CN1874279A

CN1874279A - Method for treating abnormity of registration in procedure of registering users

Info

Publication number: CN1874279A
Application number: CN 200510109520
Authority: CN
Inventors: 朱奋勤
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2005-10-21
Filing date: 2005-10-21
Publication date: 2006-12-06
Anticipated expiration: 2025-10-21
Also published as: CN100387014C

Abstract

The invention discloses method for processes abnormal registration in subscriber's registering procedure. In IMS network domain, after inquiring call session control function (I-CSCF) entity forwards message of registration to service call session control function (S-CSCF), when determining abnormal registration, the method informs home subscriber (HSS), and HSS marks marker for the said S-CSCF entity; in subsequent registering procedure of terminal device, being received query request from I-CSCF entity and detected the marker for the said S-CSCF entity, HSS carries out at lest capability data needed for selecting S-CSCF entity in response message returned back to I-CSCF entity.

Description

The processing method of registration abnormity in user registration course

Technical field

The present invention relates to IP-based IP multimedia subsystem, IMS (IMS) network of the communications field, relate in particular in the IMS network in user registration course processing method registration abnormity.

Background technology

Development along with broadband network, mobile communication not only is confined to traditional Speech Communication, by with present that business (presence), short message, webpage (WEB) are browsed, the combining of data service such as locating information, propelling movement business (PUSH) and file-sharing, mobile communication can realize the business of multiple medium types such as audio frequency, video, picture and text, to satisfy user's multiple demand.

For example, short message service can provide the service of instant message, chatroom and multimedia short message; Video traffic can provide amusement, multimedia messages service such as to exchange with daily; Electronic commerce affair can provide services such as catalogue, search engine, shopping cart, order management and payment; Game service can provide services such as solitaire game and group's recreation; Positioning service can provide services such as missing, guide and warning; The personal assistant business can provide services such as address book, schedule, bookmark management, file storage, event notification and Email.

Under the promotion of multiple application, 3rd Generation Partnership Project (3GPP) and 3rd Generation Partnership Project 2 (3GPP2) etc. are organized and have all successively been released IP-based IP multimedia subsystem, IMS (IMS) framework, its objective is and in the mobile network, use a kind of standardized open architecture to realize diversified multimedia application, so that more selection and abundanter impression to be provided to the user.

Consult shown in Figure 1ly, the IMS framework is superimposed upon on the packet field network (on the PS-Domain), and its entity relevant with safety function comprises CSCF (CSCF) entity and HSS functional entity.CSCF can be divided into serving CSCF (S-CSCF), proxy CSCF (P-CSCF) and three logic entities of inquiry CSCF (I-CSCF) again, these three logic entities may be to be positioned on the different physical equipments, also may be functional modules different in the same physical equipment.S-CSCF is the service switching center of IMS, is used to carry out session control, peace preservation association's speech phase, and managing user information produces charge information etc.; P-CSCF is the access point of terminal user access to IMS, is used to finish user's registration, service quality (QoS) control and safety management etc.; I-CSCF is responsible for the intercommunication between the IMS territory, and network topology structure and configuration information are externally hidden in the distribution of management S-CSCF, and produce metering data etc.HSS is very important customer data base, is used to support the processing of each network entity to calling and session.

IMS is only to consider to use at the 3G (Third Generation) Moblie network in initial release (R5 release protocol).Because the business on the IMS is very abundant, so operator uses IMS on the network of 2G demand occurred.But on the network of 2G what can't support based on the safety related functions of the IMS of 3G network, in order to provide IMS business to the terminal use of 2G network, TR 33.878/TR33.978 has defined EarlyIMS input field security mechanism, this scheme provides certain safety function for the IMS business on the 2G, when the complete IMS safety function based on 3G is supported in network upgrade again after 3G.

The safety function of existing IMS based on 2G is achieved in that the user at first inserts the packet domain of 3GPP, this packet field network can carry out access authentication to the user, access authentication distributes an IP address by the packet network gateway node (GGSN) of back packet network to the user, and this IP address also is the IP address that the user uses when using the IMS service of subsystem.GGSN is notified to HSS with this IP address and user's telephone number (MSIDSN) or IMSI International Mobile Subscriber Identity (IMSI) by intermediate entities, HSS finds the identify label IMPI of user in the IMS system by user's MSISDN or IMSI, and information such as this user's IMPI, MSISDN and IP address are bound preservation.When the user will use IMS, it at first can send login request message (register), this message is transmitted the back through intermediate entities and is arrived S-CSCF, S-CSCF obtains behind the binding relationship of this user's IMPI and IP address from HSS and preserves, S-CSCF checks from user's the identify label and the IP address of use thereof whether be complementary with the binding of the identify label (IMPI) of self preserving with the IP address then, if, think that then it is a validated user, controlling this user inserts, allow this user to use the IMS business, otherwise think that it is a disabled user, refuse this 2G user and insert.When the user discharged the IP address, GGSN need notify HSS.HSS can initiate the log off procedure of a network side according to this message subsequently.

When Full 3GPP Compliant method for authenticating was handled, the I-CSCF entity need judge that the user's is registered as initial registration or repeated registration.This is because if the I-CSCF entity when giving the S-CSCF entity with the SIP registration message, might cause selected S-CSCF entity to visit owing to the fault or the other reasons of S-CSCF entity self.This moment, the I-CSCF entity need judge that user's registration message is initial registration or subsequent registration according to some customizing messages in the Authorization header field in the SIP registration message, if be initial registration, this moment, the I-CSCF entity can newly select a S-CSCF entity to transmit registration message more again, if be subsequent registration message, the I-CSCF entity can not gravity treatment S-CSCF entity, can only return that 408 (request timed outs) are receiveed the response or 504 (server timeouts) are receiveed the response to the user.

Because in Early IMS method for authenticating; the registration message that UE sends will no longer carry the Authorization header field; simultaneously also do not have ipsec tunnel between UE is with P-CSCF, whether former with good grounds message is protected, judges that message is that still heavily registration is no longer feasible for initial registration.When the selected S-CSCF entity of I-CSCF entity can't be visited, the I-CSCF entity can't judge that the SIP registration message of being received is that initial registration still is follow-up heavy registration.All think initial registration (do not protect a kind of be interpreted as that protection equals " NO ") if I-CSCF will not carry Authorization, carry out gravity treatment.Can cause like this at UE, it is to carry out heavily registration, but network has been redistributed a S-CSCF to it.Therefore session status/the log-on message relevant with original S-CSCF on UE do not described according to existing standard and how to be handled, and is that UE may keep also and may delete yet, and causes causing some states that should delete of UE side not deleted thus.Distinguishing registration for needs is can't determine follow-up relevant treatment measure initial registration or the network element of repeated registration (as S-CSCF).

In addition, prior art is not distinguished registration type when registration abnormity, nullify non-follow-up heavy registration message for one of Client-initiated, can be according to present standard at S-CSCF of I-CSCF side meeting gravity treatment, if this user for the disabled user cause the cancellation can not be successful at network side, the S-CSCF of new choosing also can not replace old S-CSCF in the HSS side, cause current gravity treatment at network side without any meaning, may cause the burden of network on the contrary.Therefore I-CSCF need judge for non-follow-up heavy registration message, is not all to need gravity treatment at every turn.

Summary of the invention

The invention provides a kind of method of in user registration course, handling registration abnormity,, when registration abnormity, exist the network equipment can't determine the problem of subsequent treatment measure to solve prior art under the situation that can't distinguish initial registration and heavily registration.

The present invention also solves when registration abnormity, and prior art is not distinguished registration type and may be had the problem that increases network burden.

For addressing the above problem, the invention provides following technical scheme:

A kind of in user registration course the processing method of registration abnormity, this method comprises the steps:

Inquiry CSCF (I-CSCF) entity in the IMS network domains is forwarded to the registration message of terminal equipment when determining registration abnormity behind service call conversation control function (S-CSCF) entity, notifying home user server (HSS) carries out mark by HSS to described S-CSCF entity; And

In the subsequent registration process of described terminal equipment, when HSS accepts the query requests of I-CSCF entity and detects the described mark of S-CSCF entity, in the response message that returns to the I-CSCF entity, carry the capacity data of selecting the described needs of S-CSCF at least.

Wherein:

Also further comprise the S-CSCF entity of having distributed to public user identity (IMPU) in the described response message, if the I-CSCF entity can't judge whether to be initial registration message according to the sip message that receives, then preferentially select this S-CSCF entity and transmit registration message.

Described terminal equipment is adopted Early IMS method for authenticating in registration process.

In described subsequent registration process,, then select another one S-CSCF entity and transmit registration message to it according to the described capacity data that has issued if the I-CSCF entity is determined registration abnormity after registration message is forwarded to the S-CSCF entity.

The I-CSCF entity takes a step forward to judge whether described registration message is the non-subsequent message of cancellation at notice HSS, if, then directly return failed message to terminal equipment, otherwise, if subsequent message is then handled according to present standard.If otherwise register non-subsequent message, then notify HSS.

Return response message to the I-CSCF entity behind the HSS mark S-CSCF entity, after the I-CSCF entity receives this response message,, then return registration failure message to terminal equipment if the I-CSCF entity can't judge whether to be initial registration message according to the sip message that receives.If the I-CSCF entity can be judged as initial registration message according to the sip message that receives, then can be for further processing according to response message to the I-CSCF entity.

The reason that comprises registration failure in the described failed message.

After terminal equipment received described failed message, further the login state of other public user identity (IMPU) that deletion is relevant reached relevant session status.

A kind of method of handling registration abnormity in user registration course, this method comprises the steps:

The registration message that inquiry CSCF (I-CSCF) entity in the IMS network domains is initiated terminal equipment is forwarded to when determining registration abnormity behind service call conversation control function (S-CSCF) entity, judges the type of this registration message;

If described registration message then returns failure response to terminal equipment for nullifying non-follow-up type, if subsequent message then handle according to present standard, otherwise if described sip message is that registration type is then carried out follow-up abnormality processing.

Wherein:

When carrying out abnormality processing, if I-CSCF determines that described terminal equipment adopts the early IMS security mode in registration process, then notify HSS, by HSS described S-CSCF is carried out mark.

The present invention is in the registration process that adopts Early IMS authentication and similar authentication mode, and notice HSS carries out mark by HSS when I-CSCF finds that S-CSCF lost efficacy; In the follow-up registration process of terminal equipment, the S-CSCF that HSS response I-CSCF inquiry distributes and when detecting this mark, in the message of returning to I-CSCF, must carry the capacity data of the S-CSCF that requires distribution, therefore, in the subsequent registration process, when I-CSCF finds that the S-CSCF of appointment lost efficacy, and presently used method for authenticating can't judge whether just can select the suitable S-CSCF of another one to carry out subsequent treatment according to this capacity data for initial registration message according to the sip message that receives, thereby can finish registration process smoothly.

Description of drawings

Fig. 1 is the existing IMS schematic network structure;

Fig. 2 is the main process chart during registration abnormity among the present invention;

Fig. 3 is the detailed process schematic diagram when I-CSCF finds the S-CSCF inefficacy in the embodiment of the invention.

Embodiment

In registration process, I-CSCF sends out Cx-UAR command request HSS according to the normal handling flow process to HSS and distributes S-CSCF, according to receiveing the response, the processing of HSS can be divided into three kinds of situations:

A, return the S-CSCF of an appointment;

B, return required S-CSCF capability set, select suitable S-CSCF for I-CSCF;

C, return the S-CSCF of an appointment, comprise also that simultaneously required S-CSCF capability set selects suitable S-CSCF for I-CSCF.

I-CSCF needs to select a S-CSCF under above-mentioned three kinds of situations, the SIP registration message is transmitted to the S-CSCF of this appointment.Under abnormal conditions, as other reasonses such as S-CSCF or network failures, the S-CSCF that sip message is forwarded to appointment does not have receives the response.And in present 3GPP standard; I-CSCF need be according to the related content in the Authorization header field in the SIP registration message; judge whether this SIP registration message receives protection, and processing is receiveed the response, receive the response as S-CSCF of gravity treatment or to user's failure.After 3GPP has introduced Early IMS method for authenticating, in Early IMS authorizing procedure, the SIP registration message that UE starts will no longer comprise the Authorization header field, cause utilizing this header field to judge whether sip message is protected thus.Therefore; for login request message does not have the registration process of information whether login request message be subjected to safeguard protection; I-CSCF is at the S-CSCF of a selected appointment and after transmitting the registration message failure, can't be by judging the whether protected subsequent treatment of carrying out of sip message.A kind of understanding thinks, to be equal to this message be not exactly initial registration message to this header field, but because UE place lacks the relevant treatment behavior, can cause handling unusually.

At Early IMS authorizing procedure, return the situation of the S-CSCF of an appointment for HSS, this is because user's IMPU or other relevant IMPU have been registered on the S-CSCF of an appointment, and HSS must guarantee that the relevant IMPU of this user is on same S-CSCF.In addition might the user relevant IMPU being arranged is the Unregistered state, be retained on the S-CSCF of a certain appointment, and HSS thinks and do not need to redistribute a S-CSCF this moment.

The present invention returns a situation of specifying S-CSCF for registration process that adopts Early IMS authentication and HSS, when after I-CSCF is forwarded to registration message service call conversation control function (S-CSCF) entity, determining registration abnormity (having fault) as S-CSCF, notifying home user server (HSS) carries out mark by HSS to described S-CSCF entity; Under same user or same IMS SUBSCRIPTION in the subsequent registration process of other IMPU, when HSS accepts the query requests of I-CSCF entity and detects the S-CSCF entity of distributing to this user to have described mark, in the response message that returns to the I-CSCF entity, carry the capacity data of selecting the described needs of S-CSCF at least, can reselect S-CSCF according to capacity data for I-CSCF.

Consult shown in Figure 2ly, the main processing procedure during registration abnormity is as follows:

1, I-CSCF determines that S-CSCF lost efficacy after registration message being forwarded to the S-CSCF of appointment, and judges that registration message is an Early IMS authentication mode, and there is fault in I-CSCF by this S-CSCF of Cx interface notice HSS.

Further, I-CSCF can be optimized processing, that is: judge that earlier sip message is registration message or logout message, if sip message is logout message (is in the sip message Expire value be 0), then I-CSCF can directly return corresponding error message to terminal equipment; If it is registration message (be in the sip message Expire value be not 0) that I-CSCF judges this sip message, then continue subsequent step 2.

2, after HSS receives the fault notification message of I-CSCF, determine that this IMPU is an Early IMS authentication type, its S-CSCF with the former registration of this IMPU does a special marking.

For the non-Early IMS of IMPU authentication type, HSS should return error response message to S-CSCF.

Admissible employing method such as I-CSCF are the needs acquisition capability by explicit declaration in the Cx-UAR message, after HSS obtains this message and judges that this IMPU is Early IMS authentication type, the S-CSCF that this IMPU distributed is put a last special marking, have disabled possibility to show this S-CSCF.Follow-up HSS should also comprise the S-CSCF ability information simultaneously to the S-CSCF that I-CSCF returns this IMPU registration when receiving user's UAR inquiry response.Promptly tell I-CSCF, specified S-CSCF just recommends, and is not mandatory requirement.

3, after I-CSCF receives receiveing the response of HSS, no matter receive the response whether comprised the information that can further carry out the S-CSCF gravity treatment this moment, I-CSCF can not carry out the S-CSCF gravity treatment this moment immediately, and should just return failed message to the user, (by prior art, generally as the above-mentioned explicit S-CSCF ability that requires of I-CSCF, HSS can the resettability data as 408/500/504, I-CSCF is at this moment according to this capacity data, and I-CSCF can carry out follow-up S-CSCF and select).

The reason that can further comprise failure in this failed message is as former because S-CSCF fault.

4, after UE receives this failed message,, be judged as the original S-CSCF fault of registering of network side, carry out the local back UE that handles and initiate the new registration of IMPU according to the information that comprises in the message or additive method (as registration failure repeatedly).

If UE has other relevant IMPU registrations or subscribed to some relevant informations this moment in this locality, this moment, UE should delete the login state of other IMPU, after UE confirms that local all login states have been removed, initiated the new registration of IMPU.

5, I-CSCF initiates query requests to HSS after receiving the register requirement of UE.

6, HSS is after receiving the Cx-UAR order, IMPI under the IMPU of inquiry is included as Early IMS authentication type and learns that according to the special marking of S-CSCF may there be fault in the S-CSCF of the original registration of this IMPU, HSS gives in the message that this IMPU returns, and will comprise S-CSCF (this IMPU original register) and S-CSCF capacity data.

I-CSCF preferentially generally speaking selects the S-CSCF that recommends and transmits sip message to it after receiving the message that HSS returns.If the I-CSCF entity determines that S-CSCF is unusual after registration message is forwarded to the S-CSCF entity, then fibrous root is according to the SIP registration message that receives, judge the presently used method for authenticating of user, if presently used method for authenticating makes I-CSCF judge whether to be initial registration message according to the sip message that receives, then I-CSCF selects the suitable S-CSCF entity of another one and transmits registration message to it according to described capacity data.

Consult shown in Figure 3ly, adopt in the registration process of Early IMS authentication mode, as follows to the treatment step of registration abnormity:

The UE of step 1-4, employing Early IMS authentication mode sends registration message to network, and this message is transmitted to the I-CSCF of this user's home network through P-CSCF.

Step 5-6, I-CSCF send Cx-UAR message to HSS, obtain the S-CSCF positional information that this IMPU registers.Suppose that herein this IMPU has had the S-CSCF of a distribution at network side.Therefore HSS only returns the S-CSCF of this appointment to I-CSCF.

Handling process A:I-CSCF is transmitted to the SIP registration message S-CSCF of this appointment.Suppose the S-CSCF fault herein, cause S-CSCF can not give the correct response of I-CSCF thus.

After step 7-8, I-CSCF judge the S-CSCF fault, and judge that according to the SIP registration message this IMPU is an Early IMS authentication type.I-CSCF also can further adjudicate the registration message of being received simultaneously and be registration or logout message, has the possibility of further process optimization.Judge that as I-CSCF this registration message is a logout message, then I-CSCF no longer sends the S-CSCF faulty indication toward HSS, receives the response and just return registration failure to the user.Certainly I-CSCF also can not carry out this optimization process, and promptly I-CSCF does not judge that this registration message is registration message or logout message.

I-CSCF sends the S-CSCF faulty indication to HSS, and there is the possibility of fault in this S-CSCF of notice HSS.HSS returns a message authentication to I-CSCF and has received this message.In this process, HSS must judge under this IMPU IMPI whether contract and comprise Early IMS authentication type, if IMPI comprises Early IMS authentication type under this IMPU, then need the S-CSCF that this IMPU is distributed to put for last one special mark beginning, there is the possibility of fault to show this S-CSCF.

Step 9-10, I-CSCF returns this registration failure message to the user after confirming that HSS has received this faulty indication.In this registration failure message, it is former because the indication information of network side S-CSCF fault further to comprise this time registration failure.

After handling process B:UE received this registration failure response message, indication information in receiveing the response according to failure or additive method judgement may be the S-CSCF fault of network side.UE nullifies all IMPUs relevant with this S-CSCF on it, and in this process, UE can send logout message to network side, also can not send logout message to network side.

Step 11-14, when the definite all relevant IMPU thereon of UE were in non-registered state, UE can send registration message to network side again.This registration message is transmitted to I-CSCF according to above-mentioned similar approach through P-CSCF.

Step 15-16, I-CSCF sends Cx-UAR message to HSS, and the requester network side is given the S-CSCF that this IMPU distributed.HSS had originally distributed a S-CSCF to IMPU, and HSS has made special marking to it in user's registration process of last time, had the possibility (step 7-8) of fault with the S-CSCF that writes down this distribution.

Therefore whether IMPI comprised Early IMS authentication type under HSS must judge the IMPU that carries out the Cx-UAR inquiry.IMPI comprises Early IMS authentication type under the IMPU that determines to carry out the Cx-UAR inquiry, HSS is when returning to the S-CSCF that this IMPU of I-CSCF distributed, if the S-CSCF of while return recording and this IMPU (are not comprised Early IMS authentication type if determine to carry out IMPI under the IMPU of Cx-UAR inquiry the desired S-CSCF capacity data of gravity treatment S-CSCF, then HSS handles according to normal mode, and promptly HSS can only return the S-CSCF of appointment).

After handling process C:I-CSCF receives the S-CSCF and S-CSCF capacity data of the appointment of returning from HSS, then I-CSCF then fibrous root according to the SIP registration message that receives, judge the presently used method for authenticating of user, if presently used method for authenticating makes I-CSCF judge whether to be initial registration message according to the sip message that receives, then I-CSCF preferentially selects to use the S-CSCF of appointment, and transmits registration message to it.If find that this S-CSCF does not respond, or other faults, the I-CSCF fibrous root is selected next S-CSCF according to capacity data.

After step 17, I-CSCF determined selected S-CSCF, I-CSCF was transmitted to the S-CSCF of this appointment with registration message, and the S-CSCF of appointment carries out follow-up processing according to common register flow path.

For other registration processes that does not comprise the safety indication in registration message, its processing method is identical with the processing mode of the registration of above-mentioned employing Early IMS authentication mode when registration abnormity, repeats no more.

In addition, for the registration process that adopts Early IMS authentication mode or FULL authentication mode, the registration message that I-CSCF initiates terminal equipment is forwarded to when determining registration abnormity behind service call conversation control function (S-CSCF) entity, can judge the type of this registration message earlier; If described registration message then returns failure response to terminal equipment for nullifying non-subsequent message type.If subsequent message is then handled according to present standard, otherwise if described sip message is that the non-subsequent message of registration type is then carried out follow-up abnormality processing.For the registration process of FULL authentication mode, can be undertaken by existing mode the processing of registration abnormity; For the registration process of early IMS security mode, the processing of registration abnormity can be carried out as stated above, promptly by I-CSCF notice HSS, by HSS described S-CSCF is carried out mark; The description of front is consulted in all the other processing.

Obviously, those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, if of the present invention these are revised and modification belongs within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and modification interior.

Claims

1, a kind of method of handling registration abnormity in user registration course is characterized in that this method comprises the steps:

2, the method for claim 1, it is characterized in that, also further comprise the S-CSCF entity of having distributed to public user identity (IMPU) in the described response message, if the I-CSCF entity can't judge whether to be initial registration message according to the sip message that receives, then preferentially select this S-CSCF entity and transmit registration message.

3, method as claimed in claim 1 or 2 is characterized in that, described terminal equipment is adopted Early IMS method for authenticating in registration process.

4, method as claimed in claim 3, it is characterized in that, in described subsequent registration process,, then select another one S-CSCF entity and transmit registration message to it according to described capacity data if the I-CSCF entity is determined registration abnormity after registration message is forwarded to the S-CSCF entity.

5, the method for claim 1, it is characterized in that, the I-CSCF entity takes a step forward at notice HSS and judges whether described registration message is logout message and is non-subsequent message, if, then directly return failed message to terminal equipment, if otherwise subsequent message, then according to present standard processing, if otherwise register non-subsequent message, then notify HSS.

6, the method for claim 1, it is characterized in that, return response message to the I-CSCF entity behind the HSS mark S-CSCF entity, after the I-CSCF entity receives this response message, if the I-CSCF entity can't judge whether to be initial registration message according to the sip message that receives, then return registration failure message to terminal equipment.If the I-CSCF entity can be judged as initial registration message according to the sip message that receives, then can be for further processing according to response message to the I-CSCF entity.

7, method as claimed in claim 6 is characterized in that, comprises the reason of registration failure in the described failed message.

8, method as claimed in claim 6 is characterized in that, after terminal equipment received described failed message, further the login state of other public user identity (IMPU) that deletion is relevant reached relevant session status.

9, a kind of method of handling registration abnormity in user registration course is characterized in that this method comprises the steps:

If described registration message then returns failure response to terminal equipment for nullifying type and be non-subsequent message,, be registration type and then carry out follow-up abnormality processing for non-subsequent message as if described sip message if subsequent message is then handled according to present standard.

10, method as claimed in claim 9 is characterized in that, when carrying out abnormality processing, if I-CSCF determines that described terminal equipment adopts Early IMS authentication mode in registration process, then notifies HSS, by HSS described S-CSCF is carried out mark.

11, method as claimed in claim 10, it is characterized in that, in the subsequent registration process of described terminal equipment, when HSS accepts the query requests of I-CSCF entity and detects the described mark of S-CSCF entity, in the response message that returns to the I-CSCF entity, carry the capacity data of selecting the described needs of S-CSCF at least.

12, method as claimed in claim 10, it is characterized in that, also further comprise the S-CSCF entity of having distributed to public user identity (IMPU) in the described response message, if the I-CSCF entity can't judge whether to be initial registration message according to the sip message that receives, then preferentially select this S-CSCF entity and transmit registration message.