WO2010112738A1 - Notification message transmission method, access sessions server and communications system - Google Patents

Abstract

In accordance with the invention, the method for transmitting a notification message to a multimedia network access control device comprises: - a step (E20) in which information is recorded by a first server of a first access network, said information relating to an access session established by a terminal in order to access the multimedia network; and, upon detection (E130) of a change affecting at least one of said items of information, a step (E150) in which a notification message (M3) is transmitted by the first server on its own initiative, notifying the access control device of said change.

Description

 Method of sending a notification message, access session server and communications system

BACKGROUND OF THE INVENTION The present invention relates to the general field of telecommunications.

It relates more particularly to the accessibility, by a device for controlling access to a multimedia network, to information on a session of access of a terminal to this network.

For the purposes of the invention, such information is, for example, information relating to the geographical location of the terminal (or access point used by the terminal), the type of network access used, the bit rate proposed by the network. access, etc.

This information can be advantageously used by the access control device to guarantee the security of the multimedia network. For example, the access control device may limit access to the multimedia network by the terminal according to its geographical location, especially if its subscription does not allow it to access the multimedia network from any location.

This information can also be used by the multimedia network to adapt a service required by the terminal according to the characteristics of its access (eg type of access, speed, location, etc.).

The invention thus applies in a preferred but non-limiting manner to an IP (Internet Protocol) network, and more particularly to an IP network based on an IMS (IP Multimedia Subsystem) architecture.

In known manner today, when a terminal registers with an IMS telecommunications network, for example to access a service, an access control entity to this network, the P-CSCF ( CaII Session Control Function Proxy), queries an access network server, to obtain information about the access session used by the terminal. This server is also known as the server or base of CLF (Connectivity Location Function) access sessions.

This information is obtained using the IP address assigned to the terminal by the access network. It should be noted that the reliability of the information contained in the CLF server is guaranteed by the operator of the access network.

The information obtained by the P-CSCF is then transmitted to an application server (Application Server, AS) of the core network IMS, so that it can adapt the parameters of the service session established with the terminal according to the network environment of the latter. However, this information may change during a service session. Indeed, for example, the user's terminal may be required to change access point or even access network to connect to the multimedia network, which can affect in particular the information relating to the geographical location of this terminal and / or the type of access, the bit rate, etc., of the access session.

However, this change of access point or access network can take place without the terminal changing IP address and / or without having to re-register with the IMS network to signal this change.

This is particularly the case when the terminal is attached to the access network by the Mobile IP protocol. Indeed, according to this protocol, the terminal is identified with the P-CSCF by a unique IP address (the IP address assigned by its nominal access network), and this, regardless of the access network and / or the access point to which it is attached. It is the same for the DHCP protocol (Dynamic Host Configuration Protocol), according to which the same IP address can be assigned to a terminal although it connects to the network via two separate access points.

In such cases, the change of access point or access network by the terminal is completely transparent for the P-CSCF: it is indeed not able to detect it, the address IP remaining unchanged. Consequently, the P-CSCF relies on erroneous information for the control of the access of the terminal to the IMS network without knowing it. The same applies to application servers of the IMS core network, located upstream of the P-CSCF, providing the service required by the terminal.

Object and summary of the invention

The present invention aims in particular to overcome these disadvantages by providing a method of sending a notification message to an access control device to a multimedia network comprising:

a step of recording, by a first server of a first access network, information relating to an access session established by a terminal to access the multimedia network; and

- On detection of a change affecting at least one of these information, a step of sending a notification message of this change to the access control device, by the first server, on its own initiative.

Correlatively, the invention also relates to an access session server of a first network access to a multimedia network, comprising:

means for recording information relating to an access session, established by a terminal to access the multimedia network;

means for detecting a change affecting at least one of this information; and

- Means, activated on detection of this change and at the initiative of the server, to send to a device for controlling access to the multimedia network, a notification message of this change.

In an IMS network, the network access control device within the meaning of the invention is preferably an entity of the IMS network whose role includes ensuring the security of the multimedia network and the control of access to the services offered by this network. In other words, it is an equipment of the IMS network which is at the junction between the access network and the IMS core network. The P-CSCF server represents such a device.

In addition, the access session server of the invention is preferably a CLF server, as specified in the TISPAN standard, and adapted to implement the invention. As described above, the reliability and the timeliness of the information relating to the access sessions of the terminals contained in this server are guaranteed by the operator of the access network.

This information may include in particular at least one of the following:

a geographical location information of the terminal;

a type of access used by the terminal for the access session;

an IP address assigned to the terminal;

- a bitrate available for the terminal to access the multimedia network. It should be noted that the access network and the IMS core network can be operated by different actors, between whom cooperation and information exchange agreements have been previously concluded.

The invention thus makes it possible to keep the access control device informed of any change affecting the access session of the terminal and thereby its network environment. Such a change is for example a change of IP address of the terminal, a change of access point to the access network, a change of geographical location, etc.

In this way, the access control device can in turn inform the multimedia network of this change. An appropriate action can thus be envisaged by the control device and / or the multimedia network to take this change into account. For example, the control device may require a new registration or a new authentication of the terminal.

For this purpose, the invention advantageously provides for the spontaneous sending of a notification message by the access control access session server, as soon as a change affecting a piece of information relating to the session is detected. terminal access. By "spontaneous" is meant here that the access session server notifies, on its own initiative, the access control device. In other words, the access control device does not need to subscribe, for example through a subscription mechanism, to the server for access sessions to such notifications, nor to regularly scan the server. access sessions for detecting a change in information relating to the terminal access session. It will be noted that the standard document EETSI ES 282 004 entitled "Telecommunications and Internet Converged Services and Protocols for Advanced Networking"(ΗSPAN); NGN Functional Architecture; Network Attachment Subsystem (NASS) ", v2.0.0, 2008-02, provides for sending notification messages of a change of access session information, by a CLF server to an application function (Application Function or AF), in an environment

ΗSPAN. However, this sending on the one hand, is done only on express request of the AF or after subscription of this one with the server CLF, and on the other hand, this notification is not envisaged for the P-CSCF. It aims to transmit information to an AF adapted to provide a given service (for example to a Web server on the Internet), and not to an IMS network or even less to a P-CSCF that is not in directly charge for the provision of services.

In addition, even if one would consider applying such a mechanism to the P-CSCF, this would require the P-CSCF to send a subscription message (and then unsubscribe) to the CLF server, and this for each terminal for which it is responsible and for each access session associated with this terminal. This would result in a significant increase in the CPU load of the P-CSCF, which is difficult to envisage in an operational network in which the P-CSCF is responsible for about 100,000 simultaneous sessions.

The invention thus makes it possible to limit the interactions between the P-CSCF and the CLF server, while ensuring that the P-CSCF has up-to-date information on the terminal's access session. In a particular embodiment, the method according to the invention comprises a step of sending, by the first server to said access control device, an update of the information affected by said change.

This sending of updated information to the control device can be done, for example, directly in the notification message in an appropriate field. In this way, the access control device has, upon notification, updated information.

Alternatively, the notification message may include only an indication that a change affecting information relating to the access session has been detected. A message comprising the updated information can then be sent to it later, for example, only on its request. In a particular embodiment of the invention, the sending method further comprises a step of interrogating a second server of a second access network to the multimedia network, this interrogation being carried out by the first server, on its own initiative, in order to obtain an update of the information affected by the change.

Correlatively, in this embodiment, the server according to the invention comprises means, activated on detection of the change and on its own initiative, to interrogate a second server of a second access network to the multimedia network, in order to obtain an update of the information affected by the change.

This embodiment advantageously makes it possible to apply the invention in a context of mobility of the terminal, and in particular when this mobility is managed by the Mobile IP protocol. In such a context, the first access network is for example a terminal access network (or "home network") and the second access network, an access network visited by the terminal (or "visited"). network "). Advantageously, in this embodiment, the access session server of the nominal network spontaneously polls the access session server of the visited network as soon as it detects a change relative to the access session of the terminal. This interrogation is automatic so that the server of the nominal network can contain updated information, to be able, if necessary, provide this information to the access control device.

In this embodiment, a change may be detected when a match (also known as a "binding table") is stored by the home access network server between an IP address assigned to the terminal in the network. nominal access and an IP address assigned to the terminal in the visited access network. In a manner known to those skilled in the art, such correspondence is stored by the access session server of the nominal network in order to route the messages adequately to the terminal. This correspondence is updated during a change of visited network, on signaling the terminal to the nominal network.

In another embodiment of the invention, the server further comprises means, activated on detection of the change and at the initiative of the server, to send another access session server of another network. access to the multimedia network, a notification message of this change.

Thus, the invention also makes it possible to notify another access session server of the detected change. This embodiment notably makes it possible to exchange information on the access session between CLF servers of a nominal access network and a visited access network.

In a particular embodiment, the various steps of the method of sending a notification message are determined by instructions of computer programs.

Accordingly, the invention also relates to a computer program on an information medium, this program being capable of being implemented in a database or more generally in a computer, this program comprising instructions adapted to the implementing the steps of a method of sending a notification message as described above.

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 computer-readable information medium, comprising instructions of a computer program as mentioned above.

The information carrier may 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 information medium can be a transmissible medium such as an electrical or optical signal, which 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 information carrier may be 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.

According to a second aspect, the invention also aims at a communication system comprising:

a device for controlling access to a multimedia network;

an access session server of an access network to said multimedia network, this access session server including information relating to an access session established by a terminal for accessing the multimedia network; and wherein the access session server is in accordance with the invention.

The multimedia network is for example an IMS network, the control device, a P-CSCF entity of the IMS network, and the access session server, a CLF server. This system enjoys advantages similar to those mentioned above for the access session server according to the invention.

In a particular embodiment of the system according to the invention, the access control device comprises means for sending the terminal an authentication request, following the reception of the notification message of the access session server. Thus, advantageously, the access control device can force the terminal to re-register with it, so as to be able to apply an access control policy adapted to the access of the terminal.

It should be noted that today, the ΗSPAN standard requires a terminal having changed access point to re-register with the multimedia network. However, we note that the implementation of multimedia services on the terminals does not always comply with this aspect of the standard. In addition, software implementations of services, performed by the users themselves on their terminals, do not fulfill this condition either. The invention then makes it possible, in such cases, to ensure that the terminal re-registers well, that is to say that it authenticates well with the access control device. As a variant, obtaining up-to-date information from the access control device may enable it to free itself from a new registration of the terminal, and thus reduce the time required for attachment of the terminal to the terminal. service.

Note also that the invention applies not only in the case envisaged previously or the terminal changes access point without changing IP address, but also in other circumstances.

In particular, the invention also applies in a context where the terminal changes IP address without however registering with the access control device of the multimedia network. The invention then allows the access control device to know the new IP address of the terminal to which to route the required service without asking it to re-register.

A saving of time can thus be observed.

In a particular embodiment, the access control device comprises means, activated upon receipt of the notification message of the access session server, for notifying at least one equipment of the multimedia network of said change affecting the access session. of the terminal.

This equipment is for example the S-CSCF of an IMS network, an equipment of the IMS core network, or an application server of the IMS network. This information thus enables application servers to adapt the parameters of the service provided to the user's terminal (eg throughput, etc.).

It will be noted that the notification of the equipment of the multimedia network can be done via a specific notification message or, alternatively, in a signaling message.

In addition, it is thus possible to inform all the application servers concerned in a centralized manner, for example via the S-CSCF in an IMS network. The use of subscription mechanisms of each of these servers with the access session server or the access control device is thus avoided. The operations performed by the access session server are also simplified, since it can simply inform only the control device. The invention therefore enables an application service platform relying on an access network to use up-to-date information produced and guaranteed by this access network, in order to best manage the services delivered to a terminal of a network. user by adapting them to their network environment.

In a particular embodiment of the invention, the access control device further comprises means, activated upon receipt of the notification message, for sending to the access session server a message requesting the transmission of a call. updating at least one predetermined information among the information affected by the change.

This embodiment makes it possible to simplify the monitoring carried out by the access session server in order to inform the control device. Indeed, the server does not need to know what information relating to the user's access session may be affected by a change, which are relevant to the control device. It is sufficient for it to notify the control device that a change affecting the terminal access session has been detected.

The user will then interrogate the access session server by himself in order to know the updates of the information likely to interest him. It may also be envisaged, in other embodiments, that the method of sending a notification message, the access session server and the communication system according to the invention present in combination all or part of the characteristics above. Brief description of the drawings

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate embodiments having no limiting character. In the figures:

- Figure 1 shows a communication system in its environment, in a first embodiment of the invention;

FIG. 2 represents an access session server according to the invention, in a particular embodiment; FIG. 3 represents the main steps of a method of sending a notification message according to the invention, implemented by the access session server represented in FIG. 1, in the first embodiment;

FIG. 4 represents an example of context relating to an access session that can be memorized by an access session server according to the invention; FIG. 5 represents a communication system, in its environment, in a second embodiment of the invention;

- Figure 6 shows the main steps of a method of sending a notification message according to the invention, implemented by the access session server shown in Figure 5, in the second embodiment.

Detailed description of an embodiment

FIG. 1 represents, in its environment, a communication system 1 according to the invention, in a first embodiment.

In this example, a multimedia network R1 based on an IMS architecture is considered. Such a network comprises a CSCF (CaII Session Control Function) entity, composed of three I-CSCF (Interrogating CaII Session Control Function) servers, S-CSCF (Serving CaII Session Control Function) and P-CSCF (CaII Session Control Function Proxy). .

In a known manner, the P-CSCF server is the first point of contact of a terminal with the IMS core network R1. Its role is to guarantee the security of the IMS network and in particular to control the access to this network by the terminals, for example by the implementation of authentication (or registration) procedures. The P-CSCF server of the network R1 is an access control device within the meaning of the invention.

The network R1 also comprises a plurality of application servers AS, hosting and providing services. The structure and components of an IMS network are known to those skilled in the art and will not be detailed further here. 3GPP TS 22.228 "Service Requirements for the IP Multimedia Core Network Subsystem (Stage 1)" presents the main elements of an IMS architecture. The network R1 can inter-operate with any type of access network, fixed or mobile, wired or wireless.

Thus, in the example described here, there is considered a terminal T wishing to access a service offered by the network R1, by connecting to an access network R2, via an APl access point.

The access network R2 is here a WIR (WIreless FIdelity) network. Alternatively, it may be an Asymmetric Digital Subscriber Line (ADSL), Worldwide Interoperability for Microwave Access (WIMAX), Universal Mobile Telecommunications System (UMTS), and so on.

The terminal T is for example a laptop. Of course, the invention applies to other types of terminals (eg mobile phones, etc.).

In a known manner, to route a service from the network R1 to the terminal T, an IP resource must be reserved within the access network R2. This IP resource is here in the form of an IP address allowing the terminal T to be reachable on the network R2. This IP address is assigned by a DHCP server in the R2 network. As a variant, other protocols for attaching the terminal to the network R2 could be envisaged, such as, for example, Point-to-Point Protocol (PPP), Mobile IP, Internet Control Message Protocol (ICMP), etc.

The assignment of an IP address by the DHCP server to the terminal T, then the return of this IP address, respectively mark the beginning and the end of an access session to the network R2. Subsequently, there will be distinguished an access session, a service session established by the network Rl, to deliver a service to the terminal.

In known manner, as soon as an IP address is assigned to a terminal by the DHCP server, in other words, as soon as an access session is set up, a CLF access session server (Connectivity session Location and repository Function) of the R2 network is updated. This CLF server stores the contexts of the access sessions established by the access network and more particularly by the IP address assignment server as here, the DHCP server (or alternatively, by a Radius server, Diameter, etc. .).

In the example envisioned here, the CLF server has the hardware architecture of a computer. As illustrated in FIG. 2, it comprises a processor 11, a RAM type RAM 12, a ROM type ROM 13 and a non-volatile memory 14.

The read-only memory 13 constitutes a recording medium in accordance with the invention, readable by the server CLF, and on which is recorded a computer program according to the invention, comprising instructions for the execution of the steps of a method of sending a notification message according to the invention. The main steps of this method are shown, in a particular embodiment of the invention, in Figure 3 described later.

The server CLF also comprises means of communication with the DHCP server on the one hand, and with the access control device P-CSCF on the other hand. The CLF server is an access session server according to the invention. Note that this server may be included in the IP address assignment server, i.e. here, in the DHCP server.

We will now describe, with reference to FIG. 3, the main steps of a method of sending a notification message according to the invention, in this first embodiment, when it is implemented by the server. CLF shown in Figures 1 and 2.

It is assumed here that the terminal T wishes to access a multimedia type service proposed by the IMS network R1. Other services could of course be considered.

For this, the terminal T connects to the APl access point and sends, to the DHCP server, an attachment request to the access network R2 (step ElO). The operating principle of the DHCP protocol is known and will not be described in more detail here.

In response to this request, the DHCP server assigns an IP address, @IP, to the terminal on the access network R2. An access session S between the terminal T and the access network R2 is thus established.

In addition, the DHCP server maintains, in a base of the CLF server, a context associated with the access session S, in particular to keep in memory the @IP address assigned to the terminal T. For this, it transmits to the server CLF the IP address assigned to the terminal as well as information relating to the access session (step E20).

The base is recorded, for example, in the nonvolatile memory 14 of the CLF server.

An example of a CNT context, recorded by the server CLF, is shown in FIG. 4. Thus, in the example described here, for each access session S established by the DHCP server, the base of the server CLF is updated. with the following Access Session II information:

an identifier, denoted CLJD (for "Calling An Identification"), of the access line used by the terminal; an identifier ID_TERM of the terminal (for example its MAC address);

an identifier IDJJSER of the client associated with the access line;

the IP address, @IP, allocated to the terminal by the DHCP server;

and other information on the access session S, such as, for example, a geographical location LOC of the terminal, a postal address, the profile of its connection to the access network such as the type of access used. TYPE (ADSL, FTTH, etc.), the RATE rate attributed to this access, the start and end of the access session, etc.

Alternatively, the number and type of information envisaged may be different from the above example, given for illustrative purposes.

This access session information can be obtained by the DHCP server in a manner known per se and not detailed here, for example by inserting a line identifier in the DHCP messages by the DHCP relay (once the client line identified it is then possible to locate the terminal geographically and at the level of the network R2), or by interrogating the information system of the access network. Note that the DHCP server updates the base of the CLF access session server each IP address renewal or at the end of a lease allocated to the terminal for this IP address, which makes it possible to have of the CLF server, information on the updated terminal access session. The DHCP server then sends the IP address, @IP, to the terminal T in a message

(step E30). This message may also contain the IP address of the call server (i.e. the P-CSCF server), from which the terminal T must register to access the multimedia service. Alternatively, the IP address of the P-CSCF server can be configured in the terminal T.

Upon receipt of the @IP address, the terminal T initiates a registration phase with the P-CSCF server (step E40).

The P-CSCF server cooperates with the other devices of the IMS core network R1 for registration of the terminal and establishes a service session for this terminal, once the successful registration.

It also queries the CLF server for information on the access session used by the terminal (step E50). This interrogation is carried out using an interrogation request Ml comprising the IP address of the terminal, retrieved by the server P-CSCF of the received registration message. It may relate to all the information II mentioned above or only to a part of this information.

The interrogation request Ml also includes a service IDT identifier, associated with the service session of the terminal. This identifier uniquely identifies the terminal service session at the P-CSCF server. Its format is left to the discretion of the P-CSCF server. It can in particular be made uninterpretable by the access network, which can be advantageous when the access network R2 and the IMS network R1 are not managed by the same operator. The server CLF responds to this interrogation request Ml by sending to the server P-

CSCF, in an M2 message, the II information required (step E60) and extracted from the CNT context. Note that prior to this sending, the CLF server can verify that the P-CSCF server has the right to obtain such information.

In addition, the CLF server updates, in its base, the CNT context linked to the access session of the terminal by inserting the IDT service identifier and the IP address of the P-CSCF server, both extracted from the interrogation request Ml.

In the example described here and according to the invention, the CNT context is also updated with an LJST list of access session information II for which the P-CSCF must be notified, when a change affecting them is detected. This list is initialized according to the list of access session information II requested by the P-CSCF at the base CLF, in the interrogation request M1. Like the CLF server, the P-CSCF server maintains a CNT 'context for the terminal T (not shown), notably comprising the access session information received from the CLF server (step E70). This CNT context is uniquely identified by the IDT service identifier.

Thanks to the access session information II received from the CLF, the P-CSCF server can control the access of the terminal T to the IMS network R1, for example according to the geographical location of the terminal.

In the example described here, the P-CSCF server also transmits the information II by inserting them in signaling messages (in accordance with the Session Initiation Protocol (SIP)) to the network R1 (IMS). This information can thus be processed by the IMS and more specifically by the AS (Application Server) application servers adapted to deliver the service required by the terminal (step E80). These can, thanks to information II, adapt the parameters of the service session (eg quality of service) to the network environment of the terminal (E90). The provision of services adapted to the network environment of a terminal by an application server is known to those skilled in the art and will not be detailed further here. Note that when the terminal T de-register with the P-CSCF server while keeping however its IP address (and therefore the same access session), the P-CSCF server is adapted to send a message to the server CLF for inform him of this de-registration. More specifically, upon receipt of this message, the CLF server updates the CNT context, deleting the IDT service identifier, the IP address of the P-CSCF server and the LJST list. It is now assumed that the terminal T moves and connects to the network R2 via the AP2 access point (step ElOO).

It is further assumed here that the terminal T requests the DHCP server of the access network R2, the same IP address, @IP, as that used on its old network access link R2 (step EI10), and that the server DHCP accepts (step E120). Due to the very short time elapsing during the change of access points, the access session of the terminal is maintained by the DHCP server (in other words, the reassignment of the same IP address to the terminal corresponds to the same context) .

The DHCP server then notifies the CLF server of the access point change by the terminal and updates the CNT context contained in the base of the CLF server (step E130). Specifically, it transmits to the CLF server terminal access session information impacted by this change. Such a change may affect in particular the network location of the terminal and the information that is derived from this network location, such as the geographical location of the terminal.

Note that the DHCP server can notify the CLF server of a change in the access session in other circumstances than the aforementioned: for example, if the terminal T changes access network without changing the IP address , if the terminal T disconnects from the access network, if a problem is identified on the access network imparting the access session, or following an update of the information system of the access network. Upon detection of a change affecting at least one information II relating to the access session S, the server CLF checks whether a service identifier is associated with this access session (step E140).

In an alternative embodiment, the control performed by the server CLF can relate to the presence in the CNT context of an IP address of a P-CSCF server.

In the example described here, as previously described, the change is notified by the DHCP server to the CLF server. The reception of the notification message by the server CLF is a detection of a change affecting at least one access session information within the meaning of the invention. It will be noted that the reception of access session information updated by the CLF also constitutes such detection.

If the server CLF determines that a service identifier is associated with the access session S in the context CNT, then it checks, in a second time, if the detected change affects information specifically contained in the list sent by the P -CSCF.

If necessary, a notification message of such a change is sent to the P-CSCF server.

It is assumed here that the identifier IDT is contained in the CNT context and that the detected change impacts a geographical location information of the terminal T, identified as belonging to the list LJST stored in the context CNT.

The CLF server then sends an M3 notification message to the P-CSCF server to inform it of a change imparting the information specified in the list LIST (step E150). This M3 message contains updates to the access session information of the LJST list. It is sent by the CLF server on its own initiative, that is, without interrogation by the P-CSCF server or setting up an event subscription procedure between the P-CSCF server and the CLF server. As a variant, the message M3 can take the form of a "simple" signaling message of a change, without, however, specifying the nature of this change or the information impacted by this change. The updates of this information will then be sent later to the P-CSCF server at the express request of this one.

If there is no service identifier associated with the access session S updated in the context of the server CLF, then it updates its database without sending a notification.

If there is at least one service identifier associated with the updated access session S, but if the change does not affect the information specified in the list LIST, then the server CLF updates its database but does not send no notification message to the P-CSCF server.

On receipt of the message M3, the P-CSCF updates the context CNT 'relating to the access session S and identified by the identifier IDT (step E160), and sends an acknowledgment message to the server CLF confirming that he has received the notification message.

In the example described here, following the receipt of the message M3, the server P-CSCF sends a request to the terminal T for it to re-register (step E170). It can also send to the heart network RI (IMS), a notification of the change and the access session information updates, so I ¹ IMS can process the information. Among other things, the application servers AS can then adapt the service delivered to the terminal based on updated information. It is now assumed that the terminal T disconnects from the access network R2.

The IP address initially assigned to the terminal, @IP, is then released at the DHCP server

(step E180), and the access session S is closed.

Upon detection of this change of state of the access session, the DHCP server notifies the CLF server (step E190), which updates the CNT context of the access session S in the database. Upon detection of this change, the server CLF checks whether a service identifier is associated with the CNT context and if necessary, notifies the corresponding P-CSCF server as described above (step E200).

The latter, upon receipt of the notification message sent by the server CLF, updates the context CNT 'and closes the service session of the terminal T (step E210). We will now describe, with reference to Figures 5 and 6 a second embodiment of the invention. In this second embodiment, the terminal T is adapted to connect to various access networks to access an IMS network. The mobility of the terminal T is then managed using the Mobile IP protocol.

In a known manner, the Mobile IP protocol makes it possible to manage the mobility of a user's terminal by assigning him a unique IP address, regardless of the access network on which he is located. This unique IP address or "home address" is an address of the administrative network or nominal network of the terminal. This address in the nominal network makes it possible to contact a particular router also known as the home agent or "home agent".

When the terminal is on a network separate from its nominal network, in other words on a visited network, it is identified by an IP address called "care-of address", which is a temporary IP address allocated in the visited network. This address can be in particular the address of a router of the visited network also called relay agent or "foreign agent".

Each message sent by the terminal to a correspondent includes only the address in the nominal network. A binding table between the address in the nominal network and the temporary address of the terminal in the visited network is maintained at the level of the home agent at each registration of the terminal, in order to be able to properly route the messages intended for the terminal. This correspondence is also recorded in a CLF server of the nominal network, for a session of access of the terminal in the nominal network identified by the address in the nominal network. FIG. 5 represents a communication system according to the invention, in its environment, in this second embodiment. In this example, we consider an IMS network R1 similar to the IMS network previously described with reference to FIG. 1. Similarly, the access control server P-CSCF of the network R1 is similar to the server described with reference to FIG. 1.

In the example envisaged here, a terminal T having a nominal network access network Rh (the first access network to the multimedia network in the sense of the invention) is also considered. In this network Rh, the terminal is associated with a mother agent HA, adapted to communicate on the one hand with a DHCPh server and on the other hand with an access session server CLFh. In accordance with the Mobile IP protocol, the DHCPh server assigns the terminal T a unique IP address in the nominal network, denoted @lPh, for the management of its mobility. The access session server CLFh is in accordance with the invention. It has a hardware architecture similar to that of the previously described CLF access session server.

The terminal T is also adapted to connect to visited access networks to access the IMS network R1, two of them RvI and Rv2 (second access networks in the sense of the invention) are represented on the network. In these networks visited, the terminal T is associated respectively with routers or relay agents FA1 and FA2.

The FAl and FA2 relay agents are adapted to communicate respectively with DHCPvI and DHCPv2 servers, and with the CLFvI and CLFv2 access session servers. The role of the DHCPvI and DHCPv2 servers is to assign IP addresses in the RvI and Rv2 networks, according to the DHCP protocol. Alternatively, other protocols could be envisaged, such as for example PPP or ICMP.

The CLFvI and CLFv2 access session servers are in accordance with the invention.

With reference to FIG. 6, the mobile terminal T requests from the DHCPvI server an IP resource on the visited network RvI via its relay agent FA1, and this, in order to access a multimedia service offered by the network R1 ( step FlO).

The DHCPvI server assigns a temporary IP address to the terminal, denoted @lPvl. An access session Sl is thus established for the terminal T. It then transmits, to the CLFvI server, this IP address as well as other information relating to the session S1, to update a CNT1 context stored in a server base. CLFvI with this information (step F20). This step is similar to step E20 previously described.

It will be noted that, in a variant, rather than the DHCPvI server, it is the relay agent FAvI which can itself notify the server CLFvI about the information relating to the access session of the terminal on the visited network for setting CNTl context update. The @IPvl address is then sent by the DHCPvI server to the terminal T (step

F30).

On receiving this address, the terminal sends a message to its home agent HA to register on its nominal network, so that it can manage its mobility (step F40). Upon receipt of this message, the home agent HA updates the base of the access session server CLFh nominal network (step F50). It reports in particular in this database, the correspondence between the @IPh address of the terminal on its nominal network and a temporary IP address of the terminal, allocated by the network currently visited by the terminal. In other words here, the mother agent HA stores in the base of the access session server CLFh, for the access session in the nominal network identified by the address @IPh, the correspondence with the address @IPvl. It also indicates on which network visited RvI is the terminal.

In addition, a CNT context for the access session in the nominal network associated with the terminal T, and identified by the address in the nominal network @iPh, is recorded in the base of the server CLFh.

Once this update is done, the access session server CLFh sends an acknowledgment message to the home agent, which in turn transmits a message of acceptance of the attachment of the terminal to the visited network RvI ( step F60).

The terminal then initiates a registration phase with the P-CSCF server of the network R1, in order to access a multimedia service (step F70). According to the protocol Mobile IP, the registration message of the terminal T includes the address @IPh.

The P-CSCF server cooperates with the other devices of the IMS core network R1 for registration of the terminal and establishes a service session for this terminal, once the successful registration. It queries, moreover, the access session server CLFh of the nominal network (step

F80), using the @lPh address, to obtain information relating to the access session used by the terminal. The M4 interrogation request of the P-CSCF server comprises a service IDT identifier, associated with the service session of the terminal.

Upon receipt of this request, the CLFh server queries the CLFvI access session server of the visited network RvI, in order to obtain the information relating to the access session Sl used by the terminal on this network (step F90).

The interrogation request M5 sent by the server CLFh to the base CLFvI comprises for this purpose the address @IPvl and the service identifier IDT.

The server CLFvI transmits the required information to the server CLFh in response to the request M5 (step FlOO). In addition, it updates the CNTl context associated with the access session Sl, by inserting the IDT service identifier and the IP address of the session server CLFh contained in the request M5.

In this way, upon detection of a change affecting at least any of the information or predetermined information relating to the access session Sl, the CLFvI server spontaneously sends the server CLFh, a message notifying this change and including the updates of the information affected by the change.

Upon receipt of the access session information, the CLFh server transmits, in an M6 message, to the server P-CSCF (FIlO step). It also reports, in the CNT context, the information received, as well as the IDT service identifier and the IP address of the P-CSCF server, both extracted from the interrogation request M4.

In this way, as soon as a change affecting at least any of the information or predetermined information relating to the access session of the terminal T is detected, the server CLFh spontaneously sends to the server P-CSCF a notifying message. this change and including the updates of the information affected by the change.

Upon receipt of the message M6, the P-CSCF server updates a context CNT 'associated with the service session identified by the identifier IDT, with the information contained in the message. It also transmits the received access session information to the IMS core network R1 and, among other things, to the AS application servers in charge of delivering the required service to the terminal.

(step F120).

The service delivered is then adapted to the network environment of the terminal by the application servers AS (step F130). It is now assumed that the terminal T performs an access network transfer or

"Handover" and connects to the visited access network Rv2 (step F140).

It then asks the DHCPv2 server for an IP resource on the visited network Rv2, via its new relay agent FA2 (step F150).

The DHCPv2 server assigns a new temporary IP address to the terminal T in the visited network Rv2, denoted @ IPv2. An access session S2 is thus established for the terminal T. The DHCPv2 server then transmits to the server CLF2 information relating to the access session

S2, for updating a CNT2 context stored in a base of the CLFv2 server (step

F160). This step is similar to step E20 previously described.

The @ IPV2 address is then sent by the DHCPv2 server to the terminal T (step F170).

Upon receipt of this address, the terminal re-registers with its parent agent HA (step F180).

Upon receipt of the registration message from the terminal, the home agent HA updates the base of the access session server CLFh of the nominal network (step F190). In particular, it updates the correspondence between the @IPh address and the temporary address of the terminal using the @ IPv2 address of the terminal T in the visited network Rv2 (ie, it stores the correspondence between @IPh and @ IPv2, within the meaning of the invention). It also indicates on which network visited Rv2 is the terminal.

Once this update has been performed, the access session server CLFh sends an acknowledgment message to the home agent, which in turn transmits an acceptance message of the attachment of the terminal T to the visited network Rv2. .

In addition, on detection of the change in the IP address match in the nominal network and IP address in the visited network (detection of a change affecting at least information relating to the access session within the meaning of the invention), the server CLFh spontaneously sends an M7 message to the access session server of the visited network Rv2, in order to obtain information on the access session of the terminal used on this network (step F200). For this purpose, the interrogation request M7 includes the address @ IPv2 as well as the service identifier IDT. The server CLFv2 transmits the required information to the server CLFh in response to the request M7 (step F210). In addition, it updates the context CNT2 associated with the access session S2 of the terminal T on the visited network Rv2, by inserting the service identifier IDT and the IP address of the session server CLFh, after having excerpt from the M7 request.

In this way, as soon as a change affecting at least any of the information or predetermined information relating to the access session S2 is detected, the server CLFv2 spontaneously sends, to the server CLFh, a message notifying this change and comprising the updates of the information affected by the change.

Upon receipt of the access session information, the CLFh server transmits, on its own initiative, in an M8 message to the P-CSCF server (step F220), having checked that in the CNT context, an identifier IDT was associated with the access session of the terminal T. This step is similar to the previously described step E140.

The P-CSCF server then updates the context associated with the service session, identified by the identifier IDT, with this information, and transmits them to Rl and among other things to the AS application servers in charge of delivering the required service. at the terminal (step F230). The delivered service is adapted to the new network environment of the terminal by the AS application servers (step F240).

In the second embodiment described here, the access session servers of the nominal and visited networks are distinct. Alternatively, these CLF servers can be collocated.

In addition, in this second embodiment, the mobility management of the terminal relies on the use of the Mobile IP protocol. However, this hypothesis is not limiting. Indeed, other application cases of the present invention could be envisaged, for example in the context of an enterprise network using the PPP and L2TP protocols, or in a context of using VPN (Virtual Private Network (IPSEC, VPN TLS ...)).

Claims

A method of sending a notification message to an access control device (P-CSCF) to a multimedia network (R1), comprising: a recording step (E20, F50), by a first server (CLF, CLFh) of a first access network (R2, Rh), information relating to an access session established by a terminal (T) to access the multimedia network; and - on detection (E130, F190) of a change affecting at least one of said information, a step of sending (E150, F220) a notification message (M3, M8) of this change to said access control device by said first server on its own initiative. 2. Method of sending according to claim 1 comprising a step of sending (E150, F220), by the first server to said access control device, an update of the information affected by said change. 3. The sending method according to claim 1 further comprising a step of interrogating (F200) a second server (CLFv2) of a second access network (Rv2) to the multimedia network, said interrogation being carried out by said first server (CLFh), on its own initiative, to obtain an update of the information affected by said change. The sending method according to claim 3 wherein a change is detected when a match is stored (F190), at the first server (CLFh), between an IP address assigned to said terminal in the first access network ( Rh) and an IP address assigned to said terminal in said second access network (Rv2). The sending method according to claim 1, wherein said information (II) relating to the access session comprises at least one of the following elements: an information (LOC) of the geographical location of the terminal; a type of access (TYPE) used by the terminal for the access session; an IP address (@IP) allocated to the terminal; - A rate (RATE) available for the terminal to access the multimedia network. 6. Server (CLF, CLFh, CLFv1, CLFv2) of access sessions of a first access network (R2, Rh) to a multimedia network (R1), comprising: - means for storing information relating to a an access session established by a terminal, to access said multimedia network; means for detecting a change affecting at least one of said information; and - Means, activated on detection of this change and at the initiative of said server, for sending to an access control device (P-CSCF) to the multimedia network, a notification message (M3, M8) of this change. 7. Server (CLFh) according to claim 6 further comprising means, activated on detection of change and at the initiative of the server, to query a second server (CLFv2) access sessions of a second access network to the multimedia network, in order to obtain an update of the information affected by the change. The server of claim 7, further comprising means for storing a correspondence between an IP address assigned to said terminal in the first access network and an IP address assigned to said terminal in the second access network, said means for detecting a change detecting a change when said match is stored. 9. server (CLFvI, CLFv2) according to claim 6 further comprising means, activated on detection of change and at the initiative of the server, to send to another access session server (CLFh) of another network access to the multimedia network, a notification message of this change. A computer program comprising instructions for performing the steps of the method of sending a notification message according to claim 1 when said program is executed by a computer. A computer-readable recording medium on which is recorded a computer program comprising instructions for performing the steps of the method of sending a notification message according to claim 1. 12. Communication system (1,1 ') comprising: an access control device (P-CSCF) to a multimedia network (R1); a server (CLF, CLFh) for access sessions of an access network to said multimedia network (R1), said server comprising information relating to an access session established by a terminal to access the multimedia network; said system being characterized in that said server is in accordance with claim 6. The communication system of claim 12 wherein, said multimedia network being an IMS network (Rl) and said control device being a P-CSCF entity of the IMS network, said access control device (P-CSCF) comprises means to send audit terminal a request for authentication of this terminal following receipt of the notification message from the server. The communication system of claim 12, wherein said access control device (P-CSCF) further comprises means, activated upon receipt of the notification message from said access session server, for notifying at least one equipment (S-CSCF, AS) of said multimedia network of said change. 15. Communication system according to claim 12 wherein said access control device (P-CSCF) further comprises means, activated upon receipt of said notification message, to send to said server a message requiring the transmission of a bet. updating at least one predetermined information among said information affected by the change.