WO2001063956A1

WO2001063956A1 - Wireless access point of an ip network, and corresponding mobility management method

Info

Publication number: WO2001063956A1
Application number: PCT/FR2001/000493
Authority: WO
Inventors: Hong-Loc Nguyen
Original assignee: Eads Defence And Security Networks
Priority date: 2000-02-21
Filing date: 2001-02-20
Publication date: 2001-08-30
Also published as: FR2805432B1; EP1258162A1; AU2001235724A1; FR2805432A1

Abstract

The invention concerns an access point emitting a beacon signal on an air interface. It executes, with a mobile user equipment having detected the beacon signal, an inscription procedure of a protocol particular to the air interface, enabling said equipment to communicate through the access point. Environment data concerning the access point are carried by the beacon signal and/or at least a message transmitted on the air interface to the mobile user equipment within the framework of the inscription procedure.

Description

WIRELESS ACCESS POINT OF AN IP NETWORK, AND CORRESPONDING MOBILITY MANAGEMENT METHOD

The present invention relates to user mobility services, and finds particular application in telecommunications networks comprising several interconnected subnetworks.

The user mobility in question here consists of the capacity offered to the user to communicate via the network by connecting to it at different access points. The user can take his terminal with him when he travels. This is the typical case of a radiocommunication network with mobiles, the access points being constituted by fixed relays. Without moving equipment, the user can also connect at different points by a registration procedure comprising the transmission, to a mobility management body, of identification data supplied by the user. Another possibility is that the user has a removable data medium which he presents at the visited access point equipped with an appropriate reader to automate the registration procedure.

We can distinguish two types of mobility, one called here micromobiiity consisting in allowing the user to change access point inside a sub-network, and the other called here macromobility by which the user can connect via access points belonging to separate subnets.

We also distinguish the ability of a user to change access point outside of a session, that is to say in the absence of active data flow ("roaming"), and the ability of a user equipped with a wireless terminal to change access point during a session ("handover").

For the purposes of network administration, each mobile user generally has a nominal sub-network to which is connected a body called here nominal location register, to which requests for the user are initially addressed and coming from sources which do not know their location. When moving in another subnetwork, another member connected to this visited subnetwork, called here visitor manager, can cooperate with the nominal location register for the implementation of mobility services.

Development of applications on networks operating according to the IP protocol (J. Postel, "Internet Protocol", Request For Comments (RFC) 791, IETF, September 1981), in particular those of voice and data transport, contemporary to the development of communication systems with mobiles, naturally led to consider the question of mobility in IP networks, whether they are wide area networks (WAN, “Wide Area Network”), such as the Internet, or local area networks (LAN, “Local Area Network”).

The Internet Engineering Task Force (IETF) has standardized a network layer protocol supporting mobility in an IP network (C. Perkins, "IP Mobility Support", RFC 2002, IETF, October 1996). After the mobile user has left his nominal subnetwork, his equipment is addressed to a body called a foreign agent, connected to the visited subnetwork, to send registration information to a body called home agent, connects to the home subnet. The identity of the visited subnet is also provided to the home agent. One of the main functions of the nominal agent is then to intercept the data intended for the mobile user in order to retransmit it, by an encapsulation mechanism, to a temporary address of the mobile user (called address c / o or "care-of address") provided by the foreign agent. Once arrived at this temporary address, the data can be delivered to their recipient.

This mobility scheme thus imposes a triangular path on the IP packets bound for the mobile user. On the other hand, the data originating from the mobile user is delivered to their destination via the usual IP routing mechanisms. In addition, it supposes the use of a fixed address for the mobile user. Its implementation therefore poses difficulties in networks where address management is dynamic, which is the case for example when a DHCP server is used in the nominal subnet (see for example EP-A-0 938 217). The DHCP protocol is specified in RFC 2131 published by the IETF (R. Droms, "Dynamic Host Configuration Protocol", March 1997)

A path optimization process, designed as an extension of the RFC 2002 protocol, has been proposed (C. Perkins, D Johnson, "Route Optimization in Mobile IP", Internet Draft, IETF, February 25, 1999) in order to overcome the disadvantages of the triangular routing mode. This method notably provides for the sending of update messages allowing the possible correspondents of a mobile user to keep the addresses in memory. temporary c / o of the latter. These can then send directly to the temporary address of the mobile user, thus avoiding the operations carried out on the data by the nominal agent.

Some authors have criticized the complexity of implementing such a method, and have suggested supporting mobility under IP using an application layer signaling protocol such as the SIP protocol (M.

Handley et al., "SIP: Session Initiation Protocol", RFC 2543, IETF, March

1999).

SIP describes client and server entities, as well as procedures enabling them to communicate (see also HG Schulzrinne and JD Rosenberg, "The Session Initiation Protocol: Providing Advanced Telephony Services Across the Internet", Bell Labs Technical Journal, October-December 1998, pages 144-159). There are two types of SIP servers: proxy servers and redirect servers. On receipt of a request, a proxy server determines the next node on the path to the recipient and then transfers the request to this node, while a redirect server simply tells the client the next node to which it should address its request. .

SIP addresses are similar to e-mail addresses, that is, in the form user @ host, where the "user" field designates, for example, a user name or telephone number, and the " host ”a domain name or address in numeric form. The SIP protocol notably provides methods called INVITE, BYE, REGISTER, OPTIONS, ACK and CANCEL. The responses to messages sent within the framework of these methods are defined by code classes. The INVITE method is used to initiate a call session between two SIP users.

The SIP protocol provides personal mobility capabilities, and allows a user to obtain the same services regardless of their location or the terminal used, in particular thanks to the REGISTER methods. It has been proposed (E. Wedlund, H. Schulzrinne, "Mobility Support using

SIP ", Proc. of the 2 ^πd ACM International Workshop on Wireless Mobile Multimedia, Seattle, August 20, 1999, pages 76-82) of mobility methods using the SIP protocol in which wireless equipment connected to the network via an air interface can , after appropriate signaling exchanges, execute a handover, that is to say change the network address (IP) by a DHCP mechanism while a communication is in progress. A SIP server connected to the user's nominal subnet manages the nominal location register for the latter. The SIP servers used in mobility management can be proxy servers or redirect servers. Any mobility gives rise to a registration with the nominal SIP server, which can then process requests from other SIP clients to the mobile user. When the wireless equipment determines the need to execute a handover (by detecting beacons emitted by the wireless access points), it obtains a dynamic address by a DHCP transaction, then it sends an INVITE message to its correspondent by indicating the reference of the call in progress and its new network address so that the correspondent updates the destination IP address of the packets which he sends. At the same time, the wireless equipment communicates its new address to its nominal SIP server, using the REGISTER method. One option provides for decentralization of the SIP servers used in mobility management: a proxy SIP server connected to the visited subnet manages micromobility, so that the REGISTER methods to the nominal SIP server, for redirection, can only concern macromobiity (change of micromobility server).

The main drawback of the process is the delay it can introduce in the execution of the handover. The INVITE method to the mobile user's correspondent requires significant routing time if this correspondent is far from the visited subnetwork. This delay can lead to a perceptible break in the communication in progress.

It should be noted that a similar drawback exists in the context of the IP mobility protocol of RFC 2002. When the mobile equipment is connected to a visited subnet remote from the nominal subnet, it is necessary to route a message location update to the home agent running the handover, which takes time. If the protocol is implemented with the aforementioned path optimization method, there is added the time necessary for the routing of a c / o address update packet to the user's correspondent. mobile.

On the other hand, within the framework of a network based on the IP protocol, there is no notion of physical connection, so that a communication with a wireless terminal does not suppose any knowledge, even implicit, of the geographic location of the terminal, unlike a circuit switched network for example. Terminal correspondents and its nominal location registers only "locate" it logically, via one or more IP addresses. However, a certain number of applications may need such geographic location information, for example to render services differentiated according to the location of the terminal or also to provide an indication of this location to the correspondents of the mobile user.

An object of the present invention is to provide quickly and efficiently to a wireless terminal communicating via an IP network information relating to the mobility of the user. According to the invention, there is proposed a wireless access point of a telecommunications network operating according to the IP protocol for transmitting packets in unconnected mode, comprising means for transmitting a signal on an air interface. beacon and means for executing, with the equipment of a mobile user having detected the beacon signal, a procedure for registering a protocol specific to the air interface, allowing said equipment to communicate on said network through the access point. Access point environment data is carried by the beacon signal and / or at least one message transmitted on the air interface to the equipment of the mobile user as part of said registration procedure. The environmental data may in particular include geographic location information of the access point. By inserting this geographic location information in the beacon signal or in the link layer signaling, it is made available to wireless terminals which can then communicate it to the mobility server of their nominal subnetwork or to correspondents in the framework of applications using such information.

For a telecommunications network comprising several subnets respectively equipped with mobility servers operating according to an application layer signaling protocol, the environmental data advantageously include an IP address of a mobility server of a connecting subnetwork to which the access point is connected.

This makes it possible to limit the delays due to signaling in the execution of handovers, since it is not necessary to transmit IP packets before the terminal can address the mobility server. The mobility server of the visited subnetwork will be able to play the role of proxy agent for both the signaling flows, notably concerning the mobility of the user, and for traffic flows (voice, images, data, etc.) Thus, during a handover, only local flows between the mobility server and the user are affected. The mobile user "sees" the proxy server as being his correspondent, so that he is the one to contact to report his change of access point. On the other hand, nothing is changed for exchanges between the server and the remote correspondent. Signaling information does not have to be sent remotely during the handover, to the nominal sub-network or to the correspondent. As it will interfere with the routing of messages within a sub-network is very rapid, this results in an optimization of the execution time of the handover.

The method can be applied with various application layer signaling protocols. Currently, SIP is a preferred protocol because it constitutes a good compromise between functional richness and complexity of implementation, while having a good capacity for extension. Other examples, well known to those skilled in the art, are the H.225.0 ("Call signaling protocols and media stream packetization for packet-based multimedia communication Systems") and H.245 ("Control protocol for multimedia communication") protocols. ) specified by the International Telecommunication Union (ITU-T) within the framework of Recommendation H.323 (“Packet-based multimedia communications Systems”, February 1998), and the MGCP protocol (M. Arango et al., “ Media Gateway Controller Protocol (MGCP) ”, RFC 2705, IETF, October 1999) or its Megaco variant (F Cuervo et al.,“ Megaco Protocol ”, Internet Draft, IETF, February 8, 2000).

Another aspect of the present invention relates to a wireless access point of a telecommunications network operating according to a packet transmission protocol in unconnected mode, the access point comprising means for transmitting on a air interface of a beacon signal and means for executing, with the equipment of a mobile user having detected the beacon signal, a procedure for registering a protocol specific to the air interface, allowing said equipment to communicate on said network through the access point, and in which access point environment data including information representative of the geographic environment of said access point is carried by the beacon signal and / or at least a message transmitted on the air interface to the mobile user's equipment as part of said registration procedure

Another aspect of the present invention relates to a method of mobility management in a telecommunications network comprising several subnets respectively equipped with mobility management bodies, in which one of the subnets constitutes a nominal subnetwork for a mobile user and is equipped with a nominal register containing a location information of said user, in which a procedure for locating the mobile user near an access point connected to a visited subnetwork comprises the following steps:

- reception by a mobile user equipment of a beacon signal transmitted on an air interface by said access point; - execution by said equipment and said access point of a procedure for registering a protocol specific to the air interface; and

- Transmission by said equipment of a location update message to a mobility management unit of the visited subnetwork, and in which one includes in said beacon signal and / or in at least one transmitted message on the air interface by said access point to the equipment of the mobile user as part of said registration procedure, a network address of a mobility management unit associated with said access point.

Other features and advantages of the present invention will appear in the following description of nonlimiting exemplary embodiments, with reference to the appended drawings, in which:

- Figure 1 is a diagram of a telecommunications network to which the invention is applied;

- Figures 2 to 4 are diagrams illustrating the exchange of messages involved in mobility management according to an embodiment of the invention;

- Figure 5 is a diagram of a subnetwork to which an embodiment of the invention can be applied;

- Figure 6 is a diagram illustrating the exchange of messages that can intervene in mobility management within a subnetwork according to Figure 5; and

- Figures 7 and 8 are diagrams showing examples of information blocks which can be transmitted by wireless access points in one embodiment of the invention. Figure 1 schematically shows an Intranet network distributed over three sites 1, 2, 3. On each site, a subnet 1 1, 12, 13 is installed to offer access to a certain number of users. These subnets 11-13 are for example of the Ethernet type (ISO standard 8802-3, “Local Area Networks, Part 3 - Carrier Sensé Multiple Access with Collision Detection - Access Method and Physical Layer Specifications”), and operate according to the protocol IP network. In the example shown, each subnet has an output router 4 connected to a backbone network 5 such as the Internet.

The network can in particular be provided to support real-time signal communications, for example telephony, between users connected to it and / or with correspondents accessible by the backbone network 5. In this case, the terminals can use known manner the UDP transport layer protocol (J. Postel, “User Datagram Protocol”, RFC 768, IETF, August 1980) and the real-time protocol RTP (H. Schulzrinne et al., “RTP: A Transport Protocol for Real -Time Applications ”, RFC 1889, IETF, January 1996) for the transmission of coded speech or video. For call signaling, a preferred embodiment of the invention uses the SIP protocol, which also works with the UDP transport protocol. However, other signaling protocols (H.323, MGCP, ...) could be used, in addition to or instead of SIP.

At least some of the network users are mobile users equipped with wireless terminals 6. To enable them to access the network, the latter includes radio access points 7 connected to the subnets 11-13. The radio access points 7 are for example DECT base stations (ETSI standard, “European Telecommunications Standards Institute”) or also according to the IEEE 802.11 standard, etc., depending on the type of wireless terminals used. Each of these radio access points 7 broadcasts a beacon signal on the air interface. On the basis of the beacon signals which it receives, an active terminal selects the access point which provides it with the best radio link.

This access point is used for communications involving the terminal.

A wireless terminal thus has the possibility of connecting to the network via several access points 7 belonging to different sub-networks (macromobility) or to the same sub-network (micromobility). When the terminal has a communication in progress and moves around a site, it is possible for it to change the access point while maintaining the continuity of the communication (handover). When a communication of signals in real time, for example of telephony, is in progress, it is desirable that these handovers are executed in a minimum time in order to avoid cuts noticeable.

For the management of mobility services, each subnetwork (at least those having wireless access points) has a mobility server 8 using the SIP protocol in the preferred embodiment of the invention. Each mobile user has a nominal subnet. In the illustration of FIG. 1, the subnet 1 1 is nominal for the holder of the wireless terminal 6. The SIP server 8 of this subnet is associated with a location register 9 known as the nominal register, which contains the IP address of the SIP server 8 of the subnet 12 visited by the mobile user. The SIP server 8 of the visited subnet 12 is itself associated with a location register 10 called the visitor register, which contains an address making it possible to reach the terminal 6 inside the visited subnet 12, for example an IP address associated with the terminal.

Each SIP server 8 can be associated with a nominal register 9 for the users attached to its subnet and with a visitor register for the users attached to other subnets, only the registers relating to the terminal 6 being represented on Figure 1. In practice, registers 9, 10 can be part of the same unit as the SIP server 8 with which they are associated, or they can be separate entities linked separately to the subnet. On the other hand, it is possible to provide several SIP servers per subnet, for example in the case where the functions of nominal SIP server and of visited SIP server are provided by separate machines, or in the case where several SIP servers are provided to distribute the signaling load in the subnetwork. FIG. 2 shows how the registration and the updating of the location of a visiting mobile user can take place in a subnet 12 different from his nominal subnet 11, and the initiation of a communication with this user on the initiative of a remote correspondent.

In the illustration of FIG. 1, the remote correspondent uses a fixed terminal 15 connected to a sub-network 13 different from the nominal sub-network 1 1 and from the visited sub-network 12. It will however be noted that a similar procedure is also applies:

- if this correspondent is another mobile user;

- if it is connected to the subnet 1 1 or 12 or to the backbone 5; - if the connection with the correspondent goes through another network, for example a switched telephone network, for which the Intranet network is equipped with a gateway (in the latter case, it is this gateway which constitutes the SIP client relating to the remote correspondent illustrated in FIGS. 2 to 4).

With reference to FIG. 2, the wireless terminal 6 belonging to the nominal sub-network 11 first picks up on the air interface the beacon signal emitted by an access point 7 belonging to the visited sub-network 12. In response upon detection, it triggers a registration procedure for the MAC layer protocol used on the air interface, by sending a registration message to the access point

(Register). In response to this message, the access point 7 returns an acknowledgment (Register Ack) validating the registration of the wireless terminal with the access point.

In the example of FIG. 2, the location information of the wireless terminal recorded in the visitor register 10 is a dynamic IP address obtained by the terminal after its registration with the access point 7. The subnet 12 is equipped with a DHCP server 16 which locally manages dynamic addresses. A classic DHCP transaction (DHCP_Dιscover, DHCP_Offer, DHCP_Request, DHCP_Ack messages) is executed between the roaming terminal 6 and the DHCP server 16, after which the terminal 6 has an IP address. In another embodiment using the IPv6 protocol, the transaction

DHCP is useless since the IPv6 address intrinsically allows a subnet / equipment hierarchy.

The next step consists of the SIP client sending the terminal 6 with a SIP REGISTER message to the SIP server 8 of the visited subnet 12.

The IP address of the SIP server 8 was provided by the access point 7 in the beacon signal broadcast on the air interface, which allows the wireless terminal to have this IP address without having to carry out transactions for this purpose via the subnetwork 12. If the beacon signal broadcast on the air interface does not have an available field large enough to contain the IP address of the SIP server 8, this can be completed, or provided in full, in the Register Ack message validating the registration of the terminal on the air interface.

The SIP REGISTER message sent by the terminal 6 allows the visited SIP server 8 to determine the terminal's IP address, obtained in the IP header of the packet containing the SIP REGISTER message, and to associate it with the SIP address (in the form user (α ⁾ host) contained in the SIP REGISTER message. This association is recorded in register 10.

After having received this SIP REGISTER message, the visited SIP server 8, if it does not already manage the mobile user, transmits another SIP REGISTER message to the SIP server 8 of the nominal subnet 1 1. The latter sets up update the entry of the nominal register 9 concerning the mobile user identified in the SIP REGISTER message, by memorizing the IP address of the visited SIP server which sent this SIP REGISTER message. It then returns a validation message (code 200 OK) of the SIP protocol. The SIP server visited in turn sends the validation message 200 OK to the terminal 6, through the access point 7.

At this stage, the wireless terminal 6 has registered with the access point 7, and updated its location with respect to the SIP servers 8.

When a call from the remote correspondent 15 is initialized, the latter sends a SIP INVITE message requesting the mobile user to the SIP server 8 of the nominal subnet 11 of the mobile user. The nominal SIP server being a redirect server in the example considered, it sends the remote correspondent a SIP message (code 302 Move) indicating to the latter that it must direct its INVITE method towards the SIP server of the visited subnet 12 for which it provides the IP address. The correspondent again transmits the SIP INVITE message to this visited SIP server.

The visited SIP server then initiates another session with the mobile user, by transmitting to it a SIP INVITE message, which the wireless terminal acknowledges with a SIP 200 OK message if it is available for establishing communication. The session between the wireless terminal and the visited SIP server is opened when the latter has received the message 200 OK. It then retransmits another SIP 200 OK message to the remote correspondent to validate the opening of the session with it.

From this moment, the remote correspondent communicates with the visited SIP server as if the latter was the wireless terminal, and the wireless terminal communicates with the visited SIP server as if it were the terminal of the remote correspondent. In each session opened with the SIP server visited, data is exchanged, typically according to the RTP / UDP / IP protocol stack when it represents coded speech or video, and additional signaling can be provided. according to the SIP / UDP / IP protocol stack. The visited SIP server 8 transmits the flow to the wireless terminal 6 RTP / UDP received from the remote party. Likewise, the RTP / UDP data stream received in the session established with the wireless terminal is passed on to the remote party. The visited SIP server also plays the role of proxy agent. FIG. 3 illustrates the registration of the wireless terminal 6 with another access point 7 of the same visited subnetwork 12, and the location update carried out with the SIP server of this subnetwork. The registration of the wireless terminal with the new radio access point is carried out by a MAC layer transaction identical to that described with reference to FIG. 2. If necessary, a DHCP transaction (not shown) can be carried out for that the terminal acquire a new IP address. The wireless terminal then sends a SIP REGISTER message to the visited SIP server, whose address it obtained in the tag of the new access point and / or in the Register Ack message. As the wireless terminal does not change the visited SIP server, it does not need to send a SIP REGISTER message to the SIP server of nominal subnet 11. After modifying the entry in the visitor register 10 relating to the mobile user, the SIP server visited validates its location update, by sending it a SIP 200 OK message.

To initiate a call to a remote correspondent (lower part of Figure 3), the wireless terminal sends a SIP INVITE message to its visited SIP server and the latter, which always acts as a proxy server, transmits another SIP message INVITE to the nominal SIP server of the called party. This nominal, redirecting SIP server returns a SIP 302 Move message indicating the IP address to which the correspondent can be reached. This IP address can be the address of the remote correspondent in its nominal subnet 13 or, as in the case of FIG. 2, the address of a SIP server visited if the remote correspondent uses a wireless terminal outside of its nominal subnet.

The establishment of the communication then ends as in the case of FIG. 2. SIP 200 OK messages are sent from the remote correspondent to the SIP server of the visited subnet 12, and from this SIP server to the wireless terminal 6 , after which the visited SIP server manages the two UDP streams as explained above to relay the communication.

FIG. 4 illustrates the handover procedure executed when the wireless terminal 6 has a call in progress and changes radio access point 7 while moving inside the site visited 2. It is assumed here that the same SIP server visited 8 is associated with the two access points 7, that is to say that the IP address of this server 8 is indicated in the beacon signal of these access points and / or in the message Register Ack. The upper part of Figure 4 shows the data flows relayed by the SIP server visited as explained above.

After the wireless terminal 6 has detected the beacon of the new access point and decided to change the access point, the registration procedure with the new access point and location update with the SIP server visited is executed as in FIG. 3. When the wireless terminal has received acknowledgment of its location update (SIP message 200 OK), it sends an INVITE message to the visited SIP server, containing in particular a reference of the current call. After validation of the INVITE method (SIP 200 OK message returned to the wireless terminal by the SIP server visited), the data exchange resumes without any signaling from the SIP server visited to the nominal SIP server or the remote correspondent.

The execution of the handover is particularly rapid since the signaling messages exchanged remain inside the visited subnetwork 12 without having to be routed by the extended interconnection network 5. On the other hand, the fact for the wireless terminal 6 to have the IP address of the visited SIP server directly, in the radio beacon or in the radio MAC layer signaling, saves time by avoiding a process of finding this address in the IP network.

FIG. 5 schematically shows another possible architecture of the subnetwork installed on the site visited 2, comprising several subnets 120, 121 interconnected by means of one or more routers. In the example drawn, the router 4 connected to the backbone network 5 also serves to interconnect the sub-subnets 120, 121.

The SIP server 129 of the visited subnet, which locally manages the mobility of the holder of the wireless terminal 6 in the manner previously explained, is connected to one of the subnets 120. It also acts as an agent nominal in an adaptation of the Mobile IP protocol which is the subject of RFC 2002. This adapted Mobile IP protocol is implemented inside the visited subnet in order to manage in the network layer the mobility of users between the sub- its subnets (but not at the scale of the grouping of subnets, where a layer protocol is used application, namely SIP in the example considered) Insofar as the agent 129 does not belong to the nominal sub-network of the mobile user, we will call it agent "pseudo-nominal", and we will say that a “pseudo-mobile IP” protocol is implemented. In each sub-sub-network 121 different from that provided with the pseudo-nominal agent 129 and equipped with one or more radio access points 7, a routing module is provided as a foreign agent 130 in the sense of RFC 2002.

After the wireless terminal 6 has detected the beacon of a new access point 7 belonging to such a sub-sub-network 121 and decided to change the access point, the registration procedure with the new access point d 'access is executed as in the case of Figure 3 or 4 (upper part of Figure 6). Terminal 6 then sends a request to register the Mobile IP protocol (REGISTRATION REQUEST in the terminology of RFC 2002) to the foreign agent 130, which relays it to the pseudo-nominal agent 129.

The terminal 6 places in the REGISTRATION REQUEST message, in addition to its own IP address, the IP address of the pseudo-nominal agent and the c / o address which was previously supplied to it. This c / o address may have been obtained by the agent discovery mechanisms specified in RFC 2002. But in a preferred embodiment, the two IP addresses (that of the pseudo-nominal agent and the c / o address) are provided in the beacon signal broadcast by the access point 7, and / or in the Register Ack message. The c / o address is then an IP address of the foreign agent 130, and can be used as the destination address by the terminal for sending the REGISTRATION REQUEST message.

After acknowledgment of the registration request (REGISTRATION REPLY messages of FIG. 6), the mobile terminal transmits its SIP REGISTER message to update its location with respect to the SIP server visited 129. The SIP REGISTER message can be sent directly to the IP address of the SIP server visited 129. As this message is seen as data by the Mobile IP protocol, it can also be relayed by the foreign agent 130 to the SIP server visited / pseudo-nominal agent 129 To acknowledge the SIP REGISTER method (after an exchange with the SIP server of the nominal subnet 11 if there has been a change in the visiting subnet), the SIP server visited 129 uses two levels of IP header to transmit the message SIP 200 OK, the internal level having the IP address of the wireless terminal 6 and the external level having the c / o address which was supplied by the foreign agent 130. The foreign agent 130 removes the external level to retransmit the message 200 OK to the terminal. The same encapsulation mechanism will be used for all the packets sent to terminal 6 by the visited SIP server 129 (SIP protocol or data from a remote correspondent). Similarly, the packets sent by the terminal 6 are relayed by the foreign agent 130 to their destination, namely the visited SIP server 129 since this is seen by the terminal as if it were its correspondent.

The location update executed according to FIG. 6 takes place in the same way in the case of “roaming” (FIGS. 2 and 3) and in the case of the “handover” (FIG. 4). The location information associated with the terminal 6 in the visitor register 10 then consists of the address c / o which allows the SIP server to route the data to their destination.

FIG. 7 illustrates a possible structure of the beacon signal broadcast by a wireless access point 7 connected to a subnetwork. This signal is formed by modulation of a digital data block B, and is transmitted in a radio signal frame, or possibly in a time interval of a frame if time division multiple access is used on the air interface.

The digital data of block B includes a predetermined synchronization pattern 20, the detection of which allows the wireless terminals located within range of the access point to synchronize in time and in frequency to demodulate the signal of the frame, and certain conventional fields 21-23 containing system information required by the physical layer and link layer protocols. This system information typically includes:

- an identification of the network to which the access point belongs (field 21);

- system synchronization information (field 22), identifying the position of the current frame in the temporal organization of the radio signal transmitted on the carrier of the beacon (frame index in a current superframe, superframe number, ...) ; - other system information (field 23), such as for example a minimum received field level from which a wireless terminal is authorized to register with the access point, or indications of the carrier frequencies of the beacon signals of a few neighboring access points so that the terminals can monitor these carrier frequencies in order to determine the access point providing the best radio link.

Advantageously, the block B also comprises a field 24 in which the access point 7 places data describing its environment.

This data can represent the geographical environment where the access point is installed: location of the site visited 2, precise position of the access point (for example building, corridor, office, ...). As the network is based on the IP protocol in which there is no notion of physical connection, communication with a wireless terminal does not imply any knowledge, even implicit, of the geographic location of the terminal. The remote correspondents and the nominal location register 9 "logically" locate the terminal only, via one or more IP addresses. However, a certain number of applications may need such geographic location information, for example to render services differentiated according to the location of the terminal or also to provide an indication of this location to the correspondents of the mobile user. By inserting this geographic location information (explicitly or in coded form) into the beacon signal, it is made available to wireless terminals which can then communicate it to the mobility server of the nominal subnetwork or to correspondents in the context apps like that. The environmental data placed in field 24 of block B can also include one or more IP addresses of mobility management bodies, namely:

- The IP address of the SIP server (or H.323, MGCP, Megaco, ...) visited in an embodiment according to Figures 1 to 4; - in an embodiment according to FIGS. 5 and 6, the IP address of the SIP server

(or H.323, MGCP, Megaco, ...) also playing the role of pseudonominal agent 129 and the IP address of the foreign agent 130;

- in an embodiment where mobility between the subnets is managed by a network layer protocol such as that of RFC 2002, the IP address of the foreign agent.

The environmental data of field 24 can still include a UDP or TCP port number used by the mobility server 8, 129 associated with the access point, if it is not a default port number. This allows the terminal to send requests to the application layer signaling protocol directly to the correct port number. It is also possible to include in the environment data a MAC (Ethernet) address of the mobility management unit 8, 129 connected to the same subnetwork or subnetwork as the access point.

If field 24 of block B does not provide enough space to insert all the planned environmental data into the beacon signal, it is possible to insert some (or all) of it in the Register Ack message of FIGS. 2, 3, 4 or 6. In the example illustrated by FIG. 8, this Register Ack message is formed from a block of digital data B 'comprising:

a field 25 identifying the previous registration request and / or the wireless terminal which sent it;

- a field 26 containing codes indicating the response to the registration request (access authorized, refused or conditioned, parameters, ...);

- a possible field 27 to contain additional system information in addition to that provided in fields 21-23 of block B;

- a field 28 to repeat the environmental data or provide those which have not been in field 24 of block B.

Claims

1. Wireless access point of a telecommunications network operating according to the IP protocol, the access point (7) comprising means for transmitting a beacon signal on an air interface and means for executing, with equipment (6) of a mobile user having detected the beacon signal, a procedure for registering a protocol specific to the air interface, allowing said equipment to communicate on said network through the access point, and in which environmental data of the access point are carried by the beacon signal and/or at least one message transmitted over the air interface to the mobile user equipment as part of said procedure. registration.

2. Wireless access point according to claim 1, for a network comprising at least one mobility management body (8; 129, 130), in which said environment data includes an IP address of a management body mobility associated with the access point (7).

3. Wireless access point according to claim 2, wherein said environment data further includes a UDP or TCP port number used by a mobility management unit (8; 129) associated with the access point ( 7).

4. Wireless access point according to claim 1 or 2, wherein said environment data further includes a MAC address of a mobility management unit (8; 130) associated with the access point (7) .

5. Wireless access point according to any one of claims 1 to

4. for a telecommunications network comprising several subnetworks (11-13) respectively equipped with mobility servers (8) operating according to an application layer signaling protocol, said subnetworks comprising a connection subnetwork (12) to which the access point (7) is connected, in which said environment data includes an IP address of a mobility server of the connection subnetwork.

6. Wireless access point according to claim 5, wherein said application layer signaling protocol is the SIP, H.323, MGCP or Megaco protocol.

7. Wireless access point according to claim 5 or 6, in which the connection subnetwork comprises several interconnected sub-subnetworks (120, 121) respectively equipped with mobility agents (129, 130) used in a network layer mobility management protocol, said sub-sub-networks comprising a first sub-sub-network (120) provided with a mobility server (129) constituting a nominal mobility agent for mobile users visiting the the connection sub-network and a second sub-sub-network (121) to which the access point (7) is connected, in which said environment data includes, in addition to the IP address of the mobility server constituting the nominal mobility agent, an IP address of a foreign mobility agent (130) connected to the second sub-subnet (121).

8. Wireless access point according to any one of claims 1 to 7, wherein said environment data includes information representative of the geographical environment of the access point (7).

9. Wireless access point of a telecommunications network operating according to a packet transmission protocol in non-connected mode, the access point (7) comprising means for transmitting a signal on an air interface beacon and means for executing, with equipment (6) of a mobile user having detected the beacon signal, a procedure for registering a protocol specific to the air interface, allowing said equipment to communicate on said network through the access point, and in which environmental data of the access point including information representative of the geographical environment of said access point are carried by the beacon signal and or at least one message transmitted on the air interface to the mobile user equipment as part of said registration procedure.

10. Wireless access point according to claim 9, wherein said protocol for transmitting packets in non-connected mode is the protocol

IP.

11. Mobility management method in a telecommunications network comprising several sub-networks (11-13) respectively equipped with mobility management bodies (8; 129, 130), in which one of the sub-networks (11) constitutes a nominal subnetwork for a mobile user and is equipped with a nominal register (9) containing location information of said user, in which a procedure for locating the mobile user at an access point (7) connected to a visited subnetwork includes the following steps:

- reception by equipment (6) of the mobile user of a beacon signal transmitted on an air interface by said access point;

- execution by said equipment and said access point of a procedure for registering a protocol specific to the air interface; And

- transmission by said equipment of a location update message to a mobility management body of the visited subnetwork, and in which we include in said beacon signal and/or in at least one transmitted message on the air interface by said access point to the mobile user's equipment as part of said registration procedure, a network address of a mobility management body associated with said access point.

12. Method according to claim 11, wherein the location update message relates to an application layer signaling protocol.

13. Method according to claim 11, wherein the location update message relates to a network layer protocol.