Access session controller, IP multimedia subsystem and registration and session method thereof

Disclosed are an access session controller, an IP multimedia subsystem and registration and session establishment methods thereof, where the access session controller includes a message reception module, a service trigger configuration module, a session control module and a message transmission module. The IP multimedia subsystem includes the access session controller and a network-wide home subscriber server system. The registration method includes: initiating, by the access session controller, an authentication information request to the network-wide home subscriber server system. The session establishment method includes: directly process, by the access session controller, the request message initiated from a user to establish a session. The foregoing solutions can simplify the signaling processing flow and reduce the network complexity.

TECHNICAL FIELD

The present invention relates to an IP Multimedia Subsystem (IMS) network technology and particularly to an access session controller, an IMS and a method for establishing a session and for registering a user equipment.

BACKGROUND OF THE INVENTION

As illustrated inFIG. 16, an existing IMS network supported by an operation and charging support system6is divided into three layers of an access layer9, a session control layer8and an application layer7, the access layer9includes a GPRS Gateway Support Node (GGSN)91, a Serving GPRS Support Node (SGSN)92and an IP access network93, and a user equipment accessing the access layer9may enjoy a service provided by an IMS system. The IMS system located at the session control layer8in the network supports an IMS Service Control (ISC) interface75, via which the IMS system may support application servers71and73based upon the Session Initiation Protocol (SIP) providing a supplementary service and a self-owned value-added service, and support a service capability server74based upon the Open Service Architecture (OSA) providing a third-party service as well as an original intelligence network service platform72. The IMS system10having a structure as illustrated inFIG. 17includes physical entities of a Proxy-Call Session Control Function (P-CSCF) module161, an Interrogating-Call Session Control Function (I-CSCF) module163, a Service-Call Session Control Function (S-CSCF) module162, a Media Gateway Control Function (MGCF) module14, a Multimedia Resource Function Controller (MRFC)13, a Multimedia Resource Function Processor (MRFP)11, an IMS Media Gateway (IMS-MGW)12, a Breakout Gateway Control Function (BGCF) module15, a Home Subscriber Server (HSS)17, etc., where the S-CSCF162is a control core of the IMS system, the P-CSCF161is an entrance for an IMS user to access the network, the P-CSCF161forwards a service request from the user to the S-CSCF162for processing by a service platform of a home network; the MGCF14and the IMS-MGW12provide interconnectivity between the IMS system10and a Universal Mobile Telecommunications System (UMTS) network Circuit Switched (CS) domain or a Public Switched Telephone Network (PSTN)1; the MRFC13and the MRFP11provide media resources and relevant control functions required in a service; and the BGCF15, which is an interface point between an IMS network2′ and an external network, selects a connection point with the PSTN1of the CS domain. A legacy mobile signaling network3is connected with the HSS17via interfaces Gr, Gc, C and D; the IMS network2′ and the MRFP11are connected via an interface Mb, and the MRFP11and the IMS-MGW12are connected via an interface Mb; the PSTN1is connected with the IMS-MGW12and the MGCF14via interfaces PSTN; the IMS-MGW12and the MGCF14are connected via an interface Mn; the BGCF15is connected with another BGCF15and the IMS network2′ via interfaces Mk; the BGCF15and the MGCF14are connected via an interface Mj; the MGCF14and the S-CSCF162are connected via an interface Mg; the MRFP11and the MRFC13are connected via an interface Mp; the MRFC13and the S-CSCF162are connected via an interface Mr; the BGCF15and the S-CSCF162are connected with an interface Mi; the S-CSCF162is connected with the P-CSCF161and the I-CSCF163via interfaces Mw; the IMS network2′ and the S-CSCF162are connected via an interface Mm; the S-CSCF162is connected with the HSS17, the SLF18and an application server (AS)5respectively via interfaces Cx, Dx and ISC; the P-CSCF161and a user equipment4are connected via an interface Gm; and the AS5is connected with the HSS17and the SLF18respectively via interfaces Sh (Si) and Dh. Reference may be made to the standard 3GPP TS 23.002 for details of the foregoing interfaces.

The existing IMS system suffers from such drawbacks that the system is of such a complicated structure that excessive operations are involved in a call signaling processing flow, resulting in a prolonged flow of establishing a session. For example, to establish a call session, an initial call request (Invite) message transmitted from a calling user firstly arrives at a P-CSCF of the calling user, which in turn routes the Invite message to an S-CSCF of a calling user to trigger a service; then an I-CSCF in a network of the called user determines a home S-CSCF of the called user, and the Invite message arrives at the home S-CSCF of the called user to trigger the service and then is transmitted to a home P-CSCF of the called user and finally to the called user. If both the calling user and the called user are roaming, the call signaling flow will be even more complicated to cause more signaling interactions in the network and hence an increased delay during the session establishment procedure.

BRIEF SUMMARY OF THE INVENTION

An aspect of embodiments of the invention lies in provision of an access session controller to simplify a signaling processing flow.

Another aspect of the embodiments of the invention lies in provision of an IP multimedia subsystem to simplify the signaling processing flow and reduce complexity of a network.

A further aspect of the embodiments of the invention lies in provision of a method for establishing a session via an IP multimedia subsystem to simplify a session establishment flow, shorten the duration of session establishment and improve the session establishment efficiency.

A further aspect of the embodiments of the invention lies in provision of a method for registering a user equipment via an IP multimedia subsystem to simplify the user equipment registration flow and improve the registration efficiency.

An aspect of the invention provides in some embodiments an access session controller, which includes a message reception module, a session control module, a service trigger configuration module and a message transmission module. The message reception module is adapted to receive a call request message and a response message from a user or a call request message and a response message from a network device; the service trigger configuration module is adapted to configure trigger information; the session control module is adapted to generate a command for transmitting a message triggering a corresponding application server and establish, maintain and release a session upon determining from the trigger information configured by the service trigger configuration module that the call request message or the response message satisfies a condition of triggering the application server, and to generate during establishment of the session a command to transmit the call request message directly to an access session controller at the side of a called user or a corresponding breakout gateway control function module; and the message transmission module is adapted to transmit the message according to the command from the session control module.

With the service trigger configuration module and the session control module, the inventive solution enables the call request message transmitted from a user to be transmitted directly to an access session controller at the side of the called user, so that when the called user and the calling user pertain to the same access session controller, signaling in a signaling flow between the calling and called users can be transmitted to the counterpart of calling and called parties after being processed by the only access session controller to thereby simplify the signaling processing flow and improve the efficiency of processing the call request message.

Another aspect of the invention provides in some embodiments an IP multimedia subsystem including the access session controller and a network-wide home subscriber server system connected with the access session controller and adapted to store network-wide subscriber information and indexes thereof for inquiring by the access session controller.

With the access session controller, this solution can enable the IP multimedia subsystem to directly process the request message transmitted from the user or trigger it to the corresponding application server through the access session controller to thereby simplify the signaling processing flow and improve the signaling processing efficiency. Furthermore, the IP multimedia subsystem can also be simplified greatly due to the network-wide home subscriber server system.

Another aspect of the invention provides in some embodiments a method for establishing a session via an IP multimedia subsystem, which includes: receiving a call request message by an access session controller in the IP multimedia subsystem; triggering, by the access session controller, a corresponding application server upon determining from configured trigger information that the call request message satisfies a condition of triggering the application server; and establishing, by the access session controller, a session according to a message returned from the corresponding application server.

With the access session controller, this solution can enable the call request message transmitted from a user to be routed directly to an access session controller at the side of a called user, so that when the called user and the calling user pertain to the same access session controller, signaling in a signaling flow between the calling and called users can be transmitted to the calling and called parties to perform corresponding operations after being processed by only the access session controller to thereby avoid multiple forwarding of the call request message, simplify the session establishment flow and improve the session establishment efficiency.

A further aspect of the invention provides in some embodiments a method for registering a user equipment in an IP multimedia subsystem, which includes:

transmitting, by an access session controller in the IP multimedia subsystem, a multimedia authentication request message to a network-wide home subscriber server system upon reception of a registration request message transmitted from the user equipment;

returning, by the network-wide home subscriber server system, to the access session controller an authentication condition for a user transmitting the registration request message; and

retrieving, by the access session controller, authentication information of the user from the user equipment, transmitting a server assignment request message to the network-wide home subscriber server system upon determining that the authentication information satisfies the authentication condition, and returning a registration success message to the user upon reception of a server assignment answer message and relevant data of the user returned from the network-wide home subscriber server system; and transmitting a registration failure message to the user upon determining that the authentication information does not satisfy the authentication condition.

With the access session controller in the inventive solution, the network-wide home subscriber server system may be requested for authentication information directly according to the registration request message transmitted from the user to thereby avoid multiple forwarding of the registration request message, simplify the registration flow and improve the registration efficiency.

The technical solutions of the invention will be further described in detail hereinafter with reference to the drawings and the embodiments.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment of Controller

FIG. 1is a structural schematic diagram of the first embodiment of an access session controller according to an embodiment of the invention, which includes a message reception module061, a registration control module062, a service trigger configuration module063, a session control module064and a message transmission module065, where the message reception module061is adapted to receive a registration request message, a call request message and a response message from a user equipment, or receive a call request message and a response message from a network device, e.g., an application server, and a message transmitted from the user equipment can be transmitted directly to the access session controller without being forwarded through an existing P-CSCF or I-CSCF; and the registration control module062is adapted to control a registration procedure of a user, and specifically in the registration procedure, the registration control module062requests authentication information of the user equipment from a network-wide home subscriber server system upon reception of the registration request message from the message reception module061, determines from the authentication information retrieved from the network-wide home subscriber server system whether the user has been authenticated, and reports registration status information, e.g., whether the user has been registered, to the network-wide home subscriber server system to maintain the registration status information of the user in a subsequent procedure, so that the access session controller can control directly the registration procedure of the user equipment. The service trigger configuration module063is adapted to store and configure trigger information, e.g., a table of correspondence relationships between called numbers and Uniform Resource Identifiers (URIs) of corresponding application servers. The session control module064compares the call request or response message with the trigger information stored in the service trigger configuration module063and determines whether a trigger condition is satisfied, for example, whether a called number in the call request message is stored in the service trigger configuration module063, and when the trigger condition is satisfied, the session control module064is linked to a URI corresponding to the called number to trigger a corresponding application server so as to avoid multiple forwarding of the call request message from the P-CSCF to an S-CSCF and even from the P-CSCF to the I-CSCF and further to the S-CSCF before the application server is triggered, thereby simplifying greatly the flow of processing the call request message and improving the efficiency of processing the call request. The session control module064further establishes and maintains a session table according to the call request message received by the message reception module061and releases a session at the end of the session in a processing flow similar to that in the prior art except that it is executed by the access session controller according to an embodiment of the invention; the session control module064rejects establishment of the session when the call request message does not satisfy the trigger condition or the application server triggered by the session control module064returns a message indicating that the user is not qualified for the session, for example, due to an insufficient balance of an account in the case of a prepaying user; and when the session control module064triggers the corresponding application server or rejects establishment of the session, the session control module064firstly generates a command to transmit a corresponding message, e.g., a command to transmit the call request message, the response message and a session establishment rejection message, and the message transmission module065executes the transmission. During establishment of the session, the session control module064generates a command to route the call request message directly to an access session controller at the side of a called user or a corresponding breakout gateway control function module, and the message transmission module065executes the command from the session control module064to transmit the call request message. The message reception module061and the message transmission module065can be coupled together. Particularly, the call request message is initiated from an authenticated user determined by the registration control module062or initiated from a network device, or initiated according to a network deployment strategy from an unauthenticated user and at this time the registration control module062can be omitted in the access session controller, for example, the registration is not required when a user dials an emergency telephone number, e.g.,110. At the end of the session, the session control module064processes a session release request message to release the session. Particularly, reference may be made to descriptions of an embodiment of an IP multimedia subsystem for details of the network-wide home subscriber server system.

Second Embodiment of Controller

FIG. 2is a structural schematic diagram of a second embodiment of an access session controller according to an embodiment of the invention, which further includes a routing module066based upon the foregoing embodiment, the routing module066is adapted to inquire, with a user identifier in the call request message. the network-wide home subscriber server system and a corresponding server executing a domain name service (simply a DNS) and obtain address information for next-hop forwarding of the message, e.g., address information of an access session controller of the opposite party, or address information of a BGCF, in combination with a relevant routing strategy. The session control module064releases the session, establishes the session between the user and the application server or routes the call request message to the called party according to the message returned from the triggered application server; and in order to route the call request message to the called party, the session control module064forwards the call request message directly to the access session controller of the called party according to the address information obtained by the routing module066or further forwards the message returned from the triggered application server to the access session controller of the called party in the case that the trigger condition is satisfied, thus avoiding multiple forwarding of the call request message from the P-CSCF to the S-CSCF of the caller to the S-CSCF of the callee and even from the P-CSCF to the I-CSCF and further to the S-CSCF of the caller and further to the I-CSCF and further to the S-CSCF of the callee before being transmitted to the call session control module of the called party to thereby simplify greatly the flow of processing the call request message, improve the efficiency of processing the call request message and shorten the duration of session establishment.

In the foregoing embodiment, the session control module064is further adapted to maintain status information of the session. In the event that each of a plurality of users initiates a call request message, the session control module064further associates other messages generated in the procedure of processing the call request message of the user according to the user identifier of the user, so that the access session controller can exactly process the call request message of each user.

Based upon the foregoing embodiment, the access session controller further includes a signaling compression module adapted to compress an SIP message to save a network transmission bandwidth.

Based upon the foregoing embodiment, the access session controller further includes a charging module adapted to charge for the session established according to the call request message, for example, via a Call Detail Record (CDR).

Embodiment of System

FIG. 3is a structural schematic diagram of an embodiment of an IP multimedia subsystem according to an embodiment of the invention. As shown inFIG. 3, an IP multimedia subsystem (IMS)00is connected in communication with a Public Switched Telephone Network (PSTN)1, an IP multimedia subsystem network or a simplified IP multimedia subsystem network2, a legacy mobile signaling network3, a user equipment4and an application server5. The IMS00includes an MRFP01, an IMS-MGW02, an MRFC03, an MGCF04, a BGCF05, an Access Session Controller (A-CSCF)06and a network-wide home subscriber server system07. Particularly, the MRFC03parses information of the A-CSCF06and executes a corresponding operation, for example, to subscribe for, release or modify a resource; the MGCF04selects an A-CSCF06according to a called number and an incoming call condition and performs conversion of call control protocols between the PSTN1and the IMS00; the BGCF05selects an appropriate interface point of the PSTN1or the CS domain according to the call request from the A-CSCF06to thereby route the call request to a network connected with the interface point of the PSTN1or the CS domain or to another IMS network or to the simplified IMS network2consisted of the IMS system according to an embodiment of the invention; the A-CSCF06routes the call request from the user equipment4to a corresponding network element, for example, triggers and routes the call request to the corresponding application server5when determining that the call request satisfies a trigger condition; and the A-CSCF06retrieves authentication information from the network-wide home subscriber server system07according to a registration request transmitted from the user equipment4to verify legitimacy of the user equipment4, i.e., whether it has been authenticated. The A-CSCF06can be implemented with the A-CSCF in the foregoing embodiments of the controller. The network-wide home subscriber server system07may store network-wide subscriber information, e.g., authentication and authorization information, accessed A-CSCF information and service information of subscribers, and indexes corresponding to the information by separating the data from the indexes to thereby expand the amount of stored data as desired and satisfy a demand for storing the network-wide subscriber information data, and the network-wide home subscriber server system may be constructed with a product such as an MmHLR server from UTSTARCOM Corp. and a large distributed database from Oracle Corp. The IP multimedia subsystem can be simplified greatly due to the A-CSCF and the network-wide home subscriber server system.

An IMS network consisted of the foregoing embodiment of the system may also be simplified greatly, and as illustrated inFIG. 4, a unified network-wide home subscriber server system07may be constructed with a distributed computer technology, so that it is not necessary to distinguish between a home area and a roam area, and the session control functions in the respective areas may be implemented with the unified A-CSCFs06.

Embodiment of Registration Method

To use a subscribed service via a user equipment, the user is firstly required to be registered to be authorized for use, that is, the user shall be registered before the A-CSCF determines whether the call request message transmitted from the user satisfies a condition of triggering an application server, as illustrated inFIG. 5.FIG. 5is a flow chart of an embodiment of a method for registering a user equipment via an IP multimedia subsystem according to an embodiment of the invention, andFIG. 6is a flow chart of signaling corresponding toFIG. 5. It is assumed that a user equipment accessing a user access network (IP CAN) is assigned with an A-CSCF through a dynamic host configuration protocol (DHCP) and a DNS inquiring mechanism and then initiates to the assigned A-CSCF a registration request (Register) message containing ID information of the assigned A-CSCF. A specific procedure to register the user equipment via the IMS includes:

Process101: The A-CSCF transmits a Multimedia Authentication Request (MAR) message102′ directly to the network-wide home subscriber server system upon reception of the “Register” message101′ to request the network-wide home subscriber server system for authentication information relevant to the user equipment requesting for registration to thereby simplify greatly the flow of processing the Register message.

Process102: The network-wide home subscriber server system returns to the A-CSCF a Multimedia Authentication Acknowledgement (MAA) message103′ containing the authentication information of the user equipment.

Process103: The A-CSCF transmits a Un-Authorization (401) message104′ to the user equipment according to the received authentication information of the user equipment to initiate an authentication challenge to the user equipment.

Process104: The A-CSCF receives a “Register” message105′ retransmitted from the user equipment to the network, which contains authentication information stored in the user equipment itself, and determines whether the authentication information transmitted from the user equipment matches that transmitted from the network-wide home subscriber server system to thereby determine whether the user equipment has been authenticated. If the user equipment has been authenticated, the flow goes to Process105; otherwise, the flow goes to Process108.

Process105: The A-CSCF transmits a Server Assignment Request (SAR) message106′ to the network-wide home subscriber server system to request the network-wide home subscriber server system to store ID information of the present A-CSCF, and thereafter the present A-CSCF or another A-CSCF upon reception of a call request message of the user equipment acting as a callee can obtain the A-CSCF serving the user through inquiring the network-wide HSS according to the ID information and route the call request message to the A-CSCF corresponding to the ID information for call switching.

Process106: The network-wide home subscriber server system returns to the A-CSCF a Server Assignment Acknowledgement (SAA) message107′ to accept the request of the A-CSCF and returns service data relevant to the user equipment.

Process107: The A-CSCF returns a registration success message (200OK)108′ to the user equipment for successful registration.

Process108: The A-CSCF transmits a registration failure (403) message to the user equipment.

The present embodiment can assign directly the user equipment with the A-CSCF in the access network to receive the registration request message of the user equipment to thereby avoid multiple forwarding of the registration request message among the P-CSCF, the S-CSCF and the I-CSCF, so that the multimedia authentication request can be initiated directly from the A-CSCF to the network-wide HSS after the user equipment transmits the registration request message, to thereby simplify greatly the registration flow and improve the registration efficiency.

The user registered successfully can use the subscribed service, and a session may be established through the IMS system according to the embodiments of the invention.

First Embodiment of Session Establishment Method

FIG. 7is a flow chart of a first embodiment of a method for establishing a session via an IP multimedia subsystem according to an embodiment of the invention, andFIG. 8is a flow chart of signaling corresponding to the method shown inFIG. 7. It is assumed that a user equipment initiates a conference establishment request to any IMS according to the foregoing embodiments of the system, and a Uniform Resource Identifier (URI) of a conference factory is used in an initial call request (Invite) message201′ because no conference instance has been created at that time. A procedure to establish a session via the IMS includes:

Process201: The A-CSCF in the IMS determines whether the “Invite” message201′ satisfies the condition of triggering an AS upon reception of the “Invite” message201′, and if the “Invite” message201′ satisfies the condition of triggering an AS, the flow goes to Process202; otherwise, the flow goes to Process210.

Process202: The A-CSCF routes the “Invite” message201′ to the AS according to an initial Filter Criterion (iFC). Since the user equipment uses the URI of the conference factory to request for the conference, the AS upon reception of the “Invite” message201′ assigns a URI of a conference instance and transmits Session Description Protocol (SDP) information available during the conference to the A-CSCF via a session progress (183) message202′; and a connection resource of the conference is created in the MRFP.

Process203: The A-CSCF forwards the “183” message202′ to the user equipment, and upon reception of the “183” message202′, the user equipment transmits the SDP information selected by the user to the A-CSCF via a provisional acknowledgement (Prack) message203′ and applies for a local resource.

Process204: The A-CSCF forwards the “Prack” message203′ to the AS, and the AS responds to the “Prack” message203′ of the user equipment by transmitting to the A-CSCF a response message (200OK)204′ which may carry the SDP information.

Process205: The A-CSCF forwards the “200OK” message204′ to the user equipment, and the user equipment updates the SDP information and transmits the updated SDP information to the A-CSCF via a update message (Update)205′.

Process206: The A-CSCF forwards the “Update” message205′ to the AS, the AS transmits to the A-CSCF a “200OK” message206′ in response to the “Update” message205′, and the MRFP activates a media connection with the user equipment.

Process207: The A-CSCF forwards the “200OK” message206′ to the user equipment.

Process208: The A-CSCF receives a response message (a “200OK” message207′ with the “Contact” header carrying the URI of the conference instance) in response to the “Invite” message201′, which is returned from the AS, and forwards the response message to the user equipment; and upon reception of the “200OK” message207′ carrying the URI of the conference instance, the user equipment transmits to the A-CSCF an acknowledgement message (ACK)208′ acknowledging the “Invite” message, to acknowledge successful establishment of the conference.

Process209: The A-CSCF forwards the “ACK” message208′ to the AS to complete the present establishment of the session.

Process210: The A-CSCF returns an establishment rejection or failure message to the user equipment.

In the present embodiment, when the calling user equipment uses a prepaid service, the A-CSCF upon reception of the “Invite” message initiated from the user equipment firstly triggers an application server of the prepaid service and determines from a message returned from the application server of the prepaid service whether the user equipment is still capable of paying for the present service, and if the user equipment is still capable of paying for the present service, the A-CSCF further determines whether the “Invite” message satisfies a condition of triggering another application server and further triggers the application server of conference establishment, for example, upon satisfaction of a condition of triggering the application server of conference establishment in the present embodiment. If the user has an account with an insufficient balance, the application server returns a message to the A-CSCF to notify the A-CSCF about the insufficient balance of the user account, and the A-CSCF transmits a message to the user equipment according to the message returned from the application server to reject establishment of the session.

The present embodiment may enable the “Invite” message of the user equipment to be received through the A-CSCF to thereby avoid multiple forwarding thereof among the P-CSCF, the S-CSCF and the I-CSCF before the AS is triggered, so that the AS can be triggered directly by the A-CSCF after the user equipment transmits the “Invite” message to thereby simplify greatly the session establishment or call flow, shorten the period of time for session establishment and improve the session establishment efficiency.

Second Embodiment of Session Establishment Method

FIG. 9is a flow chart of a second embodiment of a method for establishing a session via an IP multimedia subsystem according to an embodiment of the invention, and

FIG. 10is a flow chart of signaling corresponding to the method ofFIG. 9. It is assumed that a user equipment UE_1with subscription for a calling number display restriction service transmits to any IMS network according to the foregoing embodiments of the system an “invite” message301′ to call another user equipment UE_2with subscription for a calling number display service. The user equipment UE_1corresponds to an A-CSCF referred to as A-CSCF_1, and the calling number display restriction service corresponds to an application server referred to as AS_1; and the user equipment UE_2corresponds to an A-CSCF referred to as A-CSCF_2, and the calling number display service corresponds to an application server referred to as AS_2. A procedure for the IMS network at the side of the called user equipment to establish the session includes:

Process301: The A-CSCF_1determines whether the “invite” message301′ satisfies a condition of triggering an AS (the “invite” message301′ satisfies a condition of triggering the application server AS_1in the present embodiment) upon reception of the “invite” message301′.

Process302: The A-CSCF_1triggers the application server AS_1by routing the “invite” message301′ thereto; and the application server AS_1executes a relevant service control logic of, for example, modifying a value of the “Privacy” header in the “invite” message301′ to “id”, upon reception of the “invite” message301′, and then transmits a modified “invite” message302′ to the A-CSCF_1.

Process303: The A-CSCF_1transmits a Location Information Request (LIR) message303′ to the network-wide home subscriber server system to request for inquiring about location or address information of the A-CSCF at the side of the user equipment UE_2.

Process304: The network-wide home subscriber server system returns a Location Information Answer (LIA) message304′ carrying the location or address information of the A-CSCF at the side of the user equipment UE_2, the A-CSCF_2in the present embodiment.

Process305: The A-CSCF_1routes the “invite” message302′ to the A-CSCF_2according to the LIA message304′.

Process306: The A-CSCF_2determines whether the “invite” message302′ satisfies a condition of triggering an AS. In the present embodiment, it is determined that the “invite” message302′ satisfies a condition of triggering the application server AS_2.

Process307: The A-CSCF_2routes the “invite” message302′ to the application server AS_2; and the application server AS_2knows from the “Privacy” value in the “invite” message302′ that the calling number can not be displayed and thus modifies a display name in the “invite” message302′ to “anonymous” and then transmits a modified “invite” message305′ to the A-CSCF_2.

Process308: The A-CSCF_2routes the modified “invite” message305′ to the user equipment UE_2.

Process309: The A-CSCF_2performs corresponding coordination and control (e.g., forwarding a “183” message306′, a “Prack” message307′, and “200OK” message308′) between the user equipment UE_2and the application server AS_2as required for the service until forwarding an “ACK” message to complete establishment of the session.

It should be noted that the A-CSCF_1and the A-CSCF_2are the same A-CSCF when both the user equipment UE_1and the user equipment UE_2are served by one A-CSCF or in an area served by one A-CSCF.

The present embodiment may enable the “invite” message to be received through the A-CSCF to thereby avoid multiple forwarding thereof among the P-CSCF, the S-CSCF and the I-CSCF of calling and called parties before the AS is triggered, so that the AS can be triggered directly by the A-CSCF according to the “invite” message after the user equipment transmits the “invite” message to thereby simplify greatly the session establishment or call flow, shorten the period of time for session establishment and improve the session establishment efficiency.

Third Embodiment of Session Establishment Method

FIG. 11is a flow chart of a third embodiment of a method for establishing a session via an IP multimedia subsystem according to an embodiment of the invention, andFIG. 12is a flow chart of signaling corresponding toFIG. 11. Taking a supplementary service of calling number display as an example, it is assumed that a user equipment UE_1transmits to any IMS according to the foregoing embodiments of the system an “invite” message401′ to call another user equipment UE_2. The user equipment UE_1corresponds to an A-CSCF referred to as A-CSCF_1, and the user equipment UE_2corresponds to an A-CSCF referred to as A-CSCF_2. A procedure for the IMS network at the side of the called user equipment to establish the session includes:

Process401: When determining that the “invite” message401′ does not satisfy a condition of triggering an AS, the A-CSCF_1transmits an “LIR” message402′ to the network-wide home subscriber server system to request for inquiring about the A-CSCF at the side of the user equipment UE_2.

Process402: The network-wide home subscriber server system returns to the A-CSCF_1an “LIA” message403′ carrying address information of the A-CSCF at the side of the user equipment UE_2, the A-CSCF_2in the present embodiment.

Process403: The A-CSCF_1routes the “invite” message401′ to the A-CSCF_2according to the “LIA” message403′ returned from the network-wide home subscriber server system.

Process404: The A-CSCF_2determines whether the “invite” message401′ satisfies a condition of triggering an AS, and the “invite” message401′ satisfies a condition of triggering the application server AS_2assumed as an application server of a calling number display service in the present embodiment.

Process405: The A-CSCF_2routes the “invite” message401′ to the application server AS_2according to an iFC; and the application server AS_2firstly determines whether the “invite” message401′ carries the “Privacy” header and if it is not carried or has a value other than “id” or “user”, which indicates that the user equipment UE_1does not use a Calling Line Identification Restriction (CLIR) service, the application server AS_2modifies the “invite” message401′ to an “invite” message404′ according to the “P-Asserted-Identity” header in the “invite” message401′ so as to display the user number of the user equipment UE_1to the user equipment UE_2and transmits the “invite” message404′ to the A-CSCF_2.

Process406: The A-CSCF_2routes the “invite” message404′ to the user equipment UE_2; and the user equipment UE_2displays the user number of the user equipment UE_1according to the calling user information modified by the application server AS_2in the “invite” message404′. It should be noted that a specific header containing information to be displayed as a calling number may vary from one network to another and further detailed description is omitted here. Then, the user equipment UE_2transmits a “183” message405′ to the A-CSCF_2.

Process407: The A-CSCF_2forwards the “183” message405′ to the application server AS_2.

Process408: The A-CSCF_2performs corresponding coordination and control (e.g., forwarding a “Prack” message, a “200OK” message) between the user equipment UE_2and the application server AS_2as required for the service until forwarding an “ACK” message to complete establishment of the session. These subsequent messages can be processed similarly to interaction logic of a basic call flow in an existing IMS network except that the session process is accomplished by the A-CSCFs of the calling and called parties in the present embodiment.

In the present embodiment, when the user equipment UE_2uses a prepaid service and has an account with an insufficient balance, the application server AS_2upon determining the insufficient balance of his account notifies the A-CSCF_2about that information, and the A-CSCF_2rejects establishment of the session and notifies the user equipment UE_2.

For the user equipment UE_2with subscription for a call-forward-on-no-answer service, the following operations are executed as illustrated inFIG. 12andFIG. 13after the A-CSCF_2routes the “invite” message401′ to the application server AS_2in the Process405:

Process501: The A-CSCF_2further determines whether the “invite” message404′ satisfies a condition of triggering another application server; and the called number in the “invite” message404′ satisfies a condition of triggering an application server of call-forward-on-no-answer, e.g., an application server AS_3, in the present embodiment, and then the A-CSCF_2transmits the “invite” message404′ to trigger the application server AS_3, and the application server AS_3initiates a timer and also returns the “invite” message404′.

Process502: The A-CSCF_2transmits to the user equipment UE_2the “invite” message404′ returned from the application server AS_3; and the user equipment UE_2returns a ring message (“180” message)501′ to the application server AS_3; and the application server AS_3transmits the “180” message501′ to the A-CSCF_2.

Process503: The A-CSCF_2forwards the “180” message501′ to the user equipment UE_1through the A-CSCF_1, and the user equipment UE_1rings; the application server AS_3determines from the timer whether the user equipment UE_2responds in a predetermined period of time and transmits an answer forward message (“181” message)502′ to the A-CSCF_2if exceeding the predetermined period of time.

Process504: The A-CSCF_2forwards the “181” message502′ to the user equipment UE_1through the A-CSCF_1to notify the caller of that the callee is transferring a call to a third user equipment, e.g., the user equipment UE_3.

Process505: The A-CSCF_2receives an “invite” message503′ initiated from the application server AS_3and transfers the call to the user equipment UE_3in a processing flow similar to a call initiation flow in the prior art.

After establishing the session according to the foregoing embodiments, the A-CSCF may further release the session in the case of completing the session. As illustrated inFIG. 14andFIG. 15, for example, initiation of a release request message from the called user equipment particularly includes:

Process601: The called user equipment UE_2transmits a “bye” request message601′; the A-CSCF_2determines whether the “bye” request message601′ satisfies a condition of triggering an application server upon reception of the “bye” request message601′ and transmits the “bye” request message601′ to the application server AS_2if it satisfies the condition of triggering, for example, the application server AS_2, and the application server AS_2analyzes the received “bye” request message601′ to execute a corresponding operation and transmits the processed “bye” request message601′ to the A-CSCF_2. Otherwise, the flow goes to Process602.

Process602: The A-CSCF_2routes the “bye” request message601′ to the A-CSCF_1of the calling user equipment.

Process603: The A-CSCF_1determines whether the “bye” request message601′ satisfies a trigger condition and performs triggering as a result of determination.

Process604: The A-CSCF_1transmits the “bye” request message601′ to the calling user equipment UE_1, and the user equipment UE_1returns a “200OK” message602′.

Process605: The “200OK” message602′ is processed similarly to the foregoing flow and returned to the user equipment UE_2to release the session.

The session release request message may alternatively be initiated from the calling user equipment, the A-CSCF of the calling end, the application server or the A-CSCF of the called party and processed in a similar flow to a session release flow in the prior art except that it is performed by the access session controller.

The present embodiment can enable the “invite” message to be received through the A-CSCF to thereby avoid both multiple forwarding thereof among P-CSCFs, S-CSCFs and I-CSCFs of the calling and called parties before being forwarded to the CSCF of the called party and multiple forwarding thereof among the P-CSCF, the S-CSCF and the I-CSCF of the called party before the AS is triggered, so that the “invite” message can be routed from the caller A-CSCF to the callee A-CSCF directly after be transmitted from the user equipment and the callee A-CSCF can trigger the AS according to the “invite” message to thereby simplify greatly the session establishment or call flow, shorten the period of time for session establishment and improve the session establishment efficiency.

It should be noted that the foregoing embodiments are merely intended to illustrate but not to limit the technical solutions of the invention. Although the invention has been detailed in connection with the foregoing embodiments, it should be appreciated to those ordinarily skilled in the art that the technical solutions recited in the foregoing respective embodiments can be modified or partial technical features of the solutions can be substituted equivalently without departing from the scope of the technical solutions in the respective embodiments of the invention.