CN102714830B

CN102714830B - Method and device for handing over voice over internet protocol (VoIP) call from packet switch domain to circuit switch domain

Info

Publication number: CN102714830B
Application number: CN201080061859.3A
Authority: CN
Inventors: 雷正雄
Original assignee: Alcatel Lucent Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2010-01-29
Filing date: 2010-01-29
Publication date: 2014-12-10
Anticipated expiration: 2030-01-29
Also published as: CN102714830A; WO2011091597A1

Abstract

A method for handing over a voice over internet protocol (VoIP) call from packet switch (PS) domain to circuit switch (CS) domain in a communication system is provided. The communication system includes a VoIP session anchor device, a CS control device of the CS domain and a PS control device of the PS domain. When the CS control device receives a handover request from the PS control device, the method includes the following steps: the first time period is computed, wherein the first time period is the required time for the CS control device sending a message to the remote terminal of the VoIP call; the first time period and the preset second time period are compared, wherein the second time period is the required time for the CS control device sending a message to the local terminal of the VoIP call; according to the comparison result, sending a session handover request to the VoIP session anchor device and sending a cell handover request to the PS control device are controlled, enabling the session handover of IP multimedia subsystem (IMS) layer and the cell handover of layer 2 to occur simultaneously or nearly simultaneously. The present invention also relates to a device for handing over a VoIP call from the PS domain to the CS domain.

Description

Voip call is switched to the method and apparatus of circuit commutative field from packet-switched domain

Technical field

The present invention relates to communication network, be specifically related to voip call to be switched to from packet-switched domain the method and apparatus of circuit commutative field.

Background technology

IMS is that one global, access is independent and measured IP tunnel and Service control system, and it makes to use dissimilar multimedia service to become possibility based on the terminal use of general the Internet agreement.IMS system not only provides plurality of access modes, and the interoperability between circuit commutative field (CS territory) is also provided.For being in the multi-mode mobile terminal in packet-switched domain (PS territory), when it move to PS territory cover network edge or outside, or current PS territory cover network become unavailable and other in CS territory cover network in time, can call be switched to from PS territory CS territory with ensure speech quality.

In the prior art, if user terminal can carry out reception and the transmission of information via PS territory and CS territory simultaneously, conventionally before disconnecting current connection, complete switching.That is to say, user terminal creates and calls out or session in CS territory, simultaneously maintains existing audio call in PS territory, after the calling in telephone exchange territory or session establishment complete, just voice medium is switched in the calling or session in CS territory, then discharges the Internet resources in the PS territory before switching.This mode has minimum break period conventionally.But, for can not be simultaneously being undertaken for the reception of information and the terminal of transmission, cannot using above-mentioned method by two territories.

Therefore, 3GPP TS 23.216 has specified to be anchored on calling in IMS system by EPS(evolved packet system) PS access and by UTRAN/GERAN(universal land radio access web/GSM EDGE Radio Access Network) CS access between SRVCC(single radio frequency continuous voice call) solution, for keeping the continuity of audio call, in this case, UE(subscriber equipment) in the given a certain moment, can only send or receive data by the one in aforesaid two kinds of Access Networks.

But the SRVCC scheme that 3GPP TS 23.216 specifies also exists some defects, as confirmable voice interruption time not, complicated signaling process etc.Why by labor can there is the uncertain voice interruption time in it below.

Fig. 1 illustrates the VoIP that 3GPP TS 23.216 specifies and converses from E-UTRAN(evolved universal terrestrial wireless access network) be switched to the network architecture figure of the SRVCC of UTRAN/GERAN.

As shown in Figure 1, UE accesses IMS by E-UTRAN, S-GW/PDN GW.E-UTRAN is also referred to as LTE(Long Term Evolution), comprise several E-Node B, be responsible for wireless access mesh portions.EPS carries out the integration in function by NodeB, RNC to existing WCDMA and TD-SCDMA system, CN, is reduced to two kinds of network element of eNodeB and EPC.EPC comprises: MME(Mobility Management Entity), serve as control node, be responsible for the signaling processing of core net; S-GW(gateway)/PDN-GW(grouped data network gateway), the data processing of responsible core net.Wherein, non-3GPP wireless access network can access EPC by PDN-GW, and 3GPP wireless access network can access EPC by S-GW.

In the environment shown in Fig. 1, when outside the covering edge of UE in E-UTRAN or overlay area, can determine to be switched to the CS territory that UTRAN/GERAN provides.In UTRAN/GERAN, UE is via base station, MSC(mobile switching centre) server is linked into IMS network.

UTRAN has become the more important a kind of access way of UMTS at present; GERAN is formulated and the key component of the GSM that safeguards by 3GPP, is also included within UMTS/GSM network.。Conventionally, the network of mobile operator is made up of multiple GERAN, in the network of UMTS/GSM, combines with UTRAN.

About details such as communication modes between other network element in Fig. 1 and each network element, can be with reference to TS 23.216.

Fig. 2 shows the associated call flow chart that is switched to the SRVCC of UTRAN/GERAN in the situation that 3GPP TS 23.216 specifies from E-UTRAN.In order to complete the switching of voice conversation, need in advance in IMS, for example in SCC AS(services set and application server for continuity) upper, this audio call of grappling.Fig. 2 is corresponding to Fig. 6 .2.2.1-1 of 3GPP TS 23.216.

As shown in Figure 2, when source E-UTRAN is according to the measurement report that is received from this locality/source UE, while determining that the switching from PS territory to CS territory is carried out in ongoing voip call to local UE, send handover request, i.e. step 203 to local MME.In step 204, carrying is divided to (for the follow-up transfer to voice service) with opisthogenesis MME, and send the corresponding handover request from PS territory to CS territory to the MSC server/media gateway that can cover at present local UE in step 205.Corresponding MSC/ media gateway is switched and is prepared and set up after circuit, initiation session transfer.Here it should be noted that the step 206 of dotted portion, 208,209 can be omitted (step 220,221 is also like this) if the target MSC that this this locality UE will be switched to is when to receive from the MSC of the handover request of MME be same.

Next, SRVCC comprises the session handoff procedure and layer 2 the cell switch process that is switched to Target cell that are positioned at IMS layer.That is to say, it comprises the switching of two user levels:

1) step 210 is to 212, carries out session handoff procedure by the SCC AS in IMS, the other side who upgrades long-range UE(and namely set up voip conversation with local UE with the SDP of target CS access leg (access leg)), and source of release EPC PS access leg.Above-mentioned steps transforms to MGW in user level from EPC by the phonological component that causes ongoing session.In Fig. 2, the INVITE in step 210 is session handover request, because its SDP information that comprises MGW, long-range UE receives this INVITE via SCC AS and starts session handoff procedure.

2) step 215-221, the switching from E-UTRAN to UTRAN/GERAN of carrying out on local UE and Access Network, this is the RAT(wireless access type of carrying out at local UE and access network place) between switching, will cause local UE to be switched to target UTRAN/GERAN community from current E-UTRAN community.

In above-mentioned two handoff procedures, all can produce the interruption of voip call, i.e. the interruption of voice flow.Although each step is numbered with continuous numeral in Fig. 2,, this be not show step 210 to 212 and step 215 to the time relationship between 221 two parts.In fact on the contrary, step 210 may just start to carry out to 212 completely after step 215, also may carry out simultaneously.That is to say there is no synchronization mechanism between these two handoff procedures, with regard to making the time of voice interruption become uncontrollable, there is uncertainty like this.In the worst situation, the time of voice interruption can be very long, makes user's sensation variation.

Fig. 3 illustrates the time span of the VoIP dropped calls in above-mentioned SRVCC scheme.Wherein, T1 is the break period of the cell switch process of layer 2, also shows the zero hour and the finish time of interruption simultaneously.T2 is the break period of the session handoff procedure of IMS layer, also shows the zero hour and the finish time of interruption simultaneously.

The caused interruption of session handoff procedure of situation 1:IMS layer is than the Zao generation of the caused interruption of cell switch process.In this case, by the maximum being greater than in T1 and T2, in the worst situation, equal T1+T2 the break period that SRVCC produces.

The caused interruption of session handoff procedure and the caused interruption of cell switch process of situation 2:IMS layer occur simultaneously.In this case, equal the maximum in T1 and T2 the break period that SRVCC produces.

Situation 3: the caused interruption of cell switch process is than the Zao generation of the caused interruption of the session handoff procedure of IMS layer.In this case, similar with situation 1, by the maximum being greater than in T1 and T2, in the worst situation, equal T1+T2 the break period that SRVCC produces.

Based on above analysis, can see that the voice interruption having in SRVCC scheme is mainly that the cell switch process to Target cell (switching of the carrying out) two parts that carry out by the session handoff procedure of IMS layer with at layer 2 produce between local UE and access network.And the randomness that these two processes are carried out, the time of voice interruption becomes uncontrollable, has uncertainty.Voice interruption can worsen user's experience undoubtedly for a long time.

Summary of the invention

In order to solve defect of the prior art, the present invention proposes to introduce synchronization mechanism between the session handoff procedure of IMS layer and the cell switch process of layer 2, these two handoff procedures are simultaneously or almost simultaneously started, thus reduced to minimum steady state value the break period of whole SRVCC, thereby improve user's experience.

It should be noted that the control appliance MSC server in CS territory may support the service interface of IMS, also may not support IMS interface and only support the interface of ISUP/BICC.In this application, mainly consider latter event, MSC server is only supported the interface of ISUP/BICC.Can brief overview once: ISUP(ISDN User Part) be the main agreement of one of SS7/C7 signaling system, agreement and program are defined, for setting up, manage and discharging repeat circuit, this repeat circuit is in the upper transmission of PSTN (PSTN) voice and data call.Bearer Independent Call Control Protocol (call control protocol of bearer independent) is the agreement that ITU-TSG11 group works out, and by ISDN User Part evolution, is a kind of control protocol that uses the calling irrelevant with service bearer that realizes in backbone network.

For realizing above object, according to embodiments of the invention, a kind of method that voip call is switched to circuit switching (CS) territory in communication system from packet switching PS territory is provided, described communication system comprises the CS control appliance in voip conversation anchoring arrangement, CS territory and the PS control appliance in PS territory, in the time that described CS control appliance receives the handover request from described PS control appliance, the method comprises:

Calculated for the first period, described the first period is to send a message to from described CS control appliance the required time of remote terminal that reaches voip call;

More described the first period and and predefined the second period, described the second period is that described CS control appliance sends a message to the required time of local terminal that reaches voip call; And

According to comparative result, control to described voip conversation anchoring arrangement session handover request transmission and to the transmission of the community handover request of described PS control appliance.

In a preferred embodiment of the invention, described communication system also comprises neutral-controlled plant, wherein calculates for the first period further to comprise:

The neutral-controlled plant that described CS control appliance triggers described communication system sends non-session handover request to described voip conversation anchoring arrangement; And

Described CS control appliance receives response message from described neutral-controlled plant, and described response message is at described voip conversation anchoring arrangement and described remote terminal is mutual and described neutral-controlled plant generates from message is replied in described voip conversation anchoring arrangement reception.

According to embodiments of the invention, calculate the moment that the first period comprised that the described CS control appliance of storage triggered described neutral-controlled plant, store the moment of described CS control appliance from described neutral-controlled plant reception response message, and be 0.4 to 0.6 times of time span between these two moment by described the first period value, be preferably 0.5 times.

According to embodiments of the invention, in the situation that described the first period is greater than described the second period, described CS control appliance, in starting and sending session handover request to described voip conversation anchoring arrangement, arranges time-out time and equals the timer of the difference of described the first period and described the second period; And after described timer expiry, described CS control appliance sends community handover request to described PS control appliance.

According to embodiments of the invention, in the situation that described the first period equals described the second period, described CS control appliance starts to described voip conversation anchoring arrangement transmission session handover request, and sends community handover request to described PS control appliance simultaneously.

According to embodiments of the invention, in the situation that described the first period is less than described the second period, described CS control appliance, in sending community handover request to described PS control appliance, arranges time-out time and equals the timer of the difference of described the second period and described the first period; And after described timer expiry, start to described voip conversation anchoring arrangement and send session handover request.

On the other hand, embodiments of the invention also provide a kind of CS control appliance that voip call is switched to circuit switching (CS) territory in communication system from packet switching PS territory, described communication system also comprises the PS control appliance in voip conversation anchoring arrangement and PS territory, and described CS control appliance comprises:

Calculation element, for when the handover request receiving from described PS control appliance, calculated for the first period, and described the first period is to send a message to from described CS control appliance the required time of remote terminal that reaches voip call;

Comparison means, for more described the first period and predefined the second period, described the second period is that described CS control appliance sends a message to the required time of local terminal that reaches voip call; And

Control device, for control to according to comparative result described voip conversation anchoring arrangement session handover request transmission and to the transmission of the community handover request of described PS control appliance.

According to embodiments of the invention, described control device is configured to: in the time that described the first period is greater than described the second period, in starting and sending session handover request to described voip conversation anchoring arrangement, time-out time be set equal the timer of the difference of described the first period and described the second period; And after described timer expiry, send community handover request to described PS control appliance.

According to embodiments of the invention, described control device is configured to: in the time that described the first period is equal with the second period, starts to described voip conversation anchoring arrangement and send session handover request, and send community handover request to described PS control appliance simultaneously.

According to embodiments of the invention, described control device is configured to: in the time that described the first period is less than described the second period, in sending community handover request to described PS control appliance, time-out time be set equal the timer of the difference of described the second period and described the first period; And after described timer expiry, start to described voip conversation anchoring arrangement and send session handover request.

On the other hand, the present invention also provides the neutral-controlled plant in a kind of communication system, described communication system also comprises the PS control appliance in voip conversation anchoring arrangement, PS territory and voip call is switched to the CS control appliance in circuit switching (CS) territory from packet switching PS territory

Described neutral-controlled plant comprises auxiliary calculation element, and this device is configured to: by the triggering of described CS control appliance, send non-session handover request to described voip conversation anchoring arrangement; After the remote terminal of described voip conversation anchoring arrangement and voip call is mutual, receives and reply message from described voip conversation anchoring arrangement; And, send response message to described CS control appliance, so that described CS control appliance calculated for the first period, described the first period is that described CS control appliance sends a message to the required time of remote terminal that reaches voip call,

Described control appliance also comprises sub controlling unit, this device is configured to: more described the first period of described CS control appliance with represent that described CS control appliance sends a message to and reaches the local terminal of voip call the second period of required time after, start to described voip conversation anchoring arrangement and send session handover request through described CS control appliance.

The method and apparatus of the application of the invention, the session handoff procedure that two main handoff procedures that cause voice interruption in SRVCC scheme are IMS layer and introduced synchronization mechanism between the cell switch process of layer 2, the interruption of two handoff procedures is simultaneously or almost simultaneously occurred, so just make the interruption of whole SRVCC process become controlled and constant, and be reduced to a minimum value, improve systematic function, obviously improved user's service quality.And the solution of the present invention does not affect substantially for existing network environment, thereby there is very high compatibility.

Brief description of the drawings

By reading the detailed description of non-limiting example being done referring to accompanying drawing, it is more obvious that other features, objects and advantages of the present invention will become.

Fig. 1 is the network architecture of the SRVCC of regulation in 3GPP TS 23.216;

Fig. 2 is at the related SR VCC schematic flow sheet that there is no to be switched to from E-UTRAN under DTM/PSHO support object GERAN in prior art;

Fig. 3 is the schematic diagram of SRVCC length break period of the prior art;

Fig. 4 is message sequence chart according to a particular embodiment of the invention;

Fig. 5 is flow chart according to an embodiment of the invention; And

Fig. 6 is the functional block diagram of CS control appliance and neutral-controlled plant according to an embodiment of the invention.

Embodiment

In Fig. 4, local UE will be switched to from PS territory CS territory.In figure, in MMEShiPS territory, source, be responsible for the control appliance of processing signaling.MSC server is the control appliance of being responsible for processing signaling in CS territory (comprising the CS territories such as WCDMA, GSM, TD-SCDMA).Certainly, basic thought of the present invention can also be applied to the MSC server in cdma network.SCC AS can be used as the voip conversation anchoring arrangement in IMS, and certainly, voip conversation anchoring arrangement can be also IBCF(interconnection boundary Control function) or other logic entities.In one embodiment of the invention, MSC server is only supported the interface of ISUP/BICC, also needs a neutral-controlled plant to complete the signaling Processing tasks that may need.MGCF serves as the neutral-controlled plant of processing signaling in this embodiment.Correspondingly, IM-MGW(IP multimedia gateway) for the treatment of the media encoding and decoding conversion of user plane.

The VoIP handover mechanism proposing in order to complete the present invention need to preset a value P2 in MSC server, and this value representation MSC server sends the required time of message of switching with CS to local UE.Specifically, represent that sending PS to CS Response message from MSC server receives required average time of HO from EUTRAN Command to MME to last local UE.Mainly be made up of 2 parts this average time: message summation and the message in the communication node of the process processing time to message in network, transmit the required time.Because message transmission arrive UE the interstitial content of process fix, so these needed times of node processing messages can calculate out.In addition, because MSC server and local UE are at same local network, local in-network message from MSC server arrive UE the change of distance of process little, it is also little that therefore message is transmitted the variation of needed time in network, can estimate by experience.As can be seen here, message is issued to the required time of the local UE of last arrival from MSC server can be based on experience measuring and calculating and estimation, and therefore, P2 can preset.

Fig. 4 shows according to signaling message sequence chart of the present invention.Although it is pointed out that each step in figure is that these do not represent the precedence that each step is carried out with continuous numeral number.

Step 401 is similar to step 209 to the step 201 in Fig. 2 to step 409, no longer launches narration here.

In step 409a, in the time that MSC server detects that will carry out SRVCC switches, send with STN-SR(Session Hand-off number-single radio frequency to MGCF) BICC IAM message.In this embodiment, this IAM message is carried out follow-up operation for triggering MGCF.In addition, MSC server sends storage the time of this IAM message, for example, be T4 this time mark.

In step 410, in the time receiving the IAM message that comprises STN-SR, MGCF detects that this is a SRVCC process.So MGCF sends an empty INVITE request that does not comprise the SDP information of IM-MGW to the S-CSCF in IMS, and this sky INVITE request is transmitted to voip conversation anchoring arrangement, i.e. SCC AS in the present embodiment by S-CSCF secundum legem program.It should be noted that this sky INVITE request does not comprise the SDP information of IM-MGW.In other words, this message is not traditional session handover request, and we can call it " non-session handover request ", to distinguish with session handover request in general sense.Certainly, other for measuring MSC, to send out message be also possible to the message of far-end UE required time.

In step 410a, when SCC AS receives after above-mentioned INVITE, and long-range UE carries out alternately.Mutual process can comprise: the INVITE request of SCC AS based in step 410, is transmitted to long-range UE by the re-INVITE request without SDP information.Process after this request at long-range UE, respond SCC AS with the 200OK message of the SDP information with oneself.

In step 410b, MGCF, before response message ANM sends to MSC server, sends ACM message to MSC server.Here need brief overview once, in CS territory, ACM message refers to Address Complete, represents that the remote terminal of repeat circuit is reserved.ANM is response message, represents that called off-hook replys.

There is the several mode that how to send ACM message of determining.Can use in this embodiment following two kinds: MGCF sends BICC ACM message to MSC server after the timer expiry of the 7.2.3.2.4 of TS 29.163 joint definition.Alternative dispensing means is for example, in the time receiving final success response (, 200OK response), and MGCF sends ACM message and BICC ANM to MSC server.Can certainly make otherwise.

In step 411, after communicating by letter with long-range UE, SCC AS responds MGCF by the 200OK message of the SDP information with long-range UE.Because long-range UE does not obtain the SDP information of IM-MGW, therefore, the handoff procedure of long-range UE cannot start, and so far, the Media Stream of current sessions still keeps connecting.

In step 411a, define as TS 29.163, MGCF sends ANM to MSC server.In the time that MSC receives this ANM, it is stored this time and can be T5 by this time mark.In this moment, the Media Stream of ongoing session still connects.Due in step 410, MGCF has detected that this is a SRVCC process, and therefore it does not now send ACK message to SCC AS.

After step 411a, once MSC server stores mark T5, it will calculate the duration (for example this duration can be expressed as to P1) of spending to long-range UE transmission signaling message from MSC server according to T4 and T5.In this embodiment, from T4 within the T5 time period (step 409a is to step 411a) sending and receiving BICC message and sip message, MSC server can calculate it according to the round trip of above-mentioned message and send a message to and reach the required time P1 of long-range UE, such as P1 being calculated as to certain ratio of time span between moment T4 and moment T5, this ratio can rule of thumb be set with network condition.The in the situation that of round trip symmetry, this ratio can be 0.5.Consider the possible inconsistent of round trip, this ratio is that 0.55. or 0.45 is also possible.Generally, ratio setting can be adjusted between 0.4 and 0.6 and according to actual conditions.As previously mentioned, MSC server can be preset by operator to the value that CS switches the duration P2 of relevant message to local UE transmission.Calculate after P1, MSC server can compare the size of P1 and predefined P2.According to different comparative results, MSC server will be carried out different actions.

The step that MSC server calculates P1 and comparison P1 and P2 size does not clearly mark in Fig. 4, still should be appreciated that the step of calculating and comparison is carried out immediately after step 411a.This is an open-and-shut algorithm, can take hardly the extra resource of MSC.

The following will discuss step 411b and 413: when MSC server receives after the ANM from MGCF, calculate and compare through, MSC can determine whether will arrange a timer according to comparative result.For example, in the time that P1 and P2 vary in size, MSC server can arrange timer, and the timeout value of this timer can be set as the difference of P1, P2.

Example 1:P1 is greater than P2, shows that MSC server sends a message to reach the required time of long-range UE and be greater than it and send a message to the required time of local UE that reaches.In this case, for MSC server, the session that should first start IMS layer is switched, and for example, it can start MGCF and send session handover request to SCC AS.

The in the situation that of example 1, MSC server will perform step 411b and step 413 simultaneously.On the one hand, MSC server sends the initial IAM message identical with IAM message in step 409a again to MGCF, and we can be re-IAM this IAM message marking, with step 409a in message difference.On the other hand, MSC server can start a timer simultaneously, and the time-out time of this timer is P1-P2.

Under the startup of the re-IAM message sending at MSC server or driving, as shown in step 412, MGCF sends to the SCC AS of IMS the ACK message that comprises IM-MGW, and this is an actual session handover request message.In step 417,418, SCC AS receives after the ACK message with the SDP of MGW, will be immediately send ACK message to start session handoff procedure and to upgrade long-range UE based on this ACK message to long-range UE, follow-up process and existing 3GPPTS 23.216 normalized definitions similar.

Note, after the timer expiry arranging in step 413, MSC server just sends community handover request to source MME, such as the PS to CS Response message shown in step 14 in Fig. 4, perform step subsequently 15 and step 16, thereby start the cell switch process that is switched to Target cell of local UE side, follow-up process and 3GPP TS 23.216 normalized definitions similar, be not described in detail, in order to avoid unnecessarily fuzzy the present invention herein.

Example 2: if P1 equals P2, show that MSC server sends a message to and reach the required time of long-range UE it sends a message to that to reach the required time of local UE identical.In this case, MSC server does not need to arrange timer, and performs step 411b and step 414 simultaneously.On the one hand, MSC server is by again sending the initial IAM message identical with IAM message in step 409a, i.e. re-IAM message, drives or start MGCF to send real session handover request to SCC AS; On the other hand, as shown in step 414, MSC server sends PS to CS Response message to source MME.In other words,, in Fig. 4, re-IAM message and PS to CS Response message send simultaneously.

And in step 412 below, in the time receiving re-IAM message, MGCF finds to call out also in continuation and relevant to SRVCC process.Therefore, MGCF abandons this re-IAM message and sends the ACK message of SDP information with IM-MGW to SCC AS.Certainly, this SDP information should be consistent with the SDP information the 200OK receiving from SCC AS/remote UE in step 411.SCC AS receives after above-mentioned ACK message, to send ACK message to start session handoff procedure and to upgrade long-range UE based on this ACK message to long-range UE immediately, and source MME will start the cell switch process of local UE side after receiving described PS to CS Response message.

Example 3:P2 is greater than P1, and MSC server sends a message to and reaches the required time of local UE and be greater than it and send a message to the required time of long-range UE that reaches, and MSC server should first send community handover request to source MME, restart afterwards session handoff procedure.Therefore, the time-out time of timer will be set to P2-P1.

In step 414 in Fig. 4, MSC server sends PS to CS Response message to source MME, starts the cell switch process of local UE side.When performing step 414, MSC server can start timer (being step 413), and the time-out time of timer is P2-P1.Only, after timer expiry, MSC server just starts the session switching of IMS layer, for example, send re-IAM message to MGCF and switch to start session, be i.e. step 411b.In other words, if P2 is greater than P1, step 411b will carry out after step 414, and timer starts in step 414, and only after timer expiry, just performs step 411b.

For the ease of understanding, Fig. 5 illustrates the corresponding method flow diagram of signaling message sequence chart of Fig. 4.

As shown in the figure, when receiving in step 405 after the PS to CS req message of source MME transmission, MSC server calculates P1 by the step 409a to 411a in Fig. 4, send to long-range UE the duration that signaling message is spent from MSC server, and after step 411a and in other possible steps (step 411b, 413 or 414) before, start the comparison procedure of P1 and preset value P2.Relatively produce three kinds of possible results, in the time of P1>P2, step 411b and 413 will carry out simultaneously, and the timer that time-out time is P1-P2 is set when starting session switching.When after timer expiry, just perform step 414, start the switching of local UECe community by send PS to CS Req to source MME.In the time of P1=P2, timer needn't be set, and perform step 411b and 414 simultaneously.In the time of P1<P2, step 414 and 413 is carried out simultaneously, and the timer that time-out time is P2-P1 is set when starting the switching of local UECe community.When after timer expiry, execution step 411b, for example, start session switching by send re-IAM message to MGCF.

It should be noted that, step 409a is that the session that starts IMS layer in order to calculate P1 instead of reality is switched to the object of step 411a.The session of the actual startup of the step 210(IMS layer in this and Fig. 2 is switched) be fundamental difference.In addition, the method for calculating P1 is not limited only to above-mentioned INVITE – 200OK message pair, also can adopt other message, such as INVITE – 183 Temporary Response message.

It should be noted that MSC server is not supported SIP interface in the embodiment describing with reference to Fig. 4.In other embodiments of the invention, when MSC server is supported, in the situation of SIP interface, still can adopt the flow process shown in Fig. 5 to reduce the break period of whole SRVCC process.For example, can be sent by MSC server the value that does not comprise the INVITE of IM-MGW, calculates P1 from SCC AS reception with the 200OK message of the SDP of long-range UE to SCC AS, and be sent the request of the session switching that starts IMS layer by MSC server.Under these circumstances, MGCF entity is not essential.

Fig. 6 is taking MSC server and MGCF equipment as exemplifying according to the CS control appliance 601 of the embodiment of the present invention and the functional block diagram of neutral-controlled plant 602 according to an embodiment of the invention.

In Fig. 6, MSC server comprises: calculation element 611, comparison means 612 and control device 613.MGCF equipment 602 comprises auxiliary calculation element 621 and sub controlling unit 622.Existence that it should be noted that MGCF equipment is not essential, therefore being shown in broken lines alternately between mutual and control device 613 and the sub controlling unit 622 between calculation element 611 and auxiliary calculation element 621.It should be noted that shown in more than Fig. 6 of functional module that above equipment comprises, for example, also comprise various message sinks and transmitting element, the part relevant with embodiments of the invention is only shown, in order to avoid unnecessarily fuzzy the present invention in figure.Various devices in figure can be realized by computer program code on the basis of existing capability entity.

Calculation element 611, in the time of the handover request (PS to CS Req) for example receiving, from PS control appliance (source MME), calculates and sends a message to from CS control appliance (being MSC server) the required time P1 of remote terminal that reaches voip call.

In the situation that MSC server is supported SIP interface, for " measurement " sends a message to from MSC server the time P1 that remote terminal experiences, calculation element 611 can be configured to: to voip conversation anchoring arrangement SCC AS, to send empty INVITE be non-session handover request and receive response message, the half of elapsed time section or the only about half of value as P1 between above sending and receiving message from SCC AS after SCC AS and remote terminal are mutual.

In the situation that MSC server is not supported SIP interface, for " measurement " sends a message to from MSC server the time P1 that remote terminal experiences, calculation element 611 for example sends non-session handover request by the auxiliary calculation element 621 of IAM message trigger to SCC AS, auxiliary calculation element 621 receives the response message of for example 200OK from SCC AS at SCC AS and remote terminal after alternately, and returns to the response message of for example ANM to MSC 601.MSC calculates P1 according to the moment of the moment of " triggering " and reception response message.

Comparison means 612 compares P1 and presets P2, the above, P2 is that MSC server sends a message to the required time of local terminal that reaches voip call.

Control device 613 is by the start-up time of switching according to the comparative result control session switching of P1 and P2 and community.

A timer 614 is also shown in the frame 601 in Fig. 6, it should be noted that timer 614 neither be essential.In the time that P1 is identical with P2, MSC server 601 is without timer is set, and starts that session is switched and the switching of local UE community simultaneously.Only, in the time that P1 is different with P2, time-out time etc. is just set in the timer of ∣ P1-P2 ∣.In the time of P1>P2, control device 613 starts when session is switched timer is set, and only has and just starts community switching after timer expiry.In the time of P2>P1, control device 613 starts when switch community timer is set, and only has and just starts session switching after timer expiry.

In the situation that MSC server is supported SIP interface, MSC server 601 for example starts the session switching of IMS layer by send session handover request to SCC AS, for example start community switching by for example, send community handover request to PS control appliance (, source MME).

In the situation that MSC server is not supported SIP interface, control device 613 for example starts session switching by send re-IAM message to sub controlling unit 622.

With reference to accompanying drawing, specific embodiments of the invention are described above.It will be appreciated that, the present invention is not limited to above-mentioned specific implementations, and those skilled in the art can make various distortion or amendment within the scope of the appended claims.

Claims

1. one kind is switched to voip call the method in circuit switching (CS) territory in communication system from packet switching PS territory, described communication system comprises the CS control appliance in voip conversation anchoring arrangement, CS territory and the PS control appliance in PS territory, in the time that described CS control appliance receives the handover request from described PS control appliance, the method comprises:

More described the first period and predefined the second period, described the second period is that described CS control appliance sends a message to the required time of local terminal that reaches voip call; And

2. the method for claim 1, also comprises neutral-controlled plant, wherein calculates for the first period further to comprise:

3. method as claimed in claim 2, wherein calculate the moment that the first period comprised that the described CS control appliance of storage triggered described neutral-controlled plant, store the moment of described CS control appliance from described neutral-controlled plant reception response message, and be 0.4 to 0.6 times of time span between these two moment by described the first period value, be preferably 0.5 times.

4. the method as described in claims 1 to 3 any one, further comprise: in the situation that described the first period is greater than described the second period, described CS control appliance, in starting and sending session handover request to described voip conversation anchoring arrangement, arranges time-out time and equals the timer of the difference of described the first period and described the second period; And after described timer expiry, described CS control appliance sends community handover request to described PS control appliance.

5. the method as described in claims 1 to 3 any one, further comprise: in the situation that described the first period equals described the second period, described CS control appliance starts to described voip conversation anchoring arrangement transmission session handover request, and sends community handover request to described PS control appliance simultaneously.

6. the method as described in claims 1 to 3 any one, further comprise: in the situation that described the first period is less than described the second period, described CS control appliance, in sending community handover request to described PS control appliance, arranges time-out time and equals the timer of the difference of described the second period and described the first period; And after described timer expiry, start to described voip conversation anchoring arrangement and send session handover request.

7. a CS control appliance that voip call is switched to circuit switching (CS) territory in communication system from packet switching PS territory, described communication system also comprises the PS control appliance in voip conversation anchoring arrangement and PS territory, described CS control appliance comprises:

8. CS control appliance as claimed in claim 7, wherein said control device is configured to: in the time that described the first period is greater than described the second period, in starting and sending session handover request to described voip conversation anchoring arrangement, time-out time be set equal the timer of the difference of described the first period and described the second period; And after described timer expiry, send community handover request to described PS control appliance.

9. CS control appliance as claimed in claim 7, wherein said control device is configured to: in the time that described the first period is equal with the second period, start to described voip conversation anchoring arrangement and send session handover request, and send community handover request to described PS control appliance simultaneously.

10. CS control appliance as claimed in claim 7, wherein said control device is configured to: in the time that described the first period is less than described the second period, in sending community handover request to described PS control appliance, time-out time be set equal the timer of the difference of described the second period and described the first period; And after described timer expiry, start to described voip conversation anchoring arrangement and send session handover request.

Neutral-controlled plant in 11. 1 kinds of communication systems, described communication system also comprises the PS control appliance in voip conversation anchoring arrangement, PS territory and voip call is switched to the CS control appliance in circuit switching (CS) territory from packet switching PS territory,