CN1801998A - Conversation switching method from multimedia subsystem domain to circuit subsystem domain - Google Patents

Abstract

The invention discloses a method for realizing session switching at the application layer based on SIP and a system for realizing the method. The method includes: 1) the mobile terminal establishes a session with another terminal through a handover application server in the IMS network; 2) the mobile terminal initiates a request to switch to the CS domain to the handover application server; 3) through a media gateway The control server establishes a CS domain call with the mobile terminal in the CS domain, connects the CS domain call to the handover application server, and switches the mobile terminal from the IMS network to the CS domain. The present invention introduces the logic entity of the switching processing application server. Since the switching is implemented on the application server as a service, it has no impact on the existing network except that there is an expansion requirement for the terminal. The present invention can guarantee switching delay through the control of the application server, and can apply a new QoS mechanism in the new access network by performing media renegotiation on the new access network.

Description

Session switching method from multimedia subsystem domain to circuit subsystem domain

technical field

The invention relates to a session switching method, in particular to a method for switching media streams from an IP Multimedia Subsystem (IMS) domain to a Circuit Subsystem (CS) domain at an application layer.

Background technique

The concept of handover in wireless technology means that a mobile user terminal is in a session state and roams from one wireless coverage area to another. When the service is carried, it is necessary to maintain the ongoing session control and the continuity of the user plane media flow, and switch the session to a new wireless coverage area.

Session Initiation Protocol (SIP) has been widely used for the establishment of multimedia sessions. For example, the IP Multimedia Subsystem (IMS) network is a service network based on the SIP architecture of 3GPP R5 and R6 and adopting various access technologies such as 3G/2G GPRS and WLAN. Since the SIP protocol naturally supports the mobility of the terminal, the handover of the SIP session is a problem that needs to be considered in the SIP network.

Due to the importance of voice services, operators give priority to deploying CS networks when deploying 2G and 3G networks. Therefore, the CS network domain covers a wider range. After the IMS supports the voice service, an application scenario is how to ensure that the IMS network voice session is handed over from the IMS domain to the CS domain. According to the current specification, the handover of the IMS network voice session from the IMS domain to the CS domain requires the above-mentioned terminal to disconnect the IMS session connection, and then realize the handover by establishing a new session in the CS domain. The disadvantages of this kind of hard handover are: the handover delay is relatively long, the voice quality cannot be guaranteed; the session re-establishment process is easy to drop calls.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for session switching based on the SIP protocol.

A method for session switching from the multimedia subsystem domain to the circuit subsystem domain based on the SIP protocol according to the present invention includes: 1) the mobile terminal establishes a session with another terminal through a switching application server in the IMS network; 2) the mobile terminal The terminal initiates a request to the switching application server to switch to the circuit subsystem domain; 3) establishing a CS domain call with the mobile terminal in the CS domain through a media gateway control server, and making the CS domain call Connected with the handover application server, handover the mobile terminal from the IMS network to the CS domain.

According to the present invention, the current network and the next network may be an IMS network or an NGN network, and the mobile terminal and the other terminal support multiple IP addresses; the mobile terminal is a calling party or a called party.

The present invention introduces the switching processing application server logic entity. Since the switching is implemented on the application server as a service, it has no impact on the existing network except for the expansion requirement on the terminal. In the present invention, through the control of the application server, the switching of the media flow is based on the standard media renegotiation flow or the switching flow of the CS, which can ensure the switching delay. At the same time, by performing media renegotiation on the new access network, a new QoS mechanism can be applied to the new access network.

Brief description of the drawings

Fig. 1 is the system schematic diagram that is used for the present invention of prior art;

FIG. 2 is a schematic diagram of the application of the method for handing over the IMS voice session to the circuit domain according to the present invention;

Fig. 3 is a schematic diagram of the implementation flow of the mobile terminal requesting handover in the IMS network of the present invention;

Fig. 4 is a flow chart of the program of the handover server in the IMS network according to the present invention.

Detailed ways

The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a wireless communication system supporting session switching based on SIP protocol used in the present invention. As shown in FIG. 1 , the system includes a mobile terminal (UE1) 10, a service support network 20, a service application server 30, a switching application server 40 and a location server 50.

Wherein, the mobile terminal UE1 includes but not limited to 2G and 3G various SIP terminals. In addition to conventional mobile terminal functions, in order to realize the present invention, the mobile terminal UE1 also includes the following parts:

Handover trigger condition detection unit 1001: it can continuously detect the quality index (such as signal strength) of the received wireless signal. When the index is lower than the preset switching threshold, it will automatically search whether there is a wireless network coverage area of the same type as the current supported network. If not, continue to search for other types of wireless network coverage areas, and then select a new wireless access network. The same type of access network can be preferentially selected. If the same type of network cannot be found, other available access can be selected according to the pre-configured priority order (generally set according to the access fee from low to high) network.

Handover request unit 1002: If the mobile terminal UE1 is performing a voice-related IMS session as described above, it detects that the session needs to be handed over to the CS domain. Generally speaking, the coverage of the CS domain is wider than that of the packet access domain. If the mobile terminal UE1 detects that the CS domain is available according to the above handover trigger detection conditions, it initiates a location update request to the CS domain, and then the handover request unit 1002 initiates a handover request to the IMS network through SIP signaling (extended SIP signaling may be required).

Handover processing unit 1003: used to support special processing of the signaling plane in the session handover process, such as omitting the ringing process (that is, omitting the 180 provisional response message in the SIP protocol), etc.

The service support network 20 is used to transmit SIP signaling, which is a service-triggered network system. For the next generation network (NGN), the service support network 20 is a call server (Call Server). For an IMS system, the service support network 20 is a system with call state control function (CSCF) entities.

A service application server (AS) 30 is a logical entity for processing application services. In the present invention, it may be all application servers except the switching application server, or an application server including the switching application server function. In the NGN network, it can be integrated in the service support network; in the IMS network, it generally exists independently. It should be noted that in the present invention, the service application server is a generic concept, which generally refers to other ASs except the handover application server.

Handover application server (HO-AS) 40 is an application server specially used to control session handover. Its function and specific operation will be explained below. The switching application server 40 may exist independently, or may be integrated in the service support network 20 or the service application server 30 . The switching application server can be regarded as a special business application server.

The location server 50 is a logical entity for storing user location information and subscription information, and for IMS, it refers to a Home Subscriber Server (HSS). The location server is a concept in the SIP protocol and is not used in the handover process. But it is different in NGN and IMS. The purpose listed here is to give the correspondence between network entities and the comparison of system structures, so as to facilitate a unified description of the two networks.

Taking the IMS network as an example, the method for session switching based on the SIP protocol of the present invention will be described below with reference to FIGS. 2-4 .

According to the method of the present invention, when the user signs a contract, the operator assigns a mobile subscriber ISDN (MSISDN) number dedicated to the CS domain to the user. The MSISDN number is used as a CS call, and the number cannot be resolved by the ENUM protocol in the IMS. Wherein, ENUM is a well-known protocol defined by the Telephone Number Mapping Group of the Internet Engineering Task Force (IETF). Reference may be made to RFC2916, and details will not be described here.

As shown in Figure 2 and Figure 3, the mobile terminal UE1 in the service area of the IMS access network first registers on the IMS network using the Public User Identity (Public User Identity) and the Private User Identity (Private User Identity), and through the first The three-party registration (protocol term, means that the service call state control function unit (S-CSCF) registers the user to the application server at the same time when the user registers) is registered on the handover application server 40 . Thereafter, UE1 establishes a session with another called IMS network terminal 70 (UE2) in calling or called mode (step 101).

It should be noted that the present invention configures handover as a service in the user's service trigger filter rule (see 3GPP 23.218 for this rule). If the mobile terminal UE1 is a user in the home domain who has signed an application layer handover service (that is, the operator has configured the user's service data according to the user's service requirements), the S-CSCF of the IMS home network to which the mobile terminal UE1 belongs Trigger an initial filter rule (iFC) to trigger the session to be processed on the handover application server 40 (step 102).

For the calling service, set the highest priority in the above trigger filtering rules, and set the lowest priority in the above trigger filtering rules for the called service. This setting takes into account that the calling service must ensure that the switching application server is triggered first, and the called service must ensure that the switching application server is triggered last, so that the switching can be effectively controlled without affecting the user's business. The handover application server 40 may perform a third-party registration of the registration message through the S-CSCF, or obtain user registration information by subscribing to the registration event of the S-CSCF.

A session is triggered to the handover application server 40 when the session is initially established. The handover application server 40 divides the above session into two segments Leg1 and Leg2 from signaling by means of back-to-back user agent (B2BUA) (step 103). The Leg1 is located between the mobile terminal UE1 and the switching application server 40, and is used to control signaling and/or media switching of the mobile terminal UE1. Leg2 is located between the switching application server 40 and another terminal, and is used for controlling signaling and/or media switching with the called network session terminal.

Steps 101-103 described above in conjunction with FIG. 3 are behaviors in which UE1 establishes a session for the calling party. For the case where UE1 is the called party, UE1 processes session establishment after steps 102/103 are processed.

The mobile terminal UE1 in the IMS session detects the handover trigger condition, that is, the mobile terminal UE1 continuously detects the quality of the received wireless signal through the handover trigger condition detection unit 1001 (step 104), and judges the quality of the received wireless signal Whether the indicator is lower than the switching threshold (step 105). If the result of the judgment is that the quality index is lower than the handover threshold, the mobile terminal UE1 automatically searches whether there is a wireless network coverage area of the same type (step 106).

If there is a wireless network coverage area of the same type, the wireless network of the same type is selected. Otherwise, the mobile terminal UE1 continues to search for other types of wireless network coverage areas (step 107), such as WLAN, etc. These networks should be various access networks supported by the mobile terminal and allowed to access. If present, select that wireless network.

After selecting a new wireless access network, the mobile terminal UE1 further judges whether the selected target network is a CS domain, that is, further judges whether the CS domain is selected according to the above-mentioned handover trigger detection condition, and the current session includes a language service (step 108 , step 109), while maintaining the connection with the original access network.

If the result of the above judgment is that the CS domain is selected as the target handover network, the mobile terminal UE1 first initiates a location update request in the CS domain, that is, registers with the CS network, and then the mobile terminal UE1 sends an extended SIP message to the handover application in the IMS network. Server 40 initiates a handover request (step 110). The extended SIP message may be, for example, a manner of adding relevant parameters in message header fields such as REFER, or adding a new SIP message, and the message carries handover-related information. This is non-standard information, as long as it complies with the extension requirements of the SIP protocol. The switching application server 40 performs switching processing according to the switching request (step 111).

With reference to Fig. 4, after receiving above-mentioned handover request (step 201), handover application server 40, at first according to the media capability in the SIP agreement negotiated when setting up the current session, with the user's MSISDN number as the called party, through the media gateway control Server (MGCF) 90 establishes session leg Leg3. The session leg Leg3 is located between the handover server 40 of the IMS network and the MGCF 90 (step 202). The MGCF90 establishes a CS domain call between the MGCF and UE1 through the CS domain to connect to Leg3. When the session leg Leg3 is established, the original session leg Leg1 is not affected.

In the above session establishment process, if the media capability negotiated by session leg Leg3 changes compared with session leg Leg2, then when session leg Leg3 is carried out media capability negotiation, also session leg Leg2 is carried out media capability re-negotiation (step 203 ). The methods for negotiating and re-negotiating the media capability adopt known technologies, which will not be repeated in this specification. After the session legs Leg3 and Leg2 agree on the media capabilities, the handover application server transfers the media connection of the session leg Leg1 to the session leg Leg3 (step 204 ). At the same time, the SIP signaling association of session leg Leg1 and session leg Leg2 is transferred to the association of session leg Leg3 and session leg Leg2. Then the session leg Leg1 is released, that is, the original Leg1 is replaced by the CS domain call and Leg3 (step 205). In this way, a new connection is established and the handover process is completed. In this way, the communication between the terminal 10 in the CS network 80 and the terminal (UE2) 70 of the called IMS network can be completed through the MGCF 90.

During the establishment process of the above-mentioned session leg Leg3, the switching application server 40 should omit the 180 ringing process (that is, the 180 provisional answer message). This is because the handover process is performed smoothly and should not be felt by the end user.

When the MGCF is processing the media stream communication between the media corresponding to Leg3 and the CS domain, if the media encoding formats on both sides are inconsistent, the MGCF needs to control the IP multimedia media gateway (IM-MGW: IPMultimedia-Media Gateway)) (not shown in the figure ) converts the encoding format of the media stream. If the media streams do not match (for example, the IMS media stream supports audio and video, while the CS domain media stream only supports audio), the MGCF needs to re-negotiate the Leg3 media resources to make both parties reach a consensus.

Back to Figure 3. After judging that the handover is completed in step 120, the mobile terminal UE1 is deregistered from the original wireless access network (ie, the IMS network) (step 130).

According to another embodiment of the present invention, when the media resource is sufficient, that is, the media resource processor (MRFP) is rich in media resources and can provide a transition point for two terminal media connections, the handover method of the 3GPPS CS domain can also be referred to , to achieve switching of media streams.

In this embodiment, the specific process is similar to the embodiment described above. The difference is that when the handover application server 40 processes the session established between the mobile terminal UE1 and UE2, it can control the media resource control while dividing the session into two segments Leg1 and Leg2 from signaling through the B2BUA method as in the previous embodiment. A converter (MRFC) (not shown in the figure) inserts two IP endpoints of MRFP into the media stream, and divides the media stream into two segments corresponding to session legs Leg1 and Leg2 respectively. The media stream corresponding to Leg1 is from the mobile terminal UE1 to MRFP, and the media stream corresponding to Leg2 is from MRFP to another terminal UE2 having a conversation with the mobile terminal UE1.

In addition, after UE1 selects the CS domain as the target handover network, the handover application server 40 and MGCF90 establish a media connection between the MRFP (not shown in the figure) and the IM-MGW controlled by MGCF90 through the session leg Leg3. A media connection in the CS domain is established between the MGCF90 and the UE1 through related call signaling in the CS domain. When establishing Leg3, there is no need to renegotiate the media capabilities of the session leg Leg2. Instead, the original media connection between UE1 and MRFP corresponding to session leg Leg1 is replaced with the media connection between MGCF90 and MRPF corresponding to session leg Leg3. The media stream switching method is to switch the media stream corresponding to the session leg Legl to the media stream corresponding to the session leg Leg3 by modifying the topology relationship of the IP endpoint on the MRFP. If the encoding formats of the two media streams are inconsistent, the switching will cause the session leg The media capability of Leg3 is inconsistent with that of session leg Leg2. In this case, MRFP needs to convert the media stream from one encoding format to another encoding format for media intercommunication. If the media streams do not match (for example, the IMS media streams support audio and video, while the CS domain media streams only support audio, and the Leg3 media streams do not need video streams), the MRFP needs to shield the unmatched media streams. Of course, the media flow control of MRFP can also be processed on the IM-MGW as in the previous solution. In this implementation solution, the operation after the handover is completed is also similar to that of the previous implementation solution, and will not be repeated here.

Of course, those skilled in the art should recognize that during the process of renegotiating the media capabilities of the session leg Leg2, the original media capabilities of the session leg Leg2 can be maintained, or the media capabilities of the session leg Leg2 can be changed. Can be set as needed.

Although the above description of the invention is carried out with reference to its specific embodiments, those of ordinary skill in the art should appreciate that various improvements, additions and substitutions are possible within the true spirit and scope of the present invention. And all are within the scope of protection defined by the claims of the present invention.

Claims (10)

1. the method for switching from the session of IP multimedia subsystem, IMS (IMS) domain to circuit subsystem domain comprises:

1) portable terminal is set up session at the IMS network by a switching application server and another terminal;

2) described portable terminal initiates to switch to the request in circuit subsystem territory to described switch application server;

3) call out by the circuit subsystem territory of a media gateway controlling server between foundation of described circuit subsystem territory and described portable terminal, and described circuit subsystem territory called out link to each other with described switch application server, described portable terminal is switched to the circuit subsystem territory from described IMS network.

2. the method for claim 1 is characterized in that, described step 1) comprises:

1-1) when the described session of described portable terminal and described another terminal was set up, described current network was utilized service call State Control function, according to triggering filtering rule described session was triggered on the described switch application server;

1-2) described switch application server is divided into first session leg between described portable terminal and the described switch application server and second session leg between described switch application server and described another terminal by the back-to-back user agent mode with described session.

3. method as claimed in claim 2 is characterized in that, described step 1) also comprises:

1-3) described switch application server controls one media resource function controller, two IP end points of Media Resource Function Processor are inserted in the Media Stream of described session, Media Stream is divided into Media Stream between described portable terminal and the described Media Resource Function Processor and the Media Stream between described Media Resource Function Processor and described another terminal.

4. the method for claim 1 is characterized in that, when described portable terminal was calling service, the priority in described triggering filtering rule was the highest, and when described portable terminal was called service, the priority in described triggering filtering rule was minimum.

5. method as claimed in claim 2 is characterized in that, described step 3) further comprises:

3-1) described switch application server receives handoff request;

3-2) described switch application server as called, is set up the 3rd session leg with described mobile subscriber's ISDN number between a media gateway controlling server and described switch application server;

3-3) described media gateway controlling server is set up the circuit subsystem territory calling of described media gateway controlling server to described mobile subscriber terminal in described circuit subsystem territory;

3-4) described media gateway controlling server is called out described circuit subsystem territory and is connected with described the 3rd session leg;

3-5) described portable terminal is nullified from described IP Multimedia System network.

6. method as claimed in claim 3 is characterized in that, described step 3) further comprises:

3-1) described switch application server receives handoff request;

3-2) described switch application server as called, is set up the 3rd session leg with described mobile subscriber's ISDN number between a media gateway controlling server and described switch application server;

3-3) described media gateway controlling server is set up the circuit subsystem territory calling of described media gateway controlling server to described mobile subscriber terminal in described circuit subsystem territory;

3-4) described media gateway controlling server is called out described circuit subsystem territory and is connected with described the 3rd session leg;

3-5) described portable terminal is nullified from described IP Multimedia System network.

7. method as claimed in claim 5 is characterized in that, at step 3-2) in also comprise the process of a media re-negotiation, the process of described media re-negotiation is:

The described media resource function controller of described switch application server controls is inserted into two IP end points of Media Resource Function Processor in the Media Stream, keep the Media Stream attribute of described second terminal constant, switch by mode and the modification topology of inserting the encoding and decoding resource, perhaps heavily consult the Media Stream of described second terminal, revise described medium end points topological relation then and switch.

8. method as claimed in claim 6 is characterized in that, at step 3-2) in also comprise the process of a media re-negotiation, the process of described media re-negotiation is:

The described media resource function controller of described switch application server controls is inserted into two IP end points of Media Resource Function Processor in the Media Stream, keep the Media Stream attribute of described second terminal constant, switch by mode and the modification topology of inserting the encoding and decoding resource, perhaps heavily consult the Media Stream of described second terminal, revise described medium end points topological relation then and switch.

9. as each described method of claim 1-8, it is characterized in that described step 2) also comprise:

2-1) described portable terminal constantly detects the quality of the wireless signal that is received, and judges whether the quality index of the wireless signal of described reception is lower than predetermined handoff threshold;

2-2) when at described step 2-1) in the result that judges be lower than described predetermined handoff threshold, and have the circuit subsystem territory, then select described circuit subsystem territory as target handover network;

2-3) described portable terminal is initiated position updating request in described circuit subsystem territory, sends the request that switches to described circuit subsystem territory to described switch application server then.

10. method as claimed in claim 9 is characterized in that, described circuit subsystem territory is 2G or 3G network, and described portable terminal and described another terminal are supported many IP address, and described portable terminal is calling party or callee.

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