Method and system for maintaining session continuity when changes occur at the terminal during a session

• US RE47,858 E1
• Filed: 12/29/2014
• Issued: 02/11/2020
• 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: Zhu, Dongming, Li, Hui, Gu, Jiongjiong, Zhang, Baofeng, Huang, Shibi
• Primary Examiner(s): Ferris, III, Fred O
• Application Number:
  US14/584,662
• Time in Patent Office: 1,870 Days
• Field of Search: 354331, 455436
• CPC Class Codes: N/A

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 establish a session with the second user. The method further includes that, 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 access address or access technology of the terminal changes, or even the terminal changes during a session, the method and the system 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, comprising:

triggering a Handover Anchor Function-Control Plane (HOAF-CP) on a home network side of a first user, and establishing a first connection, wherein the first connection comprises a control plane first connection between a Handover Source Function (HOSF) of the first user and the HOAF-CP and a user plane first connection between the HOSF and a Handover Anchor Function-User Plane (HOAF-UP) of a second user;

establishing a control plane connection between the HOAF-CP and a terminal side of the second user, and establishing a session between the first user and the second user through the user plane first connection, the control plane first connection and the control plane connection between the HOAF-CP and a terminal side of the second user;

determining that a handover condition is satisfied, and establishing a second connection, wherein the second connection comprises a control plane second connection between a Handover Destination Function (HODF) of the first user and the HOAF-CP and a user plane second connection between the HODF and the HOAF-UP; and

continuing the session between the first user and the second user through the user plane second connection between the HODF and the HOAF-UP, the control plane second connection between the HODF and the HOAF-CP, and the control plane connection, which is already established between the HOAF-CP and the terminal side of the second user before the handover condition is satisfied.

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

configuring a Handover Control Function (HOCF) on the home network side of the first user, wherein the first connection and the second connection are established under control of the HOCF.

3. The method according to claim 2, wherein if it is the HOSF that detects the handover condition is satisfied, the method comprising at least one of:

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, and the HODF or the HOAF-CP which receives the handover indication message initiating to establish the second connection;

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, and the HODF or the HOAF-CP which receives the handover indication message initiating to establish the second connection.

4. The method according to claim 2, wherein if it is the HODF that detects that the handover condition is satisfied, the method comprising at least one of:

the HODF sending a handover request to the HOCF, the HOCF performing an authorization and if the authorization succeeds, the HOCF sending a handover indication message to the HODF or the HOAF-CP, and the HODF or the HOAF-CP, which receives the handover indication message, initiating to establish the second connection;

or

the HODF sending a handover request to the HOCF, the HOCF sending a handover indication message to the HOSF and the HOSF sending the handover indication message to the HODF or the HOAF-CP; and

the HODF or the HOAF-CP, which receives the handover indication message, initiating to establish the second connection.

5. The method according to claim 2, wherein if it is the HOCF that detects the handover condition is satisfied, the method comprising at least one of:

the HOCF sending a handover indication message to the HODF or the HOAF-CP, and the HODF or the HOAF-CP, which receives the handover indication message, initiating to establish the second connection;

or

the HOCF sending a handover indication message to the HOSF and the HOSF sending the handover indication message to the HODF or the HOAF-CP, and the HODF or the HOAF-CP, which receives the handover indication message, initiating to establish the second connection.

6. The method according to claim 2, wherein the HOSF and the HODF of the first user have different IP Multimedia public identities (IMPUs), and

the method comprises:

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

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, and then the home network of the first user sending the session establishment request to the HODF;

the HODF determining whether to accept the session establishment request from the third user.

7. The method according to claim 2, wherein the HOCF is implemented in a same Application Server (AS) with the HOAF-CP.

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

the HOCF updating the handover condition correlated with a terminal and pre-stored in the HOCF through signaling interaction between the HOCF and the terminal.

9. The method according to claim 2, wherein the HODF initiates to establish the second connection and the method further comprises:

the HODF acquiring an identifier pointing to the HOAF-CP and initiating a connection establishment request according to the identifier pointing to the HOAF-CP;

wherein the identifier pointing to the HOAF-CP is obtained by the HOSF during the establishment of the first connection and sent to the HODF by the HOSF, or the identifier pointing to the HOAF-CP is obtained by the HOCF during the control of the establishment of the first connection and sent to the HODF by the HOCF.

10. The method according to claim 2, wherein the HODF initiates to establish the second connection and the method further comprises:

the HODF obtaining session information of the first connection and initiating a connection establishment request to the HOAF-CP carrying the session information of the first connection;

wherein the session information of the first connection is obtained by the HOCF during the control of the establishment of the first connection and sent to the HODF by the HOCF.

11. The method according to claim 2, wherein the HOAF-CP initiates to establish the second connection and the method further comprises:

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

wherein the HODF identifier is sent to the HOAF-CP by the HOSF or the HODF identifier is obtained by the HODF during the control of the establishment of the first connection and sent to the HOAF-CP by the HOCF.

12. The method according to claim 1, wherein if it is the HOSF that detects the handover condition is satisfied, the HOSF sending a handover indication message to the HODF, and the HODF initiating to establish the second connection;

or the HOSF sending a 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, the HODF initiating to establish the second connection.

13. The method according to claim 12, wherein if it is the HOSF that detects the handover condition is satisfied, the HOSF detecting that a communication quality by using the HODF is higher than a communication quality by using the HOSF.

14. The method according to claim 1, wherein the step of establishing the second connection comprises:

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;

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

15. The method according to claim 14, further comprising:

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

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

if the connection establishment request is legal, the HOAF-CP executing the step of interacting with the HODF to establish the control plane second connection and the user plane 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 with the HOSF.

16. The method according to claim 14, wherein the handover indication is represented by a REPLACES header field, and the session information is carried by the REPLACES header field;

or, the handover indication is represented by an address pre-configured as a destination address of the connection establishment request.

17. The method according to claim 14, wherein the connection establishment request is transmitted through an IP Multimedia Subsystem (IMS) network or a Next Generation Network (NGN) from the HODF to the HOAF-CP;

the method further comprises;

network entities in the IMS network or the NGN providing the handover indication to a charging system to indicate whether a connection is the second connection to perform charging reduction.

18. The method according to claim 14, wherein the session information of the first connection is obtained by the HOSF during the establishment of the first connection and sent to the HODF by the HOSF;

or,

a Handover Control Function (HOCF) is configured on the home network side of the first user, the session information of the first connection is obtained by the HOCF during the establishment of the first connection and sent to the HODF by the HOCF.

19. The method according to claim 1, wherein the HODF initiates to establish the second connection, the HODF is located in a Circuit Switched (CS) domain, and the HOAF-CP is located in an IP Multimedia Subsystem (IMS) domain, the method comprising:

the HODF initiating in the CS domain a CS call establishment request carrying a called party number; and

the CS domain sending the CS call establishment request to an interworking gateway between the CS domain and the IMS domain;

wherein the called party number is at least one of;

a Mobile Station Integrated Service Digital Network (MSISDN) number of the second user, an E.164 number in a Public User Identity of the second user in a Tel-Uniform Resource Identifier (Tel-URI) format, an MSISDN number with a prefix, an E.164 number with a prefix, and an E.164 number composed according to an identifier pointing to the HOAF-CP obtained by the HODF;

after receiving the CS call establishment request, the interworking gateway between the CS domain and the IMS domain converting the CS call establishment request into an IMS session establishment request, and sending the IMS session establishment request to the HOAF-CP.

20. The method according to claim 1, wherein the HOAF-CP initiates to establish the second connection, and the method comprises:

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

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

21. The method according to claim 20, wherein the connection establishment request is sent by the HOAF-CP to the HODF through an IP Multimedia Subsystem (IMS) network or a Next Generation Network (NGN), and the connection establishment request carries information of the HOSF or a handover indication, the method further comprises:

network entities in the IMS network or the NGN providing the handover indication or the information of the HOSF to a charging system to indicate whether a connection is the second connection to perform charging reduction.

22. The method according to claim 20, wherein

the HODF identifier is sent to the HOAF-CP by the HOSF, or, a Handover Control Function (HOCF) is configured on the home network side of the first user, the HODF identifier is obtained by the HOCF during the establishment of the first connection and sent to the HOAF-CP by the HOCF.

23. The method according to claim 20, wherein the connection establishment request carries information of the HOSF;

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 connection establishment request carries the information of the HOSF, checking whether the connection establishment request is legal according to a pre-configured association between the HOSF and the HODF.

24. The method according to claim 1, wherein the HODF or the HOAF-CP initiates to establish the second connection the method further comprising:

the HOAF-CP sending a session establishment request to an interworking gateway, wherein the session establishment request carries a called party number, and the called party number is a Mobile Station Integrated Service Digital Network (MSISDN) number of the first user pointing to the HODF or a Mobile Station Integrated Service Digital Network (MSISDN) number with a prefix;

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

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

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

after the CS domain receiving the CS call establishment request, the CS domain adding an identifier in a Call Detailed Record (CDR) according to the prefix or an indication carried in the CS call establishment request.

26. The method according to claim 1, wherein 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 an IMS network;

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

27. The method according to claim 1, wherein the HODF initiates to establish the second connection and the method comprises:

the HODF obtaining an identifier pointing to the HOAF-CP and initiating a connection establishment request according to the identifier pointing to the HOAF-CP, wherein the identifier pointing to the HOAF-CP is obtained by the HOSF during the establishment of the first connection and sent to the HODF by the HOSF, or the identifier pointing to the HOAF-CP is obtained by the HODF according to an advance configuration of the HODF.

28. The method according to claim 1, wherein the HOSF and the HODF of the first user have different IP Multimedia public identities (IMPUs), and

the method comprises:

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

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, and then the home network of the first user sending the session establishment request to the HODF; and

the HODF determining whether to accept the session establishment request from the third user.

29. A system for maintaining session continuity, comprising:

a Handover Source Function (HOSF), a Handover Destination Function (HODF), a Handover Anchor Function-Control Plane (HOAF-CP), a Handover Anchor Function-User Plane (HOAF-UP) and a Handover Detection Function;

wherein the HOSF and the HODF are located in a same terminal of a first user or different terminals of the first user, the HOAF-CP is located on a home network side of the first user, the HOAF-UP is located on a terminal side of a second user, and the HOAF-CP is a control resource;

the HOSF is configured to establish a first connection comprising a control plane first connection between the HOSF and the HOAF-CP and a user plane first connection between the HOSF and the HOAF-UP when the first user initiates or accepts a session;

the HODF is configured to establish a second connection comprising a control plane second connection between the HODF and the HOAF-CP and a user plane second connection between the HODF and the HOAF-UP when a handover condition is satisfied;

the HOAF-CP is configured to establish the control plane first connection between the HOSF and the HOAF-CP when the first user initiates or accepts the session;

establish a control plane connection between the terminal side of the second user and the HOAF-CP;

establish the control plane second connection between the HODF and the HOAF-CP when the handover condition is satisfied;

the HOAF-CP is further configured to perform control over the control plane first connection, the control plane second connection and the control plane connection with the terminal side of the second user, and replace the control plane first connection between the HOSF and the HOAF-CP with the control plane second connection between the HODF and the HOAF-CP;

the HOAF-UP is configured to establish the user plane first connection between the HOSF and the HOAF-UP during the establishment of the control plan plane first connection and the control plane connection between the HOAF-CP and the terminal side of the second user;

establish the user plane second connection between the HODF and the HOAF-UP during the establishment of the control plan plane second connection; and

replace the user plane first connection with the user plane second connection; and

the Handover Detection Function is configured to detect whether the handover condition is satisfied.

30. The system according to claim 29, wherein the HOAF-CP is configured to perform control over the establishment of the control plane first connection and the control plane connection between the HOAF-CP and the terminal side of the second user, control to establish the user plane first connection 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, initiate a re-negotiation on the control plane connection between the HOAF-CP and the terminal side of the second user and accomplishing the re-negotiation by interacting with the terminal side of the second user, control to establish the user plane second connection between the HODF and the HOAF-UP and indicating the HOAF-UP to replace the user plane first connection with the user plane second connection, and when media capabilities of the HODF and the HOSF are different from each other, add or delete media stream or modify attribute of exchanged media stream according to the media capability of the HODF.

31. The system according to claim 29, further comprising:

an HOCF on the home network side of the first user, configured to control the establishments of the first connection and the second connection by sending signal streams between the HOSF and the HOAF-CP, or between the HODF and the HOAF-CP.

32. The system according to claim 31, wherein the Handover Detection Function is a logic unit in the HOCF, and the HOCF is further configured to send to the HODF or the HOAF-CP, or send a handover indication to the HODF through the HOSF when detecting that the handover condition is satisfied.

33. The system according to claim 31, wherein the Handover Detection Function is further configured to send a handover request message to the HOCF when detecting that the handover condition is satisfied, and send a handover indication to the HODF or the HOAF-CP after receiving an authorization pass notification from the HOCF;

and

the HOCF is further configured to perform an authorization when receiving the handover request message, and send the authorization pass notification to the Handover Detection Function after authorization succeeds.

34. The system according to claim 32, wherein the HODF is further configured to initiate a second connection establishment request to the HOAF-CP after receiving the handover indication.

35. The system according to claim 32, wherein the HOAF-CP is further configured to initiate a second connection establishment request to the HODF after receiving the handover indication.

36. The system according to claim 29, wherein the Handover Detection Function is further configured to send a handover indication to the HODF or the HOAF-CP when detecting that the handover condition is satisfied.

37. The system according to claim 29, wherein the Handover Detection Function is a logic unit in the HODF, the HODF is further configured to initiate a second connection establishment request to the HOAF-CP when-the handover condition is satisfied.

38. The system according to claim 29, wherein when receiving a connection establishment request from a third user to the HOSF of the first user, the HOCF or the HOAF-CP located on the home network side of the first user is configured to send a new session from the third user to the HODF of the first user.

39. A system for maintaining session continuity, comprising:

a handover Source Function (HOSF), a Handover Destination Function (HODF), a Handover Anchor Function-Control Plane (HOAF-CP), a Handover Anchor Function-User Plane (HOAF-UP) and a Handover Detection Function;

wherein the HOSF and the HODF are located in a same terminal or different terminals of a first user, the HOAF-CP and HOAF-UP are located on a home network side of the first user, the HOAF-CP is control resource, the HOAF-UP is media resource;

the HOSF is configured to establish a first connection comprising a control plane first connection between the HOSF and the HOAF-CP and a user plane first connection between the HOSF and the HOAF-UP when the first user initiates or accepts a session;

the HODF is configured to establish a second connection comprising a control plane second connection between the HODF and the HOAF-CP and a user plane second connection between the HODF and the HOAF-UP when a handover condition is satisfied;

the HOAF-CP is configured to establish the control plane first connection between the HOSF and the HOAF-CP when the first user initiates or accepts the session;

establish a control plane connection between a terminal side of a second user and the HOAF-CP;

establish the control plane second connection between the HODF and the HOAF-CP when the handover condition is satisfied;

the HOAF-CP is further configured to perform control over the control plane first connection, the control plane second connection and the control plane connection between the terminal side of the second user and the HOAF-CP, replace the control plane first connection between the HOSF and the HOAF-CP with the control plane second connection between the HODF and the HOAF-CP;

the HOAF-UP is configured to establish the user plane first connection between the HOSF and the HOAF-UP;

establish a user plane connection between the terminal side of the second user and the HOAF-UP, and connect the user plane connection between the HOAF-UP and the terminal side of the second user with the user plane first connection;

establish the user plane second connection between the HODF and the HOAF-UP; and

connect the user plane connection between the HOAF-UP and the terminal side of the second user with the user plane second connection instead of the user plane first connection; and

the Handover Detection Function is configured to detect whether the handover condition is satisfied.

40. The system according to claim 39, wherein the HOAF-CP is configured to:

perform control over the establishments of the control plane first connection and the control plane connection between the terminal side of the second user and the HOAF-CP, control to establish the user plane first connection between the HOAF-UP and the HOSF and the user plane connection between the terminal side of the second user and the HOAF-UP, and control the HOAF-UP to connect the user plane first connection and the user plane second connection; and

during the establishment of the control plane second connection between the HOAF-CP and the HODF, control to establish the user plane second connection between the HOAF-UP and the HODF, control the HOAF-UP to connect the user plane connection between the HOAF-UP and the terminal side of the second user, with the user plane second connection instead of the user plane first connection, and

when media capabilities of the HODF and the HOSF are different from each other, during the establishment of the control plane second connection, initiate 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, add or delete media stream or modifying attribute of exchanged media stream between the HOAF-UP and the terminal side of the second user according to the media capability of the HODF.

41. A method for maintaining session continuity, comprising:

triggering a Handover Anchor Function-Control Plane (HOAF-CP) on a home network side of a first user, and establishing a first connection comprising a control plane first connection between a Handover Source Function (HOSF) of the first user and the HOAF-CP and a user plane first connection between the HOSF and a Handover Anchor Function-User Plane (HOAF-UP) on the home network side of the first user, establishing a control plane connection between the HOAF-CP and a terminal side of a second user and a user plane connection between the HOAF-UP and the terminal side of the second user, and establishing a session between the first user and the second user through the control plane first connection, the control plane connection between the HOAF-CP and the terminal side of the second user, the user plane first connection, and the user plane connection between the HOAF-UP and the terminal side of the second user;

determining that a handover condition is satisfied, establishing a second connection, wherein the second connection comprises a control plane second connection between a Handover Destination Function (HODF) of the first user and the HOAF-CP and a user plane second connection between the HODF and the HOAF-UP;

continuing the session between the first user and the second user through the control plane second connection between the HODF of the first user and the HOAF-CP and the control plane connection between the HOAF-CP and the terminal side of the second user, and the user plane second connection between the HODF of the first user and the HOAF-UP and the user plane connection between the HOAF-UP and the terminal side of the second user.

42. A method for maintaining session continuity, comprising:

establishing, by a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of a first user, a control plane first connection and a control plane third connection, wherein the control plane first connection is between a user terminal of the first user and the HOAF-CP, wherein the control plane third connection is between the HOAF-CP and a terminal side of a second user;

establishing a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of the IMS, wherein the control plane first connection, the control plane third connection and the user plane first connection achieves a session between the first user and the second user;

when a handover condition is satisfied, establishing, by the HOAF-CP, a control plane second connection between the user terminal of the first user and the HOAF-CP, and establishing a user plane second connection between the user terminal and the HOAF-UP; and

replacing, by the HOAF-CP, the control plane first connection with the control plane second connection, and replacing the user plane first connection with the user plane second connection, and wherein the control plane second connection, the control plane third connection and the user plane second connection achieves the session after the handover.

43. The method according to claim 42, further comprising:

receiving, by the HOAF-CP, a connection establishment request from the user terminal after the handover condition is satisfied.

44. The method according to claim 42, further comprising:

receiving, by the HOAF-CP, a handover indication from the user terminal after the handover condition is satisfied, sending, by the HOAF-CP, a connection establishment request to the user terminal.

45. The method according to claim 42, further comprising:

receiving, by the HOAF-CP, a handover indication from the user terminal after the handover condition is satisfied; and

sending a connection establishment request to the user terminal.

46. The method according to claim 42, wherein the step of establishing the control plane second connection comprises:

receiving, by the HOAF-CP, a connection establishment request from the user terminal, wherein the connection establishment request carries session information of the the control plane first connection and a handover indication;

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

47. The method according to claim 42, wherein the HOAF-UP is located on a terminal side of the second user.

58. The method of claim 42, wherein the HOAF-CP is a server of an IP multimedia subsystem (IMS).

48. A system for maintaining session continuity, comprising a Handover Anchor Function-Control Plane (HOAF-CP) on a home network side of a first user, wherein the HOAF-CP is configured to communicate with a user terminal of the first user, wherein the HOAF-CP is further configured to:

establish a control plane first connection and a control plane third connection, wherein the control plane first connection is between the user terminal and the HOAF-CP, and wherein the control plane third connection is between the HOAF-CP and a terminal side of a second user;

control to establish a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP), wherein the control plane first connection, the control plane third connection and the user plane first connection achieves a session between the first user and the second user;

when a handover condition is satisfied, establish a control plane second connection between the user terminal and the HOAF-CP, and control to establish a user plane second connection between the user terminal and the HOAF-UP; and

replace the control plane first connection with the control plane second connection, and indicate the HOAF-UP to replace the user plane first connection with the user plane second connection, and wherein the control plane second connection, the control plane third connection and the user plane second connection achieves the session after the handover.

59. The system of claim 48, wherein the HOAF-CP is a server of an IP multimedia subsystem (IMS).

49. A method for maintaining session continuity, comprising:

establishing a control plane first connection and a control plane third connection, wherein the control plane first connection is between a user terminal of the first user and a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of the first user, wherein the control plane third connection is between the HOAF-CP and a terminal side of a second user;

establishing a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of the IMS and a user plane third connection between the HOAF-UP and the terminal side of the second user, wherein the control plane first connection, the control plane third connection, the user plane first connection and the user plane third connection achieves a session between the first user and the second user;

when a handover condition is satisfied, establishing, by the HOAF-CP, a control plane second connection between the user terminal of the first user and the HOAF-CP, and establishing a user plane second connection between the user terminal and the HOAF-UP; and

replacing, by the HOAF-CP, the control plane first connection with the control plane second connection, and replacing the user plane first connection with the user plane second connection, and wherein the control plane second connection, the control plane third connection, the user plane second connection and the user plane third connection achieves the session after the handover.

60. The method of claim 49, wherein the control plane first connection and the user plane first connection are connections of Packet Switched (PS)domain, the control plane second connection and the user plane second connection are connections of Circuit Switched (CS) domain.

50. A system for maintaining session continuity, comprising a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of a first user, wherein the HOAF-CP is configured to communicate with a user terminal of the first user and a user terminal of the first user, wherein the HOAF-CP is further configured to:

establish a control plane first connection and a control plane third connection, wherein the control plane first connection is between the user terminal and the HOAF-CP, and wherein the control plane third connection is between the HOAF-CP and a terminal side of a second user;

control to establish a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of the IMS and a user plane third connection between the HOAF-UP and the terminal side of the second user, wherein the control plane first connection, the control plane third connection, the user plane first connection and the user plane third connection achieves a session between the first user and the second user;

when a handover condition is satisfied, establish a control plane second connection between the user terminal and the HOAF-CP, and control to establish a user plane second connection between the user terminal and the HOAF-UP; and

replace the control plane first connection with the control plane second connection, and indicate the HOAF-UP to replace the user plane first connection with the user plane second connection, and wherein the control plane second connection, the control plane third connection, the user plane second connection and the user plane third connection achieves the session after the handover.

61. The system of claim 50, wherein the control plane first connection and the user plane first connection are connections of Packet Switched (PS) domain, the control plane second connection and the user plane second connection are connections of Circuit Switched (CS) domain.

51. A system for maintaining session continuity, comprising a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of a first user, a Handover Anchor Function-User Plane (HOAF-UP) of the IMS,

wherein the HOAF-CP is configured to:

establish a control plane first connection and a control plane third connection, wherein the control plane first connection is between a user terminal of the first user and the HOAF-CP, and wherein the control plane third connection is between the HOAF-CP and a terminal side of a second user;

control to establish a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) and a user plane third connection between the HOAF-UP and the terminal side of the second user, wherein the control plane first connection, the control plane third connection, the user plane first connection and the user plane third connection achieves a session between the first user and the second user;

when a handover condition is satisfied, establish a control plane second connection between the user terminal of the first user and the HOAF-CP, and control to establish a user plane second connection between the user terminal and the HOAF-UP; and

replace the control plane first connection with the control plane second connection, and indicate the HOAF-UP to replace the user plane first connection with the user plane second connection, and wherein the control plane second connection, the control plane third connection, the user plane second connection and the user plane third connection achieves the session after the handover;

wherein the HOAF-UP is configured to establish the user plane first connection, the user plane second connection and the user plane third connection, and replace the user plane first connection with the user plane second connection.

62. The system of claim 51, wherein the control plane first connection and the user plane first connection are connections of Packet Switched (PS) domain, the control plane second connection and the user plane second connection are connections of Circuit Switched (CS) domain.

52. A method for maintaining session continuity, comprising:

establishing a first connection, wherein the first connection comprises a control plane first connection between a user terminal of the first user and a Handover Anchor Function-Control Plane (HOAF-CP) on a home network side of the first user and a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of a second user;

establishing a control plane connection between the HOAF-CP and a terminal side of the second user, wherein the control plane first connection, the control plane third connection, and the user plane first connection achieve a session between the first user and the second user;

determining that a handover condition is satisfied, establishing a second connection, wherein the second connection comprises a control plane second connection between the user terminal of the first user and the HOAF-CP and a user plane second connection between the user terminal and the HOAF-UP; and

wherein the user plane second connection between the user terminal and the HOAF-UP, the control plane second connection between the user terminal and the HOAF-CP, and the control plane connection, which is already established between the HOAF-CP and the terminal side of the second user before the handover condition is satisfied, achieves the session after the handover.

63. The method of claim 52, wherein the HOAF-CP is a server of an IP multimedia subsystem (IMS).

53. A method for maintaining session continuity, comprising:

establishing a first connection comprising a control plane first connection between a user terminal of the first user and a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of the first user and a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of the IMS on the home network side of the first user;

establishing a control plane connection between the HOAF-CP and a terminal side of a second user and a user plane connection between the HOAF-UP and the terminal side of the second user, wherein the control plane first connection, the control plane connection, the user plane connection and the user plane first connection achieve a session between the first user and the second user;

determining that a handover condition is satisfied, establishing a second connection, wherein the second connection comprises a control plane second connection between the user terminal of the first user and the HOAF-CP and a user plane second connection between the user terminal and the HOAF-UP;

wherein the control plane second connection between the user terminal of the first user and the HOAF-CP, the control plane connection between the HOAF-CP and the terminal side of the second user, the user plane second connection between the user terminal of the first user and the HOAF-UP, and the user plane connection between the HOAF-UP and the terminal side of the second user achieve the session after the handover.

64. The method of claim 53, wherein the control plane first connection and the user plane first connection are connections of Packet Switched (PS) domain, the control plane second connection and the user plane second connection are connections of Circuit Switched (CS) domain.

54. A method for maintaining session continuity, comprising:

establishing a first connection comprising a control plane first connection between a user terminal of a first user and a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of the first user and a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of the IMS on the home network side of the first user;

establishing a control plane connection between the HOAF-CP and a terminal side of a second user and a user plane connection between the HOAF-UP and the terminal side of the second user, and establishing a session between the first user and the second user through the control plane first connection, the control plane connection between the HOAF-CP and the terminal side of the second user, the user plane first connection and the user plane connection between the HOAF-UP and the terminal side of the second user;

when a handover condition is satisfied, establishing a second connection, wherein the second connection comprises a control plane second connection between the user terminal of the first user and the HOAF-CP and a user plane second connection between the user terminal and the HOAF-UP;

continuing the session between the first user and the second user through the control plane second connection, the control plane connection between the HOAF-CP and the terminal side of the second user, the user plane second connection and the user plane connection between the HOAF-UP and the terminal side of the second user.

56. A method for maintaining session continuity, comprising:

establishing a control plane first connection between a user terminal of a first user and a Handover Anchor Function-Control Plane (HOAF-CP) of an IP multimedia sub-system (IMS) on a home network side of the first user and a user plane first connection between the user terminal and a Handover Anchor Function-User Plane (HOAF-UP) of the IMS on the home network side of the first user;

establishing a control plane third connection between the HOAF-CP and a terminal side of a second user and a user plane third connection between the HOAF-UP and the terminal side of the second user, and establishing a session between the first user and the second user through the control plane first connection, the control plane third connection between the HOAF-CP and the terminal side of the second user, the user plane first connection and the user plane third connection between the HOAF-UP and the terminal side of the second user;

when a handover condition is satisfied, establishing a control plane second connection between the user terminal of the first user and the HOAF-CP and a user plane second connection between the user terminal and the HOAF-UP;

wherein the control plane second connection between the user terminal of the first user and the HOAF-CP, the control plane third connection between the HOAF-CP and the terminal side of the second user, the user plane second connection between the user terminal of the first user and the HOAF-UP, and the user plane third connection between the HOAF-UP and the terminal side of the second user achieve the session after the handover.

55. The method of claim 56, wherein the control plane first connection and the user plane first connection are connections of Packet Switched (PS)domain, the control plane second connection and the user plane second connection are connections of Circuit Switched (CS) domain.

57. The method of claim 56, wherein the control plane first connection and the user plane first connection are connections of Packet Switched (PS)domain, the control plane second connection and the user plane second connection are connections of Circuit Switched (CS) domain.