WO2016165758A1 - Terminating access domain selection for wireless access - Google Patents

Terminating access domain selection for wireless access Download PDF

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Publication number
WO2016165758A1
WO2016165758A1 PCT/EP2015/058171 EP2015058171W WO2016165758A1 WO 2016165758 A1 WO2016165758 A1 WO 2016165758A1 EP 2015058171 W EP2015058171 W EP 2015058171W WO 2016165758 A1 WO2016165758 A1 WO 2016165758A1
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WO
WIPO (PCT)
Prior art keywords
wlan
pdn connection
gateway
ims
routed via
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PCT/EP2015/058171
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French (fr)
Inventor
Håkan ÖSTERLUND
Afshin Abtin
Daniel Nilsson
Ann-Christine Sander
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Telefonaktiebolaget Lm Ericsson (Publ)
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Priority to PCT/EP2015/058171 priority Critical patent/WO2016165758A1/en
Publication of WO2016165758A1 publication Critical patent/WO2016165758A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/10—Architectures or entities
    • H04L65/1016—IP multimedia subsystem [IMS]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W76/00—Connection management
    • H04W76/10—Connection setup
    • H04W76/12—Setup of transport tunnels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/10—Architectures or entities
    • H04L65/102—Gateways
    • H04L65/1033—Signalling gateways
    • H04L65/104—Signalling gateways in the network
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/10—Architectures or entities
    • H04L65/1063—Application servers providing network services
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
    • H04L65/1066—Session management
    • H04L65/1069—Session establishment or de-establishment
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W76/00—Connection management
    • H04W76/10—Connection setup
    • H04W76/15—Setup of multiple wireless link connections
    • H04W76/16—Involving different core network technologies, e.g. a packet-switched [PS] bearer in combination with a circuit-switched [CS] bearer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/16—Gateway arrangements

Definitions

  • the present invention relates to terminating access domain selection in a telecommunications network comprising an IMS.
  • the invention relates to improved methods for terminating access domain selection, and apparatus for implementing the methods.
  • Terminating Access Domain Selection is a procedure in an IMS-enabled telecommunications network to determine the access which should be used to route a terminating voice call to a user equipment (UE) (i.e. a call directed to the UE).
  • UE user equipment
  • the SCC-AS of the IMS needs to know which access type the UE is connected via, for example the handling of the call will differ significantly between a 2G access such as GSM, and an LTE access such as E-UTRAN.
  • the SCC-AS In order to obtain the radio access type (RAT) used by the UE, the SCC-AS sends a T- ADS query to the home subscriber server, HSS, of the IMS network.
  • the HSS queries the mobility management entity, MME, and/or SGSN to determine which RATs the UE is attached to, and a timestamp indicating the time of attachment or of the latest location update from the UE over each RAT.
  • the RAT corresponding to the most recent update is assumed to be the RAT currently in use by the UE, and the HSS provides the identity of this RAT to the SCC-AS so that the SCC-AS can route the call appropriately.
  • This mechanism is defined in 3GPP TS 23.292 v13.1.0, and the operation of the HSS is described in Annex E of 3GPP TS 29.328 v12.7.0.
  • WLANs wireless access networks
  • dual radio implementations mean that a UE may be active on both a WLAN and a traditional mobile RAT (i.e. a 2G, 3G, or LTE access), with different PDN connections active on different RATs.
  • the current T-ADS procedure will fail in the case where the UE is connected only to a WLAN, and will route the call via the traditional mobile RAT in the case of a dual radio connection. Therefore, the current T-ADS procedure is clearly not sufficient for the case where the UE is connected to the IMS via a WLAN.
  • a method in a telecommunication network comprising an IMS network, of determining which RAT should be used to route a terminating session directed towards a UE.
  • the HSS receives a T-ADS query from an AS, the T-ADS query relating to the terminating session and identifying the UE, and determines whether an authentication, authorisation, and accounting, AAA, server is registered for the UE.
  • AAA authentication, authorisation, and accounting
  • the HSS sends a request for IMS PDN connection information to the AAA server, the request identifying the UE.
  • the AAA server determines whether the IMS PDN connection of the UE is routed via the WLAN and sends the result to the HSS.
  • the HSS determines whether or not the result indicates that the IMS PDN connection is routed via the WLAN. In the case where the result indicates that the IMS PDN connection is routed via the WLAN, the HSS sends a T- ADS response to the AS indicating that the terminating session should be routed via the WLAN. In the case where an AAA server is not registered or the result does not indicate that the PDN connection routed via the WLAN, the HSS performs a further procedure to determine which non-WLAN RAT should be used to route the terminating call, and sends a T-ADS response from the HSS to the AS indicating a result of the further procedure.
  • apparatus configured to operate as an HSS.
  • the HSS comprises a first transceiver, a second transceiver and a T-ADS processor.
  • the first transceiver is configured to communicate with an AS of the telecommunications network.
  • the second transceiver is configured to communicate with the AAA server.
  • the T-ADS processor is configured to:
  • T-ADS query from the AS, the T-ADS query relating to a terminating session and identifying a user equipment, UE;
  • apparatus configured to operate as an AAA server.
  • the AAA server comprises a first transceiver, a PDN connection information request processor, and may further comprise a second transceiver.
  • the first transceiver is configured to communicate with the HSS.
  • the PDN connection information request processor is configured to:
  • an IMS PDN connection information request from the HSS, the IMS PDN information request identifying a user equipment, UE;
  • the AAA server may further comprise a second transceiver configured to communicate with the gateway and the step of determining whether the IMS PDN connection is routed via the WLAN may comprise, in the case where the gateway is registered:
  • apparatus configured to operate as a gateway interconnecting a WLAN and a telecommunications network.
  • the gateway comprises a first transceiver, a second transceiver, and a PDN connection information request processor.
  • the first transceiver is configured to communicate with the AAA server.
  • the second transceiver is configured to communicate with the UE.
  • the PDN connection information request processor is configured to:
  • a computer program comprising computer readable code which, when run on an apparatus, causes the apparatus to perform a method according to the first aspect.
  • Figure 1 is a schematic overview of the network architecture for a telecommunications network comprising an IMS network
  • Figure 2 shows the signalling involved in a method of an embodiment
  • FIG. 3 shows the signalling involved in an alternate case of the embodiment of Figure
  • Figure 4 is a flowchart of a method according to a further embodiment
  • Figure 5 is a flowchart of a method according to a yet further embodiment
  • Figure 6 is a schematic diagram of a system for implementing methods according to various embodiments.
  • Enhancements to the T-ADS procedure are proposed here to allow calls to be routed correctly if the UE is on a WLAN.
  • the method proposed here adds to the currently used T-ADS mechanism by detecting whether the UE is connected to the WLAN, and then, in the case where the IMS PDN connection of the UE is not routed via the WLAN, performing a further procedure (e.g. T-ADS according to the current standard) in order to determine which other RAT the UE is connected to. In this way the RAT will be correctly determined in the single access scenario.
  • this method allows the HSS to determine whether the IMS PDN connection is routed via WLAN. This ensures that the terminating call is routed correctly in the dual access scenario, as the call should be routed via the IMS PDN connection.
  • the network architecture in the case of a UE connected to a non-3GPP IP access is shown in Figure 1.
  • This architecture is defined by 3GPP TS 23.402 V13.1.0.
  • the connection is routed via an enhanced packet data gateway (ePDG) (30).
  • ePDG enhanced packet data gateway
  • the only other node of the home PLMN which connects directly to the UE is the authentication, authorisation, and accounting (AAA) server (20), as this is required in order to authenticate the UE so that it can attach to the ePDG.
  • AAA authentication, authorisation, and accounting
  • the ePDG acts as a gateway between the WLAN and the PLMN.
  • TWAN trusted WLAN
  • TWAP TWAN gateway or proxy
  • Both the ePDG and the TWAP/TWAG connect to the PDN gateway (PDN-GW) (40), which connects to the rest of the PLMN.
  • PDN gateway PDN gateway
  • the registration of the UE with the ePDG or TWAP/TWAG is stored in the AAA server.
  • the term "gateway" will refer to either the ePDG, the TWAG, or the TWAP.
  • the AAA server also stores the registration between the PDN-GW and the UE, and the identity of the AAA server serving the UE is stored in the HSS (10).
  • the present method relies partially on the fact that if an AAA server is not registered, this means that the RAT cannot be packet switched (as all packet switched RATs use the AAA server), and if no gateway is registered, the RAT cannot be WLAN.
  • An exemplary signalling flow for the proposed method is shown in Figures 2 and 3, with Figure 2 showing a successful query to the gateway, and Figure 3 showing possible failures to query the gateway.
  • the HSS receives a T-ADS query (X1 ) from the SCC-AS.
  • the T-ADS query identifies the UE for which the RAT is to be determined.
  • the HSS determines whether an AAA server is registered for the UE. If an AAA server is not registered (A1 ), then the access type cannot be WLAN, and the HSS proceeds to the further procedure (X6) (e.g. to a T-ADS procedure as currently defined in standards).
  • the HSS sends a PDN information request (X2) to the AAA server.
  • the PDN information request identifies the UE and requests the RAT used for the IMS PDN connection.
  • the AAA server determines whether a gateway (i.e. ePDG, TWAP, or TWAG) is registered for the UE. If no gateway is registered (B1 ), the RAT cannot be WLAN, and the AAA server sends a response (B2) to the HSS indicating this. Similarly, if a gateway is registered, but connection to the gateway fails, a response is sent indicating that the UE is not connected to the WLAN. This situation can occur if the UE has only just disconnected from the WLAN, but this has not yet been recorded in the AAA server.
  • a gateway i.ePDG, TWAP, or TWAG
  • the AAA server may send a response to the HSS indicating that the RAT is WLAN.
  • the AAA server may send the PDN information request (X3) to the gateway.
  • the latter approach prevents false identification of the WLAN as RAT in the case where a UE has only just moved off the WLAN, and the AAA server has not yet been updated.
  • the gateway determines whether the IMS PDN connection is routed via the gateway, and passes the result (X4) to the AAA server, which then passes the result (X5) to the HSS. Additionally, the gateway may perform a liveliness check, i.e.
  • ICMPv4/ICMPv6 echo request/reply between TWAN and UE (commonly known as a "ping")
  • ARP request/reply (if UE and TWAN is on the same L2 subnet)
  • the gateway If the liveliness check fails, the gateway returns a result that the UE is not connected to the WLAN. This can occur if the UE has left the WLAN silently.
  • the HSS receives a response indicating that the IMS PDN connection is routed via the WLAN (or equivalently, via the gateway), it sends a T-ADS response (X7) to the SCC-AS indicating that the RAT is WLAN. If the HSS receives an error response, or a response indicating that the IMS PDN connection is not routed via the WLAN/gateway, the HSS performs a further procedure (X6) to identify by which non-WLAN access the IMS PDN connection is routed (e.g. a T-ADS procedure according to current standards) and sends a T-ADS response (X7) to the SCC-AS indicating the result.
  • a further procedure e.g. a T-ADS procedure according to current standards
  • FIG. 4 is a flowchart of a method of determining which access network should be used to route a terminating session directed towards a UE.
  • the HSS receives (S101 ) a T-ADS query relating to a terminating session for the UE from an AS, and determines (S102) whether an AAA server is registered for the UE. In the case where an AAA server is registered (S121 ), the HSS sends (S103) a request for IMS PDN connection information to the AAA server, the request identifying the UE.
  • the AAA server receives (S104) the request, determines (S105) whether the IMS PDN connection of the UE is routed via WLAN, and sends (S106) the result to the HSS.
  • the HSS receives (S107) the result, and determines (S108) whether the result indicates that the IMS PDN connection is routed via WLAN. In the case that the IMS PDN connection is routed via WLAN (S123), the HSS sends (S109) a T-ADS response to the AS indicating that the terminating session should be routed via WLAN. In the case that the IMS PDN connection is not routed via WLAN (S124), or in the case where no AAA server is registered (S122), the HSS performs (S1 10) a further procedure to determine by which non WLAN access the terminating call should be routed, and sends (S1 1 1 ) a T-ADS response to the AS indicating the result of the further procedure.
  • FIG. 5 shows a more detailed method at the AAA server.
  • the AAA server receives (S200) an IMS PDN information request from the HSS, and determines (S201 ) whether a gateway (i.e. ePDG or TWAN) is registered for the UE. In the case where a gateway is not registered (S222), the AAA server sends (S208) an IMS PDN information response to the HSS indicating that the IMS PDN connection is not routed via WLAN. In the case where a gateway is registered (S221 ), the AAA server sends (S202) the IMS PDN information request to the gateway.
  • a gateway i.e. ePDG or TWAN
  • the gateway receives (S203) the IMS PDN connection information request, determines (S204) whether the IMS PDN connection of the UE is routed via the gateway (i.e. via WLAN), and sends (S205) an IMS PDN information response to the AAA server indicating the result.
  • the AAA server receives (S206) the IMS PDN information response, and sends (S207) it to the HSS.
  • FIG 6 is a schematic diagram of a system for implementing the above methods. Only the elements which differ from current standards are shown.
  • the system comprises an HSS (100), and an AAA server (200).
  • the system may further comprise a gateway (300).
  • the HSS (100) comprises a first transceiver (101 ), a second transceiver (102) and a T- ADS processor (103).
  • the first transceiver (101 ) is configured to communicate with an AS of the telecommunications network.
  • the second transceiver (102) is configured to communicate with the AAA server.
  • the T-ADS processor (103) is configured to:
  • T-ADS query from the AS, the T-ADS query relating to a terminating session and identifying a user equipment, UE;
  • the AAA server (200) comprises a first transceiver (201 ), a PDN connection information request processor (203), and may further comprise a second transceiver (202).
  • the first transceiver (201 ) is configured to communicate with the HSS.
  • the PDN connection information request processor (203) is configured to:
  • the AAA server (200) may further comprise a second transceiver (202) configured to communicate with the gateway and the step of determining whether the IMS PDN connection is routed via the WLAN may comprise, in the case where the gateway is registered:
  • the gateway (300) comprises a first transceiver (301 ), a second transceiver (302), and a PDN connection information request processor (302).
  • the first transceiver (301 ) is configured to communicate with the AAA server.
  • the second transceiver (302) is configured to communicate with the UE.
  • the PDN connection information request processor (303) is configured to:
  • the methods described above may be implemented by a computer program which, when run on an apparatus, causes the apparatus to perform the method.

Abstract

A method, in a telecommunication network comprising an IMS network, of determining which RAT should be used to route a terminating session directed towards a UE. The HSS receives a T-ADS query from an AS, the T-ADS query relating to the terminating session and identifying the UE, and determines whether an authentication, authorisation, and accounting, AAA, server is registered for the UE. In the case where the AAA server is registered, the HSS sends a request for IMS PDN connection information to the AAA server, the request identifying the UE. The AAA server determines whether the IMS PDN connection of the UE is routed via the WLAN and sends the result to the HSS. The HSS determines whether or not the result indicates that the IMS PDN connection is routed via the WLAN. In the case where the result indicates that the IMS PDN connection is routed via the WLAN, the HSS sends a T- ADS response to the AS indicating that the terminating session should be routed via the WLAN. In the case where an AAA server is not registered or the result does not indicate that the PDN connection routed via the WLAN, the HSS performs a further procedure to determine which non-WLAN RAT should be used to route the terminating call, and sends a T-ADS response from the HSS to the AS indicating a result of the further procedure. Also provided are apparatus for implementing the method.

Description

Terminating Access Domain Selection for Wireless Access
Technical Field The present invention relates to terminating access domain selection in a telecommunications network comprising an IMS. In particular, the invention relates to improved methods for terminating access domain selection, and apparatus for implementing the methods. Background
Terminating Access Domain Selection (T-ADS) is a procedure in an IMS-enabled telecommunications network to determine the access which should be used to route a terminating voice call to a user equipment (UE) (i.e. a call directed to the UE). In order to correctly handle the call, the SCC-AS of the IMS needs to know which access type the UE is connected via, for example the handling of the call will differ significantly between a 2G access such as GSM, and an LTE access such as E-UTRAN.
In order to obtain the radio access type (RAT) used by the UE, the SCC-AS sends a T- ADS query to the home subscriber server, HSS, of the IMS network. The HSS then queries the mobility management entity, MME, and/or SGSN to determine which RATs the UE is attached to, and a timestamp indicating the time of attachment or of the latest location update from the UE over each RAT. The RAT corresponding to the most recent update is assumed to be the RAT currently in use by the UE, and the HSS provides the identity of this RAT to the SCC-AS so that the SCC-AS can route the call appropriately. This mechanism is defined in 3GPP TS 23.292 v13.1.0, and the operation of the HSS is described in Annex E of 3GPP TS 29.328 v12.7.0.
Summary
Many users now desire the ability to make and receive voice calls over wireless access networks (WLANs), e.g. WiFi networks. Furthermore, dual radio implementations mean that a UE may be active on both a WLAN and a traditional mobile RAT (i.e. a 2G, 3G, or LTE access), with different PDN connections active on different RATs. The current T-ADS procedure will fail in the case where the UE is connected only to a WLAN, and will route the call via the traditional mobile RAT in the case of a dual radio connection. Therefore, the current T-ADS procedure is clearly not sufficient for the case where the UE is connected to the IMS via a WLAN. According to an aspect of the present invention, there is provided a method, in a telecommunication network comprising an IMS network, of determining which RAT should be used to route a terminating session directed towards a UE. The HSS receives a T-ADS query from an AS, the T-ADS query relating to the terminating session and identifying the UE, and determines whether an authentication, authorisation, and accounting, AAA, server is registered for the UE. In the case where the AAA server is registered, the HSS sends a request for IMS PDN connection information to the AAA server, the request identifying the UE. The AAA server determines whether the IMS PDN connection of the UE is routed via the WLAN and sends the result to the HSS. The HSS determines whether or not the result indicates that the IMS PDN connection is routed via the WLAN. In the case where the result indicates that the IMS PDN connection is routed via the WLAN, the HSS sends a T- ADS response to the AS indicating that the terminating session should be routed via the WLAN. In the case where an AAA server is not registered or the result does not indicate that the PDN connection routed via the WLAN, the HSS performs a further procedure to determine which non-WLAN RAT should be used to route the terminating call, and sends a T-ADS response from the HSS to the AS indicating a result of the further procedure.
According to a further aspect of the present invention, there is provided apparatus configured to operate as an HSS. The HSS comprises a first transceiver, a second transceiver and a T-ADS processor. The first transceiver is configured to communicate with an AS of the telecommunications network. The second transceiver is configured to communicate with the AAA server. The T-ADS processor is configured to:
receive, via the first transceiver, a T-ADS query from the AS, the T-ADS query relating to a terminating session and identifying a user equipment, UE;
determine whether a AAA server is registered for the UE;
in the case where the AAA server is registered:
send, via the second transceiver, an IMS packet delivery network, PDN, connection information request to the AAA server, the IMS PDN connection information request identifying the UE; receive, via the second transceiver, a result from the AAA server;
determine whether or not the result indicates that the IMS PDN connection is routed via the WLAN;
in the case where the result indicates that the IMS PDN connection is routed via the WLAN:
send, via the first transceiver a T-ADS response to the AS indicating that the terminating session should be routed via the WLAN; in the case where an AAA server is not registered or the result does not indicate that the IMS PDN connection is routed via the WLAN:
perform a further procedure to determine by which non-WLAN access the terminating call should be routed;
send, via the first transceiver, a T-ADS response to the AS indicating a result of the further procedure. According to a further aspect, there is provided apparatus configured to operate as an AAA server. The AAA server comprises a first transceiver, a PDN connection information request processor, and may further comprise a second transceiver. The first transceiver is configured to communicate with the HSS. The PDN connection information request processor is configured to:
receive, via the first transceiver, an IMS PDN connection information request from the HSS, the IMS PDN information request identifying a user equipment, UE;
determine whether the IMS PDN connection of the UE is routed via a wireless access network, WLAN;
send the result to the HSS.
The AAA server may further comprise a second transceiver configured to communicate with the gateway and the step of determining whether the IMS PDN connection is routed via the WLAN may comprise, in the case where the gateway is registered:
sending a further IMS PDN connection information request to the gateway; receiving a further IMS PDN connection information response from the gateway.
According to a further aspect, there is provided apparatus configured to operate as a gateway interconnecting a WLAN and a telecommunications network. The gateway comprises a first transceiver, a second transceiver, and a PDN connection information request processor. The first transceiver is configured to communicate with the AAA server. The second transceiver is configured to communicate with the UE. The PDN connection information request processor is configured to:
receive, via the first transceiver, an IMS PDN connection information request from the AAA server;
determine whether an IMS PDN connection of the UE is routed via the WLAN; send an IMS PDN connection information response to the AAA server indicating a result of said step of determining.
According to a final aspect of the present invention, there is provided a computer program comprising computer readable code which, when run on an apparatus, causes the apparatus to perform a method according to the first aspect. Further specific embodiments of the invention are provided in the dependent claims.
Brief Description of the Drawings
Figure 1 is a schematic overview of the network architecture for a telecommunications network comprising an IMS network;
Figure 2 shows the signalling involved in a method of an embodiment;
Figure 3 shows the signalling involved in an alternate case of the embodiment of Figure
2;
Figure 4 is a flowchart of a method according to a further embodiment;
Figure 5 is a flowchart of a method according to a yet further embodiment;
Figure 6 is a schematic diagram of a system for implementing methods according to various embodiments.
Detailed Description
Enhancements to the T-ADS procedure are proposed here to allow calls to be routed correctly if the UE is on a WLAN. The method proposed here adds to the currently used T-ADS mechanism by detecting whether the UE is connected to the WLAN, and then, in the case where the IMS PDN connection of the UE is not routed via the WLAN, performing a further procedure (e.g. T-ADS according to the current standard) in order to determine which other RAT the UE is connected to. In this way the RAT will be correctly determined in the single access scenario. In the dual access scenario, this method allows the HSS to determine whether the IMS PDN connection is routed via WLAN. This ensures that the terminating call is routed correctly in the dual access scenario, as the call should be routed via the IMS PDN connection.
The network architecture in the case of a UE connected to a non-3GPP IP access (i.e. a WLAN) is shown in Figure 1. This architecture is defined by 3GPP TS 23.402 V13.1.0.
In the case where the UE connects via an untrusted WLAN (1 ), the connection is routed via an enhanced packet data gateway (ePDG) (30). The only other node of the home PLMN which connects directly to the UE is the authentication, authorisation, and accounting (AAA) server (20), as this is required in order to authenticate the UE so that it can attach to the ePDG. The ePDG acts as a gateway between the WLAN and the PLMN.
In the case where the UE connects via a trusted WLAN (TWAN) (2), a node of the trusted WLAN acts as the gateway between the WLAN and the PLMN. This node is called a TWAN gateway or proxy (TWAP or TWAG). In general, where the methods below refer to a step being performed in the TWAN, this is done by the TWAP or TWAG.
Both the ePDG and the TWAP/TWAG connect to the PDN gateway (PDN-GW) (40), which connects to the rest of the PLMN. The registration of the UE with the ePDG or TWAP/TWAG is stored in the AAA server. For brevity, from here onwards the term "gateway" will refer to either the ePDG, the TWAG, or the TWAP.
The AAA server also stores the registration between the PDN-GW and the UE, and the identity of the AAA server serving the UE is stored in the HSS (10). The present method relies partially on the fact that if an AAA server is not registered, this means that the RAT cannot be packet switched (as all packet switched RATs use the AAA server), and if no gateway is registered, the RAT cannot be WLAN. An exemplary signalling flow for the proposed method is shown in Figures 2 and 3, with Figure 2 showing a successful query to the gateway, and Figure 3 showing possible failures to query the gateway. The HSS receives a T-ADS query (X1 ) from the SCC-AS. The T-ADS query identifies the UE for which the RAT is to be determined.
Firstly, the HSS determines whether an AAA server is registered for the UE. If an AAA server is not registered (A1 ), then the access type cannot be WLAN, and the HSS proceeds to the further procedure (X6) (e.g. to a T-ADS procedure as currently defined in standards).
If the AAA server is registered, the HSS sends a PDN information request (X2) to the AAA server. The PDN information request identifies the UE and requests the RAT used for the IMS PDN connection. In response to receiving the request, the AAA server determines whether a gateway (i.e. ePDG, TWAP, or TWAG) is registered for the UE. If no gateway is registered (B1 ), the RAT cannot be WLAN, and the AAA server sends a response (B2) to the HSS indicating this. Similarly, if a gateway is registered, but connection to the gateway fails, a response is sent indicating that the UE is not connected to the WLAN. This situation can occur if the UE has only just disconnected from the WLAN, but this has not yet been recorded in the AAA server.
If the gateway is registered, and the IMS PDN connection is routed via the gateway, the AAA server may send a response to the HSS indicating that the RAT is WLAN. Alternatively, the AAA server may send the PDN information request (X3) to the gateway. The latter approach prevents false identification of the WLAN as RAT in the case where a UE has only just moved off the WLAN, and the AAA server has not yet been updated. In response the receiving the request, the gateway determines whether the IMS PDN connection is routed via the gateway, and passes the result (X4) to the AAA server, which then passes the result (X5) to the HSS. Additionally, the gateway may perform a liveliness check, i.e. determining whether it can contact the UE via the WLAN, before returning a result that the IMS PDN connection is routed via the WLAN. Several different methods can be used for doing this e.g.: 1 . ICMPv4/ICMPv6 echo request/reply between TWAN and UE (commonly known as a "ping")
2. ICMPv6 neighbour discovery (if UE and TWAN is on the same L2 subnet)
3. ARP request/reply (if UE and TWAN is on the same L2 subnet)
4. Extending WLCP (Wireless LAN Control Protocol, TS 24.244) with a liveliness check procedure.
If the liveliness check fails, the gateway returns a result that the UE is not connected to the WLAN. This can occur if the UE has left the WLAN silently.
If the HSS receives a response indicating that the IMS PDN connection is routed via the WLAN (or equivalently, via the gateway), it sends a T-ADS response (X7) to the SCC-AS indicating that the RAT is WLAN. If the HSS receives an error response, or a response indicating that the IMS PDN connection is not routed via the WLAN/gateway, the HSS performs a further procedure (X6) to identify by which non-WLAN access the IMS PDN connection is routed (e.g. a T-ADS procedure according to current standards) and sends a T-ADS response (X7) to the SCC-AS indicating the result.
Figure 4 is a flowchart of a method of determining which access network should be used to route a terminating session directed towards a UE. The HSS receives (S101 ) a T-ADS query relating to a terminating session for the UE from an AS, and determines (S102) whether an AAA server is registered for the UE. In the case where an AAA server is registered (S121 ), the HSS sends (S103) a request for IMS PDN connection information to the AAA server, the request identifying the UE. The AAA server receives (S104) the request, determines (S105) whether the IMS PDN connection of the UE is routed via WLAN, and sends (S106) the result to the HSS. The HSS receives (S107) the result, and determines (S108) whether the result indicates that the IMS PDN connection is routed via WLAN. In the case that the IMS PDN connection is routed via WLAN (S123), the HSS sends (S109) a T-ADS response to the AS indicating that the terminating session should be routed via WLAN. In the case that the IMS PDN connection is not routed via WLAN (S124), or in the case where no AAA server is registered (S122), the HSS performs (S1 10) a further procedure to determine by which non WLAN access the terminating call should be routed, and sends (S1 1 1 ) a T-ADS response to the AS indicating the result of the further procedure. Figure 5 shows a more detailed method at the AAA server. The AAA server receives (S200) an IMS PDN information request from the HSS, and determines (S201 ) whether a gateway (i.e. ePDG or TWAN) is registered for the UE. In the case where a gateway is not registered (S222), the AAA server sends (S208) an IMS PDN information response to the HSS indicating that the IMS PDN connection is not routed via WLAN. In the case where a gateway is registered (S221 ), the AAA server sends (S202) the IMS PDN information request to the gateway. The gateway receives (S203) the IMS PDN connection information request, determines (S204) whether the IMS PDN connection of the UE is routed via the gateway (i.e. via WLAN), and sends (S205) an IMS PDN information response to the AAA server indicating the result. The AAA server receives (S206) the IMS PDN information response, and sends (S207) it to the HSS.
Figure 6 is a schematic diagram of a system for implementing the above methods. Only the elements which differ from current standards are shown. The system comprises an HSS (100), and an AAA server (200). The system may further comprise a gateway (300).
The HSS (100) comprises a first transceiver (101 ), a second transceiver (102) and a T- ADS processor (103). The first transceiver (101 ) is configured to communicate with an AS of the telecommunications network. The second transceiver (102) is configured to communicate with the AAA server. The T-ADS processor (103) is configured to:
receive, via the first transceiver, a T-ADS query from the AS, the T-ADS query relating to a terminating session and identifying a user equipment, UE;
determine whether a AAA server is registered for the UE;
in the case where the AAA server is registered:
send, via the second transceiver, an IMS packet delivery network, PDN, connection information request to the AAA server, the IMS PDN connection information request identifying the UE;
receive, via the second transceiver, a result from the AAA server;
determine whether or not the result indicates that the IMS PDN connection is routed via the WLAN;
in the case where the result indicates that the IMS PDN connection is routed via the WLAN: send, via the first transceiver a T-ADS response to the AS indicating that the terminating session should be routed via the WLAN; in the case where an AAA server is not registered or the result does not indicate that the IMS PDN connection is routed via the WLAN:
perform a further procedure to determine by which non-WLAN access the terminating call should be routed;
send, via the first transceiver, a T-ADS response to the AS indicating a result of the further procedure. The AAA server (200) comprises a first transceiver (201 ), a PDN connection information request processor (203), and may further comprise a second transceiver (202). The first transceiver (201 ) is configured to communicate with the HSS. The PDN connection information request processor (203) is configured to:
receive, via the first transceiver, an IMS PDN connection information request from the HSS, the IMS PDN information request identifying a user equipment,
UE;
determine whether the IMS PDN connection of the UE is routed via a wireless access network, WLAN;
send the result to the HSS.
The AAA server (200) may further comprise a second transceiver (202) configured to communicate with the gateway and the step of determining whether the IMS PDN connection is routed via the WLAN may comprise, in the case where the gateway is registered:
sending a further IMS PDN connection information request to the gateway; receiving a further IMS PDN connection information response from the gateway.
The gateway (300) comprises a first transceiver (301 ), a second transceiver (302), and a PDN connection information request processor (302). The first transceiver (301 ) is configured to communicate with the AAA server. The second transceiver (302) is configured to communicate with the UE. The PDN connection information request processor (303) is configured to:
receive, via the first transceiver, an IMS PDN connection information request from the AAA server; determine whether an IMS PDN connection of the UE is routed via the WLAN; send an IMS PDN connection information response to the AAA server indicating a result of said step of determining. The methods described above may be implemented by a computer program which, when run on an apparatus, causes the apparatus to perform the method.
Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:
1 . A method, in a telecommunication network comprising an IP multimedia subsystem, IMS, network, of determining which radio access type, RAT, should be used to route a terminating session directed towards a user equipment, UE, the method comprising:
receiving a terminating access domain selection, T-ADS, query at a home subscriber server, HSS from an application server, AS, the T-ADS query relating to the terminating session and identifying the UE, and determining whether an authentication, authorisation, and accounting, AAA, server is registered for the UE;
in the case where the AAA server is registered:
sending a request for IMS packet data network, PDN, connection information from the HSS to the AAA server, the request identifying the UE;
determining at the AAA server whether the IMS PDN connection of the UE is routed via the WLAN and sending the result to the HSS; and
determining at the HSS whether or not the result indicates that the IMS PDN connection is routed via the WLAN,
in the case where the result indicates that the IMS PDN connection is routed via the WLAN:
sending a T-ADS response from the HSS to the AS indicating that the terminating session should be routed via the WLAN;
in the case where an AAA server is not registered or the result does not indicate that the PDN connection routed via the WLAN:
performing a further procedure to determine at the HSS which non-WLAN RAT should be used to route the terminating call;
sending a T-ADS response from the HSS to the AS indicating a result of the further procedure.
2. A method according to claim 1 , wherein the step of the AAA server determining whether the IMS PDN connection is routed via the WLAN comprises determining whether a gateway between the telecommunications network and the WLAN is registered for the UE, wherein if such a gateway is not registered the AAA server determines that the IMS PDN connection is not routed via the WLAN.
3. A method according to claim 2, wherein the step of the AAA server determining whether the IMS PDN connection is routed via the WLAN further comprises, in the case where the gateway is registered:
sending a further IMS PDN connection information request to the gateway; receiving a further IMS PDN connection information response from the gateway;
the method further comprising, in the case where the gateway is registered for the UE, at the gateway:
receiving the further IMS PDN connection information request from the AAA server;
determining whether the IMS PDN connection is routed via the WLAN;
sending the further IMS PDN connection information response to the AAA server indicating whether the IMS PDN connection is routed via the WLAN.
4. A method according to claim 2, wherein the step of the AAA server determining whether the whether the IMS PDN connection is routed via the WLAN further comprises, in the case where the gateway is registered, determining that the IMS PDN connection is routed via the WLAN.
5. A method according to claim 3, wherein the step of determining whether the IMS PDN connection is routed via the WLAN comprises determining whether the UE is attached to the WLAN.
6. A method according to claim 5, wherein determining whether the UE is attached to the WLAN comprises any one of:
sending an ICMPv4 or ICMPv6 echo request/reply;
performing ICMPv6 neighbour discovery;
sending an ARP request.
7. A method according to any one of claims 2 to 6, wherein the gateway is an enhanced packet data gateway, ePDG, or wherein the WLAN is a trusted wireless access network, TWAN, and the gateway is a node of the TWAN.
8. Apparatus configured to operate as a home subscriber server, HSS, in a telecommunications network comprising an IP multimedia subsystem, IMS, network, the apparatus comprising:
a first transceiver configured to communicate with an application server, AS, of the telecommunications network;
a second transceiver configured to communicate with an authentication, authorisation, and accounting, AAA, server of the telecommunications network; a terminating access domain selection, T-ADS, processor configured to:
receive, via the first transceiver, a T-ADS query from the AS, the T-ADS query relating to a terminating session and identifying a user equipment,
UE;
determine whether a AAA server is registered for the UE; in the case where the AAA server is registered:
send, via the second transceiver, an IMS packet delivery network, PDN, connection information request to the AAA server, the IMS PDN connection information request identifying the UE; receive, via the second transceiver, a result from the AAA server; determine whether or not the result indicates that the IMS PDN connection is routed via the WLAN;
in the case where the result indicates that the IMS PDN connection is routed via the WLAN:
send, via the first transceiver a T-ADS response to the AS indicating that the terminating session should be routed via the WLAN;
in the case where an AAA server is not registered or the result does not indicate that the IMS PDN connection is routed via the WLAN:
perform a further procedure to determine by which non-WLAN access the terminating call should be routed;
send, via the first transceiver, a T-ADS response to the AS indicating a result of the further procedure.
9. Apparatus configured to operate as an authentication, authorisation, and accounting, AAA, server in a telecommunications network comprising an IP multimedia subsystem, IMS, network, the apparatus comprising: a first transceiver configured to communicate with a home subscriber server, HSS, of the telecommunications network;
a packet delivery network, PDN, connection information request processor configured to:
receive, via the first transceiver, an IMS PDN connection information request from the HSS, the IMS PDN information request identifying a user equipment, UE;
determine whether the IMS PDN connection of the UE is routed via a wireless access network, WLAN;
send the result to the HSS.
10. Apparatus according to claim 9, wherein said step of determining whether the IMS PDN connection is routed via the WLAN comprises determining whether an gateway between the telecommunications network and the WLAN is registered for the UE, wherein if such a gateway is not registered the IMS PDN connection information processor determines that the IMS PDN connection is not routed via the WLAN.
1 1 . Apparatus according to claim 10, wherein the apparatus further comprises a second transceiver configured to communicate with the gateway and the step of determining whether the IMS PDN connection is routed via the WLAN further comprises, in the case where a gateway is registered:
sending a further IMS PDN connection information request to the gateway; receiving a further IMS PDN connection information response from the gateway.
12. Apparatus according to claim 10, wherein, in the case where a gateway is registered for the UE, the PDN connection information processor determines that the IMS PDN connection is routed via the WLAN.
13. Apparatus according to any one of claims 10 to 12, wherein the gateway is an enhanced packet data gateway, ePDG, or wherein the WLAN is a trusted wireless access network, TWAN, and the gateway is a node of the TWAN.
14. Apparatus configured to operate as a gateway between a telecommunications network comprising an IP multimedia subsystem, IMS, network and a wireless access network, WLAN, the apparatus comprising:
a first transceiver configured to communicate with an authentication, authorisation, and accounting, AAA, server;
a second transceiver configured to communicate with a user equipment, UE; a packet data network, PDN, connection information request processor configured to:
receive, via the first transceiver, an IMS PDN connection information request from the AAA server;
determine whether an IMS PDN connection of the UE is routed via the WLAN;
send an IMS PDN connection information response to the AAA server indicating a result of said step of determining.
15. Apparatus according to claim 14, wherein the PDN connection information request processor is configured to determine whether the UE is attached to the WLAN.
16. Apparatus according to claim 13, wherein determining whether the UE is attached to the WLAN comprises any of the following via the second transceiver:
sending an ICMPv4 or ICMPv6 echo request;
ICMPv6 neighbour discovery;
sending an ARP request.
17. Apparatus according to any one of claims 14 to 16, wherein the gateway is an enhanced packet data gateway, ePDG, or wherein the WLAN is a trusted wireless access network, TWAN, and the gateway is a node of the TWAN.
18. A computer program comprising computer readable code which, when run on an apparatus, causes the apparatus to perform a method according to any one of claims 1 to 7.
PCT/EP2015/058171 2015-04-15 2015-04-15 Terminating access domain selection for wireless access WO2016165758A1 (en)

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