IMS ELIGIBILITY FOR AN EU-SAT-EU COMMUNICATION SCHEME

Abstract

A method for establishing a communication of the IP multimedia subsystem in local routing mode where user data are routed directly at one or more interconnected satellites, without passing through the ground, between two UE terminals connected to a regenerative satellite of a communication network comprising a satellite constellation. A session control function of the IMS core network interrogates a server linked to the satellite constellation with the information relating to the satellite access networks of the two terminals. The server is able to determine, by verification of an inter-satellite link between the regenerative satellites corresponding to the information relating to the satellite access networks of the two terminals, whether local routing of the user plane without passing through the ground is available to directly connect the two terminals are connected by link.

Claims

1. A method for establishing a communication of the IP multimedia subsystem (IMS) between two user equipment (UE) terminals each having IMS clients within a communication network comprising a core network and a satellite constellation comprising regenerative satellites providing the radio cells, the communication being established in a local routing mode where user data are routed directly at one or more interconnected satellites, without passing through the ground, the method comprising the following steps integrated in real time in a session initiation protocol SIP as predefined: for the calling terminal connected to a regenerative satellite, via its IMS client, insert information relating to its satellite access network into a message according to the SIP session initiation protocol, for the called terminal connected to a regenerative satellite, via its IMS client, insert information relating to its satellite access network into a message according to the SIP session initiation protocol, a session control function of the core network, retrieving the information related to the satellite access networks of the two terminals, the session control function of the core network, interrogating a server linked to the satellite constellation able to determine, based on the information relating to the satellite access networks of the two terminals, if local routing of the user plan without passing through the ground is available to connect the two terminals directly, for the server linked to the constellation, verifying that the regenerative satellites corresponding to the information relating to the satellite access networks of the two terminals are connected by inter-satellite link (ISL), for the session control function of the core network, transmitting the IP addresses of the two terminals to a session management function (SMF) for configuration of the local routing, for the session management function, configuring the local routing and implementing the communication in local routing mode where user data are routed directly at one or more interconnected satellites, without passing through the ground, between the two terminals.

2. The method according to claim 1, wherein the information relating to the access networks is inserted into a P-Access-Network-Info field as predefined in the session initiation protocol SIP.

3. The method according to claim 1, wherein the information relating to the access network of the calling terminal is inserted into a communication invitation message as predefined in the session initiation protocol SIP and the information relating to the proxy access of the called terminal is inserted into the ringing message for setting up the communication as predefined in the session initiation protocol SIP.

4. The method according to claim 1, wherein the information relating to the access network of the called terminal is inserted into the established ringing message of the communication as predefined in the session initiation protocol SIP and the information relating to the access network of the calling terminal is inserted into an acknowledge of receipt message for a communication agreement as predefined in the session initiation protocol SIP.

5. A core network of an IP multimedia communication network (IMS) connected to a 5G network comprising a satellite constellation with regenerative satellites providing the radio cells and a 5G core network, the IP multimedia core network IMS comprising at least one session control function and a session management function and being configured to establish communication of the IP multimedia subsystem IMS between two user equipment (UE) terminals each having IMS clients within the communication network, the communication being in local routing mode where user data are routed directly at one or more interconnected satellites, without passing through the ground, the session control function of the IMS core network being configured to receive information in real time relating to the satellite access networks of the calling and called terminals, both connected to a regenerative satellite of the constellation, in messages according to the session initiation protocol SIP as predefined, and to interrogate a server linked to the satellite constellation capable of determining, based on the information relating to the satellite access networks of the two terminals, whether a local routing of the user plane without passing through the ground is available to connect the two terminals directly, this server verifying that the regenerative satellites corresponding to the information relating to the satellite access networks of the two terminals are connected by inter-satellite link ISL, the session control function of the core network further being configured to transmit the IP addresses of the two terminals to the session management function SMF for configuration of the local routing and implementation of the communication in local routing mode where user data are routed between the two terminals directly at one or more interconnected satellites, without passing through the ground.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The following description and the accompanying drawings illustrate in detail some illustrative aspects and represent only a few of the various ways in which the principles of the invention can be employed. Other advantages and features will become apparent from the following detailed description, when considered in conjunction with the drawings, and the disclosed embodiments are intended to include all these aspects and equivalents thereof.

[0045] FIG. 1 schematically shows the overall architecture of the 5th generation core network and IMS layers comprising non-terrestrial cells;

[0046] FIG. 2 schematically shows the SIP signaling stream between 2 IMS clients in a general case;

[0047] FIG. 3 schematically shows the basic concept of the UE-SAT-UE communications using cells integrated into different low-orbit satellites and connected by Inter-Satellite Links (ISL),

[0048] FIG. 4 is a time diagram showing a method according to the invention.

DETAILED DESCRIPTION

[0049] For a more complete understanding of the invention, this will now be described in detail with reference to the appended figures. The detailed description will illustrate and describe what is considered to be a preferred embodiment of the invention. It is of course understood that various modifications and changes of shape or detail could easily be made without departing from the scope of the invention. It is therefore provided that the invention is not limited to the exact shape and details shown and described herein, nor to anything less than the entirety of the invention disclosed herein and claimed below. The same elements have been designated by the same references in the various drawings. For clarity's sake, only the elements and the steps which are useful to understanding the present invention have been shown in the drawings and will be described.

[0050] FIG. 1 shows the architecture hypotheses of the Rel-19 3GPP, where satellite access with a regenerative payload allows 5G core access to provide an IMS service as in Voice over New Radio (VoNR), or Video over New Radio (ViNR).

[0051] FIG. 2 shows the SIP signaling stream between two IMS clients in a general case where the two terminals do not have the same serving function S-CSCF. A first terminal UE_A sends an invitation INVITE for communication to a second terminal UE_B to the proxy function P-CSCF, which transfers it to the serving function S-CSCF of the first terminal. Ringing information RINGING on the terminal UE_B is returned to the terminal UE_A until the user of the terminal UE_B responds. In this case, OK to establish communication information 200 is returned to the terminal UE_A, which acknowledges receipt ACK in return. The media stream, depicted by a bold double arrow, is then established. Then, the terminal which is hung up first, here UE_A, sends end-of-communication information BYE that the second terminal consents to by an OK information 200. In the case where the two terminals are subscribers to the same IMS network, i.e., outside roaming, which is the case envisaged by the 3GPP study in release 19, there is only one S-CSCF.

[0052] When a satellite network is implemented, for various reasons, such as for example latency optimization during a communication or else saving resources on the link between the satellite and the ground gateway, it is possible to connect two user terminals UE by directly switching the communication data in the satellite SAT, without returning to the ground, provided that the two terminals are served by the same satellite or by a set of satellites connected via inter-satellite links (ISLs). Reference is then made to UE-Sat(s)-UE communication.

[0053] Thus, 3GPP Release 19 introduces the notion of regenerative satellite and the resulting possibility of having a scheme of the UE-Sat(s)-UE type according to FIG. 3, explained in study document TR 23.700-29 currently being developed, Study on Integration of Satellites components in the 5G architecture, Phase 3, in English.

[0054] FIG. 3 shows the basic concept of the UE-SAT-UE communications using cells integrated into different orbit satellites and connected by Inter-Satellite Links (ISL). Once the satellites connected to the terminals are connected via an inter-satellite link ISL as defined in the present or future standard, it is possible to perform local routing of the data exchanged between the terminals, i.e. without going through the ground.

[0055] FIG. 4 schematically shows the exchanges between the entities shown in FIG. 3 when they are implementing a method according to the invention. This is an illustrative example of implementation of the method according to the invention in a case where a single S-CSCF function is present, i.e. in a case where the terminals are not in a roaming situation.

[0056] In a step E1, a calling terminal UE_A, via its IMS client, gives information to a field P_Network_Info in a message according to the session initiation protocol SIP, here an INVITE message for example, when it proposes communication to a terminal called UE_B. The P_Network_Info field is populated with information about the access networks of the terminal UE_A. This is typically information relating to the gNodeB carried by a satellite SA and to a serving cell with which the terminal UE_A is connected. This field is advantageously a P-Access-Network-Info field as defined elsewhere in the standard.

[0057] It is recalled here that document RFC7976 stipulates that this P-Access-Network-Info header field can appear in all SIP protocols and the non-100 responses, with the exception of the cancellation protocols (CANCEL methods, CANCEL responses) and the acknowledgment protocols (ACK methods) triggered by the non-2xx responses as defined in the standard.

[0058] The P-Access-Network-Info field will thus provide information on the satellite and the gNodeB that it carries, as well as on the serving cell. Advantageously, the P-Access-Network-Info field is positioned with an access-type sub-field equal to 3GPP-NR-SAT.

[0059] In this case, a utran-cell-id-3gpp parameter corresponds to the concatenation of the Mobile Country Code MCC (3 decimal digits), Mobile Network Code MNC (2 or 3 decimal digits depending on MCC value), Tracking Area TAC (6 hexadecimal digits), NR Cell Identity (NCI) (9 hexadecimal digits), and optionally, PLMN ID and Network identifier NID (11 hexadecimal digits) as specified in document TS 23.003 of the 3GPP.

[0060] The utran-cell-id-3gpp parameter is encoded in ASCII as defined in document RFC 20 also belonging to the standard. In 5G NR, the NCI corresponds to 36 bits and identifies a gNodeB and a local cell.

[0061] The P-Access-Network-Info field thus has all the data necessary for the tracking of the method according to the invention.

[0062] Advantageously, in a step E1 an IMS session control function of the core network, typically the serving session control function S_CSCF, stores the information contained in the field P-Access-Network-Info. The call invitation message is then transmitted to a terminal called UE_B in a step E2. In a step E3, the called terminal UE_B sends a return message according to the SIP protocol and in turn inserts the information from gNodeB and Cell concerning it. Thus, the terminal called UE_B, via its IMS client, in turn populates the field P-Access-Network-Info when it responds to the prompt in one of the call placement messages, for example the RINGING message as shown in FIG. 2.

[0063] Here again, the IMS core network, here the session control serving function S-CSCF, recovers the information from the called terminal UE_B. Advantageously, it also stores this information in a step E3.

[0064] The core network, here the S-CSCF (Serving Call Session Control Function) function, once in possession of the gNodeB and serving cell information for both terminals in real time, will interrogate a server linked to the constellation to determine whether the two terminals can be directly connected with routing of the user plane without passing through the ground.

[0065] Thus, in a step E4, the IMS core network, in this case the session control serving function S-CSCF, interrogates an external service ES in connection with the satellite constellation. To this end, the network core sends to the external service the information relating to the satellite access networks of the two terminals. In a step E5, the external service ES checks that the two cells/gNodeB carried by the two satellites SAT1 and SAT2 supporting the accesses of the two terminals UE_A and UE_B are connected by inter-satellite link ISL at the present instant. The service ES will thus confirm or invalidate that it is possible to implement a communication of the UE-Sat(s)-UE type between the two terminals, by verifying that the satellites are indeed interconnected via ISL.

[0066] If this is the case, the S-CSCF function is informed in a step E5. Advantageously, in a step E6, the S-CSCF function then sends a Session Management Function (SMF) the IP addresses of the two terminals for configuration of the local routing.

[0067] This corresponds to the case where an SMF function handles the IP routing and the configuration of the User Plane Function (UPF) in a step E7.

[0068] It is then possible to continue the call establishment in a UE-Sat-UE communication mode, that is, local routing where user data are routed directly at one or more interconnected satellites, without passing through the ground, in a step E8.

[0069] It is noted here that the external service in relation to a satellite operator can be implemented in a Policy Control Function (PCF) or Policy and Charging Rules Function (PCRF) and/or in a Unified Data Management (UDM) server, AUthentication Server Function (AUSF), Home Subscriber Server (HSS) and/or in a Proxy-Call Session Control Function (P-CSCF) and/or IP Multimedia Subsystem-Application Server (IMS-AS).

[0070] As noted above, according to the implementation of the invention, different pairs of session initiation protocol SIP messages can be used. Thus, it is possible to use the currently predefined INVITE & RINGING message pair, or the currently predefined RINGING & ACK message pair, or other possible combinations between the SIP messages to transmit the P-Access-Network-Info information. It is thus noted that the calling terminal can be the first to transmit the proxy access information or can also transmit this information subsequently to a first response from a called terminal. It is also noted here that the above description is carried out for communication between two terminals, but that the invention applies equally well to communication for a group of users, typically communication for a group of more than two users.

[0071] It is also noted that the invention can be implemented using the same core network functions, typically the same proxy and serving functions P-CSCF/S-CSCF, or different P-CSCF/S-CSCF functions for each of the users.

[0072] Finally, the invention implemented by IMS core network functions can be managed by the proxy function P-CSCF and/or by the serving function S-CSCF and/or by the interrogation function I-CSCF or by a combination of several functions.

[0073] In the detailed description above, reference is made to the appended drawings which show specific embodiments wherein the invention can be implemented. These embodiments are described in a sufficiently detailed manner to allow a person skilled in the art to put the invention into practice. The detailed description above should therefore not be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, interpreted appropriately.