Handover delay optimization

Abstract

A method of anchoring a packet switched session of a subscriber comprises receiving a packet switched request for a session setup, and anchoring the packet switched session in a control node (MSC-S) of a visited network of the subscriber.

Claims

1. A method of anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of a subscriber, the method executed by a control node of a home network of the subscriber and comprising: receiving, by the control node and via an IMS call session control function in the home network, a request for setup of the IMS multimedia session of the subscriber; and anchoring, by the control node, the IMS multimedia session in an access transfer function of a visited network of the subscriber.

2. The method according to claim 1, wherein said anchoring comprises sending information from the control node to the access transfer function for anchoring the IMS multimedia session in that access transfer function and for anchoring a media path in a transmission node of the visited network.

3. The method according to claim 2, wherein said sending comprises sending at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

4. The method according to claim 1, wherein the method comprises anchoring a signaling path for the IMS multimedia session in the access transfer function.

5. The method according to claim 1, wherein said anchoring comprises identifying the access transfer function, wherein said identifying comprises at least one of: using a configured Public Service Identifier (PSI) of the access transfer function; and requesting information about the access transfer function from the home network.

6. The method according to claim 5, wherein said requesting comprises requesting a Mobile Station Roaming Number (MSRN) from at least one of a Home Location Register (HLR) and a Home Subscriber Server (HSS) of the home network.

7. The control node according to claim 5, wherein the control node comprises a Service Centralization and Continuity Application Server (SCC AS) of the home network of the subscriber.

8. A control node of a home network of a subscriber for anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of the subscriber, the control node comprising: a processor and a memory, the memory containing instructions executable by the processor whereby the control node is configured to: receive, via an IMS call session control function in the home network, a request for setup of the IMS multimedia session of the subscriber; and anchor the IMS multimedia session in an access transfer function of a visited network of the subscriber.

9. The control node according to claim 8, wherein the control node comprises a Service Centralization and Continuity Application Server (SCC AS) of the home network.

10. The control node according to claim 8, wherein the memory contains instructions executable by the processor whereby the control node is configured to send information to the access transfer function for anchoring the IMS multimedia session in that access transfer function and for anchoring a media path in a transmission node of the visited network.

11. The control node according to claim 10, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

12. The control node according to claim 8, wherein the memory contains instructions executable by the processor whereby the control node is configured to anchor a signaling path for the IMS multimedia session in the access transfer function.

13. The control node according to claim 8, wherein the memory contains instructions executable by the processor whereby the control node is configured to identify the access transfer function by at least one of: using a configured Public Service Identifier (PSI) of the access transfer function; and requesting information about the access transfer function from the home network.

14. A method of anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of a subscriber, the method executed by a Mobile Switching Center server (MSC-S) implementing an access transfer function of a visited network of the subscriber, the method comprising: determining by the MSC-S that the IMS multimedia session is to be anchored in the access transfer function of the visited network; and responsive to said determining, anchoring the IMS multimedia session in the access transfer function of the visited network implemented by the MSC-S.

15. The method according to claim 14, further comprising receiving information from a control node of a home network of the subscriber for anchoring the IMS multimedia session in the access transfer function and for anchoring a media path in a transmission node of the visited network.

16. The method according to claim 15, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

17. The method according to claim 14, further comprising receiving a handover request and, responsive to the handover request, instructing a transmission node of the visited network to transfer a source access leg of the IMS multimedia session associated with packet switched access to a target access leg of the IMS multimedia session associated with a circuit switched access.

18. The method according to claim 17, further comprising using information received from a control node of a home network of the subscriber to correlate the IMS multimedia session with the handover request, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

19. A Mobile Switching Center Server (MSC-S) implementing an access transfer function of a visited network of a subscriber for anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of the subscriber, the MSC-S comprising: a processor and a memory, the memory containing instructions executable by the processor whereby the MSC-S is configured to: determine that the IMS multimedia session is to be anchored in the access transfer function of the visited network implemented by the MSC-S; and responsive to said determining, anchor the IMS multimedia session in the access transfer function of the visited network implemented by the MSC-S.

20. The MSC-S according to claim 19, wherein the memory contains instructions executable by the processor whereby the MSC-S is configured to receive information from a control node of a home network of the subscriber for anchoring the IMS multimedia session in the access transfer function and for anchoring a media path in a transmission node of the visited network.

21. The MSC-S according to claim 20, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

22. The MSC-S according to claim 19, wherein the memory contains instructions executable by the processor whereby the MSC-S is configured to receive a handover request and, responsive to the handover request, instruct a transmission node of the visited network to transfer a source access leg of the IMS multimedia session associated with packet switched access to a target access leg of the IMS multimedia session associated with a circuit switched access.

23. The MSC-S according to claim 22, wherein the memory contains instructions executable by the processor whereby the MSC-S is configured to use information received from a control node of a home network of the subscriber to correlate the IMS multimedia session with the handover request, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will be described in more detail hereinafter with reference to examples but to which the scope of the invention is not limited.

(2) FIG. 1 is a block diagram illustrating a communications architecture used during a call being anchored in a home network of a subscriber.

(3) FIG. 2. is a block diagram illustrating a communications architecture used during a call being anchored in a visited network of a subscriber according to an exemplary embodiment of the invention.

(4) FIG. 3 is a flow diagram illustrating a method of anchoring a packet switched session of a subscriber according to an exemplary embodiment of the invention.

(5) FIG. 4 is a flow diagram illustrating a method of performing a handover of a session of a subscriber from a packet switched access to a circuit switched access according to an exemplary embodiment of the invention.

(6) FIG. 5 is a block diagram illustrating a constitution of a Service Centralization and Continuity Application Server according to an exemplary embodiment of the invention.

(7) FIG. 6 is a block diagram illustrating a constitution of a Mobile Switching Centre Server according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

(8) Illustrations in the accompanying drawings are schematic. In different drawings, similar or identical elements are provided with the same reference signs or with the same abbreviations.

(9) Referring to FIG. 2, a communications architecture according to an exemplary embodiment of the invention will be described in the following.

(10) The communications architecture of FIG. 2 is similar in some respects to the communications architecture of FIG. 1.

(11) A UE is attached to IMS via a LTE access network in the visited network. The call of the UE is anchored in a SCC AS in the IMS in the home network.

(12) A UE may perform handover between different access networks of the visited network, particular from a packet-switched to a circuit-switched access network. These networks are in the shown embodiment GERAN/UTRAN/EUTRAN.

(13) A Mobile Switching center Server (MSC-S) of the visited network comprises as service functionality, a Visited Access Transfer Function, and a Media Gateway MGW comprises MRFP functionality. The SCC AS in the home network can signal to the MSC-S in the visited network and vice versa for session establishment to include the MSC-S into the signaling path and the MGW into the media path. A MME may signal to the MSC-S mobility related signaling to perform handover between the packet-switched and circuit-switched access.

(14) Referring to FIG. 3, establishing a session of a subscriber in a packet switched home network will be described in the following. Here, the SCC AS anchors the session in the VATF which is located within the MSC-S.

(15) Existing Mobile Origination procedures described in the 3GPP Technical Specification 23.228 are used to establish the session of the subscriber.

(16) The subscriber, now denoted with the reference sign UE-1, initiates an IMS multimedia session to a remote subscriber UE-2 and uses only PS media flow(s). The request of the subscriber UE-1 is forwarded to the S-CSCF of the home network following or based on normal IMS session set up procedures (depicted in FIG. 3 by a step 1).

(17) The service logic with iFC of the S-CSCF causes the request to be forwarded to the SCC AS of the home network for first anchoring the session (depicted in FIG. 3 by steps 2 and 3).

(18) The SCC AS further anchors the session in the MSC Server/VATF for both signaling traffic and media traffic (depicted in FIG. 3 by steps 4 to 8) to enable session transfer. To this end, the SCC AS sends corresponding information to the S-CSCF which in turn is forwarded by the S-CSCF to the MSC Server. The media traffic is anchored in a MGW of the visited network in that the identified MSC Server/VATF allocates the MGW to be used for transmitting the media traffic.

(19) In order to enable the SCC AS anchoring the session in the MSC Server, the SCC AS identifies or finds the correct MSC server/VATF to route the traffic to by one of the following procedures:

(20) In a first procedure, a pre-configured Public Service Identity (PSI) to the MSC Server is used based on the serving network in which the subscriber UE-1 is currently roaming. Here, the SCC AS may use e.g., the P-access-network-info header or the P-visited-network-info header to determine the network in which the subscriber UE-1 is currently registered. It is then up to the visited network, to ensure that the session is anchored in an MSC Server which can handle the subscriber. This could be done with procedures similar to those defined for dynamic user allocation to application servers. I.e., a load balancing/MSC server selection function (MSF) in the visited network is used for selecting the MSC server. The MSF, based on the Correlation Mobile Station International ISDN Number (C-MSISDN) and/or the International Mobile Subscriber Identity (IMSI), selects an appropriate MSC server instance. The selection may be based on the C-MSISDN and optionally on the IMSI. One may note that the same distribution function/MSF may be used in the MME to select the MSC server to establish the Sv reference point as shown in FIG. 2.

(21) Additionally or alternatively, in a second procedure, the SCC AS identifies the MSC Server to which the subscriber UE-1 is allocated (in case it is) by requesting a Mobile Station Roaming Number (MSRN) of the subscriber UE-1 from at least one of the Home Location Register (HLR) and the Home Subscriber Server (HSS) of the home network. The MSRN may then be used to anchor the signaling in the MSC-S.

(22) It may be noted that in case the terminal or the subscriber UE-1 is using Short Message Service (SMS) over SGs, as is specified in the 3GPP Technical Specification 23.272, the subscriber UE-1 is allocated to a MSC Server while camping on LTE.

(23) The SCC AS includes at least one of the C-MSISDN and the IMSI for the subscriber UE-1 when anchoring the session in the MSC Server/VATF. In particular, the SCC AS includes the C-MSISDN and optionally the IMSI. Additionally and alternatively, the SCC AS may include the International Mobile Equipment Identity (IMEI). The C-MSISDN is used by the VATF as correlation identifier to correlate an incoming handover request from the MME which includes the C-MSISDN with the ongoing.

(24) It may be further noted that sending invitation information from the S-CSCF to the MSC Server/VATF and sending further invitation information from the MSC Server/VATF (depicted in FIG. 3 by steps 5 and 7, respectively) may be via a Media Gateway Control Function (MGCF), with ISDN Iser Part (ISUP) or Bearer Independent Call Control (BICC) protocol signaling between the MSC Server and the MGCF within IMS in home network.

(25) It may be further noted that anchoring a session may mean that the access leg of the session is between the UE-1 and the MSC Server/VATF, while the remote leg of the session for signaling is between the MSC Server/VATF and the SCC AS in the home network.

(26) The SCC AS completes the session setup to the subscriber UE-2 and sends a response to the subscriber UE-1 (depicted in FIG. 3 by a step 9).

(27) The MSF can include a number of different values for selection of the MSC Server/VATF and is not restricted to at least one of the MSISDN and the IMSI, but may also comprise e.g., a Visitor Location Register Temporary Mobile Subscriber Identity (VLR TMSI) and a Location Area Identity (LAI). This may then require that the subscriber UE-1 is adapted to provide the corresponding information over the SIP signaling.

(28) The selected VATF needs to be in the signaling path for the duration of the call. This may require that, if SGs is used, then the new selected MME needs to establish SGs reference points to the same MSC Sever/VATF. This may be done by including the MSC Server Identity (MSC ID) into the selection algorithm (MSF) and the MSC ID also needs to be comprised in the context for the inter MME handover.

(29) Referring to FIG. 4, a transfer of a session from a PS access network of a subscriber to a CS access network will be described in the following.

(30) More precisely, the following section describes the high level or advanced procedures for an access transfer when using a VATF function in the visited network.

(31) Procedures specified in the 3GPP Technical Specification 23.216 [10], clause 6.2.2.1, result in that the MME will, based on the C-MSISDN/IMSI, determine the correct MSC Server which is currently anchoring a session of a subscriber UE-1 (denoted in FIG. 3A as UE) (depicted in FIG. 4 by steps 1 and 2, respectively). In addition to existing procedures, the MME may use the same type of distribution function (MSF) as described above with respect to FIG. 3 to find the correct MSC server.

(32) The MSC Server receives a handover request from the MME (depicted in FIG. 4 by a step 2).

(33) The MSC Server updates the media anchoring in the MGW to send and receive the media towards the target access leg (CS leg) (depicted in FIG. 4 by a step 3) and to stop the media towards the source access leg. At this point, no extra signaling is needed within the IMS network.

(34) It may be noted that the MSC server may instruct the MGW to send media both on the source access leg and the new target access leg for a certain period of time, in order to minimize the interruption delay further (using a so called Bi-casting).

(35) The source access leg may be then released (depicted in FIG. 4 by a step 4).

(36) In the following, the impact on the network will be described.

(37) A SCC AS (of a home network of a subscriber) may need a new functionality to find the access transfer function in a visited network.

(38) A MME may be impacted with a new functionality to determine a MSC server which the subscriber is currently using (in particular when the subscriber may have not been attached in CS).

(39) A MSC server may need to have special procedure to correlate an ongoing session/call with an incoming handover request from a MME, and during a period of time, may ensure that the MGW may send media to both a PS and CS leg.

(40) A MGW may be already included in the media path prior to a handover, hence the codec may be selected during a session establishment. There may be no need to change a codec after SRVCC.

(41) FIG. 5 illustrates a constitution of a control node 500 for anchoring a packet switched session of a subscriber according to an exemplary embodiment of the invention. The control node 500 is adapted as an application server, particularly a SCC AS of a home network of a subscriber.

(42) The control node 500 comprises a receiving unit 502 for receiving a packet switched request for a session setup particularly from a subscriber and an anchoring unit 504 for anchoring the packet switched session in a control node of a visited network of the subscriber.

(43) The anchoring unit 504 is adapted to anchor signaling for the packet switched session in the control node of the home network. The control node 500 may comprise a further anchoring unit for performing the latter.

(44) The anchoring unit 504 is further adapted to identify the control node of the visited network.

(45) The anchoring unit 504 is adapted for sending information to the control node of the visited network for anchoring the packet-switched session in the control node of the visited network and media in a transmission node of the visited network. The anchoring unit 504 may be adapted as a sender.

(46) The control node 500 comprises a processing unit 506, particularly a processor, in which appropriate algorithms may be executed to perform the method for anchoring a packet switched session of a subscriber and/or of performing a handover of a session of a subscriber from a packet switched access to a circuit switched access. The anchoring 504 unit may be at least partly part of the processing unit 506.

(47) The control node 500 comprises a storage unit 508 for storing information necessary during performing the method for anchoring a packet switched session of a subscriber and/or of performing a handover of a session of a subscriber from a packet switched access to a circuit switched access.

(48) FIG. 6 illustrates a constitution of a control node 600 for performing a handover of a session of a subscriber from a packet switched access to a circuit switched access. The control node 600 is adapted as a Mobile Switching Center Server MSC-S.

(49) The control node 600 comprises a receiving unit 602 for receiving a handover request and an instructing unit 604 for instructing a transmission node, particularly a Media Gateway, to transfer a source access leg of the session associated with the packet switched access to a target access leg of the session associated with the circuit switched access.

(50) The instructing unit 604 is adapted to send information particularly related to execute the method of performing a handover of a session of a subscriber from a packet switched access to a circuit switched access.

(51) The control node 600 comprises a processing unit 606, particularly a processor, in which appropriate algorithms may be executed to perform the methods of anchoring a packet switched session of a subscriber and/or of performing a handover of a session of a subscriber from a packet switched access to a circuit switched access. The instructing 604 unit may be at least partly part of the processing unit 606.

(52) The control node 600 comprises a storage unit 608 for storing information necessary during performing the methods of anchoring a packet switched session of a subscriber and/or of anchoring a packet switched session of a subscriber.

(53) The control node 600 may be located in a visited network of the subscriber.

(54) The control node 600 may comprise a visited access transfer function VATF.

(55) A transmission node or a transfer node may be adapted as a Media Gateway MGW which may be located in a visited network of a subscriber. The transmission node may comprise a Multimedia Resource Function (MRF).

(56) A mobility management node may be adapted as a Mobility Management Entity MME which may be located in a visited network of a subscriber. The mobility management node may comprise a MSC server selection function (MSF).

(57) Modifications and other embodiments of the disclosed invention will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

ABBREVIATIONS

(58) BICC Bearer Independent Call Control

(59) BSS Base Station Subsystem

(60) C-MSISDN Correlation Mobile Station International ISDN Number

(61) CS Circuit Switched

(62) DSL Digital Subscriber Line

(63) EPC Evolved Packet Core

(64) EUTRAN evolved Universal Terrestrial Radio Access Network

(65) GERAN GSM EDGE Radio Access Network

(66) 3GPP Third Generation Partnership Project

(67) GSM Global System for Mobile Communication

(68) HLR Home Location Register

(69) HO Handover

(70) HSS Home Subscriber Server

(71) ICS IMS Centralized Services

(72) iFC initial Filter Criteria

(73) IMS IP Multimedia Subsystem

(74) IMSI International Mobile Subscriber Identity

(75) IP Internet Protocol

(76) LAI Location Area Identity

(77) ISUP ISDN User Part

(78) ISDN Integrated Services Digital Network

(79) LTE Long Term Evolution

(80) MGCF Media Gateway Control Function

(81) MGW Media Gateway

(82) MME Mobile Management Entity

(83) MSF MSC Selection Function

(84) MRFP Media Resource Function Processor

(85) MSC Mobile Switching Centre

(86) MSC-S Mobile Switching Centre Server

(87) MSRN Mobile Station Roaming Number

(88) P-CSCF Proxy Call Server Control Function

(89) P-GW Packet Gateway

(90) PS Packed Switched

(91) PSI Public Service Identity

(92) RNC Radio Network Controller

(93) RTP Real Time Protocol

(94) SCC AS Service Centralization and Continuity Application Server

(95) S-CSCF Serving Call Server Control Function

(96) SDP Session Description Protocol

(97) S-GW Serving Gateway

(98) SIP Session Initiated Protocol

(99) SR-VCC Single Radio-Voice Call Continuity

(100) UE User Equipment

(101) UTRAN Universal Terrestrial Radio Access Network

(102) VATF Visited Access Transfer Function

(103) VLR Visitor Location Register

(104) VLR TMSI (Visitor Location Register) Temporary Mobile Subscriber Identity

(105) VoIP Voice over IP

(106) WCDMA Wideband Code Division Multiple Access

(107) WLAN Wireless Local Area Network