 2 via the relays 3 and 3 '. This request is for example a DSA-REQ type request described in the aforementioned IEEE document, and specifies the requested stream indicating a broadcast stream reference (multicast group). Base station 2 receives this request in step E30. Next, in step E40, the base station 2 assigns an identifier to the requested stream. For example, for each stream broadcast in cell 1, base station 2 assigns an identifier MCID. Thus, a first television channel may have an identifier MCID1 and a second television channel may have an identifier MCID2. The base station 2 also determines the transmission quality requested by the terminal. The transmission qualities that can be requested are each represented by a different prime number IDtx: The quality HD is represented by the number IDtx = 3, The quality SD is represented by the number IDtx = 5, 10 The quality Web-TV is represented by the number IDtx = 7, and The quality Mobile-TV is represented by the number IDtx = 11. In this example, the transmission quality correspond respectively, from the highest quality to the lowest quality, to prime numbers IDtx croissants. The requested transmission quality is, for example, indicated in the request received in step E30 or determined by the base station 2, for example as a function of the service contract subscribed by the user of the terminal or depending on the type of terminal. Then, in step E50, the base station 2 updates a table, hereinafter referred to as the broadcast table (Table III), containing the information for broadcasting the requested stream in the cell 1. More precisely, the station base 2 creates a row in a broadcast table indicating the Path-Id identifier of the path to the terminal that issued the request, the MCID of the requested stream, and the list of nodes in cell 1 corresponding to the path to the terminal, with for each node the prime number IDtx corresponding to the transmission quality to be transmitted. When creating a row in the broadcast table, the base station 2 determines, based on the current content of the broadcast table, whether the requested stream is not already transmitted in a MT-CID tunnel with a quality of transmission different from the requested quality. In this case, the broadcast table is updated to indicate the transmission of the highest quality. More precisely, the base station 2 looks in the broadcast table for a line with the same identifier MCID as that of the line to be created. If such a line indicates the transmission of the requested flow with a quality higher than the requested quality, the new line is created indicating the highest quality. If such a line indicates the transmission of the requested stream with a quality lower than the requested quality, the line found is modified to indicate the highest quality. For example, assuming that the broadcast table is initially empty and the terminal U1 requests stream MCID1 with HD quality, base station 2 creates a first line: Path-ID MCID MR-BS and Relay Path- ID1 MCID1 MR-BS (3), RS1 (3), RS3 (3) Dissemination Table (Table III) In the above distribution table, the number in brackets after each item in the list in the third column " MR-B and Relay "indicates the transmission quality of the stream to be transmitted to the next node of the list (or to broadcast to the terminals in the case of the last item of the list). If, at a later date, the terminal U2 requests the stream MCID2 with the quality Mobile-TV, the base station 2 adds a second line to the broadcasting table which then becomes: Path-ID MCID MR-BS and Relay Path-ID1 MCID1 MR -BS (3), RS1 (3), RS3 (3) Path-ID1 MCID2 MR-BS (11), RS1 (11), RS3 (11) Diffusion Table (Table III) Then, if the terminal U3 requests the MCID1 stream with SD quality, the base station 2 10 found, according to the first line of the broadcast table, that MCID1 stream is already transmitted in the HD quality of the base station 2 relay RS1, c ' that is, in the MT-CID1 tunnel. However, the path to the terminal U4 also borrows the MT-CID1 tunnel, as shown in the tunnel table. Thus, it is not necessary to transmit the MCID1 stream also with the SD quality in the MT-CID1 tunnel. The MR-BS 2 adds a third line to the broadcast table, indicating the highest quality of the MCID1 stream between the base station 2 and the relay RS1, i.e. the prime number IDtx = 3 The scattering table then becomes: Path-ID MCID MR-BS and Relay Path-ID1 MCID1 MR-BS (3), RS1 (3), RS3 (3) Path-ID1 MCID2 MR-BS (11), RS1 ( 11), RS3 (11) Path-ID2 MCID1 MR-BS (3), RS1 (5), RS4 (5) Diffusion table (Table III) In the above distribution table, the prime number IDtx indicating the quality transmission of the stream MCID1 to the terminal U4, in the MT-CID1 tunnel is written in bold to highlight it. Similarly, if the terminal U4 requests the stream MCID2 with the quality Web-TV, the base station 2 notes that the stream MCID2 is already transmitted with the quality Mobile-TV from the base station 2 to the relay RS1. Thus, the base station 2 updates the broadcast table by adding a new line for the requested stream and modifying the second line to indicate the highest quality: Path-ID MCID MR-BS and Relay Path-ID1 MCID1 MR-BS (3), RS1 (3), RS3 (3) Path-ID1 MCID2 MR-BS (7), RS1 (11), RS3 (11) Path-ID2 MCID1 MR-BS (3), RS1 (3) 5), RS4 (5) Path-ID2 MCID2 MR-BS (7), RS1 (7), RS4 (7) Diffusion Table (Table III) In the above diffusion table, the number 7 which, in the second line, follows MRBS, replaces the number 11 of the previous version of the mailing table. This number is shown in bold to highlight this change.

Finally, after each update of the broadcasting table, the base station 2 sends, in the step E60, a message to the relays 3 and 3 'so that they adapt their transmission table (Table IV) and their shipping table (Table V) according to the information of the mailing table. These transmission and shipping tables will be described later. For example, the latest version of the broadcast table above indicates that the relay RS1 must transmit the stream MCID1 with the quality HD to the relay RS3, the stream MCID2 with the quality Mobile-TV to the relay RS3, the stream MCID1 with SD quality to RS4 relay and MCID2 stream with Web-TV quality to RS4 relay. This message is for example of the type "Path lido TLVmessage" defined in the aforementioned IEEE document. FIG. 5 represents the steps of an aggregation process performed by an intermediate relay 3. FIG. 5 is described below in relation to the relay RS1. The steps of FIG. 5 are for example implemented by a computer program executed by relay RS1. In step F10, relay RS1 receives the message transmitted by base station 2 in step E60. Then, in step F20, the relay RS1 updates a transition table (IV) containing the information received. In the aforementioned example, the relay RS1 thus stores a transition table whose each line indicates a flow identifier MCID, a prime number IDtx representative of a transmission quality and the tunnel into which the identified flow must be sent: MCID IDtx MT-CID MCID1 3 MT-CID3 MCID1 5 MT-CID4 MCID2 11 MT-CID3 MCID2 7 MT-CID4 Transition Table (Table IV) Then, at step F30, relay RS1 updates its dispatch table ( V) by aggregation of the transition table. More precisely, the relay RS1 exploits the prime numbers IDtx corresponding to the different transmission qualities to determine an aggregation identity IDag. The dispatch table includes a line for each MT-CID tunnel indicated in the transition table. Each line includes the identifier of a MT-CID tunnel and the IDag aggregation identity which is equal to the product of the prime numbers. IDtx indicated in the transition table in correspondence with the identified tunnel. Thus, in the example of the transition table above, the corresponding shipping table is as follows: MT-CID IDag MT-CI D3 3 * 11 MT-CI D4 5 * 7 Shipping Table (Table V FIG. 6 represents steps of a dispatch method (or routing method) according to one embodiment of the invention, implemented by relay RS1. The steps of FIG. 6 are for example implemented by a computer program executed by relay RS1. In this respect, the read-only memory 6 of the relay RS1 which contains this computer program constitutes an information medium in accordance with the invention, and the relay RS1 constitutes a node according to the invention. In step F40, the relay RS1 receives a data packet (MAC PDU) of a multimedia stream sent by the base station 2. This data packet contains, in a header, typically in a MAC header, a stream identifier MCID . For example, it is a packet of data from stream MCID1 that base station 2 sends to RS1 with HD quality (IDtx = 3), as indicated by the broadcast table (III). Then, in step F50, the relay RS1 consults its transition table (IV) and determines the output interfaces and transmission qualities corresponding to the MCID flow identifier of the packet received in step F40. Thus, in the example of the MCID1 stream, the transition table indicates an output on the MT-CID3 tunnel with HD quality (IDtx = 3) and on the MT-CID4 tunnel with SD quality (IDtx = 5). After having traversed the entire transition table, the relay RS1 associates in its RAM 7 (for example in a register) the data packet with the determined output interfaces and the prime numbers corresponding to the determined qualities. Then, in step F60, the data packet is processed by the scheduler of the relay RS1. The scheduler is the mechanism of the relay RS1 which implements the prioritization of the data packets processed by the relay RS1, in particular according to a class of service of each data packet. The service class of a data packet is for example determined according to the MAC header of the data packet. For example, a data packet of a broadcast stream with HD quality may correspond to a higher priority service class than a data packet of a stream broadcast with Web-TV quality. At the output of the scheduler, the relay RS1 consults, during the step F70, its dispatch table (V) to determine on which output interface (s) must be sent the data packet, and sends the data packet to the determined output (s). Step F70 is shown in more detail in Fig. 7. A line counter L is initialized to 1 in step F71. Then, in step F72, the relay RS1 tests the condition (IDag mod IDtx) = 0, where IDag is the aggregation identity of the line L of the shipping table (V) and IDtx is one of the numbers first associates, through the transition table (IV) in step F50, to the data packet. As previously explained, IDag is a product of prime numbers IDtx. In a known way, if a prime number divides a product of prime numbers, then it is equal to one of them. If the condition of the step F72 is not verified, then it means that IDtx is not one of the primes whose IDag is the product. In this case, the data packet is not sent in the MT-CID tunnel of the line L. The relay RS1 tests, at step F76, whether all the lines of the dispatch table have been consulted. On the other hand, if the condition of step F72 is satisfied, it means that IDtx is one of the prime numbers of which IDag is the product. In this case, in step F73, IDtx is compared to a prime number IDtx representing the transmission quality of the data packet received in step F40, denoted IDtx (F40) in FIG. 7.

If IDtx is equal to IDb "F40", this means that relay RS1 must transmit, in the tunnel of line L, the data packet with the same quality of transmission as that of the packet received in step F40. Thus, in step F74, the data packet is transmitted without particular treatment of the transmission quality. On the other hand, if IDtx is not equal to IDtx (F40), this means that the relay RS1 must transmit, in the tunnel of the line L, the data packet in a transmission quality lower than that of the packet received at the end of the tunnel. step F40. Thus, in step F75, the data packet is recoded according to the lower transmission quality indicated by the IDtx number. Then, in step F74, the recoded data packet is transmitted. To facilitate the processing of step F75, the multimedia streams transmitted by the base station 2 are coded in a scalable format, for example according to the SVC standard (for "Sca / ab / e Kdeo Coding") defined jointly by the ITU-T and ISO. A scalable format means that it is possible to represent a signal at different levels of information. The signal is encoded in a single bit stream so as to provide the ability to decode a base stream and including streams whose quality increases successively. The purpose of SVC is to adapt the video to the constraints of users and the network. To do this, three types of scaling are defined: spatial scaling which makes it possible to offer several levels of resolution, time scaling which makes it possible to offer several signal time frequencies, and scaling in quality that offers different image qualities.

In the case of using a scalable format, the RS1 relay can easily determine a degraded quality data packet from a higher quality data packet. For example, from a data packet of the MCID1 stream encoded in HD quality, it is possible to determine a corresponding data packet encoded according to SD quality, Web-TV quality or Mobile-TV quality. In step F76, the relay RS1 tests whether all the P lines of the shipping table (V) have been consulted. If there are still lines to be processed, the line counter L is incremented in step F77 and the steps F72 to F76 are repeated. Steps F71 to F76 are repeated for each prime number IDtx associated with the data packet in step F50. In the example of the data packet of stream MCID1, prime numbers IDtx 3 and 5 are associated with the data packet in step F50. The IDag aggregation identities of the forwarding table are respectively 33 and 35 for lines 1 and 2. Thus, for IDtx = 3 and for the first line, the condition of step F72 is checked. Step F73 indicates that no change in transmission quality should be made. The data packet is therefore transmitted to the MT-CID3 tunnel of the first line. Then, for the second line, the condition of step F72 is not checked and the data packet is not transmitted. The relay RS1 then repeats the steps of FIG. 7 with the prime number IDtx = 5. For the first line, the condition of step F72 is not checked and the data packet is not transmitted. Then, for the second line, the condition of step F72 is checked. Step F73 indicates that a change in transmission quality must be made in step F75. The data packet is therefore transmitted to the MT-CID4 tunnel of the first line after being recoded with SD quality. It can be noted that the shipping table (Table V) of an intermediate relay contains only one line per output. An intermediate relay can therefore quickly browse its dispatch table to determine the outputs to which to transmit a data packet. The shipping time, i.e. the time between the output of a data packet from the scheduler and its dispatch, is therefore reduced. The shipping process carried out by relay RS1 is therefore efficient and fast. The time required to consult the transition table (Table IV) before the processing by the scheduler is relatively short compared to the processing time by the scheduler. It does not influence the shipping time. In the example of Figure 1, the shipping table contains two lines. Thus, the steps F72 to F74 of FIG. 7 are repeated only twice by prime number IDtx. To determine which outputs to transmit a data packet to, the base station 2 also builds a transition table and a dispatch table based on the broadcast table, and performs a forwarding method corresponding to that previously described. Thus, a shipping method according to the invention can be implemented by a node which can be a base station or an intermediate relay.

It may be noted that when a stream is requested by several terminals according to several different transmission qualities, it is sufficient to transmit a copy of the stream with the highest transmission quality on the common part of the paths to the terminals. Indeed, the steps F74 and F75 allow an intermediate relay to degrade the quality of transmission to a downstream relay if necessary. The shipping method carried out by relay RS1 thus saves network resources (bandwidth and relay processing capacity on the common parts of roads). The invention has been described above with reference to a shipping table composed of several lines. More generally, the shipping data can be stored in a shipping database composed of several records.

Claims (8)

REVENDICATIONS1. Shipping method executed by a node (2, 3) of a multi-hop access network (1), said node (2, 3) comprising a plurality of output interfaces (MT-CID1, MT-CID2 MT-CID3, MT-CID4, MT-CID5), the shipping method comprising: - a step (F40) for receiving a data packet from a multimedia stream, - a step (F60) for processing said data packet by a scheduler, and - after said processing step (F60), a step (F70) of determining at least one of said plurality of output interfaces, to which to transmit said data packet, by consulting a shipping database (Table V), characterized in that it comprises, before said processing step (F60), a step (F50) of association, with the data packet, of at least an output interface and a prime number representative of a transmission quality with which the multimedia stream is to be transmitted to said an output interface, said dispatch database (Table V) including an output interface record of said plurality of output interfaces, each record containing an aggregation identity (IDag) representing a product of prime numbers, each said prime numbers representing a transmission quality with which a media stream is to be transmitted to the output interface of said record, said determining step (F70) comprising, for each record of said dispatch database: - a step ( F72) for testing a condition representing the divisibility of the product represented by the aggregation identity of the record by said at least one prime number associated with said data packet in the association step (F50), and when said condition is verified, a step (F74) for transmitting said data packet to the output interface of said record. 30 2. Shipping method according to claim 1 further comprising, when said condition is satisfied and before said step (F74) of transmission: - a step (F73) of comparison of a prime number (IDtx (F40)) representing the transmission quality of the received data packet with said at least one prime number (IDtx) associated with said data packet at the association step (F50), and if said prime numbers are different, a step (F75) recoding said data packet according to a transmission quality corresponding to the prime number associated with said data packet in the association step (F50). 16 3. Shipping method according to claim 1 further comprising: a step (F10) of receiving a message containing shipping information, a step (F20) of updating a transition table ( Table IV) according to said shipping information, said transition table containing a plurality of lines, each line comprising an identifier of a multimedia stream, a prime number representing a transmission quality for said multimedia stream, and an identifier of one of said output interfaces for said multimedia stream, - a step (F30) of updating said dispatch database by aggregating said transition table, each aggregation identity of the dispatch database being calculated according to said prime numbers of the transition table. 4. The method of claim 1 further comprising: a step of encoding the multimedia stream in a scalable format. 15 A computer program comprising instructions for performing the steps of the shipping method according to claim 1 when said program is executed by a computer. Computer-readable information carrier (6) with instructions of a computer program according to claim 5. 7. Node (2, 3) for a multi-hop access network (1), said node (2, 3) comprising a plurality of output interfaces (MT-CID1, MT-CID2, MT-CID3, MT-CID4; MTCID5) and means (8) for receiving a data packet from a multimedia stream, - means (5) for processing said data packet by a scheduler, and - means (5) for 5) determining at least one output interface out of said plurality of output interfaces, to which to transmit said data packet, by consulting a dispatch database (Table V), characterized in that includes means (5) for associating, with the data packet, at least one output interface and a prime number representative of a transmission quality with which the multimedia stream is to be transmitted to said output interface , said shipping database (Table V) including an output interface record of said plurality of interfaces output aces, each record containing an aggregation identity (IDag) representing a product of prime numbers, each of said prime numbers representing a transmission quality with which a media stream is to be transmitted to the output interface of said record, 17 the determining means comprising, for each record of said shipping database: means for testing a condition representing the divisibility of the product represented by the aggregation identity of the record by said at least one number first associated with said data packet during the association step (F50), and - transmission means, activated when said condition is satisfied, of said data packet to the output interface of said record. A multi-hop access network (1) comprising a base station (2) and at least one intermediate relay (3) comprising a node according to claim 7, said base station (2) comprising: receiving (8) a request for a multimedia stream, - means (5) for updating a broadcast table (Table III) indicating, for each hop of a path on which said stream must be transmitted. multimedia, a quality of transmission, and - sending means (8) to said intermediate relay (3), a message containing shipping information according to said broadcast table.