Method and system for maintaining session continuity

• US 20080032695A1
• Filed: 01/03/2007
• Published: 02/07/2008
• Est. Priority Date: 12/17/2004
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: Li, Hui, Zhang, Baofeng, Zhu, Dongming, Huang, Shibi, Gu, Jiongjiong
• Granted Patent: US 8,625,527 B2
• Time in Patent Office: Days
• US Class Current: 455/442
• CPC Class Codes: H04L 65/1016 IP multimedia subsystem [IMS]
• CPC Class Codes: H04L 65/1083 In-session procedures
• CPC Class Codes: H04L 65/1094 Inter-user-equipment sessions transfer or sharing
• CPC Class Codes: H04L 65/1095 Inter-network session transfer or sharing
• CPC Class Codes: H04W 36/0022 for transferring data sessions between adjacent core network technologies
• CPC Class Codes: H04W 36/00226 wherein the core network technologies comprise IP multimedia system [IMS], e.g. single radio voice call continuity [SRVCC]
• CPC Class Codes: H04W 92/02 Inter-networking arrangements
• CPC Class Codes: H04W 92/22 between access point controllers

Abstract

A method and a system for maintaining session continuity, in which the system includes: a Handover Source Function (HOSF), a Handover Destination Function (HODF), a Handover Anchor Function-Control Plane (HOAF-CP) and a Handover Anchor Function-User Plane (HOAF-UP). The method includes: a first user establishing a connection through the HOSF with the HOAF-CP and the HOAF-UP which correspond to a second user, so as to establishing a session with the second user; during session handover, the HODF that corresponds to the HOSF establishing another connection with the HOAF-CP and HOAF-UP though which the first user continues the session with the second user, so as to maintain the session continuity. When the access address or the access means of the terminal changes, or even the terminal changes during a session, embodiments of the present invention can logically replace the connection before the handover with a new connection to ensure the session continuity.

Claims

1. A method for maintaining session continuity, wherein there exists a correlated relationship between a Handover Source Function (HOSF) and a Handover Destination Function (HODF) of a first user, comprising:

Step A;

the first user establishing a session with a second user via a first connection through the HOSF, comprising a control plane first connection with a Handover Anchor Function-Control Plane (HOAF-CP) and a user plane first connection with a Handover Anchor Function-User Plane (HOAF-UP);

Step B;

when it is detected that a handover condition is satisfied, the HODF that corresponds to the HOSF establishing a second connection, comprising a control plane second connection and a user plane second connection, respectively with the HOAF-CP and the HOAD-UP;

Step C;

the first user continuing the session with the second user through the second connection.

2. The method according to claim 1, further comprising:

configuring a Handover Control Function (HOCF) on a home network side of the first user;

the first connection and the second connection are established under the control of the HOCF triggered in the home network side of the first user.

3. The method according to claim 1, wherein, the HOSF and the HODF are located in the same terminal or different terminals of the first user, the HOAF-CP and HOAF-UP reside in the terminal side of the second user, the first connection and the second connection are end-to-end connections;

and

the session between the first user and the second user is born by the end-to-end first and second connections.

4. The method according to claim 1, wherein the HOSF and the HODF are located in the same terminal or different terminals of the first user, the HOAF-CP is located on the home network side of the first user, and the HOAF-UP is located on the terminal side of the second user, the method further comprising:

triggering the HOAF-CP on the home network side of the first user, and establishing a control plane connection between the HOAF-CP and the terminal side of the second user;

then the session between the first user and the second user being born by segmented connections on the control plane, wherein, one segment is the first connection between the HOSF of the first user and the HOAF-CP or the second connection between the HODF of the first user and the HOAF-CP, and the other segment is the connection between the HOAF-CP and the terminal side of the second user; and

Step C comprises;

the HOAF-CP indicating to replace the first connection established in Step A with the second connection established in Step B, and still using the connection on the control plane between the HOAF-CP and the terminal side of the second user, to implement the continuity of the session between the first user and the second user.

5. The method according to claim 1, wherein the HOSF and HODF are located in the same terminal or different terminals of the first user, the HOAF-CP and HOAF-UP are located at the home network side of the first user, the HOAF-CP is the control resource of the network side, and the HOAF-CP applies media resource in the network as the HOAF-UP,

the method further comprising:

triggering the HOAF-CP on the home network side of the first user, and establishing a control plane connection between the HOAF-CP and the terminal side of the second user, and a user plane connection between the HOAF-UP and the terminal side of the second user;

then, the session between the first user and the second user being born by segmented connections on both the control plane and the user plane;

wherein on the control plane, one segment is the control plane first connection between the HOSF of the first user and the HOAF-CP or the control plane second connection between the HODF of the first user and the HOAF-CP, the other segment is the control plane connection between the HOAF-CP and the terminal side of the second user;

on the user plane, one segment is the user plane first connection between the HOSF of the first user and the HOAF-UP or the user plane second connection between the HODF of the first user and the HOAF-UP, the other segment is the user plane connection between the HOAF-UP and the terminal side of the second user;

Step C comprises;

the HOAF-CP controlling to replace the first connection established in Step A with the second connection established in Step B, and reuse both the connection on the control plane between the HOAF-CP and the terminal side of the second user and the user plane connection between the HOAF-UP and the terminal side of the second user, to implement the continuity of the session between the first user and the second user.

6. The method according to claim 1, wherein, Step B comprises:

if it is the HOSF that detects the handover condition is satisfied in Step B, the HOSF directly sending a handover indication message to the HODF, and the HODF initiating to establish the second connection;

or the HOSF sending the handover indication message to the HOAF-CP, and the HOAF-CP initiating to establish the second connection;

or

if it is the HODF that detects the handover condition is satisfied in Step B, the HODF directly initiating to establish the second connection.

7. The method according to claim 1, wherein an HOCF is further configured on the home network side of the first user, and Step B comprises:

if it is the HOSF that detects the handover condition is satisfied,

the HOSF sending a handover request to the HOCF, the HOCF performing an authorization and notifying the HOSF after the authorization succeeds;

after receiving an authorization pass message from the HOCF, the HOSF sending a handover indication message to the HODF or the HOAF-CP, the second connection is initiated to establish by the HODF or the HOAF-CP which receives the handover indication message;

or, the HOSF sending a handover request to the HOCF, the HOCF performing an authorization and sending a handover indication message to the HODF or the HOAF-CP if the authorization succeeds, the second connection is initiated to establish by the HODF or the HOAF-CP which receives the handover indication message.

8. The method according to claim 1, wherein an HOCF is further configured on the home network side of the first user, and Step B comprises:

if it is the HODF detects that the handover condition is satisfied, the HODF sending a handover request to the HOCF, the HOCF performing an authorization and if the authorization succeeds, the HOCF directly sending a handover indication message to the HODF or the HOAF-CP, or the HOCF sending the handover indication message to the HOSF and the HOSF sending the handover indication message to the HODF or the HOAF-CP;

the second connection is initiated to establish by the HODF or the HOAF-CP which receives the handover indication message.

9. The method according to claim 1, wherein an HOCF is further configured on the home network side of the first user, and Step B comprises:

if it is the HOCF that detects the handover condition is satisfied, after detecting that a handover is needed, the HOCF directly sending a handover indication message to the HODF or the HOAF-CP, or sending a handover indication message to the HOSF and the HOSF sending the handover indication message to the HODF or the HOAF-CP, the second connection is initiated to establish by the HODF or the HOAF-CP which receives the handover indication message.

10. The method according to claim 6, wherein, the step of the HOSF detecting that the handover condition is satisfied comprises:

the HOSF detecting that it will lose the access to the network, or detecting that the HODF has successfully accessed the network, or detecting that the handover condition pre-configured by the user is satisfied, or detecting a handover operation indication from the user, or detecting that the communication quality by using the HODF is higher than that by using the HOSF, or detecting that the priority of the operator of the network which the HODF currently access is higher than that of the operator of the network which the HOSF currently access, or detecting that the charging rate of the communication by using the HODF is lower than that of by using the HOSF, or any combination of the above.

11. The method according to claim 8, wherein, the step of the HODF detecting that the handover condition is satisfied comprises:

the HODF judging that it has successfully accessed the network, or detecting that the HOSF will lose the access to the network, or detecting that the handover condition pre-configured by the user is satisfied, or detecting a handover operation indication from the user, or detecting that the communication quality by using the HODF is higher than that by using the HOSF, or detecting that the priority of the operator of the network which the HODF currently access is higher than that of the operator of the network which the HOSF currently access, or detecting that the charging rate of the communication by using the HODF is lower than that by using the HOSF, or any combination of the above.

12. The method according to claim 9, wherein, the step of the HOCF detecting that the handover condition is satisfied comprises:

the HOCF receiving a notification from the HOSF indicating that the HOSF will lose the access to the network, or receiving an access success notification from the HODF, or detecting that the handover condition pre-configured by the user is satisfied, or receiving a handover operation indication from the user, or determining that the communication quality by using the HODF is higher than that by using the HOSF, or determining that the priority of the operator of the network which the HODF currently access is higher than that of the operator of the network which the HOSF currently access, or determining that the charging rate of the communication by using the HODF is lower than that by using the HOSF, or any combination of the above.

13. The method according to claim 7, wherein, the HOCF performs the authorization based on the following conditions:

the HOCF determines whether the HODF is a legal user of the network; and

/or whether the user of the HODF subscribes for the capability to perform the session handover; and

/or whether the HOSF is associated with the HODF; and

/or whether the handover request complies with pre-configured policies of the user; and

/or whether the handover request complies with pre-configured policies of the network; and

/or whether the current state and attribute of the session between HOSF and the HOAF are suitable for the handover.

14. The method according to claim 6, wherein, if the HOSF and the HODF are co-located in the same equipment, they perform message interactions through internal self-defined means;

if the HOSF and the HODF are located in different physical equipment, they perform message interactions through a Session Initial Protocol (SIP) or a Service Location Protocol (SLP);

and/or, the HOSF communicates with the HOAF-CP through the SIP.

15. The method according to claim 14, wherein, when the SIP is adopted by the entities to communicate with each other, a SIP REFER message, or a SIP INFO message, or a SIP NOTIFY message is adopted to send the handover indication, and/or a SIP INFO message or a SIP NOTIFY message is adopted for a notification or a request of a handover-related event.

16. The method according to claim 7, wherein, if the HOSF and the HODF, or the HOCF and the HOAF-CP, are co-located in the same equipment, they perform message interactions through internal self-defined means;

if the HOSF and the HODF, or the HOCF and the HOAF-CP, are located in different physical equipment, they perform message interactions through a Session Initial Protocol (SIP) or a Service Location Protocol (SLP);

and/or, the HOSF communicates with the HOCF or the HOAF-CP through the SIP;

and/or, the HODF communicates with the HOCF through the SIP.

17. The method according to claim 1, wherein, the connections are established through a Circuit Switched (CS) domain, an interworking gateway between the CS domain and the network that supports multiple access technologies, and the network that supports multiple access technologies;

or through the network that supports multiple access technologies;

or through the CS domain and the network that supports multiple access technologies by an Combining CS and IP Multimedia Subsystem (IMS) Services (CSI) means;

the network that supports multiple access technologies is an IMS network, or an Next Generation Network (NGN);

the CS domain is a CS domain in a 2G or 3G network.

18. The method according to claim 1, wherein, the second connection is initiated to establish by the HODF, and Step B comprises:

Step B11;

the HODF obtaining session information of the first connection and initiating a connection establishment request to the HOAF-CP, wherein the connection establishment request carries the session information of the first connection and a handover indication;

Step B12;

after receiving the connection establishment request, the HOAF-CP interacting with the HODF to establish a control plane second connection with the HODF, and a user plane second connection between the HODF and the HOAF-UP.

19. The method according to claim 18, further comprising:

before the HOAF-CP interacts with the HODF, the HOAF-CP checking whether the connection establishment request carries a handover indication;

if it carries a handover indication, the HOAF-CP checking whether the connection establishment request is legal according to the session information in the request;

if the connection establishment request is legal, the HOAF-CP executing the step of interacting with the HODF to establish the second connection, if the connection establishment request is illegal, the HOAF-CP sending a message to the HODF to reject the connection establishment request, keeping the session connection with the HOSF, and ending the procedure.

20. The method according to claim 19, wherein, the step of the HOAF-CP checking whether the connection establishment request is legal according to the session information comprises:

the HOAF-CP checking whether the connection between an HOSF and the HOAF-CP indicated by the session information is identical with the session between the HOSF and the HOAF-CP;

if they are identical, the connection establishment request is legal, otherwise, the connection establishment request is illegal.

21. The method according to claim 18, wherein, the handover indication in Step B11 is represented by a REPLACES header filed, which carries the session information at the same time, or represented by an address pre-configured as a destination address of the connection establishment request.

22. The method according to claim 18, wherein, the connection establishment request is transmitted through the IMS network or the NGN from the HODF to the HOAF-CP, and during the transmission;

the method further comprises;

network entities in the IMS network or the NGN do not trigger any Application Server (AS) in the network during the establishment of the second connection by performing conditional configurations towards the handover indication in the user subscription data, and/or providing the handover indication to a charging system in the network to indicate whether the connection is the second connection in the session handover and so as to perform charging reduction.

23. The method according to claim 18, wherein, if the connection establishment request carries a handover indication, a ringing system of the User Equipment of the second user (second UE) is not triggered.

24. The method according to claim 18, further comprising:

before Step B11, the HODF acquiring a location identifier pointing to the HOAF-CP, and the connection establishment request being initiated according to the location identifier pointing to the HOAF-CP;

the location identifier pointing to the HOAF-CP being obtained by the HOSF during the establishment of the first connection and offered to the HODF by the HOSF;

or, an HOCF being further configured on the home network side of the first user, the location identifier pointing to the HOAF-CP being obtained by the HOCF during the control of the establishment of the first connection and offered to the HODF by the HOCF;

or, when the HOAF-CP is located on the home network side of the first user, the location identifier pointing to the HOAF-CP is obtained by the HODF according to an advance configuration of its own, wherein the advance configuration can be manually configured by the user, or configured and provided by the network, and stored by the HODF.

25. The method according to claim 18, wherein, the session information of the first connection obtained by the HODF in Step B 11 is obtained by the HOSF during the establishment of the first connection and offered to the HODF by the HOSF;

or, an HOCF is further configured on the home network side of the first user, the session information of the first connection is obtained by the HOCF during the control of the establishment of the first connection and offered to the HODF by the HOCF.

26. The method according to claim 18, wherein, if the HODF is in the CS domain, and the HOAF-CP is in the IMS domain, the step of initiating a connection establishment request to the HOAF-CP comprises:

Step B21;

the HODF initiating in the CS domain a CS call establishment request carrying a called party number which can be a Mobile Station Integrated Service Digital Network (MSISDN) number of the second user, or an E.164 number in a Public User Identity of the second user in a Tel-Uniform Resource Identifier (Tel-URI) format, or an MSISDN number with a special prefix or an E.164 number with a special prefix, or a special E.164 number composed according to the location identifier pointing to the HOAF-CP which is obtained by the HODF in advance;

then the CS domain sending the CS call establishment request to the interworking gateway between the CS domain and the network that supports multiple access technologies;

Step B22;

after receiving the call establishment request, the interworking gateway between the CS domain and the network that supports multiple access technologies converting the CS call establishment request into an IMS session establishment request, and forwarding the IMS session establishment request to the HOAF-CP.

27. The method according to claim 26, further comprising:

if the called party number is an MSISDN number with a special prefix or an E.164 number with a special prefix, or a special E.164 number, the interworking gateway comparing the special E.164 number or the prefix of the E.164 number or the MSISDN number according to local special number configuration data;

if they match, carrying a handover indication in the converted IMS session establishment request.

28. The method according to claim 26, wherein, when the HOAF-CP is located on the home network side of the first user and the called party number in Step B21 is a special E.164 number, the E.164 number is corresponding to a Public Service Identifier (PSI), and

the step of the interworking gateway converting the CS call establishment request into an IMS session establishment request and sending the converted IMS session establishment request to the HOAF-CP comprises:

converting the special E.164 number into a PSI, and sending the converted IMS session establishment request to the HOAF-CP in the IMS network according to an existing routing method for the PSI in the IMS network.

29. The method according to claim 26, wherein

in Step B21, the called number further comprises the session information of the first connection;

after the interworking gateway receives the CS call establishment request from the HODF, the method further comprises;

the interworking gateway treating appointed digits of the prefix of the E.164 number as a corresponding service prefix according to a network numbering plan, restoring the location identifier pointing to the HOAF-CP according to configuration data in the interworking gateway, acquiring the session information of the first connection from appointed digits of the rear part of the E.164 number and sending the session information to the HOAF-CP through the converted IMS session establishment request;

or, the interworking gateway converting the special E.164 number into a uniform location identifier in a telephone number format and sending the converted IMS session establishment request to the HOAF-CP in the IMS network according to an existing routing method for the PSI in the IMS network; and

, the HOAF-CP regarding the uniform location identifier as a special PSI corresponding to a wildcard PSI and obtaining the session information of the first connection from the special PSI according to the wildcard PSI.

30. The method according to claim 26, wherein the session information of the first connection is carried by an ISDN User Part (ISUP) special Information Element (IE) in the CS call establishment request in Step B21, the ISUP special IE can be a user-to-user information IE, a call reference number IE or a sub-address IE;

in Step B22, after the interworking gateway receives the CS call establishment request from the HODF, the method further comprises;

analyzing the ISUP special IE to obtain the session information of the first connection, and sending the session information of the first connection to the HOAF-CP through the converted IMS session establishment request.

31. The method according to claim 1, wherein, the second connection is initiated by the HOAF-CP, and Step B comprises:

Step B31;

the HOAF-CP obtaining a location identifier pointing to the HODF, and initiating a connection establishment request to the HODF according to the location identifier;

Step B32;

after receiving the connection establishment request, the HODF interacting with the HOAF-CP to establish the control plane connection with the HOAF-CP, and the user plane connection between the HODF and HOAF-UP.

32. The method according to claim 31, wherein

the connection establishment request in Step B31 carries information of the HOSF;

in Step B32, before the HODF interacts with the HOAF-CP, the method further comprises;

the HODF checking whether the connection establishment request carries the information of the HOSF;

if the request carries the information of the HOSF, checking whether the connection establishment request is legal according to the pre-configured association between the HOSF and the HODF, in other words, checking whether there exists a correlated relationship between the HOSF and the HODF;

if there exists, confirming that the connection establishment request is legal and executing subsequent interactions, otherwise, determining that the connection establishment request is illegal, rejecting the request and ending the procedure.

33. The method according to claim 31, wherein, in Step B31, the connection establishment request carries the information of the HOSF or a handover indication;

after receiving the connection establishment request, the HODF does not trigger its own ringing system according to the information of the HOSF or the handover indication carried in the request.

34. The method according to claim 31, wherein the connection establishment request is sent by the HOAF-CP to the HODF through the IMS network or the NGN, and the connection establishment request carries the information of the HOSF or the handover indication, and during the transmission of the connection establishment request through the IMS network or the NGN, the method further comprises:

the network entities in IMS network or NGN not triggering the AS in the network during the establishment of the second connection through conditional configurations in the user subscription data according to the information of the HOSF or the handover indication, and/or providing the handover indication or the information of the HOSF to the charging system in the network to indicate whether the connection is the second connection in the session handover and so as to perform charging reduction.

35. The method according to claim 31, wherein

the HODF identifier in Step B31 is offered to the HOAF-CP by the HOSF;

or, an HOCF is further configured on the home network side of the first user, the HODF identifier is obtained by the HOCF during the control of the establishment of the first connection and offered to the HOAF-CP by the HOCF.

36. The method according to claim 31, wherein, when the HOAF-CP is located in the network that supports multiple access technologies, and the HODF is located in the CS domain, Step B31 comprises:

Step B1001;

the HOAF-CP in the network that supports multiple access technologies sending a session establishment request to the interworking gateway, wherein, the request carries the called party number;

the called party number is an MSISDN number of the first user pointing to the HODF or an MSISDN number with a special prefix;

Step B1002;

after receiving the session establishment request, the interworking gateway converting the session establishment request into a CS call establishment request, and forwarding the converted CS call establishment request to the HODF in the CS domain according to the called party number.

37. The method according to claim 36, wherein, in Step B1001, the called party number is the MSISDN number of the called user with a special prefix;

in Step B1002, after the interworking gateway receiving the session establishment request and before forwarding the converted CS call establishment request to the HODF in the CS domain, the method further comprises;

removing the special prefix from the called party number, and adding a special indication to the converted CS call establishment request.

38. The method according to claims 36, wherein

in Step B1002, after the CS domain receiving the call establishment request, the method further comprises:

the CS domain adding a special identifier in a Call Detailed Record (CDR) according to the special prefix or the special indication, and so as to facilitate a charging center to perform charging on the first user based on specific charging strategies in subsequent steps; and

/or not invoking part of CS supplementary services according to the special prefix or the special indication, wherein the supplementary services are call forwarding and/or call barring and/or intelligent services triggering;

39. The method according to claims 36, wherein, in Step B1002, when receiving the call establishment request, the HODF recognizes that the call is an interworking handover call between the network that supports multiple access technologies and the CS domain according to the special prefix or the special indication, therefore the HODF does not trigger its own ringing system, or controls the UE of the first user (first UE) to pop up a menu or play a special notification ring for the first user.

40. The method according to claim 1, wherein, the network that supports multiple access technologies is an IMS network, the correlated relationship between the HOSF and HODF of the first user comprises:

the HOSF and the HODF are respectively corresponding to different IP Multimedia public identities (IMPUs) of a same IP Multimedia private identity (IMPI) of the first user;

or respectively corresponding to different IMPIs of a same IMPU of the first user;

or respectively corresponding to different IMPUs and IMPIs belonging to a same subscription of the first user in IMS network;

or associated with each other through the first user subscription relationship between different subsystems on the operator layer.

41. The method according to claim 40, wherein, when the HOSF and HODF of the first user correspond respectively to different IMPIs of a same IMPU of the first user,

Step B further comprises:

Step B500;

the home network of the first user receiving a session establishment request to the HOSF of the first user from a third user;

Step B501;

the home network of the first user forking the session establishment request and forwarding the session establishment request respectively to the HOSF and the HODF of the first user;

Step B502;

the HOSF of the first user returning a session reject message to the third user through the home network of the first user;

Step B503;

the HODF of the first user determining whether to accept the session establishment request according to the advance configuration or the user instruction.

42. The method according to claim 40, wherein the HOSF and the HODF of the first user have different IMPUs, and an HOCF is further configured on the home network side of the first user, or the HOAF-CP is located on the home network side of the first user, and

Step B further comprises:

Step B600;

the home network of the first user receiving a session establishment request to the HOSF of the first user from a third user;

Step B601;

the HOCF or the HOAF-CP on the home network side of the first user modifying a destination identifier pointing to the HOSF in the session establishment request to the one pointing to the HODF, then the home network of the first user sending the session establishment request to the HODF;

Step B602;

the HODF determining whether to accept the session establishment request from the third user according to the advance configuration or the user instruction.

43. The method according to claim 4, wherein when an HOCF is further configured on the home network side of the first user, the HOCF and the HOAF-CP, both of which are on the home network side of the first user, are implemented in a same Application Server (AS).

44. The method according to claim 2, wherein,

when the network that supports multiple access technologies is an IMS network, the step of triggering the HOCF on the home network side of the first user comprises:

according to a uniform service triggering procedure of the IMS, a service node Serving-Call Session Control Function (S-CSCF) currently assigned to serve the first user by the home IMS network of the first user triggering the current session to the AS which performs the functions of HOCF based on initial Filter Criteria (iFC) in the user subscription data, and

when the first user that corresponds to the HOSF is a calling party during the establishment of the first connection, the priority level of the iFC corresponding to the AS that performs the functions of the HOCF should be set to be the highest in the subscription data of the first user when it is possible;

when the first user that corresponds to the HOSF is a called party during the establishment of the first connection, the priority level of the iFC corresponding to the AS that performs the functions of the HOCF should be set to be the lowest in the subscription data of the first user when it is possible;

when the network that supports multiple access technologies is an NGN, the step of triggering the HOCF on the home network side of the first user comprises;

triggering a function logic of the HOCF in a soft switching entity which is responsible for providing services of the first user in the NGN;

or

introducing an AS into the NGN, and the soft switching entity which is responsible for providing services for the first user in the NGN triggering the current session to the AS that performs the functions of the HOCF according to the subscription data of the first user.

45. The method according to claims 4, wherein

when the network that supports multiple access technologies is an IMS network, the step of triggering the HOAF-CP on the home network side of the first user includes:

according to a uniform service triggering procedure of the IMS, a service node Serving-Call Session Control Function (S-CSCF) currently assigned to serve the first user by the home IMS network of the first user triggering the current session to the AS which performs the functions of HOAF-CP based on the iFC in the user subscription data, and when the first user that corresponds to the HOSF is a calling party during the establishment of the first connection, the corresponding priority level of the iFC corresponding to the AS that performs the functions of the HOAF-CP should be set to be the highest in the subscription data of the first user when it is possible;

when the first user that corresponds to the HOSF is a called party during the establishment of the first connection, the corresponding priority level of the iFC corresponding to the AS that performs the functions of the HOAF-CP should be set to be the lowest in the subscription data of the first user when it is possible;

when the network that supports multiple access technologies is an NGN, the step of triggering the HOAF-CP on the home network side of the first user comprises;

triggering a function logic of the HOAF-CP in a soft switching entity which is responsible for providing services of the first user in the NGN;

or

introducing an AS into the NGN, and the soft switching entity which is responsible for providing services for the first user in the NGN triggering the current session to the AS that performs the functions of the HOAF-CP according to the subscription data of the first user.

46. The method according to claim 2, further comprising:

when the HOCF is further used for centralized management of handover strategies, the HOCF updating the handover conditions correlated with a UE and pre-stored in the HOCF through signaling interaction between the HOCF and the UE.

47. A system for maintaining session continuity, comprising:

an HOSF, an HODF, an HOAF-CP, an HOAF-UP and a Handover Detection Function;

wherein,

there exists a corresponding relationship between the HOSF and the HODF; and

the HOSF is used for establishing a session control plane first connection with the HOAF-CP and a session user plane first connection with the HOAF-UP when the first user initiates or accepts a session;

the HODF is used for establishing a session control plane second connection with the HOAF-CP and a session user plane second connection with the HOAF-UP when the handover condition is satisfied;

the HOAF-CP is used for establishing the control plane first connection with the HOSF when the first user initiates or accepts a session;

establishing the control plane second connection with the HODF when the handover condition is satisfied;

replacing the control plane first connection with the HOSF with the control plane second connection with the HODF, and indicating the HOAF-UP to replace the user plane first connection between the HOAF-UP and the HOSF with the user plane second connection between the HOAF-UP and the HODF;

the HOAF-UP is used for establishing the user plane first connection with the HOSF when the first user initiates or accepts a session;

establishing the user plane second connection with the HODF when the handover condition is satisfied; and

replacing the user plane first connection with the HOSF with the user plane second connection with the HODF according to the indication of the HOAF-CP;

the Handover Detection Function is used for detecting whether the handover condition is satisfied.

48. The system according to claim 47, further comprising at least an HOCF on the network side, used for forwarding the signal streams between the HOSF or the HODF and the HOAF-CP.

49. The system according to claim 48, wherein, the Handover Detection Function is a logic unit in the HOCF, and the HOCF is further used for sending a handover indication directly to the HODF or the HOAF-CP, or sending a handover indication to the HODF through the HOSF when detecting that the handover condition is satisfied.

50. The system according to claim 47, wherein, the Handover Detection Function is further used for sending a handover indication directly to the HODF or the HOAF-CP, when detecting that the handover condition is satisfied.

51. The system according to claim 48, wherein, the Handover Detection Function is further used for sending a handover request message to the HOCF when detecting that the handover condition is satisfied, and sending a handover indication to the HODF or the HOAF-CP after receiving an authorization pass notification from the HOCF;

and

the HOCF is further used for performing an authorization when receiving a handover request message, and sending an authorization pass notification to the Handover Detection Function after authorization succeeds.

52. The system according to claim 48, wherein, the Handover Detection Function is further used for sending a handover request message to the HOCF when detecting that the handover condition is satisfied;

and

the HOCF is further used for performing an authentication when receiving the handover request message, and sending a handover indication to the HODF or the HOAF-CP after the authentication succeeds.

53. The system according to claim 49, wherein, the HODF is further used for initiating a second connection establishment request to the HOAF-CP after receiving the handover indication.

54. The system according to claim 49, wherein, the HOAF-CP is further used for initiating a second connection establishment request to the HODF after receiving the handover indication.

55. The system according to claim 50, wherein, the Handover Detection Function is a logic unit in the HOSF or the HODF.

56. The system according to claim 47, wherein, the Handover Detection Function is a logic unit in the HODF, the HODF is further used for directly initiating a second connection establishment request to the HOAF-CP when detecting that the handover condition is satisfied.

57. The system according to claim 47, wherein, the HOSF and the HODF are located in a same terminal of the first user or different terminals of the first user, and both the HOAF-CP and the HOAP-UP are located on the terminal side of the second user.

58. The method according to claim 47, wherein, the HOSF and the HODF are located in a same terminal of the first user or different terminals of the first user, the HOAP-CP is located on the home network side of the first user, the HOAF-UP is located on the terminal side of the second user, and the HOAF-CP is the control resource of the network side;

the HOAF-CP is further used for establishing a control plane connection with the terminal side of the second user while establishing the control plane first connection with the HOSF, and performing a correlative control over the control plane first connection with the HOSF, the control plane second connection with the HODF and the control plane connection with the terminal side of the second user, so as to enable the terminal side of the second user to establish an end-to-end media stream exchange with the HOSF and the HODF respectively before and after the handover.

59. The system according to claim 58, wherein,

the correlative control performed by the HOAF-CP comprises:

performing a correlative control over the establishment of the control plane first connection with the HOSF and the control plane connection with the terminal side of the second user, so as to establish an end-to-end media stream exchange between the HOSF and the HOAF-UP on the terminal side of the second user; and

during the establishment of the control plane second connection with the HODF, initiating a re-negotiation on the control plane connection with the terminal side of the second user and accomplishing the re-negotiation by interacting with the terminal side of the second user, changing the media stream originally exchanged between the HOAF-UP and the HOSF into a media stream exchanged between the HOAF-UP and the HODF, and when the media capabilities of the HODF and the HOSF are different from each other, adding/deleting the media stream or modify the attribute of exchanged media stream according to the media capability of the HODF.

60. The system according to claim 47, wherein, the HOSF and the HODF are located in a same terminal or different terminals of the first user, the HOAF-CP and HOAF-UP are located on the home network side of the first user, the HOAF-CP is the control resource of the network side, the HOAF-UP is the media resource of the network side assigned by the HOAF-CP;

the HOAF-CP is further used for establishing a control plane connection with the terminal side of the second user while establishing the control plane first connection with the HOSF; and

performing a correlative control over the control plane first connection with the HOSF, the control plane second connection with the HODF and the control plane connection with the terminal side of the second user, and so as to establish user plane connections with the HOSF, the HODF and the terminal side of the second user respectively, modifying the connection relationships among the above user plane connections, so as to enable the terminal side of the second user to establish segmented media stream exchange respectively with the HOSF and the HODF before and after the handover;

the HOAF-UP is further used for establishing a user plane connection with the terminal side of the second user, and modifying the connection relationships among the user plane connections according to the indication of the HOAF-CP.

61. The system according to claim 60, wherein

the correlative control performed by the HOAF-CP comprises:

performing a correlative control over the establishment of the control plane first connection with the HOSF and the control plane connection with the terminal side of the second user, so as to establishing the user plane first connection between the HOSF and the HOAF-UP and the user plane connection between the HOAF-UP and the terminal side of the second user, and controlling the HOAF-UP to connect the two user plane connections; and

during the establishment of the control plane second connection between the HOAF-CP and the HODF, establishing a user plane second connection between the HOAF-UP and the HODF, controlling the HOAF-UP to change the user plane connection between the HOAF-UP and the terminal side of the second user, which is originally connected with the user plane first connection, into connect with the newly established user plane second connection;

and, when the media capabilities of the HODF and the HOSF are different from each other, during the establishment of the control plane second connection, initiating a re-negotiation on the control plane connection with the terminal side of the second user and accomplishing the re-negotiation by interacting with the terminal side of the second user, adding/deleting the exchanged media stream or modifying the attribute of the exchanged media stream between the HOAF-UP and the terminal side of the second user to fit the media capability of the HODF.

62. The system according to claim 47, wherein, the HOAF-UP is further used for duplicating the media stream to the first UE, sending the duplicated media streams to the HOSF and the HODF simultaneously, and selecting a valid part of the media streams from the HOSF and the HODF to send to the terminal side of the second user or to present to the second user.

63. The system according to claim 47, further comprising an HOCF on the network side, or wherein the HOAF-CP is located on the home network side of the first user, then when receiving a connection establishment request from a third user to the HOSF of the first user, the HOCF or the HOAF-CP delivers the new session from the third user to the HODF of the first user.