CN101895947B - Method for achieving single radio voice call continuity and single radio voice call continuity system - Google Patents

Abstract

The invention provides a method for achieving single radio voice call continuity (SRVCC). The method comprises the following steps: user equipment (UE) establishes an IP multimedia core network subsystem (IMS) session anchored to a signaling anchor point with a remote user via a pocket switch (PS) network and transmits the media data of the IMS session via a first media path and a second media path; an enhanced mobile switch center (eMSC) sends a call request for switching the IMS session to the signaling anchor point after a switch request sent by the PS network and used for switching the IMS session into circuit switch (CS) network access is received; the signaling anchor point connects a third media path between the newly-built eMSC and the media anchor point with the second media path and sends a call response to the eMSC after the call request is received; and the eMSC connects the third media path with the CS media path between the UE and the eMSC after the call response is received, so that the UE can continue the call with the remote user via the CS media path, the third media path and the second media path.

Description

A kind of single radio voice call continuity implementation method and single radio voice call continuity system

Technical field

The present invention relates to the communications field, particularly relate to a kind of single radio voice call continuity implementation method and single radio voice call continuity system.

Background technology

IP Multimedia System (IP Multimedia Core Network Subsystem, be called for short IMS) be by third generation partner program (3rd Generation Partnership Project, be called for short 3GPP) the IP-based network architecture of one that proposes, construct the opening of and service environment flexibly, support multimedia application, abundant multimedia service can be provided for user.

In IMS business system, key-course is separated with operation layer, and key-course does not provide concrete business, only provides the necessary function such as triggering, route, charging to operation layer.

In key-course, the triggering of business and controlling functions are completed by CSCF (Call SessionControl Function is called for short CSCF).CSCF is divided into: Proxy Call Session Control Function (Proxy-CSCF, be called for short P-CSCF), query call conversation control function (Interrogating-CSCF, be called for short I-CSCF) and service call conversation control function (Serving-CSCF, be called for short S-CSCF) three types, what wherein take the main responsibility be S-CSCF, I-CSCF is optional network element.

Operation layer is by a series of application server (Application Server, be called for short AS) composition, can provide concrete business service, and AS can be independently entity, also may reside in S-CSCF.

Key-course (S-CSCF) triggers according to the CAMEL-Subscription-Information service control of user, calls the business on AS, realizes business function.AS and S-CSCF can be referred to as service equipment (Server Equipment is called for short SE).

End-to-end equipment in session is called subscriber equipment (User Equipment, be called for short UE), and that is responsible for user is mutual; Some UE has the mode of multiple access network, comprise packet switch (the Packet Switch by 3GPP, be called for short PS) territory access network, by the PS territory access network of other non-3 gpp, even can pass through circuit switching (Circuit Switch is called for short CS) territory access network.

If CS network configuration enhancing mobile switching centre (enhanced Mobile Switch Center, be called for short eMSC), SIP (Session Initial Protocol is provided by eMSC, initial session protocol) interface comes with IMS network mutual, then can being realized by eMSC alternately of IMS network and CS network.

For the UE with plurality of access modes, if this UE moment can only use a kind of access way, a certain business is being performed under a kind of access way, such as converse, when then needing the access way changing its use when UE moves to other regions, the business that UE and network can provide certain mode that UE is being performed is not interrupted, such ability we be referred to as single-mode terminal business continuance, be called for short single radio voice call continuity (Single Radio Voice Call Continuity is called for short SRVCC).

Fig. 1 is single radio voice call continuity schematic diagram, describe signaling paths and media path that single-mode terminal UE-1 and IMS terminal UE-2 sets up session, and after generation single radio voice call continuity, the signaling paths of UE-1 and UE-2 and media path, for simplicity of illustration and description, S-CSCF and business continuance AS (SC AS) is drawn as an entity, uses the Session Initiation Protocol communication based on IMS standard between the two.

Before single radio voice call continuity occurs, establish session between UE-1 and UE-2, its signaling paths is described below:

Signaling paths between A102:UE-1 and P-CSCF, is communicated with one another by the Session Initiation Protocol of IMS, and for SC AS, this is access end (Access leg) path;

Signaling paths between A104:P-CSCF and SC AS/S-CSCF, is communicated with one another by the Session Initiation Protocol of IMS, and for SC AS, this also belongs to access end path (Access leg);

Signaling paths between R101:SC AS/S-CSCF and UE-2, is communicated with one another by the Session Initiation Protocol of IMS, and for SC AS, this is remote subscriber path (Remote leg);

After single radio voice call continuity occurs, the signaling paths between UE-1 and UE-2 and media path all there occurs change, and wherein the change of signaling paths is described below:

Signaling paths between A112:UE-1 and eMSC, is communicated with one another by the signaling protocol in CS territory, and for SC AS, this is access end (Access leg) path;

Signaling paths between A114:eMSC and SC AS/S-CSCF, is communicated with one another by the Session Initiation Protocol of IMS, and for SC AS, this also belongs to access end (Access leg) path;

Signaling paths between R101:SC AS/S-CSCF and UE-2, communicated with one another by the Session Initiation Protocol of IMS, for SC AS, this is remote subscriber (Remote leg) path, after single radio voice call continuity occurs, this remote subscriber path does not change.

Fig. 2 is existing single radio voice call continuity Organization Chart, describes and participates in realizing each relevant portion of network or the network element of single radio voice call continuity, and interface between them or annexation, is described below:

Related network elements describes:

UE: the subscriber terminal equipment with single radio voice call continuity ability;

CS network: for user provides the network of traditional C/S business;

PS network: for user provides the network of PS business;

The handover request that eMSC: process PS network sends, shifts between the territory of execution session, is associated by CS handover operation with transfer operation between territory;

IMS network: for user provides the network of IMS business.

Relevant interface describes:

The internetwork air interface of S202:UE and CS (being called for short CS to eat dishes without rice or wine), realizes the internetwork information interaction of UE and CS, as the Um Interface of standard;

The internetwork air interface of S204:UE and PS (being called for short PS to eat dishes without rice or wine), realizes the internetwork information interaction of UE and PS, as the Uu interface of standard;

Interface (CS signaling interface can be called) between S206:CS network and eMSC, different according to the difference of concrete network element connected, interface between eMSC and base station sub-system is the Iu-CS interface of standard, interface between eMSC and other mobile switching centres is the interoffice signaling interface of standard, i.e. E interface and Nc interface;

Signaling interface (hand off signaling interface between territory can be called) between S208:PS network and eMSC, switch support to provide between territory, this interface is the Sv interface of standard;

Signaling interface between S210:PS network and internet, as the SGi interface of standard, this interface can provide IP Deta bearer for the information interaction between UE and internet, because IMS network is based on internet, therefore can calculate a kind of special internet;

Signaling paths between S212:eMSC and IMS network, can be the I2 interface of the Session Initiation Protocol based on IMS between the eMSC of standard and IMS network, also can be connected to form by the standard Nc interface between eMSC and media gateway and the standard Mg between media gateway and IMS network; If the latter, the message translation on Nc interface can be become the sip message of IMS or contrary by media gateway; Nc interface can based on Session Initiation Protocol (Nc-SIP), also can based on ISUP (ISDN User Protocol, integrated services digital network User Agreement) agreement (Nc-ISUP).Although Nc-SIP with I2 interface is the same all based on Session Initiation Protocol, but agreement specify only the form of message, the content of message is determined by application, and eMSC supports the application that IMS is relevant to use I2 interface then to show, eMSC supports the application that traditional C/S is relevant to use Nc-SIP interface then to show.

Fig. 3 is existing single radio voice call continuity implementation method flow chart, describe between UE-1 and UE-2 and establish IMS session, thus set up IMS media path, this IMS media path is made up of the internetwork media path of UE-1 and PS and the media path between PS network and UE-2, after there is single radio voice call continuity in UE-1, UE-1 and real-time performance use CS territory to set up media path by UE-1, and keep former session continuous print process, comprise the steps:

Step 301, UE-1 are by sending measurement report to the PS network of serving for it, to report cell signal strength metrical information with the internetwork S204 interface of PS;

Step 302, for the PS network (former PS network) of UE-1 service to judge according to the signal strength information of measurement report Zhong Ge community near CS network be more suitable for as UE-1 service, so determine execution handover operation;

Respective network elements in step 303, former PS network, such as Mobility Management Entity (MobileManagement Entity, be called for short MME), by the S208 interface between PS network and eMSC, handover request is sent to eMSC, such as send Handover request (handover request) message, the number information for the request of identification service continuity of the SC AS that the number information of UE-1 and PS network are obtained by home subscriber server (HomeSubscriber Server is called for short HSS) is carried in this message;

The CS switching flow of step 304, eMSC operative norm, to prepare the media link resource of target CS network;

Step 305, complete CS switching flow after, eMSC sends switching response message by S208 interface to PS network, such as sends Handover response (handoff response) message;

After step 306, PS network receive switching response message, send switching command message by S204 interface to UE-1, notice UE-1 is switched to CS territory;

After step 307, UE-1 receive switching command message, access way is adjusted to pass the access of CS territory;

So far establish CS media path between UE-1 and eMSC, this media path is made up of the internetwork CS media path of UE-1 and CS and the CS media path between CS network and eMSC.

Following steps occur after step 303, do not have ordinal relation with step 304 ~ 307.

After step 308, eMSC receive the handover request message of PS network transmission, send call request to SC AS;

Above-mentioned call request is sent by the signaling paths (can be called the signaling paths that interconnects) of S212, therefore can be INVITE (invitation) message of SIP, also can be IAM (initial address message) message of ISUP; Carry the number information of UE-1 and the number information of SC AS in this call request, wherein the number information of SC AS is as called party information, and the number information of UE-1 is as caller information.

Step 309, SC AS finally can receive the SIP INVITE being forwarded the IMS come by CSCF, and according to called party information, SC AS can judge that this is a business continuance request, then search out the ongoing calling with this correlation of call according to caller information;

Step 310, SC AS, on the signaling paths of the ongoing calling of association, send the update request of IMS to UE-2 by CSCF, such as send UPDATE (renewal) or reINVITE (heavily inviting) message;

After step 311, UE-2 receive update request, respond the agreement updating message of IMS, such as send " 200OK " message;

After step 312, SC AS receive and forward by CSCF the agreement updating message come, call answering message is sent to eMSC by the signaling paths of S212, such as send " 200OK " message, what eMSC finally received may be SIP " 200OK " message, also may be ANM (response message) message of ISUP;

So far, set up new media path between eMSC and UE-2, this newly-built media path and CS media path connect by eMSC, UE-1 can be continued and UE-2 converses.

As from the foregoing, because the SC AS being arranged on home network does not carry out the grappling of media path, therefore existing single radio voice call continuity implementation method is adopted, in step 310 ~ 311, need to perform renewal rewards theory to remote subscriber, and the delivery lag performing the IMS signaling of renewal rewards theory is long, this will still need to wait for that long period new media path just can establish after CS media be caused to establish, thus makes dropped calls overlong time.

Summary of the invention

Technical problem to be solved by this invention overcomes the deficiencies in the prior art, provides a kind of single radio voice call continuity implementation method without the need to upgrading the media of remote subscriber and single radio voice call continuity system.

In order to solve the problem, the invention provides a kind of single radio voice call continuity implementation method, the method comprises:

UE sets up the IMS session anchoring to signaling anchor point by PS network and remote subscriber, and transmits the media data of described IMS session by the first media path and the second media path; Described first media path is the IMS media path between the media anchor point of UE and described IMS session, and described second media path is the IMS media path between described media anchor point and remote subscriber;

Receive that PS network sends for after described IMS session is switched to the handover request by CS network insertion, eMSC sends the call request being used for switching described IMS session to described signaling anchor point;

After receiving described call request, the 3rd media path between newly-built eMSC with described media anchor point is connected with described second media path by described signaling anchor point, and sends call answering to eMSC;

After receiving described call answering, the described 3rd CS media path between media path with UE and eMSC is connected by eMSC, makes UE continue to converse by described CS media path, the 3rd media path and the second media path and remote subscriber;

Wherein, described signaling anchor point is: PGW or GGSN in described PS network, and described media anchor point is AGW; Or

Described signaling anchor point and media anchor point are PGW or GGSN in described PS network.

In addition, described signaling anchor point is: PGW or GGSN in described PS network, and described media anchor point is AGW; In the following way described 3rd media path is connected with described CS media path with described second media path:

The transport address of the port H carried in described call request is included in mapping request and sends to AGW by described signaling anchor point;

After receiving described mapping request, AGW sets up the incidence relation of port H and described second media path, and the transport address of port J is included in map response in send to described signaling anchor point;

After receiving described mapping response, the transport address of port J is included in call answering and sends to eMSC by described signaling anchor point;

After receiving described call answering, eMSC sets up the incidence relation of described CS media path and described port J;

Described port H is for receiving the media data that remote subscriber sends in eMSC, and it is sent to the 3rd media path port of UE by described CS media path; Described port J is for receiving the media data that UE sends in AGW, and it is sent to the 3rd media path port of remote subscriber by described second media path.

In addition, described signaling anchor point is: PGW or GGSN in described PS network, and described media anchor point is AGW; In the following way described 3rd media path is connected with described CS media path with described second media path:

The line number L1 that the eMSC carried in described call request holds is included in mapping request and sends to AGW by described signaling anchor point;

After receiving described mapping request, AGW distribute AGW end line number L2, the 3rd media path identify with line number L1 with L2 is connected with described second media path, and line number L2 is included in map respond in send to described signaling anchor point;

After receiving described mapping response, line number L2 is included in call answering and sends to eMSC by described signaling anchor point;

After receiving described call answering, the 3rd media path identified with line number L1 with L2 is connected with described CS media path by eMSC.

In addition, described signaling anchor point is: PGW or GGSN in described PS network, and described media anchor point is AGW; In the following way described 3rd media path is connected with described CS media path with described second media path:

The line number L1 that the eMSC carried in described call request holds is included in lane assignment request and sends to AGW by described signaling anchor point;

After receiving described lane assignment request, AGW distribute AGW end line number L2, and line number L2 is included in lane assignment response in send to described signaling anchor point;

After receiving the response of described lane assignment, line number L1 and/or line number L2 is included in mapping request and sends to AGW by described signaling anchor point;

After receiving described mapping request, the 3rd media path identified with line number L1 with L2 is connected with described second media path by AGW, and to described signaling anchor point return mapping response;

After receiving described mapping response, line number L2 is included in call answering and sends to eMSC by described signaling anchor point;

After receiving described call answering, the 3rd media path identified with line number L1 with L2 is connected with described CS media path by eMSC.

In addition, described signaling anchor point and media anchor point are PGW or GGSN in described PS network; In the following way described 3rd media path is connected with described CS media path with described second media path:

After receiving the described call request of the transport address of carrying port H, described PGW or GGSN sets up the incidence relation of port H and described second media path, and is included in call answering the transport address of port J and sends to eMSC;

After receiving described call answering, eMSC sets up the incidence relation of described CS media path and described port J;

Described port H is for receiving the media data that remote subscriber sends in eMSC, and it is sent to the 3rd media path port of UE by described CS media path; Described port J is for receiving the media data that UE sends in described PGW or GGSN, and it is sent to the 3rd media path port of remote subscriber by described second media path.

In addition, described signaling anchor point and media anchor point are PGW or GGSN in described PS network; In the following way described 3rd media path is connected with described CS media path with described second media path:

After receiving the described call request of the line number L1 carrying eMSC end, described PGW or GGSN distributes local line number L2, the 3rd media path identified with line number L1 with L2 is connected with described second media path, and line number L2 is included in call answering sends to eMSC;

After receiving described call answering, the 3rd media path identified with line number L1 with L2 is connected with described CS media path by eMSC.

The present invention also provides a kind of single radio voice call continuity system, comprises PS network, CS network, eMSC, comprises: PGW and GGSN in described PS network; It is characterized in that, this system also comprises: AGW; When UE sets up the IMS session anchoring to described PGW or GGSN by described PS network and remote subscriber, and transmitted the media data of described IMS session by the first media path and the second media path after:

Described eMSC for receive that described PS network sends for described IMS session being switched to the handover request by described CS network insertion, and send the call request for switching described IMS session to described PGW or GGSN after receiving described handover request;

Described PGW or GGSN is used for after receiving described call request, is connected by newly-built described eMSC with the 3rd media path between described AGW with described second media path, and sends call answering to described eMSC;

Described eMSC is also for after receiving described call answering, described 3rd media path is connected with the CS media path between described UE and described eMSC, makes UE continue to converse by described CS media path, the 3rd media path and the second media path and remote subscriber;

Wherein, described first media path is the IMS media path between described UE and described AGW, and described second media path is the IMS media path between described AGW and remote subscriber.

In addition, the interface based on SIP or ISUP is adopted to send described call request and call answering message between described eMSC and described PGW or GGSN.

The present invention also provides a kind of single radio voice call continuity system, comprises PS network, CS network, eMSC, comprises: PGW and GGSN in described PS network; When UE sets up the IMS session anchoring to described PGW or GGSN by described PS network and remote subscriber, and transmitted the media data of described IMS session by the first media path and the second media path after:

Described eMSC for receive that described PS network sends for described IMS session being switched to the handover request by described CS network insertion, and send the call request for switching described IMS session to described PGW or GGSN after receiving described handover request;

Described PGW or GGSN is used for after receiving described call request, is connected by newly-built described eMSC with the 3rd media path between described PGW or GGSN with described second media path, and sends call answering to described eMSC;

Described eMSC is also for after receiving described call answering, described 3rd media path is connected with the CS media path between described UE and described eMSC, makes UE continue to converse by described CS media path, the 3rd media path and the second media path and remote subscriber;

Wherein, described first media path is the IMS media path between described UE and described PGW or GGSN, and described second media path is the IMS media path between described PGW or GGSN and remote subscriber.

In addition, the interface based on SIP or ISUP is adopted to send described call request and call answering message between described eMSC and described PGW or GGSN.

In sum, the present invention passes through signaling and the media of grappling IMS session, and upgrades the near-end of media path when single radio voice call continuity occurs, and keeps distant end media path, avoid the operation that the media of remote subscriber are upgraded, decrease the break period of call.

Accompanying drawing explanation

Fig. 1 is single radio voice call continuity schematic diagram;

Fig. 2 is existing single radio voice call continuity Organization Chart;

Fig. 3 is existing single radio voice call continuity implementation method flow chart;

Fig. 4 is single radio voice call continuity first framework embodiment schematic diagram of the present invention;

Fig. 5 is single radio voice call continuity first method flow diagram that the present invention is based on the first framework embodiment;

Fig. 6 is single radio voice call continuity second method flow diagram that the present invention is based on the first framework embodiment;

Fig. 7 is single radio voice call continuity second framework embodiment schematic diagram of the present invention;

Fig. 8 is the single radio voice call continuity third method flow chart that the present invention is based on the second framework embodiment;

Fig. 9 is single radio voice call continuity the 4th method flow diagram that the present invention is based on the second framework embodiment.

Embodiment

Core concept of the present invention is, using the signaling anchor point of PGW or GGSN in PS network as IMS session, after single radio voice call continuity occurs, signaling terminating no longer continues to transmit by correlating sessions by signaling anchor point, and upgrade the near-end in former conversation media path, keep distant end media path constant.

Describe the present invention below in conjunction with drawings and Examples.

first framework embodiment

Fig. 4 is single radio voice call continuity first framework embodiment schematic diagram of the present invention, and Fig. 4 describes each relevant portion of the network realizing single radio voice call continuity or network element, and interface between them or annexation; Specifically describe as follows:

Related network elements describes:

UE: the subscriber terminal equipment with single radio voice call continuity ability;

CS network: for user provides the network of traditional C/S business;

PS network: for user provides the network of PS business;

Comprise in PS network: the network elements such as MME, PGW (Packet Data Network GateWay, grouped data network gateway) and GGSN (Global GPRS Support Node, overall GPRS support node).

PGW/GGSN is the network element be connected with internet in PS network, mutual for the treatment of between PS network and IP network; In PGW/GGSN, IMS control point (IMS ControlPoint) function is increased newly in the present embodiment, as the signaling anchor point of IMS session, and control AGW (Access GateWay, access gateway) Resources allocation, map or association media path.

AGW: as the media anchor point of IMS session, for realizing the forwarding of IP media data or the forwarding between CS media data and IP media data;

The handover request that eMSC: process PS network sends, shifts between the territory of execution session, is associated by CS handover operation with transfer operation between territory;

IMS network: for user provides the network of IMS business.

Relevant interface describes:

S402 ~ S408: identical with the S202 ~ S208 in Fig. 2;

IMS signaling interface between S412:UE and PGW or GGSN, for being transmitted the IMS signaling between UE and P-CSCF by PGW/GGSN, can be such as the Gm of IMS standard;

CS signaling interface between S414:eMSC and PGW/GGSN, for transmitting the message in eMSC and PGW/GGSN (ICP) link setup process, the such as Nc interface of CS territory standard, this interface can be the Nc-SIP interface based on SIP, also can be the Nc-ISUP interface based on ISUP;

Signaling interface between S416:PGW/GGSN (ICP) and AGW, makes PGW/GGSN control AGW Resources allocation, maps or association media path;

Signaling interface between S418:PGW/GGSN (ICP) and IMS network element, for being transmitted the IMS protocol message between UE and P-CSCF by PGW/GGSN, can be such as the Gm of IMS standard.

first pass embodiment

Fig. 5 is single radio voice call continuity first method flow diagram that the present invention is based on the first framework embodiment; Fig. 5 describes the process setting up IMS session between UE-1 and far-end (UE-2), and after IMS session establishment completes, there is single radio voice call continuity in UE-1, the media path that how UE-1 and network realize allowing UE-1 use CS territory is set up, and keep former session continuous print process, wherein use Nc-SIP interface between eMSC and PGW/GGSN (ICP); The method comprises the steps:

Step 501, UE-1 initiate IMS call request, such as send INVITE, and this call request is carried on the IP carrying of PS network foundation, is therefore sent to PS network; Carry the transport addresses information of UE-1 for receiving media data in this call request, be expressed as B;

PGW/GGSN in step 502, PS network to AGW request dispatching address resource, such as sends allocation request message as signaling anchor point, carries transport addresses information B in this message;

Step 503, AGW distribute port resource C and F, and set up the incidence relation of port F and transport address B, make the media data received from port F all need to be forwarded to transport address B; Wherein, the media data that port F sends for receiving remote subscriber, the media data that port C receives for forwarding port F; Then AGW agrees to distribute to PGW/GGSN, such as sends assignment response message, carries the transport addresses information of port F in this message; In order to simplified characterization, the transport addresses information that port F is corresponding is still expressed as F, and transport addresses information comprises IP address and port numbers;

If UE-1 comprises more than a kind of media for the calling of setting up, then B comprises the transport addresses information of multiple UE-1 for receiving media data, step 502 can be a message, the transport addresses information of multiple UE-1 for receiving media data is carried in this message, also can be multiple message, in each message, carry the transport addresses information of a UE-1 for receiving media data respectively; Correspondingly, step 503 also can be a message of carrying multiple port transmission address information, or multiple message of carrying a port transmission address information respectively, and concrete methods of realizing does not affect essence of the present invention.

Step 504, PGW/GGSN preserve transport address F, and use the transport address B of the IMS call request in transport address F replacement step 501, and then distally user forwards IMS call request;

After step 505, remote subscriber receive IMS call request, send IMS call answering, such as send " 200OK " message, carry the transport addresses information of remote subscriber for receiving media data in this message, be expressed as X;

After step 506, PGW/GGSN receive IMS call answering, to AGW request dispatching address resource, such as send allocation request message, in this message, carry transport addresses information X;

Step 507, AGW distribute port resource D and E as media anchor point, and set up the incidence relation of port D and transport address X, and the media data that port D is received all needs to be transmitted to transport address X; Wherein, the media data that port D sends for receiving UE-1, the media data that port E receives for forwarding port D; Then AGW agrees to distribute to PGW/GGSN, and such as send assignment response message, carry the transport addresses information of port D in message, be simplified characterization, the transport addresses information that port D is corresponding is still expressed as D;

If X comprises the transport addresses information of multiple remote subscriber for receiving media data, step 506 can be a message, the transport addresses information of multiple receiving media data is carried in this message, also can be multiple message, in each message, carry the transport addresses information of a receiving media data respectively; Correspondingly, step 507 also can be a message of carrying multiple port transmission address information, or multiple message of carrying a port transmission address information respectively, and concrete methods of realizing does not affect essence of the present invention.

Step 508, PGW/GGSN preserve transport address D, and use the transport address X in the IMS call answering in transport address D replacement step 505, then forward IMS call answering to UE-1;

So far, UE-1 and remote subscriber establish IMS media path, comprising the IMS media path 1 (being called for short IMS media 1) between UE-1 and AGW and the IMS media path between AGW and remote subscriber 2 (being called for short IMS media 2).

The step below occurred when switching between territory for UE-1 describes.

Step 509, UE-1 send measurement report, to report cell signal strength metrical information to the PS network of serving for it;

Step 510, for the PS network of UE-1 service to judge according to the signal strength information of measurement report Zhong Ge community near CS network be more suitable for as UE-1 service, so determine execution handover operation;

Respective network elements in step 511, PS network, such as MME sends handover request to eMSC, such as sends Handover request (handover request) message, carries the number information of UE-1 in this message;

The CS switching flow of step 512, eMSC operative norm, to prepare the media link resource of target CS network;

Step 513, complete CS switching flow after, eMSC sends switching response message to PS network, such as sends Handover response (handoff response) message;

After step 514, PS network receive switching response message, send switching command message to UE-1, notice UE-1 is switched to CS territory;

After step 515, UE-1 receive switching command message, access way is adjusted to pass the access of CS territory;

So far establish CS media path between UE-1 and eMSC, this media path is made up of the internetwork CS media path of UE-1 and CS and the CS media path between CS network and eMSC.

Following steps occur after step 511, do not have ordinal relation with step 512 ~ 515.

After step 516, eMSC receive the handover request message of PS network transmission, call request is sent to the PGW/GGSN in this PS network, this request is sent by the signaling paths of S414, in the present embodiment, S414 interface uses Nc-SIP interface, what therefore send is INVITE (invitation) message of SIP, carry the number information of UE-1 and the number information of PGW/GGSN in this message, wherein the number information of PGW/GGSN is as called party information, and the number information of UE-1 is as caller information; In addition, eMSC is also carried in this message for receiving the transport address H of the media data of remote subscriber transmission;

The call request that step 517, PGW/GGSN determination step 516 receive is the handover request of the call request that step 501 receives, therefore AGW is asked to perform map operation, such as send Maprequest (mapping request) message, in this message, carry transport address H; In addition, the transport address F of IMS media path 2 in this message, is also carried, or the transport address D of IMS media path 1;

In this step, PGW/GGSN can carry out the call request that determination step 516 receives according to the specific PGW/GGSN number carried in call request be handover request; Or the all-calls request that eMSC sends all is judged to be handover request.

Step 518, AGW find IMS media path 2 according to transport address F or transport address D, and perform map operation, newly-built media path between eMSC and AGW is carried out associating with IMS media path 2 and (namely sets up the incidence relation of port F and transport address H, the media data received from port F is made all to be forwarded to transport address H), and distribute new near-end media data reception port J, for receiving the media data that eMSC sends, for simplified characterization, the transport addresses information that port J is corresponding is still expressed as J; After map operation completes, AGW sends mapping response message by S416 interface to PGW/GGSN, such as sends Map response (mapping response) message, carries the transport address J of AGW for receiving media data in this message;

Step 519, PGW/GGSN send the call answering message of Nc-SIP after receiving and mapping response to eMSC by S414 interface, such as send " 200OK " message, carry transport address J in this message;

After eMSC receives call answering message, the transport address G being used for distally user in eMSC and sending media data is associated with transport address J, the media data received from transport address G is made to be forwarded to transport address J, and transport address G and the CS media path between transport address H and UE and eMSC are associated, be respectively used to receive the media data that UE sends and the media data being sent remote subscriber by this CS media path to UE from this CS media path.

So far, set up new IMS media path between eMSC and AGW, this newly-built media path associates with CS media path by eMSC, and this newly-built media path associates with IMS media path 2 by AGW, UE-1 can be continued and UE-2 converses.

Above-mentioned newly-built media path comprises: eMSC side is used for the media data receiving UE from CS media path, and sends it to the port G of remote subscriber; EMSC side for receiving the media data of remote subscriber, and sends to the port H of UE by CS media path; AGW side is used for the media data that receiving port G sends, and it is sent to the port J of remote subscriber by port E; AGW side is used for the port I of the media data forwarding remote subscriber to port H.

second flow embodiment

Fig. 6 is single radio voice call continuity second method flow diagram that the present invention is based on the first framework embodiment; Fig. 6 describes the process setting up IMS session between UE-1 and far-end (UE-2), and after IMS session establishment completes, there is single radio voice call continuity in UE-1, the media path that how UE-1 and network realize allowing UE-1 use CS territory is set up, and keep former session continuous print process, wherein use Nc-ISUP interface between eMSC and PGW/GGSN (ICP); The method comprises the steps:

Step 601 ~ 615, identical with step 501 ~ 515;

Following steps occur after step 611, do not have ordinal relation with step 612 ~ 615.

After step 616, eMSC receive the handover request message of PS network transmission, call request is sent to the PGW/GGSN in this PS network, this request is sent by the signaling paths of S414, in the present embodiment, S414 interface uses Nc-ISUP interface, what therefore send is the IAM message (also can be called the call request of ISUP) of ISUP, carries eMSC for transmitting the line number L1 of the line resource of CS media in this message; In addition, also carry the number information of UE-1 and the number information of PGW/GGSN in this message, wherein the number information of PGW/GGSN is as called party information, and the number information of UE-1 is as caller information;

The call request received in step 617, PGW/GGSN determination step 616 is the handover request of the call request received in step 601, alternatively, PGW/GGSN asks AGW to perform lane assignment operation, such as send Line Alloc request (lane assignment request) message, carry the line number L1 of acquisition in this message, this message is by the transmission of S416 interface;

After step 618, AGW receive lane assignment request, divide the line resource being used in transmission CS media, the line number of its correspondence is L2, then S416 interface transmitting line assignment response is passed through to PGW/GGSN, such as send Line Alloc response (lane assignment response) message, in this message, carry the line number L2 of distribution;

Step 619, PGW/GGSN ask AGW to perform map operation, such as send Map request (mapping request) message, carry the line number L1 of acquisition in this message; If perform step 617 ~ 618, in this message, also can carry the line number L2 of acquisition, in this message, also carry the transport address F of IMS media path 2, or the transport address D of IMS media path 1;

Step 620, AGW perform map operation, media path between eMSC and the AGW identified with line number L1 and L2 is associated with IMS media path 2, and send mapping response message by S416 interface to PGW/GGSN, such as send Map response (mapping response) message;

If do not perform step 617 ~ 618, before the above-mentioned map operation of execution, AGW distributes the new line resource for transmitting CS media data, and corresponding line number is set to L2;

If do not perform step 617 ~ 618, in above-mentioned mapping response message, carry line number L2; If perform 617 ~ 618, in this message, line number L2 can not be carried.

After step 621, PGW/GGSN receive and map response, the call answering message sending Nc-ISUP to eMSC by S414 interface, such as sending ANM, carrying the AGW of acquisition for transmitting the line number L2 of CS media data in this message;

After eMSC receives above-mentioned call answering message, the above-mentioned media path identified with line number L1 and L2 is associated with the CS media path between UE and eMSC.

So far new CS media path is set up between eMSC and AGW, CS media path between this newly-built media path with UE and eMSC associates by eMSC, this newly-built CS media path associates with IMS media path 2 by AGW, UE-1 can be continued and UE-2 converses.

second framework embodiment

Fig. 7 is single radio voice call continuity second framework embodiment schematic diagram of the present invention, and Fig. 7 describes each relevant portion of the network realizing single radio voice call continuity or network element, and interface between them or annexation; Specifically describe as follows:

Related network elements describes:

UE: the subscriber terminal equipment with single radio voice call continuity ability;

CS network: for user provides the network of traditional C/S business;

PS network: for user provides the network of PS business;

Comprise in PS network: the network elements such as MME, PGW and GGSN; In the present embodiment, newly-increased IMS control point (IMS Control Point) function and AGW (Access GateWay in the PGW/GGSN of PS network, access gateway) function, be collectively referred to as IACP (IMS Access and ControlPoint, IMS access and control point) function, as signaling anchor point and the media anchor point of IMS session, for realizing Resources allocation, map or association media path, and for the forwarding of IP media data or the forwarding between CS media data and IP media data;

The handover request that eMSC: process PS network sends, shifts between the territory of execution session, is associated by CS handover operation with transfer operation between territory;

IMS network: for user provides the network of IMS business.

Relevant interface describes:

S702 ~ S708: identical with the S202 ~ S208 in Fig. 2;

IMS signaling interface between S712:UE and PGW/GGSN, for being transmitted the IMS signaling between UE and P-CSCF by PGW/GGSN, this interface can be the Gm of IMS standard;

CS signaling interface between S714:eMSC and PGW/GGSN, for transmitting the message in eMSC and PGW/GGSN link setup process, the such as Nc interface of CS territory standard can be the interface (Nc-SIP) based on SIP, also can be the interface (Nc-ISUP) based on ISUP;

Signaling interface between S718:PGW/GGSN and IMS network element, for being transmitted the IMS protocol message between UE and P-CSCF by PGW/GGSN, can be such as the Gm of IMS standard.

3rd flow embodiment

Fig. 8 is the single radio voice call continuity third method flow chart that the present invention is based on the second framework embodiment; Fig. 8 describes the process setting up IMS session between UE-1 and far-end (UE-2), and after IMS session establishment completes, there is single radio voice call continuity in UE-1, the media path that how UE-1 and network realize allowing UE-1 use CS territory is set up, and keep former session continuous print process, wherein use Nc-SIP interface between eMSC and PGW/GGSN (IACP); The method comprises the steps:

Step 801, UE-1 initiate IMS call request, such as send INVITE, and this call request is carried on the IP carrying of PS network foundation, is therefore sent to PS network; Carry the transport addresses information of UE-1 for receiving media data in this call request, be expressed as B;

PGW/GGSN in step 802, PS network distributes port resource C and F as signaling anchor point and media anchor point, and sets up the incidence relation of port F and transport address B, makes the media data received from port F all need to be forwarded to transport address B; Wherein, the media data that port F sends for receiving remote subscriber, the media data that port C receives for forwarding port F; In order to simplified characterization, the transport addresses information that port F is corresponding is still expressed as F, and transport addresses information comprises IP address and port numbers;

Step 803, PGW/GGSN use the transport address B of the IMS call request in transport address F replacement step 801, and then distally user forwards IMS call request;

After step 804, remote subscriber receive IMS call request, send IMS call answering, such as send " 200OK " message, carry the transport addresses information of remote subscriber for receiving media data in this message, be expressed as X;

After step 805, PGW/GGSN receive IMS call answering, distribute port resource D and E, and set up the incidence relation of port D and transport address X, the media data that port D is received all needs to be transmitted to transport address X; Wherein, the media data that port D sends for receiving UE-1, the media data that port E receives for forwarding port D; For simplified characterization, the transport addresses information that port D is corresponding is still expressed as D;

Step 806, PGW/GGSN use the transport address X in the IMS call answering in transport address D replacement step 804, then forward IMS call answering to UE-1;

So far, UE-1 and remote subscriber establish IMS media path, comprising the IMS media path 1 (being called for short IMS media 1) between UE-1 and PGW/GGSN and the IMS media path between PGW/GGSN and remote subscriber 2 (being called for short IMS media 2).

Step 807 ~ 813, identical with step 509 ~ 515;

After following steps occur in step 809, there is no ordinal relation with step 810 ~ 813.

After step 814, eMSC receive the handover request message of PS network transmission, call request is sent to the PGW/GGSN in PS network, this request is sent by the signaling paths of S714, in the present embodiment, S714 interface uses Nc-SIP interface, what therefore send is INVITE (invitation) message of SIP, carry the number information of UE-1 and the number information of PGW/GGSN in this message, wherein the number information of PGW/GGSN is as called party information, and the number information of UE-1 is as caller information; In addition, eMSC is also carried in this message for receiving the transport address H of the media data of remote subscriber transmission;

Step 815, the call request received in PGW/GGSN determination step 814 is the handover request of the call request received in step 801, therefore map operation is performed, newly-built media path between eMSC and PGW/GGSN is carried out associating with IMS media path 2 and (namely sets up the incidence relation of port F and transport address H, the media data received from port F is made all to be forwarded to transport address H), and distribute new near-end media data reception port J, for receiving the media data that eMSC sends, for simplified characterization, the transport addresses information that port J is corresponding is still expressed as J, after map operation completes, PGW/GGSN sends the call answering message of Nc-SIP to eMSC by S714 interface, such as send " 200OK " message, carry transport address J in this message,

After eMSC receives call answering message, the transport address G being used for distally user in eMSC and sending media data is associated with transport address J, the media data received from transport address G is made to be forwarded to transport address J, and transport address G and the CS media path between transport address H and UE and eMSC are associated, be respectively used to receive the media data that UE sends and the media data being sent remote subscriber by this CS media path to UE from this CS media path.

So far, set up new IMS media path between eMSC and PGW/GGSN, this newly-built media path associates with CS media path by eMSC, and this newly-built media path associates with IMS media path 2 by PGW/GGSN, UE-1 can be continued and UE-2 converses.

4th flow embodiment

Fig. 9 is single radio voice call continuity the 4th method flow diagram that the present invention is based on the second framework embodiment; Fig. 9 describes the process setting up IMS session between UE-1 and far-end (UE-2), and after IMS session establishment completes, there is single radio voice call continuity in UE-1, the media path that how UE-1 and network realize allowing UE-1 use CS territory is set up, and keep former session continuous print process, wherein use Nc-ISUP interface between eMSC and PGW/GGSN (IACP); The method comprises the steps:

Step 901 ~ 913, identical with step 801 ~ 813;

After following steps occur in step 909, there is no ordinal relation with step 910 ~ 913.

After step 914, eMSC receive the handover request message of PS network transmission, call request is sent to the PGW/GGSN in this PS network, this request is sent by the signaling paths of S714, in the present embodiment, S714 interface uses Nc-ISUP interface, what therefore send is the IAM message of ISUP, carries eMSC for transmitting the line number L1 of the line resource of CS media in this message; In addition, also carry the number information of UE-1 and the number information of PGW/GGSN in this message, wherein the number information of PGW/GGSN is as called party information, and the number information of UE-1 is as caller information;

Step 915, the call request received in PGW/GGSN determination step 914 is the handover request of the call request received in step 901, therefore the line resource being used in transmission CS media is divided, the line number of its correspondence is L2, and perform map operation, media path between eMSC and the PGW/GGSN identified with line number L1 and L2 is associated with IMS media path 2, after map operation completes, PGW/GGSN sends the call answering message of Nc-ISUP to eMSC by S714 interface, such as send ANM, PGW/GGSN is carried for transmitting the line number L2 of CS media data in this message,

After eMSC receives above-mentioned call answering message, the above-mentioned media path identified with line number L1 and L2 is associated with the CS media path between UE and eMSC.

So far new CS media path is set up between eMSC and PGW/GGSN, CS media path between this newly-built media path and UE and eMSC connects by eMSC, this newly-built CS media path associates with IMS media path 2 by PGW/GGSN, UE-1 can be continued and UE-2 converses.

Claims (9)

1. a single radio voice call continuity implementation method, is characterized in that, the method comprises:

UE sets up the IMS session anchoring to signaling anchor point by PS network and remote subscriber, and transmits the media data of described IMS session by the first media path and the second media path; Described first media path is the IMS media path between the media anchor point of UE and described IMS session, and described second media path is the IMS media path between described media anchor point and remote subscriber;

Receive that PS network sends for after described IMS session is switched to the handover request by CS network insertion, eMSC sends the call request being used for switching described IMS session to described signaling anchor point;

After receiving described call request, the 3rd media path between newly-built eMSC with described media anchor point is connected with described second media path by described signaling anchor point, and sends call answering to eMSC;

After receiving described call answering, the described 3rd CS media path between media path with UE and eMSC is connected by eMSC, makes UE continue to converse by described CS media path, the 3rd media path and the second media path and remote subscriber;

Wherein, described signaling anchor point is: PGW or GGSN in described PS network, and described media anchor point is AGW; Or

Described signaling anchor point and media anchor point are PGW or GGSN in described PS network;

When described signaling anchor point is: PGW or GGSN in described PS network, when described media anchor point is AGW, in the following way described 3rd media path is connected with described CS media path with described second media path:

The transport address of the port H carried in described call request is included in mapping request and sends to AGW by described signaling anchor point;

After receiving described mapping request, AGW sets up the incidence relation of port H and described second media path, and the transport address of port J is included in map response in send to described signaling anchor point;

After receiving described mapping response, the transport address of port J is included in call answering and sends to eMSC by described signaling anchor point;

After receiving described call answering, eMSC sets up the incidence relation of described CS media path and described port J;

Described port H is for receiving the media data that remote subscriber sends in eMSC, and it is sent to the 3rd media path port of UE by described CS media path; Described port J is for receiving the media data that UE sends in AGW, and it is sent to the 3rd media path port of remote subscriber by described second media path.

2. the method for claim 1, is characterized in that,

When described signaling anchor point is: PGW or GGSN in described PS network, when described media anchor point is AGW, in the following way described 3rd media path is connected with described CS media path with described second media path:

The line number L1 that the eMSC carried in described call request holds is included in mapping request and sends to AGW by described signaling anchor point;

After receiving described mapping request, AGW distribute AGW end line number L2, the 3rd media path identify with line number L1 with L2 is connected with described second media path, and line number L2 is included in map respond in send to described signaling anchor point;

After receiving described mapping response, line number L2 is included in call answering and sends to eMSC by described signaling anchor point;

After receiving described call answering, the 3rd media path identified with line number L1 with L2 is connected with described CS media path by eMSC.

3. the method for claim 1, is characterized in that,

When described signaling anchor point is: PGW or GGSN in described PS network, when described media anchor point is AGW, in the following way described 3rd media path is connected with described CS media path with described second media path:

The line number L1 that the eMSC carried in described call request holds is included in lane assignment request and sends to AGW by described signaling anchor point;

After receiving described lane assignment request, AGW distribute AGW end line number L2, and line number L2 is included in lane assignment response in send to described signaling anchor point;

After receiving the response of described lane assignment, line number L1 and/or line number L2 is included in mapping request and sends to AGW by described signaling anchor point;

After receiving described mapping request, the 3rd media path identified with line number L1 with L2 is connected with described second media path by AGW, and to described signaling anchor point return mapping response;

After receiving described mapping response, line number L2 is included in call answering and sends to eMSC by described signaling anchor point;

After receiving described call answering, the 3rd media path identified with line number L1 with L2 is connected with described CS media path by eMSC.

4. the method for claim 1, is characterized in that,

When described signaling anchor point and media anchor point are PGW or GGSN in described PS network, in the following way described 3rd media path is connected with described CS media path with described second media path:

After receiving the described call request of the transport address of carrying port H, described PGW or GGSN sets up the incidence relation of port H and described second media path, and is included in call answering the transport address of port J and sends to eMSC;

After receiving described call answering, eMSC sets up the incidence relation of described CS media path and described port J;

Described port H is for receiving the media data that remote subscriber sends in eMSC, and it is sent to the 3rd media path port of UE by described CS media path; Described port J is for receiving the media data that UE sends in described PGW or GGSN, and it is sent to the 3rd media path port of remote subscriber by described second media path.

5. the method for claim 1, is characterized in that,

When described signaling anchor point and media anchor point are PGW or GGSN in described PS network, in the following way described 3rd media path is connected with described CS media path with described second media path:

After receiving the described call request of the line number L1 carrying eMSC end, described PGW or GGSN distributes local line number L2, the 3rd media path identified with line number L1 with L2 is connected with described second media path, and line number L2 is included in call answering sends to eMSC;

After receiving described call answering, the 3rd media path identified with line number L1 with L2 is connected with described CS media path by eMSC.

6. a single radio voice call continuity system, comprises PS network, CS network, eMSC, comprises: PGW and GGSN in described PS network; It is characterized in that, this system also comprises: AGW; When UE sets up the IMS session anchoring to described PGW or GGSN by described PS network and remote subscriber, and transmitted the media data of described IMS session by the first media path and the second media path after:

Described eMSC for receive that described PS network sends for described IMS session being switched to the handover request by described CS network insertion, and send the call request for switching described IMS session to described PGW or GGSN after receiving described handover request;

Described PGW or GGSN is used for after receiving described call request, is connected by newly-built described eMSC with the 3rd media path between described AGW with described second media path, and sends call answering to described eMSC;

Described eMSC is also for after receiving described call answering, described 3rd media path is connected with the CS media path between described UE and described eMSC, makes UE continue to converse by described CS media path, the 3rd media path and the second media path and remote subscriber;

Wherein, described first media path is the IMS media path between described UE and described AGW, and described second media path is the IMS media path between described AGW and remote subscriber;

When signaling anchor point is: PGW or GGSN in described PS network, when media anchor point is AGW, in the following way described 3rd media path is connected with described CS media path with described second media path:

Described signaling anchor point is used for the transport address of the port H carried in described call request to be included in mapping request to send to AGW;

Described AGW be used for after receiving described mapping request, set up the incidence relation of port H and described second media path, and the transport address of port J is included in map respond in send to described signaling anchor point;

Described signaling anchor point is used for, after receiving described mapping response, being included in call answering the transport address of port J and sending to eMSC;

Described eMSC is used for after receiving described call answering, sets up the incidence relation of described CS media path and described port J;

Described port H is for receiving the media data that remote subscriber sends in eMSC, and it is sent to the 3rd media path port of UE by described CS media path; Described port J is for receiving the media data that UE sends in AGW, and it is sent to the 3rd media path port of remote subscriber by described second media path.

7. system as claimed in claim 6, is characterized in that,

When described signaling anchor point is: PGW or GGSN in described PS network, when described media anchor point is AGW, in the following way described 3rd media path is connected with described CS media path with described second media path:

Described signaling anchor point is used for the line number L1 that the eMSC carried in described call request holds to be included in mapping request to send to AGW;

Described AGW be used for after receiving described mapping request, distribute AGW end line number L2, the 3rd media path identify with line number L1 with L2 is connected with described second media path, and line number L2 is included in map respond in send to described signaling anchor point;

Described signaling anchor point is used for, after receiving described mapping response, being included in call answering by line number L2 and sending to eMSC;

Described eMSC is used for after receiving described call answering, the 3rd media path identified is connected with described CS media path with line number L1 with L2; Or,

When described signaling anchor point is: PGW or GGSN in described PS network, when described media anchor point is AGW, in the following way described 3rd media path is connected with described CS media path with described second media path:

Described signaling anchor point is used for the line number L1 that the eMSC carried in described call request holds to be included in lane assignment request to send to AGW;

Described AGW be used for after receiving described lane assignment request, distribute AGW end line number L2, and line number L2 is included in lane assignment response in send to described signaling anchor point;

Described signaling anchor point is used for, after receiving the response of described lane assignment, being included in mapping request by line number L1 and/or line number L2 and sending to AGW;

Described AGW is used for after receiving described mapping request, the 3rd media path identified is connected with described second media path with line number L1 with L2, and to described signaling anchor point return mapping response;

Described signaling anchor point is used for, after receiving described mapping response, being included in call answering by line number L2 and sending to eMSC;

Described eMSC is used for after receiving described call answering, the 3rd media path identified is connected with described CS media path with line number L1 with L2;

The interface based on SIP or ISUP is adopted to send described call request and call answering message between described eMSC and described PGW or GGSN.

8. a single radio voice call continuity system, comprises PS network, CS network, eMSC, comprises: PGW and GGSN in described PS network; When UE sets up the IMS session anchoring to described PGW or GGSN by described PS network and remote subscriber, and transmitted the media data of described IMS session by the first media path and the second media path after:

Described eMSC for receive that described PS network sends for described IMS session being switched to the handover request by described CS network insertion, and send the call request for switching described IMS session to described PGW or GGSN after receiving described handover request;

Described PGW or GGSN is used for after receiving described call request, is connected by newly-built described eMSC with the 3rd media path between described PGW or GGSN with described second media path, and sends call answering to described eMSC;

Described eMSC is also for after receiving described call answering, described 3rd media path is connected with the CS media path between described UE and described eMSC, makes UE continue to converse by described CS media path, the 3rd media path and the second media path and remote subscriber;

Wherein, described first media path is the IMS media path between described UE and described PGW or GGSN, and described second media path is the IMS media path between described PGW or GGSN and remote subscriber;

When signaling anchor point and media anchor point are PGW or GGSN in described PS network, in the following way described 3rd media path is connected with described CS media path with described second media path:

Described PGW or GGSN is used for after the described call request receiving the transport address of carrying port H, sets up the incidence relation of port H and described second media path, and is included in call answering the transport address of port J and sends to eMSC;

Described eMSC is used for after receiving described call answering, sets up the incidence relation of described CS media path and described port J;

Described port H is for receiving the media data that remote subscriber sends in eMSC, and it is sent to the 3rd media path port of UE by described CS media path; Described port J is for receiving the media data that UE sends in described PGW or GGSN, and it is sent to the 3rd media path port of remote subscriber by described second media path.

9. system as claimed in claim 8, is characterized in that,

When described signaling anchor point and media anchor point are PGW or GGSN in described PS network, in the following way described 3rd media path is connected with described CS media path with described second media path:

Described PGW or GGSN is used for after the described call request receiving the line number L1 carrying eMSC end, described PGW or GGSN distributes local line number L2, the 3rd media path identified with line number L1 with L2 is connected with described second media path, and line number L2 is included in call answering sends to eMSC;

Described eMSC is used for after receiving described call answering, the 3rd media path identified is connected with described CS media path with line number L1 with L2;

The interface based on SIP or ISUP is adopted to send described call request and call answering message between described eMSC and described PGW or GGSN.