HK1211145B - Methods and devices for improving session continuity - Google Patents

Abstract

A method for improving session continuity for a terminal (204') in a serving communication network (202') distinct from a home communication network (200') of the terminal (204'), wherein the serving communication network (202') comprises a session transfer node (208') for transferring sessions each comprising signaling data and media data from a first access network (210') of the serving communication network (202') to a second access network (212') of the serving communication network (202') comprises the following:; Routing signaling data of a session of the terminal (204') between the first access network (210') and the home communication network (200') via the session transfer node (208') in the serving communication network (202'), receiving a session transfer request requesting the transfer of the session from the first access network (210') to the second access network (212') for the terminal (204'), and transferring the session from the first access network (210') to the second access network (212'), and routing the signaling data of the session of the terminal (204') between the second access network (210') and the home communication network (200') via the session transfer node (208').

Description

Method and apparatus for improving session continuity

Description of the cases

The application is a divisional application of a chinese patent application having an application date of 2010, 7/7, and an application number of 201080030749.0, entitled "method and apparatus for improving session continuity".

Technical Field

The present invention relates to communications, and in particular to a method and apparatus for improving session continuity for a terminal in a serving communication network that is different from a home communication network of the terminal.

Background

A user typically subscribes to an operator of a communication network and is thereby authorized to access the communication network of the operator, which is also referred to as a home communication network. The operator typically has an agreement with other operators having their own (or shared) communication networks so that access to terminals of subscribed users can be provided via so-called serving communication networks operated by one or more of the other operators. The home communication network usually covers a certain area (e.g. a country), and when the terminal moves out of the coverage of the user's home communication network, it has to access the serving communication network of the same operator or of another operator, which is also called roaming. The serving communication network of the roaming terminal is also referred to as a visited communication network.

Historically, communication technology has evolved rapidly, however, evolving paths have not followed a single and the same technological trend. For example, mobile communication networks are currently evolving from pure Circuit Switched (CS) networks to Internet Protocol (IP) based networks and are thus integrated into IP based infrastructure also used for the internet, world wide web and data communication industries. With this trend, mobile networks closely follow the evolution steps of wired communication networks, where voice over ip (voip) via Digital Subscriber Line (DSL) access or via Wireless Local Area Network (WLAN) access is an existing technology today.

Mobile operators installing IP Multimedia Subsystem (IMS) networks and providing IMS services want these services to be available to mobile terminals of users accessing global system for mobile communications (GSM) or Wideband Code Division Multiple Access (WCDMA) communication networks as well. In this regard, calls from and to the group of mobile terminals of the GSM/WCDMA user are routed through the IMS network such that the IMS service engine performs the calls and call-related services. This concept of enabling IMS services when using a CS access network is referred to as IMS Centralized Services (ICS) (see also 3GPP technical specification 23.292, which is incorporated herein by reference) and is supplemented by IMS Service Continuity (SC) (see 3GPP technical specification 23.237, which is incorporated herein by reference), which is an IMS service that supports the use of session transfer mechanisms (also denoted today as "access transfer mechanisms", see for example the newer version of 3GPP technical specification 23.237) to maintain service continuity in case of terminal movement and/or movement between terminals.

IMS SC is an intra-terminal transfer of one or more components of an IMS multimedia session across different access networks based on IMS applications of the home communication network and requires a Service Centralization and Continuity (SCC) Application Server (AS) and SC-capable terminals.

A session, also referred to as a communication session, in computer science can be considered a semi-persistent interactive exchange of information between communicating devices, which is established at a particular time and torn down at a later time. Examples are as follows:

-a TCP session, a session of TCP,

web sessions (HTTP sessions), session management using session cookies and Web servers, either client-side or server-side. The latter may be provided by a Java Session Bean, which is a web server side component, which may be stateful or stateless.

-sessions established by a certain session layer protocol.

Examples of session protocols are:

session description protocol, a format for describing initialization parameters of streaming media

Session initiation protocol, a computer network protocol, typically for IP telephony, and for setting up and tearing down end-to-end communication sessions consisting of one or more media streams

The session includes signaling data and media data, the signaling data being routed via the SCC AS. Routing signaling data via the SCC AS is also known AS anchoring. The signalling of all sessions related to the terminal is anchored centrally at the SCC AS in the home communication network, so that the IMS can transfer one or more sessions of the terminal from the first access network to the second access network, e.g. from the CS access network to the Packet Switched (PS) access network, or vice versa.

However, a terminal in the serving communication network will experience a low quality of service because all session transfer requests must be routed from the serving communication network to the home communication network, where they can then be handled accordingly by the SCC AS. Long latency and complex routing may degrade the service experience. For example, voice call interruption time may be increased, or data transfer may be interrupted.

Disclosure of Invention

It is therefore an object of the present invention to provide a method, apparatus, system and computer program for improving session continuity for a terminal in a serving communication network.

This object is achieved by the methods described in claims 1, 7 and 9. Furthermore, the invention is embodied in a session transfer node, a node of a serving communication network and a session control node according to claims 17, 18 and 19, respectively, in a system according to claim 21, and in a computer program according to claims 22 to 24 and a computer readable medium product according to claim 25. Advantageous embodiments are described in the other claims.

According to an exemplary embodiment of the invention, a method for improving session continuity for a terminal in a serving communication network, the serving communication network being different from a home communication network of the terminal, is provided, wherein the serving communication network comprises a session transfer node for transferring sessions, each session comprising signaling data and media data, from a first access network of the serving communication network to a second access network of the serving communication network, the method comprising the following steps (performed by a session transfer node (e.g. a-SCC) in the serving communication network): routing signalling data for a session of the terminal between the first access network and the home communication network via a session transfer node in the serving communication network; receiving a session transfer request requesting transfer of a session from the first access network to the second access network for the terminal; transferring a session from the first access network to the second access network; and routing signalling data for a session of the terminal between the second access network and the home communication network via the session transfer node.

According to another exemplary embodiment of the invention, a method for improving session continuity for a terminal in a serving communication network, the serving communication network being different from a home communication network of the terminal, is provided, wherein the serving communication network comprises a session transfer node for transferring sessions, each session comprising signaling data and media data, from a first access network of the serving communication network to a second access network of the serving communication network, the method comprising the following steps (performed by a node in the serving communication network): receiving an address of a session transfer node in the serving communication network; sending a session transfer request to an address of a session transfer node in the serving communication network.

According to another exemplary embodiment of the invention, a method for improving session continuity for a terminal in a serving communication network, the serving communication network being different from a home communication network of the terminal, is provided, wherein the serving communication network comprises a session transfer node for transferring sessions, each session comprising signaling data and media data, from a first access network of the serving communication network to a second access network of the serving communication network, the method comprising the following steps (performed at the session control node): determining an address of a session transfer node in the serving communication network, and sending the address of the session transfer node to a node in the serving communication network.

In the following detailed description of exemplary embodiments of the invention, reference will be made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are, however, illustrative and not intended to be limiting.

Drawings

Fig. 1a illustrates a method for improving session continuity for a terminal in a serving communication network, the serving communication network being different from a home communication network of the terminal, according to an exemplary embodiment of the present invention;

fig. 1b illustrates a method for improving session continuity for a terminal in a serving communication network, the serving communication network being different from a home communication network of the terminal, according to another exemplary embodiment of the present invention;

fig. 1c illustrates a method for improving session continuity for a terminal in a serving communication network, the serving communication network being different from a home communication network of the terminal, according to another exemplary embodiment of the present invention;

fig. 2a shows a transfer of signalling data of a session according to an exemplary embodiment of the present invention;

fig. 2b shows a signalling exchange diagram for transferring signalling data of a session according to an exemplary embodiment of the present invention;

fig. 3 shows a first exemplary embodiment for routing signaling data and media data in a communication network according to the present invention;

fig. 4 shows a second exemplary embodiment for routing signaling data and media data in a communication network according to the present invention;

figure 5 shows a first exemplary embodiment for determining a session transfer node in a serving communication network and providing the address of the session transfer node to a node in the serving communication network in accordance with the present invention;

fig. 6 shows a second exemplary embodiment for determining a session transfer node in a serving communication network and providing the address of the session transfer node to a node in the serving communication network in accordance with the present invention;

fig. 7 shows an exemplary embodiment of a device according to the present invention.

Detailed Description

The illustration in the drawings is schematically. It is noted that in fig. 2-7, similar or identical elements are provided with the same reference numerals, or with an apostrophe or a reference numeral that differs from the corresponding reference numeral only in the first digit.

Referring to fig. 1a, a method for improving session continuity for a terminal in a serving communication network that is different from a home communication network of the terminal according to an exemplary embodiment of the present invention is shown. The serving communication network comprises a session transfer node for transferring sessions, each session comprising signalling data and media data, from a first access network of the serving communication network to a second access network of the serving communication network. The method comprises the following steps: signalling data for the session of the terminal is routed between the first access network and the home communication network via a session transfer node in the serving communication network, as indicated by step 102. A session transfer request is received, as indicated by step 104. The session transfer request requests transfer of a session from the first access network to the second access network for the terminal. The session is transferred from the first access network to the second access network as indicated by step 106. Signalling data for the session of the terminal is routed between the second access network and the home communication network via the session transfer node, as indicated by step 108.

The method may also be performed by a session transfer node in a serving communication network, which may be adapted as e.g. an "auxiliary service centralization and continuity (a-SCC)" node.

In the context of the present application, the term "transfer of a session from a first access network to a second access network" may particularly refer to the transfer of signaling data and media data from the first access network to the second access network. Routing of data of the session via the same node before, during and after the session transfer may be denoted as anchoring, e.g. signaling data of the session may be anchored at the session transfer node, media data of the same session may be anchored at the session transfer node or at a node interfacing with the session transfer node.

The term "access network" may particularly denote any communication network to which a terminal may be attached for communication with a remote end. In particular, in the context of the present application, an access network may comprise nodes of a radio and core network.

In particular, a terminal may belong to a communication network and is therefore referred to as a node.

Referring to fig. 1b, a method for improving session continuity for a terminal in a serving communication network that is different from a home communication network of the terminal according to another exemplary embodiment of the present invention is shown. The serving communication network comprises a session transfer node for transferring sessions, each session comprising signalling data and media data, from a first access network of the serving communication network to a second access network of the serving communication network. The method comprises the following steps: receiving an address of a session transfer node in a serving communication network, as indicated by step 110; and sending a session transfer request to an address of a session transfer node in the serving communication network, as indicated by step 112.

In particular, the method may be performed by a node serving a communication network.

In particular, in the context of the present application, the term "receiving an address of a session transfer node" may particularly denote any reception (particularly directly or indirectly) of information related to the address of the session transfer node. In particular, the address of the session transfer node may be received via other nodes of the serving communication system.

In particular, in the context of the present application, the term "sending a session transfer request to an address of a session transfer node" may particularly denote any sending (particularly, directly or indirectly) of a session transfer request to a session transfer node. In particular, the session transfer request may be sent via other nodes of the serving communication system.

In particular, the node of the serving communication system may be a node of a first access system of the serving communication system (e.g. a proxy call/session control function (P-CSCF) or a Mobility Management Entity (MME) in case of a Packet Switched (PS) access network), a node of a second access system of the serving communication system (e.g. a mobile switching center server (MSC-S) in case of a Circuit Switched (CS) access network), or a terminal (which may belong to the serving communication network).

Accordingly, the address may be received as a local STN-SR or other suitable address information, may be received in a reattachment indication, or may be received in a relocation or handover indication.

Specifically, the session transfer request may be a handover request (message).

Referring to fig. 1c, a method for improving session continuity of a terminal in a serving communication network that is different from a home communication network of the terminal according to another exemplary embodiment of the present invention is shown. The serving communication network comprises a session transfer node for transferring sessions, each session comprising signalling data and media data, from a first access network of the serving communication network to a second access network of the serving communication network. The method comprises the following steps: determining an address of a session transfer node in a serving communication network, as indicated by step 120; and sending the address of the session transfer node to a node in the serving communication network, as indicated by step 122.

The method may be performed at (or by) a session control node.

In particular, the session control node may be part of or located in the serving communication network or in the home communication network. In particular, the session control node may be adapted to act as a proxy call/session control function (P-CSCF).

In the context of the present application, the term "determining and/or sending an address of a session transfer node" may particularly refer to determining and/or sending a signaling anchor (point) of a serving communication network (information related thereto).

The term "anchoring a session in a node" may particularly denote that signaling and/or media data may be routed through the node at any time, e.g. before, during and after a session transfer. In particular, the session may be controlled by the node at any time.

Accordingly, the session transfer node is adapted to perform the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with reference to fig. 1 a.

Accordingly, the node of the serving communication is adapted to perform the method for improving session continuity for the terminal in the serving communication network, which is different from the home communication network of the terminal, as explained above with reference to fig. 1 b.

Accordingly, the session control node is adapted to perform the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with reference to fig. 1 c.

The system comprises a session transfer node as described above, a node serving the communication network as described above, and a session control node as described above.

The computer program loadable into a processing unit of the session transfer node comprises code adapted to perform, when operating at the session transfer node, the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with respect to fig. 1 a.

The computer program loadable into a processing unit of a node of a serving communication network, the serving communication network being different from a home communication network of the terminal, comprises code adapted to perform the method for improving session continuity for the terminal in the serving communication network as explained above with respect to fig. 1b when operated at the node of the serving communication network.

The computer program loadable into a processing unit of the session control node comprises code adapted to perform, when operating at the session control node, the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with respect to fig. 1 c.

The computer readable medium product comprises a computer program as explained above.

Next, further exemplary embodiments of the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with respect to fig. 1a will be explained. However, these embodiments also apply to the respective session transfer node, to the respective system, to the respective computer program and to the respective computer readable medium.

The session transfer request may include terminal identification information, wherein the method may further include: the terminal identification information is analyzed to determine a session of the terminal that can be transferred.

The session transfer request may further include session transfer request identification information, wherein the method may further include: determining whether any of the received information complies with an available policy, and transferring the session in accordance with the determination of compliance.

The method may further comprise: sending a message to a session transfer node in the home communications network indicating to the home communications network session transfer node that the serving communications network session transfer node may be responsible for routing signalling data and transferring sessions. In particular, the session transfer node of the home communication network may be adapted AS a service centralization and continuity application server (SCC AS), wherein the message sent to the session transfer node of the home communication network may be based on the Session Initiation Protocol (SIP) and may comprise a flag or indication indicating that the session transfer node of the serving communication network may be included in the signaling routing path. Thus, the home communication network (in particular, the session transfer node of the home communication network) may be adapted to disable the session transfer related functionality in the home communication network, if such functionality is present in the home communication network.

Media data may be transferred from the first access network to the second access network together with the signaling data.

The media data may be anchored at a node in the serving communication network interfacing with the session transfer node, in particular at a media processing node (e.g. a media resource function processor, MRFP).

Next, further exemplary embodiments of the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with respect to fig. 1b will be explained. However, these embodiments also apply to the respective node of the serving communication network, to the respective system, to the respective computer program and to the respective computer-readable medium.

The method may also include receiving a message requesting a session transfer, and sending a session transfer request in response to receiving the message.

In particular, the message requesting session transfer may comprise an address of a session transfer node of the serving communication network. Specifically, the session transfer request may be a handover request (message). In particular, the node of the second access network may receive an address of the session transfer node (in particular, from the node of the first access network) and may send a session transfer request to the session transfer node. The nodes of the first and/or second access network may be adapted as serving mobility nodes, e.g. MME, SGSM and MSC-S.

Next, further exemplary embodiments of the method for improving session continuity for a terminal in a serving communication network different from a home communication network of the terminal as explained above with respect to fig. 1c will be explained. However, these embodiments also apply to the respective session control node, to the respective system, to the respective computer program and to the respective computer readable medium.

The session transfer node in the serving communication network may be determined by a session transfer node in the home communication network, wherein the method further comprises: the method comprises receiving an indication of a selected session transfer node in the serving communication network, and determining an address of the session transfer node based on the received indication. In particular, the session transfer node of the home communication network may be adapted as an SCC AC, in particular the SCC AC may determine the address of the session transfer node by selecting the address from a list comprising information about (locally configured) session transfer nodes (e.g. a-SCCs) of each serving (in case of roaming, sometimes also referred to as "visited") communication network. Alternatively or additionally, the session transfer node of the home communication network may determine the address of the session transfer node by deriving an address (string), e.g. a uniform address identifier (URI), of the session transfer node to be selected based on information relating to the serving communication network, wherein the information may be stored in or available in the session transfer node of the home communication network. In particular, the serving communication network may then select the session transfer node based on the received indication. In particular, the session control node may form part of the home communication network. In particular, the session control node may be adapted to act as a P-CSCF in the home communication network.

The session control node may be a node of the serving communication network and may determine the session transfer node. In particular, the session transfer node may be co-located with the session control node, whereby it is not necessary to explicitly determine or select the session transfer node. In particular, the session transfer node and the session control node may be separate nodes, such that the session transfer node may be (in particular, explicitly) determined or selected by the session control node. In particular, in the latter two cases, the session control node may be adapted to act as a P-CSCF. In particular, as described above, the session transfer node of the home communication network may determine or select a session transfer node of the serving communication system and may send a corresponding indication or corresponding information to the session control node, which may in turn determine or select the session transfer node.

For sending the address of the session transfer node to the node serving the communication network, the address of the session transfer node may be sent from the session control node to the terminal.

For sending the address of the session transfer node to a node of the serving communication network, the terminal may also send the address of the session transfer node to a serving mobility node (e.g. MME or Serving GPRS Support Node (SGSN)) in the serving communication network to which the terminal may attach. In particular, the terminal may send the address when performing a re-attachment to the serving communication network (in particular, to the first access network of the serving communication network).

For sending the address of the session transfer node to a node of the serving communication network, the serving mobility node may send the address to the node of the serving communication network. In particular, the serving mobility node may include the address of the session transfer node in a relocation request (in particular, a handover request) sent to the serving mobility node of the second access network of the serving communication system.

The method may further comprise: receiving at least one parameter from a terminal, the at least one parameter comprising the following information: information relating to the identity of the subscriber operating the terminal (e.g. International Mobile Subscriber Identity (IMSI)), information relating to the location of the terminal (e.g. Tracking Area (TA)), and information relating to the identity of a serving mobility node in the serving communication network to which the terminal may attach (e.g. Globally Unique Temporary Identity (GUTI)); and determining the session transfer node according to the received at least one parameter. In particular, the at least one parameter (in particular, GUTI and TA) may be allocated by a serving mobility node (in particular, MME) of a first access network of the serving communication system. In particular, determining the session transfer node according to the received at least one parameter may comprise selecting the session transfer node (in particular as a signaling anchor point) using a table mapping the at least one parameter (in particular GUTI and TA information) to the session transfer node (in particular an a-SCC instance).

For sending the address of the session transfer node to a node of the serving communication network, the address of the session transfer node may be sent to a serving mobility node, e.g. a Mobility Management Entity (MME), a Serving GPRS Support Node (SGSN) and/or a handover selection function (HOSF). In particular, the session control node may determine the address of the serving mobility node to which the address of the session transfer node has to be sent, in particular by using the at least one parameter (e.g. TA information and GUTI) received from the terminal. In particular, in case the terminal may attach to another serving mobility node and may thus send at least one other (updated) parameter, the sending of the (updated) address of the session transfer node to the other serving mobility node may have to be repeated accordingly. In particular, the serving mobility node may specifically send the address to another serving mobility node of the same or a different access network. In case of a PS first access network and a CS second access network, the serving mobility node may be adapted to act as an MME, or as a HOSF in or co-located with or separate from the MME, wherein an address may be sent to the MME, which in turn may inform the HOSF about the address to enable contacting the respective MSC-S. In the context of the present application, the "handover selection function (HOSF)" may particularly refer to a function required by the serving mobility node to select the handover support function.

Next, further exemplary embodiments of the above-described session transfer node, node of the serving communication network and session control node will be explained. However, these embodiments also apply to the respective method, the respective system, the respective computer program and the respective computer readable medium for improving session continuity for a terminal in a serving communication network, which is different from a home communication network of the terminal.

In particular, the session transfer node may be a stand-alone function or may be co-located with a particular SIP-capable network entity, such as a P-CSCF, an MSC-S (in particular, an MSC-S of the second access network serving the communication network) or an IMS Border Control Function (IBCF).

Each of these nodes may comprise a receiving unit, a transmitting unit, a processing unit and a storage unit.

A method for improving session continuity for a terminal in a serving communication network (the serving communication network being different from a home communication network of the terminal) may comprise: routing media data of the session of the terminal between the first access network and the home communication network via a media processing node in the serving communication network prior to the session transfer; and routing media data of the session of the terminal between the second access network and the home communication network via a media processing node in the serving communication network after the session transfer.

In particular, the media data may be anchored in a media processing node in the serving communication system such that the media data may be routed or transmitted by the media processing node before, during and after a session transfer from a first access network of the serving communication network to a second access network of the serving communication network.

In particular, the media processing node may be adapted as a Media Resource Function Processor (MRFP).

In particular, the media processing node may be adapted to act as a node separate from the session transfer node. In particular, the media processing node may have an interface with the session transfer node.

In particular, the media processing node may be controlled by a session transfer node in the serving communication network. The session transfer node may control the media processing node via an interface (e.g., session transfer node a-SCC308 controls media processing node MRFP 338 via interface 344, described in detail in fig. 3-6).

Fig. 2a depicts a home communication network 200 and a serving communication network 202. The terminal 204 of the home communication network 200 communicates with the remote end 206 through the home communication network 200 via the serving communication network 202, i.e. the terminal 204 and the remote end 206 may exchange signalling data and media data in a session. The remote end 206 may be, for example, a second terminal or server, which may reside in the home communication network 200 or in any other network connected to a worldwide telecommunication network. The session (i.e., the signaling portion thereof) is anchored in a session transfer node 208 in the serving communication network 202. Thereby, a fast and reliable session transfer from the first access network 210 to the second access network 212 (and a reverse transfer or a transfer to a third access network not shown in fig. 2 a) may be achieved.

In a first phase (denoted "pre-transfer"), signaling data is routed along a communication path (indicated by solid line 216) in the serving communication network 202 and the home communication network node 214 via the first access network 210 and via the session transfer node 208 (where the session is anchored). As indicated by arrow 218, the session transfer node 208 in the serving communication network 202 may transfer the session from the first access network 210 to the second access network 212. In a second time period after the transfer, denoted "post-transfer", the signaling data is routed along a communication path (indicated by dashed line 220) in the serving communication network 202 and the home communication network node 214 via the second access network 212 and via the session transfer node 208 (where the session is anchored) or one or more alternative home communication network nodes not shown in fig. 1 a.

Thus, signaling data for the session of the terminal 204 is routed via the session transfer node 208 in the serving communication network 202 before, during and after the transfer of the session, such that the session transfer node 208 maintains control of the transfer at any time, i.e. the session is anchored at the session transfer node 208 in the serving communication network 202 before, during and after the transfer.

The session transfer from the first access network 210 to the second access network 212 may be triggered by receiving a session transfer request requesting that the session be transferred from the first access network 210 to the second access network 212 for the terminal 204.

Fig. 2b depicts a signaling exchange diagram in a communication network. For illustrative reasons, fig. 2a and 2b do not describe the present invention on a node level with respect to the first access network 210, 210 'and the second access network 212, 212', however, it is clear that messages, requests, information exchanges, signaling, etc. may be communicated between the nodes (i.e., at a node level) of the first access network 210, 210 'and the second access network 212, 212' and other entities, such as the described terminals 204, 204 ', session transfer nodes 208, 208', or session control node 222.

First access network 210 '(first AN), second access network 212' (second AN), and session transfer node 208 'are part of serving communication network 202'. The session control node 222 may be part of the home communication network 200 'as described in fig. 2b, but may alternatively or additionally be part of the serving communication network 202', as described in more detail in connection with fig. 5 and 6.

The session control node 222 determines the session transfer node 208 'in the serving communication network 204', e.g. by looking up the appropriate session transfer node 208 'from a table or by performing communication (e.g. negotiation) with the session transfer node 208' not depicted in fig. 2b, and sends the determined address of the session transfer node 208 'to the first access network 210' to enable the first access network 210 'to initiate any session transfer request to the session transfer node 208'. The address of the session transfer node 208 'may be received at the first access network 210' during session establishment, indicating to the first access network 210 'to anchor the session at the session transfer node 208'. Examples for determining and transmitting are provided in more detail in connection with fig. 5 and 6.

A session between the terminal 204 'and the remote terminal 206' is performed. The signalling data for the session is routed between the terminal 204 'and the remote end 206' via the first access network 210 '(circled) and the session transfer node 208' (circled) and typically one or more further nodes not shown here.

A handover request is sent from the first access network 210 'to the second access network 212'. The handover request includes the address of the session transfer node 208' as determined by the session control node 222. Upon receiving the handover request, the second access network 212 'sends a session transfer request to the provided address of the session transfer node 208' to request transfer of the session from the first access network 210 'to the second access network 212'. The session transfer node 208 ' may signal an indication message to the first and second access networks 210 ', 212 ' to indicate the networks 210 ', 212 ' (and one or more other nodes not shown here for brevity) with respect to the transfer. After the transfer, the signalling data of the session is routed via the second access network 212 '(circled) and via the session transfer node 208' (circled).

The media data of the session is not depicted in fig. 2a and 2 b. Media data is also typically transferred from the first access network 210, 210 'to the second access network 212' along with session signaling data. The media data and the signaling data of the session may be routed via the same node and/or via different nodes, which may for example be more suitable for handling and routing the respective data types.

Exemplary embodiments of routing media data and signaling data for a session before and after a session transfer by session transfer node 308 (represented by a "secondary" SCC or a-SCC) are described in fig. 3 and 4.

Fig. 3 and 4 (and subsequent figures) describe exemplary embodiments of the invention at the node level with respect to a first access network 310 and a second access network 312. The first access network 310 according to fig. 3-6 is a PS network comprising an enodeb (enb)324, a Mobility Management Entity (MME)326, a serving gateway (S-GW)328, a packet gateway (P-GW)330 or a packet data network gateway (PDN GW), a proxy call/session control function (P-CSCF)332, and the second access network 312 is a CS network comprising a base station subsystem/radio network controller (BSS/RNC)332, a mobile switching center server (MSC-S)334 and a Media Gateway (MGW) 336. The a-SCC308 and the Media Resource Function Processor (MRFP)338 anchor the signaling data 316, 420 and the media data 340, 442, respectively, and cannot be attributed to either of the first access network 310 and the second access network 312.

The a-SCC308 may include the functionality of a session transfer node and the P-CSCF 322 may include the functionality of a session control node. The a-SCC308 and MRFP 338 may interface with each other via interface 344.

The BSS/RNC 332, MSC-S334, and MGW 336 may form part of a Universal Mobile Telecommunications System (UMTS). The RNC 332 may form part of a UMTS terrestrial RAN network (UTRAN), which may include a node b (nb).

Fig. 3 and 4 show a terminal (UE)304 exchanging signaling data ("signaling", thick solid lines 316, 420) and media data ("RTP (real time transport protocol) data", thick dashed lines 340, 442) with a remote end at the side of a home communication network 300 ("home", remote end not shown, thick dashed lines 340, 442 and solid lines 316, 420 may extend towards the remote end via a number of other nodes, which are likewise not shown for the sake of simplicity). The UE 304 roams in the serving communication network 302, and therefore, the serving communication network 302 is also referred to as a visited communication network ("visited").

According to fig. 3, the UE 304 attaches via a PS (e.g., E-UTRAN) access network 310, and the signaling data 316 is routed via the eNodeB 324, S-GW 328, P-GW 330, P-CSCF 322, session (signaling data) anchor a-SCC308 to nodes in the home network 300 (here S-CSCF 346 and SCC AS 348), and possibly other nodes to the remote end. Media data 340 is routed to MRFP 338, to one or more nodes (not shown) of home communication network 300, to the remote end via the same eNodeB 324, S-GW 328, and P-GW 330.

Fig. 4 shows the routing of signaling data 420 and media data 442 after the transfer from PS access network 310 to CS access network 312. The signaling data 420 is routed via the BSS/RNC 332, MSC-S334 and via the same a-SCC308 as before the transfer. Media data 442 is routed via BSS/RNC 332 to MGW 336 and the same MRFP 338 as before the transfer. According to an exemplary embodiment, signaling data 420 and media data 442 are also routed via node 348 in the same home network 300 prior to the transfer.

The a-SCC308 is a new function in the serving (or visited, if roaming) network 302. The a-SCC308 mainly provides an IMS-based mechanism to achieve service continuity for multimedia sessions. For IMS service continuity, and in particular for session (also referred to as "access" today) transfer as defined in 3GPP technical specification 23.237, a-SCC308 may implement one or more of the following functions:

the a-SCC308 is included within the SIP routing path. Both the originating and terminating sessions pass.

This also means that the session transfer request is terminated at the a-SCC 308.

The a-SCC308 analyzes SIP INVITE the information required for the session transfer included in (an example of a session transfer request, including session transfer request identification information allowing to identify that the received SIP invite is indeed a session transfer request, and also terminal identification information) and decides which session transfer scenario should be performed; if not (if there is an operator policy in the a-SCC308), the session transfer request is rejected. *

The a-SCC308 may retrieve the relevant mobile station international ISDN number (C-MSISDN) bound to the IMS private user identity stored in the user profile in the HSS, from the HSS or from the SCC AS 348. If the session for the PS access is anchored in the SCC AS 348, the SCC AS 348 knows that the session is in progress for the IMS private user identity used during registration.

The a-SCC308 indicates to the home IMS that it has been included in the routing path by means of a flag/indication in the SIP message. This allows the home communication network 300 to disable the functions in the home communication network 300 (if present) related to the session transfer.

The a-SCC308 correlates the session transfer request with the anchored session using the information provided in the input SIP INVITE (see also the items at "", above, e.g. by analyzing the received terminal identification information). If the session transfer request includes a C-MSISDN, SCC AS 348 may look up the corresponding session on the PS access that should be transferred.

The a-SCC308 provides session transfer specific charging data.

The a-SCC308 controls the MRFP 338 for media operations.

The a-SCC308 may act as a back-to-back user agent (B2BUA) (signaling and media) to hide such changes from the remote end.

The a-SCC308 may be stand-alone or co-located with SIP-capable network entities, such as P-CSCF 322, MSC-S334, or IMS Border Control Function (IBCF).

The a-SCC308 may perform an access transfer procedure by replacing the source access segment (e.g., via evolved universal terrestrial radio access network (E-UTRAN)) currently in communication with the remote segment with the target access segment (via the MSC server 334). The a-SCC308 may do this by looking up an existing session related to the access transfer request (using the C-MSISDN specified in 3GPP technical specification 23.237) and replacing the source access leg with the target access leg. If the media flow is not maintained in the moved access, the source access segment is released and the A-SCC308 updates the remote segment if necessary. When performing a handover of a source access segment to a target access segment, the remote segment is also typically updated to forward the media stream to the moved-in access network.

After the transfer to, e.g., the CS, signaling 420 is routed via a-SCC308, and media 442 is routed via MRFP 338.

If the A-SCC308 is placed in the visited network 302, the SCC AS 348 in the Home Public Land Mobile Network (HPLMN)/home IMS provides terminating Access Domain selection (T-ADS), AS specified in 3GPP technical Specification 23.237. In addition, SCC AS 348 may handle operator policies and inter-UE transfers.

Because the a-SCC308 is included in the routing plane,

the a-SCC308 needs to be selected for the originating and terminating sessions.

The session transfer request from the MSC server enhanced for SRVCC needs to be routed to the a-SCC 308.

There is therefore a need to determine a session transfer node in a serving communication network and to communicate an address of the determined session transfer node to a node in the serving communication network, the node in the serving communication network being adapted to trigger sending of a session transfer request for transferring a session from a first access network to a second access network.

Below, exemplary embodiments are described in the context of fig. 5 and 6, which embodiments relate to determining a session transfer node 308 in the serving communication network 302 for a session for the terminal 304 of the home communication network 300, and to a method for providing the determined address of the session transfer node 308 to the nodes 304, 322, 326, 334, 626, 650 of the serving communication network 302 for a session transfer request to be sent to the determined session transfer node 308. Note that the same reference numerals are provided to the simplified units in fig. 5, 6 that refer to similar or identical units in fig. 3, 4.

There may be different options on how to determine the a-SCC308 in the visited network 302 and how to provide the MSC server 334 with the address of the a-SCC 308.

According to a first option according to fig. 5, where P-CSCF 322 is in a serving (if roaming, visited) network 302, the following steps may be performed:

1) as a first step, the network determines the signaling anchor (a-SCC308) in the serving (if roaming, visited) network 302. This can be performed, for example, in one of two ways:

1a) the A-SCC308 is co-located in a P-CSCF 322 in the visited network 302, the P-CSCF 322 controlling the MRFP 338; in this case, the a-SCC308 need not be explicitly selected.

1b) In the case where the a-SCC308 is separate from the P-CSCF 322, the a-SCC 308:

selection by P-CSCF 322 using some local algorithm for visited network 302 (e.g., round robin, hash based on user ID, etc.), and/or

Selected/addressed by SCC AS 348 in home network 300. In this case, SCCAS 348 may address a-SCCs 308 based on a number of principles, e.g., SCC AS 348 has a list of locally configured a-SCCs 308 for each visited network 302 from which SCC AS 348 selects, SCC AS 348 may derive an a-SCC user roaming number (URI) (visited network 302 will eventually select its own physical a-SCC308) based on the visited network information it has, etc. Note that in this case, P-CSCF 322 may also be in home network 300.

2) AS another step, either a) the P-CSCF 322 (in case the P-CSCF 322 selects the a-SCC308) or b) the SCC AS 348 (in case the SCC AS 348 invokes the a-SCC308) informs the UE 304 of the address of the selected signaling anchor/a-SCC 308 using one of:

local session transfer number single radio (STN-SR, an example of an address of the session transfer node 308) to route calls from the MSC server 334 or the UE 304 to the a-SCC308, or

-other addresses

The STN-SR is an example of an address of the session transfer node 308. It is noted that the address determined by the session control node and sent to the node serving the communication network need not be the same as the address used for sending the session transfer request to the session transfer node, since address translation can be performed.

3) As another step, the UE 304 sends the address of the a-SCC308 to the MME 326, e.g., by performing a re-attach.

4) As another step, the MME 326 includes the address of the a-SCC308 in a relocation request sent to the MSC server 334 on the SV interface.

According to a second option according to fig. 6, where P-CSCF 322 is in serving (if roaming, this is visited) network 302, the following steps may be performed:

1) as a first step, the UE 304 sends a Tracking Area (TA), a globally unique temporary identity (GUTI, used in the evolved packet core (EPC, see 3GPP technical specification 23.401, EPC being part of the Evolved Packet System (EPS)), allocated by the MME 626), an International Mobile Subscriber Identity (IMSI) to the P-CSCF 322.

2) As another step, based on these parameters, P-CSCF 322 selects signaling anchor/a-SCC 308, for example, using a table that maps GUTI and TA to a-SCC instances.

3) As another step, P-CSCF 322 uses TA and GUTI to find a Handover selection function (HOSF)650 (or MME 626, with a 1: 1 relationship between HOSF 650 and MME 626) and informs A-SCC308 of HOSF 650.

When the MME 626 changes, the P-CSCF 322 needs to update the HOSF 650/MME 626 (1: 1 relationship between HOSF/MME).

Note that the HOSF 650 described in this application also supports the selection of handover functions, however, here in this context the a-SCC308 is selected, whereas in voice over LTE (VoLGA) via generic access the selection is made between VoLGA and IMS/SRVCC.

4) During Handover (HO), the MME 626 contacts the HOSF 650, and the HOSF 650 contacts the MSC 334 and includes a signaling anchor.

Note that, as described above, HOSF 650 may be the same node as MME 626. For purposes of this application, the HOSF 650 is a function required by the MME 626 to select a handover support function.

VoLGA forum (see e.g. thehttp://www.volga-forum.com/) The following handover select functions have been defined in their architecture: in case of handover, the HOSF decides whether the HO request from the MME is for VoLGA/SRVCC or for IMS/SRVCC and routes the request accordingly (i.e. to the serving VANC (VoLGA access network controller) or to the MSC server enhanced for SRVCC). The HOSF should support the VANC-UE binding creation and deletion procedure so that it can make these decisions based on the records stored by the serving VANC for the UE. HOSF is a logical functional entity that can be deployed according to the needs of the operator (e.g. a separate entity, embedded in the MME or VANC).

MSC server 334 may use the address of a-SCC308 as follows:

MSC server 334 uses the received address of a-SCC308 to route the access transfer request to the selected a-SCC308 in visited network 302. The session transfer request is sent when MSC server 334 receives the SRVCC PS-CS request (also referred to as handover (request) in fig. 2 b) specified in 3GPP technical specification 23.216. In addition to (or instead of) the STN-SR, the address of the a-SCC308 is used in the session transfer request to route messages to the a-SCC 308.

There may be additional required changes independent of the alternative (option) selected, e.g. with respect to SRVCC call flows, the session transfer request may be sent later, since the session transfer will be fast when done in the visited network 308. MSC server 334 can determine the time to send the session transfer request based on whether a-SCC308 is in visited network 302.

In summary, the present invention enables the use of the A-SCC308 in the visited network, rather than the SCC AS 348 in the home network 300. The a-SCC308 enhances SRVCC by providing a mobility anchor point in the visited network 302 and thus a shorter signaling segment and less time required to complete SRVCC if the P-GW 330 is in the visited network: media path optimization is enabled.

The above description sometimes illustrates the inclusion of a signaling anchor in a message such as a request: for this, included is the address of the session transfer function. In a corresponding manner, expressions like "… sends a signaling anchor to …" should be understood as "sending an address of a session transfer node in the serving communication network to …".

The invention is also implemented in a device, an exemplary embodiment of which is described in more detail below with respect to fig. 7. The references are for illustrative purposes only and are not intended to be limiting.

Fig. 7 schematically shows devices D100, D200, D300 representing exemplary embodiments of a session transfer node of a serving communication network, a node of a serving communication network and a session control node, respectively.

Describing an exemplary embodiment of the session transfer node D100, the session transfer node D100 includes a receiving unit R100, a transmitting unit T100, a processing unit P100, and a storage unit C100. The session transfer node D100 with its respective units R100, T100, P100, C100 may be adapted to perform the steps of the method described herein as far as the session transfer node is concerned, wherein the receiving unit R100 is adapted to receive data, the transmitting unit T100 is adapted to transmit data, and the processing unit P100 is adapted to process data, e.g. store data at the storage unit C100 and/or retrieve data from the storage unit C100 and/or initiate transmission of data via the transmitting unit T100.

An exemplary embodiment of a node D200 (of a serving communication network) is described, the node D200 comprising a receiving unit R200, a transmitting unit T200, a processing unit P200 and a storage unit C200. The node D200 with its individual units R200, T200, P200, C200 may be adapted to perform any of the methods described herein as far as it relates to a node serving a communication network, wherein the receiving unit R200 is adapted to receive data, the transmitting unit T200 is adapted to transmit data, and the processing unit P200 is adapted to process data, e.g. store data at the storage unit C200 and/or retrieve data from the storage unit C200 and/or initiate transmission of data via the transmitting unit T200.

Having described an exemplary embodiment of a session control node D300 (of a serving communication network), the session control node D300 comprises a receiving unit R300, a transmitting unit T300, a processing unit P300 and a storage unit C300. The session control node D300 with its respective units R300, T300, P300, C300 may be adapted to perform any of the methods described herein as far as the session control node D300 is concerned, wherein the receiving unit R300 is adapted to receive data, the transmitting unit T300 is adapted to transmit data, and the processing unit P300 is adapted to process data, e.g. store data at the storage unit C300 and/or retrieve data from the storage unit C300 and/or initiate transmission of data via the transmitting unit T300.

Any of the units R100-300, T100-300, P100-300, C100-300 may include one or more sub-units of the same or different technology.

The invention also concerns a computer program comprising software code portions to implement the above-mentioned method when operating at a session transfer node, a node in a serving communication network and a session control node. The computer program may be stored on a computer readable medium. The computer readable medium may be persistent or rewritable memory within the respective node or external. The computer program may also be transmitted as a sequence of signals to the respective nodes, e.g. via a cable or a wireless link. The computer program may be loaded into the processing unit of any of the aforementioned nodes.

Claims (14)

1. A session control node (222, 322, D300) comprising a receiving unit (R100), a sending unit (T100), a processing unit (P100) and a storage unit (C100), the session control node (222, 322, D300) being adapted to improve session continuity for a terminal (204, 204 ', 304) in a serving communication network (202, 202 ', 302), the serving communication network (202, 202 ', 302) being different from a home communication network (200, 200 ', 300) of the terminal (204, 204 ', 304), wherein the serving communication network (202, 202 ', 302) comprises a session transfer node (208, 208 ', 308), the session transfer node (208, 208 ', 308) being adapted to transfer from a first access network (210, 310) of the serving communication network (202, 202 ', 302) to a second access network (212, 212 ', 302) of the serving communication network (202, 202 ', 302), 212 ', 312), each session comprising signalling data (216, 220, 316, 420) and media data (340, 442), wherein the session control node (222, 322, D300) improves session continuity for the terminal (204, 204 ', 304) in the serving communication network (202, 202 ', 302) by:

-routing (102) signalling data (216, 316) of a session of the terminal (204, 204 ', 304) between the first access network (210, 210', 310) and the home communication network (200, 200 ', 300) via a session transfer node (208, 208', 308) in the serving communication network,

-receiving (104) a session transfer request requesting a transfer of a session from the first access network (210, 210 ', 310) to the second access network (212, 212 ', 312) for the terminal (204, 204 ', 304), and

-transferring (106) a session from the first access network (210, 210 ', 310) to the second access network (212, 212', 312), and

-routing (108) signalling data (220, 420) of a session of the terminal (204, 204 ', 304) between the second access network (212, 212', 312) and the home communication network (200, 200 ', 300) via the session transfer node (208, 208', 308).

2. The session control node (222, 322, D300) according to claim 1, wherein the session transfer request comprises terminal identification information, the session control node (222, 322, D300) further being adapted to:

-analyzing the terminal identification information to determine a session of the terminal (204, 204', 304) to be transferred.

3. The session control node (222, 322, D300) according to claim 2, wherein the session transfer request further comprises session transfer request identification information, the session control node (222, 322, D300) further being adapted to:

-determining whether any received information complies with an available policy, and

-transferring the session according to the determination of compliance.

4. The session control node (222, 322, D300) of any one of the preceding claims, further adapted to:

-sending a message to a session transfer node (348) in the home communication network (200, 200 ', 300) for indicating to the home communication network session transfer node (348) that the serving communication network session transfer node (208, 208', 308) is responsible for routing signalling data (216, 220, 316, 420) and transferring sessions.

5. A session control node (222, 322, D300) according to any of claims 1-3, wherein the media data (340, 442) is transferred from the first access network (210, 210 ', 310) to the second access network (212, 212', 312) together with the signaling data (216, 220, 316, 420).

6. The session control node (222, 322, D300) of claim 5, wherein the media data (340, 442) is anchored at a node (338) in the serving communication network (202, 202 ', 302) interfacing with the session transfer node (208, 208', 308).

7. A node (304, 322, 326, 334, 626, 650, D200) of a serving communication network (302), comprising a receiving unit (R200), a transmitting unit (T200), a processing unit (P200) and a storage unit (C200), the node (304, 322, 326, 334, 626, 650, D200) being adapted to improve session continuity for a terminal (204, 204 ', 304) in a serving communication network (202, 202', 302), the serving communication network (202, 202 ', 302) being different from a home communication network (200, 200', 300) of the terminal (204, 204 ', 304), wherein the serving communication network (202, 202', 302) comprises a session transfer node (208, 208 ', 308), the session transfer node (208, 208', 308) being adapted to transfer from a first access network (210, 210 ', 310) of the serving communication network (202', 302) to the serving communication network (202, 202 `), 202 ', 302), each session comprising signalling data (216, 220, 316, 420) and media data (340, 442), wherein the node (304, 322, 326, 334, 626, 650, D200) improves session continuity for the terminal (204, 204 ', 304) in the serving communication network (202, 202 ', 302) by:

-receiving (110) an address of a session transfer node (208, 208 ', 308) in the serving communication network (202, 202', 302),

-sending (112) a session transfer request to an address of a session transfer node (208, 208 ', 308) in the serving communication network (202, 202 ', 302), the session transfer request requesting a transfer of a session from the first access network (210, 210 ', 310) to the second access network (212, 212 ', 312) for the terminal (204, 204 ', 304),

such that signalling data (220, 420) for a session of the terminal (204, 204 ', 304) is routed (108) between the second access network (212, 212', 312) and the home communication network (200, 200 ', 300) via the session transfer node (208, 208', 308) after session transfer.

8. The node (304, 322, 326, 334, 626, 650, D200) of claim 7, further adapted to:

-receiving a message requesting a session transfer, an

-sending a session transfer request in response to receiving the message.

9. A session control node (222, 322, D300) comprising a receiving unit (R300), a sending unit (T300), a processing unit (P300) and a storage unit (C300), the session control node (222, 322, D300) being adapted to improve session continuity for a terminal (204, 204 ', 304) in a serving communication network (202, 202', 302), the serving communication network (202, 202 ', 302) being different from a home communication network (200, 200', 300) of the terminal (204, 204 ', 304), wherein the serving communication network (202, 202', 302) comprises a session transfer node (208, 208 ', 308), the session transfer node (208, 208', 308) being configured to transfer from a first access network (210, 310 ') of the serving communication network (202, 202', 302) to a second access network (212, 212 ', 302) of the serving communication network (202, 202', 302), 212 ', 312), each session comprising signalling data (216, 220, 316, 420) and media data (340, 442), wherein the session control node (222, 322, D300) improves session continuity for the terminal (204, 204 ', 304) in the serving communication network (202, 202 ', 302) by:

-determining (120) an address of a session transfer node (208, 208 ', 308) in the serving communication network (202, 202', 302),

-sending an address of the session transfer node (208, 208 ', 308) to a node (304, 322, 326, 334, 626, 650) in the serving communication network (202, 202', 302),

such that signalling data (220, 420) for the session for the terminal (204, 204 ', 304) is routed (108) between the second access network (212, 212', 312) and the home communication network (200, 200 ', 300) via the session transfer node (208, 208', 308) after the session transfer.

10. The session control node (222, 322, D300) according to claim 9, wherein the session transfer node (208, 208 ', 308) in the serving communication network (202, 202 ', 302) is determined by a session transfer node (348) in the home communication network (200, 200 ', 300), the session control node (222, 322, D300) further being adapted to:

-receiving (110), from a session transfer node (348) in the home communication network (200, 200 ', 300), an indication of a selected session transfer node (208, 208 ', 308) in the serving communication network (202, 202 ', 302), and

-determining an address of the session transfer node (208, 208', 308) from the received indication.

11. The session control node (222, 322, D300) of claim 9, wherein the session control node (322) is a node of the serving communication network (302) and determines the session transfer node (308).

12. The session control node (222, 322, D300) of claim 11, wherein sending the address of the session transfer node (308) to the node (304, 326, 334) of the serving communication network (302) comprises:

-sending an address of the session transfer node (308) from the session control node (222, 322) to the terminal (304).

13. The session control node (222, 322, D300) according to claim 9 or 11, further adapted to:

-receive at least one parameter from the terminal (304), the at least one parameter comprising the following information: information on the identity of a subscriber operating the terminal (304), information on the location of the terminal (304), and information on the identity of a serving mobility node (626, 650) in the serving communication network (302) to which the terminal (304) is attached,

-determining the session transfer node (308) from the at least one received parameter.

14. The session control node (222, 322, D300) of claim 13, wherein sending the address of the session transfer node (308) to the node (334, 626, 650) of the serving communication network (302) comprises:

-sending the address of the session transfer node (308) to the serving mobility node (626, 650).