WO2012025015A1

WO2012025015A1 - Method and device for switching ringing state session

Info

Publication number: WO2012025015A1
Application number: PCT/CN2011/078276
Authority: WO
Inventors: 李世涛
Original assignee: 中兴通讯股份有限公司
Priority date: 2010-08-26
Filing date: 2011-08-11
Publication date: 2012-03-01
Also published as: CN102387117B; CN102387117A

Abstract

Disclosed are a method and a device for switching a ringing state session. The method comprises: an SCC AS receiving a switching request message, when a called subscriber is handed over from a PS domain to a CS domain; and the SCC AS determining that the current session state of the called subscriber is a ringing state session, and sending session state information to an MSC server in a delay mode. The present invention solves the problem of a call failure between the subscribers due to inconsistent states of the MSC server and the called subscriber, thereby making user experience more satisfactory.

Description

TECHNICAL FIELD The present invention relates to the field of communications, and in particular, to a method and apparatus for switching a ringing state session. BACKGROUND OF THE INVENTION In today's mobile networks, a large number of PS (Packet Switch, Packet Domain Switched) based networks are deployed, such as: E-UTRAN (Evolved Universal Terrestrial Radio Access Network), UTRAN- HSPA (UTRAN-High Speed Packet Access, the universal terrestrial radio access network for high-speed packet access technology), but its coverage is not all-network-wide. In some places, the signal of the PS network will be very poor. Provide users with switching from PS to traditional CS (Circuit Switch) network (eg UTRAN, GERAN), especially when the user is in a session. FIG. 1 is a schematic diagram of a single mode switching mode (for example, SRVCC, Single Radio Voice Call Continuity, single wireless voice call continuity), for example: UE1 (User 1) and UE2 (User 2) are in a call. And is a PS bearer based on IMS (IP Multimedia Core Network Subsystem), and its session is anchored on the SCC AS (Service Centralization and Continuity Application Serve). During the process of the call, UE1 moves to a better coverage area of the CS network. At this time, UE1 sends the received signal test report to the MME (Mobility Management Entity, mobile management device) through the original PS network. After the test report, the PS to CS handover is performed. At this time, the MME sends a handover request to an enhanced MSC (Mobile Switching Centre) that can cover the UE1. The enhanced MSC sends the extended SIP interface to the IMS network. The handover request command of the IMS includes the media resource information of the MSC, and the MSC returns a handover response to the MME. After receiving the handover response, the MME sends a notification of completion of the handover to the UE1. In the process, the MSC sends a handover response to the MME, and the MME informs the user that the handover is complete, and the MSC initiates the handover update on the IMS side simultaneously. During the entire handover process, the calling user and the called user are not aware of the handover. of. Currently, for an ongoing call, that is, the calling party sends a call request, the called party is still in the ringing state and has not answered, and the calling party can hear the called ringtone at this time. The called party can also switch when the switching condition is satisfied at this time. The following is an example in which the UE-1 accesses the IMS network through the E-UTRAN, or the UTRAN PS network, and receives a call request in the PS network. For example, refer to the ringing session shown in FIG. Flowchart, the session switching process includes: Step 201: The calling user UE-2 initiates a call request, and the called IMS network element arrives at the called IMS network element. Step 202, the called side SCC AS anchors the call, and then forwards the call to the called side S. -CSCF network element; Step 203, the called side S-CSCF network element routes the call request to the called user UE-1; Step 204, after receiving the call request, the UE-1 may return to the UE-2 180 ringing response, indicating

UE-1 has received the call request; Step 205 206, the IMS network element forwards the 180 ringing response to the calling UE-2; Step 207, UE-1 may change position at this time, causing the surrounding network environment to occur. Transform, for example: The signal of the original PS network may not be very good, but the surrounding CS network signal is better. Then, the UE-1 sends a network signal test report to the original PS network. After receiving the test report, the MME decides to switch the user from the PS domain to the CS domain. When the MME detects that the handover condition is met, the UE detects the handover condition. The MSC server (sometimes abbreviated as MSC) sends a request to notify the handover; Step 208a, after receiving the notification handover request from the MME, the MSC server sends a SIP signaling-based handover request to the IMS, where the media of the MSC server is included. After the IMS side network element receives the handover request, the IMS side network element sends an update request to the remote UE-2 through the SCC AS, and informs that the media access address of the UE-1 is the address of the MSC server at this time; Step 208b The MSC server sends the handover request to the MME, and returns a handover reception response to the MME. Step 209b: After receiving the handover reception response, the MME notifies the UE to perform handover, and notifies the UE of the address of the MSC, and the UE -1, the access of the PS can be disconnected, and access to the MSC server that completes the handover through the CS domain network; Step 212, after receiving the update request, the UE-2, when agreeing to the update request, is to the UE- The first side returns the update response. Step 213 214, after the SCC AS receives the update response sent by the UE-2, the SCC AS returns an 18X response to the MSC, because the session being switched is a ringing session. Medium information carried by UE-2; Step 215 216, because the MSC server does not know that the handover session is in the ringing state when the handover request is sent, the SCC AS needs to send a notification message to the MSC to inform the MSC server that the session is a ringing. Session, and the MSC server needs to enter the call receiving state; Step 217, the MSC enters the CS domain call receiving state; at this time, the handover is basically completed, from the UE-1 to the MSC server is the CS connection, and the MSC server to the remote UE-2 It is a PS connection. Step 218 219, when the UE-1 answers the call at this time, the response message is sent to the MSC server by using the CS response signaling. Step 220 221, when the MSC server receives the CS response message, it enters the session-on state. The data can be forwarded for the users on both sides, and the MSC server also needs to send a notification message to inform the SCC AS that the called UE-1 has answered the call; Step 222, when the SCC AS receives the notification that the UE-1 has answered the call, Sending a 200 OK response message to the remote UE-2; Step 223, after receiving the 200 OK response message, the remote UE-2 returns an ACK message; Step 224 225, at this time, the SCC AS sends a 200 OK to the MSC server, indicating that the whole The handover process is completed. In the above handover process, if the called user has not received the handover notification message sent by the user, the called user answers the call, and the response message of the called user is sent from the original PS access to the SCC AS. If the SCC AS has notified the current session of the MSC server that it is a ringing session and requests the MSC server to enter the call receiving state, it causes the called user and the MSC server. In the CS domain, when the MSC server is in the call receiving state, it will consider that the call has not been connected yet. At this time, the MSC server will not forward the data sent by the called user (that is, the called party will say at this time, the MSC server The caller is not forwarded to the caller. As a result, the called user answers the call but cannot send it to the calling party, which affects the normal conversation between the two users and reduces the user experience satisfaction. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a method and apparatus for switching a ringing state session to at least solve the problem of call failure caused by the inconsistent state of the called user and the MSC server. According to an aspect of the present invention, a method for switching a ringing state session is provided, including:

During the handover of the PS domain to the CS domain, the SCC AS receives the handover request message; the SCC AS determines that the current session state of the called user is a ringing session, and sends the session state information to the MSC server in a delayed manner. Sending session state information to the MSC server in a delayed manner includes: The SCC AS sends the session state information to the MSC server after the specified time. After the SCC AS sends the session status information to the MSC server after the specified time, the SCC AS starts the timer. If the 200 OK response message sent by the called user from the PS domain is received within the timer start time, the 200 OK response is forwarded. The message is sent to the calling user, the timer is turned off, and the session state information is no longer sent to the MSC server; if the 200 OK response message is not received within the timer start time, the session state information is sent to the MSC server. The session state information carries the indication information that the called user is a ringing session. After the sending the session state information to the MSC server, the method further includes: after receiving the indication information of the ringing session, the MSC server enters a call receiving state. According to another aspect of the present invention, an apparatus for switching a ringing state session is provided, including: a request message receiving module, configured to receive a handover request message during a process of handover of a called user from a PS domain to a CS domain; The delay sending module is configured to determine that the current session state of the called user is a ringing session, and send the session state information to the MSC server in a delayed manner. The information delay sending module includes: a state determining unit, configured to determine that the current session state of the called user is a ringing state session; and a delay sending unit, configured to determine, by the state determining unit, that the current session state is a ringing state session, The session status information is sent to the MSC server after the specified time. The delay sending unit includes: activating subunit, configured to start a timer; and the first processing subunit, configured to forward, when receiving the 200 OK response message sent by the called user from the PS domain, within the timer starting time The 200 OK response message is sent to the calling user, the timer is turned off, and the session state information is no longer sent to the MSC server; the second processing subunit is set to if the 200 OK response message is not received within the timer startup time, The MSC server sends session state information. The session state information sent by the second processing sub-unit carries the indication information that the called user is a ringing session. The above device is set in the SCC AS. Through the invention, the session state information is sent to the MSC server by using a delay mode, which can ensure that the session state information of the MSC server is notified after the called user receives the handover notification, thereby avoiding the MSC. The server is in the call receiving state, but the called user has not completed the session switch. The problem that the call between the users caused by the inconsistency between the status of the MSC server and the called user is solved, and the user experience satisfaction is improved. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are set to illustrate,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, In the drawings: FIG. 1 is a schematic diagram of networking in a single mode switching manner according to the related art; FIG. 2 is a flowchart of switching a ringing state session according to the related art; FIG. 3 is a diagram showing a method according to an embodiment of the present invention. A flowchart of a method for switching a ringing state session; FIG. 4 is a flowchart of a method for switching a ringing state session according to Embodiment 1 of the present invention; FIG. 5 is a diagram showing a method according to Embodiment 2 of the present invention; FIG. 6 is a block diagram showing the structure of a device for switching a ringing state session according to an embodiment of the present invention; FIG. 7 is a diagram showing a switching ringing state according to an embodiment of the present invention. A detailed block diagram of the device of the session. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. The embodiment of the present invention considers that the user in the ringing session is switched from the PS domain to the CS. Because the state of the MSC server (MSC server) is inconsistent with the state of the called user, the normal call fails. Based on this, a method and apparatus for switching a ringing state session is provided. FIG. 3 is a flowchart of a method for switching a ringing state session according to an embodiment of the present invention. The method includes the following steps: Step 302: During a process in which a called user switches from a PS domain to a CS domain, the SCC AS receives Switching request message; Step 304: The SCC AS determines that the current session state of the called user is a ringing state session, and sends the session state information to the MSC server in a delayed manner. For example, the SCC AS sends session state information to the MSC server after a specified time. The SCC AS in this embodiment determines that the session state of the called user is a ringing session, and sends the session state information to the MSC server in a delayed manner, so as to ensure that the session state information of the MSC server is notified after the called user receives the handover notification. In addition, the MSC server is in a call receiving state, and the called user does not complete the session switching, so that when the called user answers the call, the status of the MSC server and the called user can be consistent, and the call between the users can be normally performed. In a specific implementation, a timer may be configured on the SCC AS to implement the foregoing delayed sending session state information. The sending of the session state information includes: the SCC AS determines that the current session state of the called user is a ringing session, and after the specified time, the SCC AS starts a timer; if the timer is started, the called party is received. When the user sends a 200 OK response message from the PS domain, the 200 OK response message is forwarded to the calling user, the timer is closed, and the session state information is not sent to the MSC server; After the 200 OK response message, the session status information is sent to the MSC server. The session state information carries the indication information that the called user is a ringing session. After receiving the indication information of the ringing session, the MSC server enters the call receiving state. In order to ensure that the state of the called user and the MSC server are consistent, and that the handover is completed in time, the time for sending the session state information in the embodiment may be set according to the time required for each message in the system, for example, the foregoing designation The time (starting time of the timer) is set to be greater than 300 nm and less than 400 nm. In this embodiment, when the called user's session state is the ringing state, the SCC AS sends the session state information to the MSC server in a delayed manner during the process of the called user switching from the PS domain to the CS domain to ensure that the MSC server is notified. The session state information is that after the called user receives the handover notification, when the called user answers the call, the status of the MSC server and the called user can be consistent, ensuring that the call between the users can be performed normally, and the user experience satisfaction is improved. Embodiment 1 This embodiment uses the networking shown in FIG. 1 as an example to provide a method for switching a ringing state session. Referring to FIG. 4, UE-1 accesses through an E-UTRAN or a UTRAN PS network. Go to the IMS network and receive a call request in the PS network. The switching process includes the following steps: Step 401 407, the process is the same as step 201 207 in FIG. 2, and details are not described herein. Step 408a: After receiving the notification handover request from the MME, the MSC server sends a handover request based on SIP signaling to the IMS, where The MSC server includes the media information of the MSC server. Step 409: After receiving the handover request, the IMS side network element sends the handover request to the SCC AS. Step 408b: After the MSC server sends the handover request to the IMS, the MSC server further sends the The MME returns a handover receiving response. Step 410: After receiving the handover request, the SCC AS starts a timer, and temporarily does not send the switched session state information to the MSC server within the timer time. Step 411: The SCC AS sends the handover session state information to the remote UE. -2: Sending an update request, informing that the media access address of the UE-1 is the address of the MSC server at this time; wherein the step 411 and the step 410 have no strict chronological order, and may occur in parallel or sequentially. Step 412: After receiving the update request, the UE-2 returns an update response to the UE-1 side when the update request is approved. Step 413 414: Since the session being switched at this time is a ringing session, the SCC AS The MSC returns an 18X response, which carries the media information carried by the UE-2 in step 412; Step 415 416, since the user UE-1 may answer the call at any time, in this embodiment, the response of the user UE-1 is earlier than step 409b. In step, the user UE-1 receives the handover notification message sent by the MME. Since the UE-1 has not received the handover notification message at this time, the UE-1 does not switch at this time, so the response message at this time (ie, 200) OK) is sent to the IMS network according to the original PS connection; Step 409b, after receiving the handover receiving response, the MME notifies the UE-1 that the handover is successful, and informs the UE of the address of the MSC, and the UE can disconnect the access of the PS. And accessing the MSC server that completes the handover through the CS domain network; Step 417 418, after the SCC AS receives the 200 OK (response message), sending the 200 OK (response message) to the remote UE-2; 419, when the UE-2 receives the response message, to the UE- 1 side sends an ACK; Step 420: Since the SCC AS receives the 200 OK response of the step 417 at the time of the timer, the SCC AS considers that the switched session has entered the ON state, and the SCC AS does not notify the MSC session state information. And closing the timer; Step 421 422, at this time, the SCC AS sends a 200 OK to the MSC server, indicating that the entire handover process is completed. The above steps 408b and 409b and steps 408a to 414 are not strictly chronological. The start time of the timer in this embodiment may be set according to the time required for each message in the system to be forwarded. For example, considering the sending time of the message in step 408b and step 409b, the start time of the timer is set to be greater than 300 nm, which is smaller than 400nm, which ensures that the called user and the MSC server are in the same state, and ensures the timely completion of the handover. In this embodiment, when the called user's session state is the ringing state, the SCC AS sends the session state information to the MSC server in a delayed manner during the process of the called user switching from the PS domain to the CS domain. During the delay process (that is, the timer startup process), the 200 OK response message sent by the user from the PS domain is received, and it is determined that the session has entered the ON state. In order to save the signaling overhead and simplify the process, the MSC server is cancelled. Session state information. When the called user answers the call in this embodiment, the status of the MSC server and the called user are the same, and all the conversations have been answered, ensuring that the call between the users can be performed normally, and the user experience satisfaction is improved. Embodiment 2 This embodiment uses the networking shown in FIG. 1 as an example to provide a method for switching a ringing state session. Referring to FIG. 5, UE-1 is accessed through an E-UTRAN, or a UTRAN PS network. In the IMS network, a call request is received in the PS network. The handover process includes the following steps: Step 501 507, the process is the same as step 201 207 in FIG. 2, and details are not described herein; Step 508a, when the MSC server receives the notification handover request from the MME, it sends SIP-based signaling to the IMS. The switching request includes the media information of the MSC server. Step 509: After receiving the handover request, the IMS side network element sends the handover request to the SCC AS. Step 510, after the SCC AS receives the handover request, Start a timer, and temporarily not send the switched session state information to the MSC within the timer time; Step 508b: The MSC server sends the handover request to the IMS, and the MSC server also returns a handover reception response to the MME. Step 509b, after receiving the handover reception response, the MME notifies the UE-1 that the handover is successful, and notifies the address of the MSC server. UE-1, at this time, UE-1 can disconnect the access of the PS and access the MS server that completes the handover through the CS domain network; Step 511, the SCC AS sends an update request to the remote UE-2, and informs this The media access address of the UE-1 is the address of the MSC server; Step 512, after receiving the update request, the UE-2 returns an update response to the UE-1 side when the update request is approved; Step 513 514, The session being switched is a ringing session, and the SCC AS returns an 18X response to the MSC, which carries the media information carried by the UE-2 in step 511. Step 515, the timer has timed out, the timer is turned off, and the timer is started. During the process, the SCC AS does not receive the 200 OK (response message) from the PS domain sent by the user, and may send the switched session state information to the MSC server; Step 516 517, because the MSC server is When the handover request is sent, it is not known that the session being switched is in the ringing state. Therefore, the SCC AS needs to send a notification message to the MSC to inform the MSC server that the session is a ringing session and requires the MSC server. Entering the call receiving state; Step 518, the MSC enters the CS domain call receiving state; at this time, the handover basic has been completed, from the UE-1 to the MSC server is a CS connection, and the MSC server to the remote UE-2 is a PS connection. Step 519 520: When the UE-1 answers the call, the response message is sent to the MSC server by using the CS response signaling. Step 521 522: After the MSC server receives the CS response message, the MSC server enters the session-on state. The data can be forwarded for the users on both sides, and the MSC server sends a notification message to inform the SCC AS that the called UE-1 has answered the call; Step 523, when the SCC AS receives the notification that the UE-1 has answered the call, The remote UE-2 sends a 200 OK (response message); Step 524, after receiving the 200 OK (response message), the remote UE-2 returns an ACK message; Step 525 526, at this time, the SCC AS sends a 200 OK to the MSC server, indicating that the entire handover process is completed; Step 508b and Step 509b above. There is no strict chronological order with steps 508a through 514. The start time of the timer in this embodiment may be set according to the time required for each message in the system to be forwarded. For example, considering the sending time of the message in step 508b and step 509b, the start time of the timer is set to be greater than 300 nm, which is smaller than 400nm, which ensures that the called user and the MSC server are in the same state, and ensures the timely completion of the handover. In this embodiment, when the called user's session state is the ringing state, the SCC AS sends the session state information to the MSC server in a delayed manner during the process of the called user switching from the PS domain to the CS domain. In the delay process (ie, the timer startup process), since the 200 OK response message sent by the user from the PS domain is not received, the session status information is sent to the MSC server after the specified time (ie, the timer expires), the MSC server After receiving the session state information, the session is in the session-on state. Since the SCC AS sends the session state information in the above-mentioned delay mode, when the MSC server performs the session-on state, the called user has received the handover notification message and completed. The corresponding switching operation. It ensures that the calls between users can be carried out normally, and the user experience satisfaction is improved. FIG. 6 is a block diagram showing the structure of a device for switching a ringing state session according to an embodiment of the present invention. The device includes: a request message receiving module 62, configured to receive a called user from a PS domain to a CS domain, and receive To the handover request message, the information delay sending module 64 is connected to the request message receiving module 62, and is configured to determine that the current session state of the called user is a ringing state session, and send the session state information to the MSC server in a delayed manner. The apparatus for switching the ringing state session of this embodiment may be set on the SCC AS. The device determines that the session state of the called user is a ringing session, and sends the session state information to the MSC server in a delayed manner, which ensures that the session state information of the MSC server is notified after the called user receives the switching notification, thereby avoiding The MSC server is in the call receiving state, but the called user does not complete the session switching, so that when the called user answers the call, the status of the MSC server and the called user can be consistent, and the call between the users can be normally performed. Referring to FIG. 7, the information delay sending module 64 of the foregoing apparatus includes: a state determining unit 642, configured to determine that the current session state of the called user is a ringing state session; and a delay sending unit 644 connected to the state determining unit 642 When the state determining unit 642 determines that the current session state is a ringing session, the session state information is sent to the MSC server after the specified time. In a specific implementation, a timer may be configured on the foregoing apparatus to implement the foregoing delayed sending session state information. At this time, the delay sending unit 644 includes: activating subunit, configured to start a timer; the first processing subunit is connected to the startup subunit, and is configured to receive the called party if the timer is started within the timer start time. When the user sends a 200 OK response message from the PS domain, the 200 OK response message is forwarded to the calling user, the timer is closed, and the session state information is not sent to the MSC server; the second processing subunit, and the promoter The unit is connected, and is set to send session state information to the MSC server if the 200 OK response message is not received within the start time of the timer. The session state information sent by the second processing sub-unit carries the indication information that the called user is a ringing session. After receiving the indication information of the ringing session, the MSC server enters the call receiving state. In order to ensure that the state of the called user and the MSC server are consistent, the handover is ensured in time. The time for delaying the transmission of the session state information in this embodiment may be set according to the time required for each message in the system to be forwarded. For example, the specified time (starting time of the timer) is set to be greater than 300 nm and less than 400 nm. In this embodiment, when the called user's session state is the ringing state, the SCC AS sends the session state information to the MSC server in a delayed manner during the process of the called user switching from the PS domain to the CS domain to ensure that the MSC server is notified. The session state information is that after the called user receives the handover notification, when the called user answers the call, the status of the MSC server and the called user can be consistent, ensuring that the call between the users can be performed normally, and the user experience satisfaction is improved. In the above embodiment, the existing IMS architecture does not need to be modified, and only the functions of some network elements (such as SCC AS) need to be enhanced, so that the call from the PS network to the CS network can be realized for the ringing call. Ensure that the user's data is not lost during the switching process, and the user experience satisfaction is improved. Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general-purpose computing device, which can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device, thereby Storing them in a storage device is performed by a computing device, and in some cases, the steps shown or described may be performed in an order different than that herein, or they may be separately fabricated into individual integrated circuit modules, or Multiple of these modules or steps are fabricated as a single integrated circuit module. Thus, the invention is not limited to any specific combination of hardware and software. The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Claim

A method for switching a ringing state session, the method comprising:

During the process of the called user switching from the packet switched PS domain to the circuit switched CS domain, the anchoring and associated application server SCC AS receives the handover request message;

The SCC AS determines that the current session state of the called user is a ringing session, and sends session state information to the mobile switching center MSC server in a delayed manner.

2. The method according to claim 1, wherein the sending the session state information to the mobile switching center MSC server by using a delay mode comprises:

The SCC AS sends session state information to the MSC server after a specified time.

3. The method according to claim 2, wherein the sending, by the SCC AS, session state information to the MSC server after a specified time comprises:

The SCC AS starts a timer;

If the 200 OK response message sent by the called user from the PS domain is received during the start time of the timer, the 200 OK response message is forwarded to the calling user, and the timer is turned off, and And sending the session state information to the MSC server;

If the 200 OK response message is not received within the timer start time, the session state information is sent to the MSC server.

The method according to claim 3, wherein the session state information carries indication information that the called user is a ringing session.

The method of claim 4, after the sending the session state information to the MSC server, further comprising:

After receiving the indication information of the ringing session, the MSC server enters a call receiving state.

6. A device for switching a ringing state session, comprising:

The request message receiving module is configured to receive a handover request message during the process of the called user switching from the packet switched PS domain to the circuit switched CS domain;

The information delay sending module is configured to determine that the current session state of the called user is a ringing state session, and send the session state information to the mobile switching center MSC server in a delay manner. The device according to claim 6, wherein the information delay sending module comprises:

a state determining unit, configured to determine that the current session state of the called user is a ringing state session; and a delay sending unit configured to determine, when the state determining unit determines that the current session state is a ringing state session, after a specified time The MSC server sends session state information. The apparatus according to claim 7, wherein the delay sending unit comprises:

Start the subunit, set to start the timer;

a first processing subunit, configured to forward the 200 OK response message to the calling user if the 200 OK response message sent by the called user from the PS domain is received during the timer start time Turning off the timer, and sending the session state information to the MSC server; the second processing subunit is configured to: if the 200 OK response message is not received within the timer startup time, Sending the session state information to the MSC server. The device according to claim 8, wherein the session state information sent by the second processing subunit carries indication information that the called user is a ringing session. Apparatus according to any of claims 6-9, wherein said apparatus is arranged in an anchoring and associated application server SCC AS.