CN101577897A

CN101577897A - Method for informing IMS about belonging network of PDN GW allocated to UE

Info

Publication number: CN101577897A
Application number: CNA2008101821217A
Authority: CN
Inventors: 李志军; 郝振武; 朱进国
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2008-11-11
Filing date: 2008-11-11
Publication date: 2009-11-11
Anticipated expiration: 2028-11-11
Also published as: CN101577897B

Abstract

The invention provides a method for informing IMS about belonging network of PDN GW allocated to UE. The method comprises the following steps that: user equipment UE is attached to a system architecture evolution SAE network; the SAE network establishes an IP bearer for the UE and returns the information of a belonging network of a packet data network gateway PDN GW allocated to the UE to the UE; the UE receives the information of the belonging network of the PDN GW and then stores the information in a local position; the UE carries the information of the belonging network of the PDN GW to an IP multimedia subsystem IMS network through session initiation protocol SIP signaling; and the IMS network judges the belonging network of the PDN GW according to the information of the belonging network of the PDN GW. Through the method provided by the invention, the IMS network can be informed whether a current media routing mode of the UE is an LBO mode, and converts the media routing mode of the UE from the LBO mode to an HR mode according to need.

Description

Method for IMS to know network of PDN GW allocated for UE

Technical Field

The present invention relates to the field of communications, and in particular, to a method for a UE (user equipment) to register to an IMS (IP multimedia Subsystem) Network of a home Network through an LTE/SAE (Long term Evolution/System architecture Evolution ) access Network under roaming, where the IMS learns a Network to which a PDN GW (Packet Data Network Gateway) allocated for the UE belongs.

Background

The IMS system is the core of a new generation communication network, and is significantly characterized in that a Session Initiation Protocol (SIP) system is adopted, communication is independent of access, and the IMS system has various capabilities of separating various media service control functions from a bearer capability, separating a call from a Session, separating an application from a service, separating a service from a network, and merging a mobile network with an internet service, and the like.

With the development of network architecture flattening and the emergence of various high-speed broadband mobile access modes, the mobile communication network is also prompted to propose the next Generation architecture concept of LTE/SAE, including enabling the evolved wireless communication system to provide higher transmission rate, shorter transmission delay, lower cost, and simultaneously supporting mobility between 3GPP (3rd Generation Partnership Project) internal access systems, and mobility between 3GPP access systems and non-3 GPP access systems, and the like. Meanwhile, LTE/SAE will also be used as an access means of IMS domain, and the evolution and development of IMS architecture are promoted.

In the SAE research process, roaming is an important application scenario, and as roaming usage becomes more and more common, how to improve the utilization efficiency of the network in the roaming scenario and reduce unnecessary roundabout of media routing becomes an important subject of SAE research.

In order to solve the problem of continuity of signaling in roaming situations, 3GPP organizations have proposed to implement uninterrupted signaling connection from a home network to a visited network using mobile IP technology. However, the introduction of the mobile IP technology creates a triangular routing problem that the media stream at the visited place must detour to the home network, which results in a great reduction in the efficiency of media transmission.

In order to solve the triangular routing problem caused by the introduction of mobile IP, 3GPP organizations have proposed a Local Breakout mode (LBO mode for short) for media routing. Under LBO mode, the media access visit network does not need to detour to the home network. In contrast to the LBO mode, a Home routing mode (HR mode) for media routing is used, i.e. a media stream must bypass to the Home network.

In order to implement the LBO mode, the 3GPP organization proposes several specific application modes, one of which is called: dual IP mode. That is, when the UE roams in the visited network, both the visited network and the home network establish an IP bearer for the UE, the IP bearer of the visited network is used for media routing, and the IP bearer of the home network is used for signaling control, that is, signaling passes through the home network by using the mobile IP technology, and media is transferred out from the visited network locally. In this mode, the home network and the visited network are both UE assigned an IP address, where the home network assigns mobile IP to the UE. The mode can realize the continuity of the signaling control under the roaming condition and solve the problem of low efficiency of the media routing detour to the home network. In this mode, the UE is required to be allocated with the P-CSCF and S-CSCF of the home network.

Another application mode is single IP mode: that is, only the visit network establishes the IP bearing for the UE, allocates the IP address, and the media route is directly transferred out from the visit network.

Fig. 1 shows a main architecture for implementing LBO mode in SAE networks, which can support dual IP mode and single IP mode simultaneously. The UE accesses to the IMS service providing network through the SAE access network. The SAE network is located in the visit network and provides the bottom access service, and the IMS service network is located in the home network and provides the service.

In fig. 1, the main network elements of the SAE network include:

E-UTRAN (Evolved UTRAN, Evolved radio access network): the next generation radio access network can provide higher uplink and downlink rates, lower transmission delay and more reliable radio transmission. Wherein the main network entity of the E-UTRAN is the eNodeB;

MME (Mobility Management Entity): a control plane functional entity, which is responsible for managing and storing UE context (such as UE/user identity, mobility management status, user security parameters, etc.), allocating temporary identity for a user, and being responsible for authenticating the user when the UE camps in the tracking area or the network;

SAE GW (SAE Gateway): the user plane functional entity is responsible for user plane data routing processing and is divided into two SAE GWs, namely Serving GW (Serving gateway, S-GW for short) and PDN GW. The S-GW is a mobility anchor between the SAE system and the conventional 3GPP system and a mobility anchor between the E-UTRAN. The PDN GW is configured to terminate downlink data of the UE in an idle state, initiate paging when the downlink data addressed to the UE arrives, and manage and store contexts of the UE, such as an IP bearer service parameter and network internal routing information.

The main network elements of the IMS service network include:

home Subscriber Server (HSS): data responsible for managing the CS domain, the packet domain (PS) and the IMS domain;

call Session Control Function (Call Session Control Function, CSCF): a core network element for controlling a session process, comprising: a Proxy call session control function (Proxy-CSCF, abbreviated as P-CSCF), an Interrogating call session control function (interworking-CSCF, abbreviated as I-CSCF), and a Serving-CSCF (S-CSCF);

policy and Charging Rules Function (Policy and Charging Rules Function, PCRF for short): the function point for controlling media connectivity, media traffic, performing charging, etc. belongs to a part of PCC (Policy and charging Control) function architecture.

In the architecture shown in fig. 1, if a PDN GW (Home PDN GW, abbreviated as H-PDN GW) of a Home network and a PDN GW (Visited PDN GW, abbreviated as V-PDN GW) of a Visited network are both UE-allocated IP addresses, a dual IP mode may be implemented. Single IP mode if IP address is allocated only by V-PDN GW. Referring to fig. 1, if the path of the media routing is "UE-E-UTRAN-S-GW-H-PDN GW", then home network routing mode (HR); if the path of the media route is 'UE-E-UTRAN-S-GW-V-PDN GW', the mode (LBO) is local breakout for the visited network.

Since the technical scheme is complex because the local roll-out of the media route is realized by using a dual-IP method, the 3GPP standard organization dominates the realization of the local roll-out of the media route by using a single-IP method. When implementing local roll-out of media routing using single IP, how to implement the transition of media routing from LBO mode to HR mode is a matter of important discussion. The media routing mode transition from LBO mode to HR mode may be required due to lawful interception required by the home network or due to the need for some special traffic handling, such as the initiation of conference traffic.

Fig. 2 shows a procedure of how to implement LBO mode of media routing and transition to HR mode in single IP mode. In fig. 2, the PDN GW is located in the visited network and can assign an IP address belonging to the visited network to the UE. The P-CSCF is located in the home network, although the P-CSCF may also be located in the visited network, and the overall architecture is not affected. Through the control of the P-CSCF, an IMS Access Gateway (IMS AGW for short) is serially connected to a path of the media route, and the media route can be converted from the LBO mode to the HR mode.

However, under the architecture of fig. 2, the P-CSCF must first know whether the UE's media route is currently LBO mode or not, and can request the media route to transition from LBO mode to HR mode. Otherwise, if the current media route egress of the UE is in the home network (i.e., HR mode), but the P-CSCF does not know, a transition of the media route from HR mode to HR mode occurs, i.e., an invalid and wasteful transition occurs.

And judging whether the media route of the UE is in an LBO mode, namely judging whether the current media exit path of the UE is in a visiting network. Since the PDN GW is responsible for processing media streams of the user, and the media of the UE is transferred out from the PDN GW, determining the media routing exit of the UE is equivalent to determining whether the PDN GW allocated to the UE is located in the visited network or the home network.

Therefore, it is necessary for the P-CSCF to know the network to which the PDN GW allocated for the UE belongs, and in the current technology, the P-CSCF cannot know the network to which the PDN GW allocated for the UE belongs.

In the prior art, when a UE is located in a visited network under roaming conditions, the UE needs to access to an IMS domain of a home network through an SAE access network. When attaching to the SAE network, the UE may request to establish the SAE network, allocate a PDN GW to the SAE network, and establish an IP bearer. In this procedure, the UE finally obtains an IP address from the network, but does not know to which network the PDN GW associated with this IP address belongs, i.e. to which network the PDN GW associated with this IP address belongs.

Fig. 3 shows a process of accessing a UE to an SAE network, executing network attachment, assigning a PDNGW, and establishing an IP bearer in the prior art, which mainly includes the following steps:

s301, UE initiates a network attachment request to eNodeB in order to access to SAE network, wherein the request carries information such as UE identification, UE network access capability, request IP allocation indication and the like;

s302, the eNodeB selects an MME serving the UE for the UE, forwards the attachment request to the MME, and simultaneously carries important information such as the identity of the UE and the like to the MME;

s303, the MME sends a position updating request to the HSS of the home network, and the message carries the identification of the MME and the identification of the UE so as to inform the UE of the current accessed area;

s304, the HSS finds out the user data of the UE according to the identity of the UE and sends the user data to the MME, and the part of the user data of the UE mainly comprises: whether to allow Access to the visited network, information such as a default Access Point Name (APN), a bandwidth size and the like, if the HSS determines that the UE uses the PDN GW of the home network, the HSS simultaneously contains the address information of the PDN GW of the home network;

in this step, for the allocation of the PDN GW, the HSS instructs the MME how to obtain the address of the PDN GW in two ways:

(1) mode 1: specifying an APN name and a specific address of a PDN GW;

(2) mode 2: an APN name is specified and an indication indicates whether the MME selects the PDN GW of the home or visited network.

If the method 1 is adopted, the HSS designates a specific address (APN and PDN GW address) of the PDN GW of the home network, and the MME definitely obtains the PDN GW of the home network according to the PDN GW address indicated by the HSS, namely the HSS replaces the MME to select.

If mode 2 is adopted, the HSS instructs the MME to select the PDN GW, and the mechanism for the MME to select the PDN GW is based on: MME expands APN to one shape as: a form of a domain name such as "apn.mnc.mcc.xxyy", and then requests the DNS server to resolve the domain name to the address of a specific PDNGW. The MNC is a Mobile Network Code (MNC for short) and is used to identify a specific Mobile Network, and the visited Network and the home Network have different Mobile Network numbers; MCC is a Mobile Country Code (MCC) to identify which Country a Mobile network belongs to. XXYY is a service type name, such as "GPRS" indicating that the APN is a specific service type of a GPRS service.

For the method 2, and the HSS indicates that the MME needs to allocate the PDN GW of the home network, the HSS needs to provide a mobile Operator Identifier (APN Identifier, APN-OI for short), which is a string like "APN. If the MME receives the indication of the HSS, the MME replaces the corresponding part in the domain name APN.MNC.MCC.XXYY' extended by the APN with the APN-OI, and then requests the DNS server of the home network to resolve the PDN GW address of the home network according to the domain name.

For the case that the mode 2 is adopted and the HSS indicates the MME to allocate the visited network PDN GW, the MME generates a domain name such as "apn.mnc.mcc.xxyy" according to the mobile network number of the MME, and requests the DNS server of the local network to resolve the PDN GW address of the local network according to the domain name.

In contrast to scheme 2, in scheme 1, the APN is an Identifier that does not include an OI part (Operator Identifier), i.e., a part that does not include "mnc.

S305, the MME receives the user data, checks whether the UE is allowed to access the network, and returns a user receiving response to the HSS;

in this step, the MME determines whether to select the home network PDN GW or the visited network PDN GW according to the instruction how to select the PDN GW returned by the HSS in the above step. In a specific procedure, only one PDN GW can be selected, and PDN GWs of the home network and the visited network cannot be selected at the same time.

S306, the HSS sends a confirmation position updating response to the MME;

s307, the MME selects an S-GW for the UE and sends a request for establishing a default bearer to the S-GW. In this request, the MME informs the S-GW of the necessary information: UE identification, MME identification, UE IP address allocation indication, default bandwidth information, PDN GW address, APN and the like;

s308, S-GW sends request for establishing default bearing to PDN GW, in the request, S-GW informs PDN GW necessary information: APN, address of S-GW, default bandwidth information, indication for allocating IP address for UE, etc.;

s309 (optional), if necessary, the PDN GW requests the PCRF for policy and charging rules configured for the UE and decision information;

s310, the PDN GW establishes a default load according to the strategy and charging decision information returned by the PCRF, and returns a load establishing response to the S-GW, wherein the load establishing response comprises IP address information distributed for the UE;

s311, the S-GW sends a response of default bearer establishment to the MME, and the bearer establishment response contains IP address information distributed for the UE;

s312, the MME sends an attach response to the eNodeB indicating that the UE' S request to attach to the network has been received. The response includes: APN, IP address information assigned for the UE, etc. This APN does not contain a network number and a country number, i.e. does not contain a suffix like mnc.mcc.xxxx;

s313, the eNodeB sends a voice bearer establishment request to the UE, and requests the UE to store important information for bearer establishment and open a corresponding port, where the message carries: carrying a network ID, a PDN GW address, an IP address allocated to the UE, bandwidth information, APN and the like;

s314, the UE sends a voice bearer establishment response to the eNodeB;

s315, the eNodeB informs the MME that the attachment process is completed;

s316, MME sends updating load request to S-GW, informs the ID and address of eNodeB serving UE;

s317, the S-GW sends a bearer updating response to the MME;

s318, if the PDN GW is not appointed by the HSS, the MME sends a location updating request to the HSS, informs the HSS of the address information of the PDN GW served by the UE, and the HSS updates the information.

In steps S312 and S313 of the flow of fig. 3, the APN information returned to the UE by the MME through the eNodeB may not include an Operator Identity (OI), that is, a network number such as 'mnc.mcc', and therefore, the UE cannot distinguish whether the assigned PDN GW is of a home network or a visited network.

After the attach and IP bearer establishment procedure shown in fig. 3 is completed, the UE attaches to the SAE network in the visited area, accesses a PDN, and establishes an IP bearer.

After the UE is assigned an IP address, the UE initiates an IMS registration procedure with the home network using the IP address. In the registration process, the UE may notify the network number of the network to which the IMS is accessed, but the network to which the UE is accessed and the PDN network that allocates the PDN GW to the UE are not necessarily the same, so the IMS service layer (specifically, P-CSCF and S-CSCF) does not know to which network the PDN GW of the UE belongs (whether the PDN GW is of a visited network or a home network), and thus cannot know whether the current media routing mode of the UE is the LBO mode.

Furthermore, under the LBO architecture of single IP, since the IMS layer (P-CSCF/S-CSCF) does not know whether the exit of the media routing of the UE (i.e. the PDN GW allocated to the UE) is located in the visited network or the home network, it cannot be determined that the media routing mode should be switched from the LBO mode to the HR mode when handling special needs (e.g. the home network requires to perform lawful interception).

Therefore, in the prior art, when the IMS service layer requires the media routing to implement the transition from the LBO mode to the HR mode, the IMS service layer cannot know which network is allocated (whether the PDN GW of the UE is allocated by the visited network or the home network), and therefore cannot know whether the current media routing mode is the LBO mode, and further cannot require the transition of the media routing mode, because the IMS service layer cannot know which network is allocated by the PDN GW of the UE (whether the PDN GW is allocated by the visited network or the home network), and lacks basic judgment information.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method for obtaining the network to which the PDN GW allocated for the UE belongs by the IMS, so that the UE accesses the SAE network in case of roaming, and the current media routing mode of the UE can be determined by the IMS service layer (P-CSCF/S-CSCF) according to the obtained network to which the PDN GW of the UE belongs, thereby performing media routing mode conversion as needed.

In order to solve the above problem, the present invention provides a method for an IMS to know a network to which a PDN GW allocated to a UE belongs, including the following steps:

user Equipment (UE) is attached to a System Architecture Evolution (SAE) network, the SAE network establishes an IP bearer for the UE and returns network information of a packet data network gateway (PDN GW) allocated for the UE to the UE, and the UE receives the network information of the PDN GW and then stores the network information locally;

and the UE carries the network information of the PDN GW to an IP Multimedia Subsystem (IMS) network through Session Initiation Protocol (SIP) signaling, and the IMS network judges the network of the PDN GW according to the network information of the PDN GW.

Further, the UE requests to allocate an IP address to the SAE network while initiating an attach request to the SAE network;

and the SAE network includes the IP address distributed for the UE in an attachment response and sends the IP address to the UE, and the attachment response carries the network information of the PDN GW distributed for the UE.

Further, after receiving the attach request initiated by the UE, a mobility management entity MME of the SAE network initiates a location update request to a home subscriber server HSS of a home network;

the HSS sends the user data of the UE to the MME, and the user data comprises an instruction of how the MME allocates PDN GW for the UE;

and after receiving the user data, the MME allocates a PDN GW of a home network or a PDN GW of a visited network to the UE according to the indication in the user data, and transmits the attached network information of the PDNGW allocated to the UE in an attachment response.

Further, if the UE is not allocated with an IP address in the process of attaching to the SAE network, the UE requests to allocate the IP address for the UE through a Dynamic Host Configuration Protocol (DHCP) mechanism after attaching to the SAE network;

and the SAE network includes the IP address distributed to the UE in a DHCP response and sends the IP address to the UE, and the DHCP response carries the network information of the PDN GW distributed to the UE.

Further, the SIP signaling includes: a registration request initiated by the UE upon registering with the IMS network, or a session invitation request initiated after registering with the IMS network.

Further, the network information of the PDN GW is:

an access point name APN information carrying network identification information, the information includes operator identification OI, namely network number, country number; or,

an independent PDN network identification number, wherein the PDN network identification number is a PDNGW network identification number distributed for the UE; or,

identification information indicating whether the PDN GW allocated for the UE belongs to the home network or the visited network.

Further, the IMS network determines, according to the belonging network information, a belonging network of the PDN GW in the following manner:

if the network information is the APN information carrying the network identification information, judging whether the PDN GW belongs to a home network or a visited network according to whether the network identification information is consistent with the home network number of the UE;

if the network information is a network identification number of the independent PDN, judging whether the PDN GW belongs to a home network or a visited network according to whether the network identification number is consistent with a home network number of the UE;

and if the information of the network belongs to one piece of identification information, directly judging whether the PDN GW belongs to a home network or a visited network according to the identification information.

Further, the IMS network determines the current media routing mode of the UE according to the network to which the PDN GW belongs, and if the PDN GW belongs to a visited network, determines that the current media routing mode of the UE is a visited network local transfer-out mode.

Further, after receiving a registration request or a session invitation request initiated by the UE and carrying the belonging network information of the PDN GW, a proxy call session control function P-CSCF, a serving call session control function S-CSCF, and an application server AS in the IMS network store the carrying belonging network information of the PDN GW.

Further, the SAE network is located in a visited network or a home network.

The method provided by the invention can solve the problem that when the IMS needs to decide that the media route is converted from the local exit mode of the visited network to the home network route mode, the basic basis for judging whether the current UE is in the LBO mode is lacked, so that the decision cannot be normally carried out.

Drawings

Fig. 1 is a schematic diagram of an architecture of a UE accessing to a home network IMS domain through an SAE access network in a roaming scenario in the prior art;

FIG. 2 is a schematic diagram of a prior art architecture for implementing LBO mode by using a single IP;

FIG. 3 illustrates a procedure of a UE accessing an SAE network, performing network attachment and IP bearer establishment in the prior art;

fig. 4 shows a procedure of a UE accessing an SAE network and the network returning belonging network information of a PDN GW allocated for the UE according to an embodiment of the present invention;

fig. 5 shows a process in which a UE learns the network information of a pdn gw allocated for the UE using a DHCP mechanism according to an embodiment of the present invention;

fig. 6 shows a procedure of registering a UE to an IMS network and carrying belonging network information of a pdn gw allocated to the UE to the IMS network according to an embodiment of the present invention.

Detailed Description

The invention provides a method for realizing UE accessing SAE network under roaming condition, IMS service layer (P-CSCF/S-CSCF/AS, etc.) knows the network of PDN GW allocated for UE, which mainly comprises the following steps:

(1) in a roaming scene, UE is attached to a visiting network SAE network, the SAE network establishes an IP bearer for the UE and returns the belonging network information of PDN GW allocated for the UE to the UE, namely whether the PDN GW belongs to a home network or a visiting network, and the UE stores the belonging network information in the local after receiving the belonging network information;

(2) and the UE carries the belonged network information to an IMS network through SIP signaling, and the IMS network judges whether the PDN GW belongs to a visiting network or not according to the belonged network information.

And if the current media routing mode of the UE is yes, judging that the current media routing mode of the UE is a local transfer-out mode of the visited network.

Further, the SIP signaling may include: a registration request initiated by the UE upon registration to the IMS network, or a session invite request initiated after registration to the IMS network.

Further, the SAE network may return the belonging network information of the PDN GW allocated for the UE to the UE through an attach response message or a DHCP response message.

Fig. 4 is a process of an embodiment of the present invention, which is used to describe a process of a UE accessing an SAE network and acquiring a network to which a PDN GW is allocated in a roaming scenario. Steps S401 to S411 and steps S414 to S418 of the process are the same as the conventional processes described in steps S301 to S311 and steps S314 to S318 of fig. 3, respectively, and are not repeated here. The main difference from the existing flow described in fig. 3 is that steps S412, S413:

s412, the MME sends an attach response to the eNodeB, where the response includes the network information of the PDN GW allocated for the UE, that is, to which network the PDN GW specifically belongs;

the network information of the PDN GW allocated to the UE may be expressed in a variety of ways as follows:

(A) an APN message carrying network identification information, which contains the Operator Identity (OI), i.e. the network number, the country number, forming a complete description of APN.

(B) And the network identification number of the independent PDN is the network identification number of the PDN GW allocated to the UE, wherein the network identification number and the country number of the PDN network are included, and the format is shown as' MNC.

(C) An identification information which indicates explicitly whether the PDN GW allocated for the UE belongs to the home network or the visited network.

S413, the eNodeB sends a voice bearer establishment request to the UE, wherein the request carries IP address information of the UE and network information of PDN GW allocated to the UE; and after receiving the IP address information distributed by the network and the network information of the PDN GW from the eNodeB, the UE stores the information locally.

If the UE receives APN information carrying network identification information or a network identification number of an independent PDN, the UE can compare the APN information with a network number of a home network of the UE and identify whether the PDN GW is located in the home network or a visited network by judging whether the APN information is consistent with the network number of the home network of the UE. I.e. if the two are identical, the PDN GW is located in the home network, otherwise in the visited network.

It is possible that the UE is not allocated an IP address when attaching to the SAE network, but requests the SAE network to allocate an IP address to it through a DHCP (Dynamic Host Configuration Protocol) mechanism in a subsequent procedure. In this case, the same method may also be adopted, and the DHCP response message not only carries the IP address of the UE, but also further carries the network information of the PDN GW allocated to the UE, so as to identify the network to which the PDN GW specifically belongs.

Fig. 5 describes a procedure in which the UE obtains an IP address using a DHCP mechanism, in which the network returns the belonging network attributes of the PDN GW to the UE through a DHCP response. In this procedure, the UE is not assigned an IP address in the process of initial attachment to the SAE network, but the network returns to the UE the address of the DHCP server that can assign an IP address in the attach response, which is assumed by the PDN GW in this procedure.

S501, UE sends a DHCP request to a network, the network is required to distribute an IP address for the DHCP request, and the DHCP request is firstly sent to eNodeB/MME;

s502, eNodeB/MME transmits DHCP request to PDN GW, PDN GW takes the role of DHCP server, and IP address is distributed for UE;

s503, the PDN GW allocates an IP address for the UE, returns a DHCP response, and stores the IP address allocated for the UE in the response. Meanwhile, the PDN GW includes the network information to which the PDN GW belongs in the DHCP response, where the network information to which the PDN GW belongs can be identified, and the identification method is as described in fig. 4;

s504, eNodeB/MME forwards DHCP response to UE, if MME finds that PDN GW does not contain the network information of PDN GW in DHCP response, then the information can be added in DHCP response.

Fig. 6 illustrates that after the UE is assigned an IP address, an IMS registration procedure is performed, and through the registration procedure, the IMS service layer (P-CSCF, S-CSCF, HSS, AS) is notified of the network information of the PDN GW allocated to the UE, and the IMS service layer can determine whether the UE is currently in the LBO mode according to the network information of the PDN GW.

S601, UE sends register request to P-CSCF, in the request, UE carries the network information of PDN GW.

S602, after receiving a registration request of UE, storing the information of the UE and the network information of a PDN GW allocated to the UE locally, the P-CSCF searches the S-CSCF allocated to the UE through the I-CSCF and sends the registration request to the S-CSCF, wherein the registration request carries the network information of the PDN GW allocated to the UE;

s603, after receiving a registration request of the UE, locally storing information of the UE and affiliated network information of a PDN GW allocated to the UE, the S-CSCF sends a user authentication request to an HSS, and optionally, the user authentication request carries the affiliated network information of the PDN GW allocated to the UE;

s604, HSS returns user authentication response to S-CSCF, the message includes UE authentication and authentication data, namely authentication vector;

s605, the S-CSCF stores the authentication vector, constructs the authentication parameter by using the authentication vector, and initiates an authentication challenge to the UE;

s606, UE calculates authentication vector and returns authentication response to S-CSCF;

s607-609, the S-CSCF completes the authentication and authorization of the UE, and searches the user data from the HSS;

s610-611, if a third party registration is to be executed, the S-CSCF initiates a registration request to a third party AS, and the registration request carries the network information of the PDNGW allocated for the UE; the third party AS completes the registration of the UE;

s612, the registration process is successful, and the S-CSCF sends a registration success response of 200OK to the UE.

In the flow shown in fig. 6, through steps S601, S602, and S610, the UE may transmit the belonging network information of the PDN GW allocated to the UE to network elements such AS a P-CSCF, an S-CSCF, and an AS through SIP signaling, and these network elements may store the belonging network information locally. If the network information of the PDN GW is an APN carrying network identification information or an independent PDN identification number, the P-CSCF/S-CSCF/AS can extract the network number therein and compare the network number with the network number of the home network of the UE, and whether the PDN GW allocated to the UE is located in the home network or the visited network can be analyzed by judging whether the network number is consistent with the network number of the home network of the UE, so that whether the UE is currently in the LBO mode can be known. In addition, if the S-CSCF obtains the information, it may also notify the HSS through the IMS registration procedure, AS described in step S603, and after obtaining the information, the HSS may save it AS a part of the user data and may subsequently provide it to the required application server AS.

The method for carrying the network information of the PDN GW allocated for the UE in the SIP signaling may adopt the following method:

(a) additional subfields are used in the field "P-Access-Network-Info" (Access Network Info field).

(b) An additional subfield is used in the field "Contact" (Contact address field of the UE).

Of course, the method for carrying the network information of the PDN GW allocated for the UE in the SIP signaling may also be represented by using another field.

After the above-mentioned procedure is executed, the IMS service layer can obtain the network information of the PDN GW allocated to the UE, so as to know whether the UE is currently located in the LBO mode.

It should be noted that, although the above-mentioned embodiment of the present invention is directed to the case where the UE roams to the visited place, the method described in the present invention can also be applied to the case where the UE is in the home network, without causing the error of the service logic.

For example, the UE does not inform the IMS service layer of the network information of the PDN GW allocated to the UE through the IMS registration process, but carries the network information through an SIP signaling such as an INVITE request initiated during a call, for example, the SIP header information or SDP (Session Description Protocol) information used for describing a media negotiation format therein, and the basic principle of the present invention is the same as that of the IMS registration process.

Claims

1. A method for knowing a network to which a PDN GW allocated for a UE belongs by an IMS (IP multimedia subsystem), is characterized by comprising the following steps:

2. The method of claim 1,

the UE requests to allocate an IP address for the SAE network when initiating an attachment request to the SAE network;

3. The method of claim 2,

after receiving the attachment request initiated by the UE, a mobile management entity MME of the SAE network initiates a location update request to a home subscriber server HSS of a home network;

4. The method of claim 3,

if the UE is not allocated with an IP address in the process of attaching to the SAE network, the UE requests to allocate the IP address for the UE through a Dynamic Host Configuration Protocol (DHCP) mechanism after attaching to the SAE network;

5. The method according to any one of claims 1 to 4,

the SIP signaling comprises: a registration request initiated by the UE upon registering with the IMS network, or a session invitation request initiated after registering with the IMS network.

6. The method of claim 5,

the network information of the PDN GW is as follows:

7. The method of claim 6,

the IMS network judges the network of the PDN GW according to the network information in the following modes:

8. The method of claim 1 or 7,

and the IMS network judges the current media routing mode of the UE according to the network to which the PDN GW belongs, and if the PDN GW belongs to a visited network, the current media routing mode of the UE is judged to be a visited network local transfer-out mode.

9. The method of claim 5,

and after receiving a registration request or a session invitation request which is initiated by the UE and carries the affiliated network information of the PDNGW, a proxy call session control function (P-CSCF), a service call session control function (S-CSCF) and an Application Server (AS) in the IMS network respectively store the affiliated network information of the PDN GW carried in the registration request or the session invitation request.

10. The method of claim 1,

the SAE network is located in a visited network or a home network.