WO2016159843A1

WO2016159843A1 - Communication of an identifier for a terminal device

Info

Publication number: WO2016159843A1
Application number: PCT/SE2015/050390
Authority: WO
Inventors: Fredrik Gunnarsson; Pontus Wallentin
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2015-03-31
Filing date: 2015-03-31
Publication date: 2016-10-06
Anticipated expiration: 2017-09-30

Abstract

According to an aspect there is provided a method of operating a first terminal device (42) in a telecommunication network (32), the first terminal device (42) having a direct communication link with a second terminal device (42). The method comprises sending (803) a request for an identifier for the second terminal device to the second terminal device via the direct communication link; receiving (805) the identifier for the second terminal device from the second terminal device via the direct communication link; and sending (807) the identifier for the second terminal device to a first network node in the telecommunication network.

Description

Communication of an identifier for a terminal device Technical Field

The present disclosure relates to direct communication between terminal devices, and in particular relates to techniques for providing an identifier for a terminal device that is in direct communication with another terminal device to a network node.

Background

Device-to-device communication is a well-known and widely used component of many existing wireless technologies, including ad hoc and cellular networks. Examples include Bluetooth and several variants of the IEEE 802.1 1 standards suite such as Wi- Fi Direct. These systems operate in the unlicensed spectrum.

Recently, device-to-device (D2D) communications (also known as ProSe - Proximity Service - Direct Communication) have been proposed as an underlay to cellular networks to take advantage of the proximity of communicating terminal devices and at the same time to allow terminal devices to operate in a controlled interference environment. It has been suggested that such device-to-device communication share the same spectrum as the cellular system, for example by reserving some of the cellular uplink resources for device-to-device purposes. Allocating dedicated spectrum for device-to-device purposes is a less likely alternative as spectrum is a scarce resource and (dynamic) sharing between the device-to-device services and cellular services is more flexible and provides higher spectrum efficiency. The transmission mode when sending data during D2D communication may be either:

Unicast - a specific terminal device (also known as a user equipment, UE) is the receiver

Multicast (may also be denoted groupcast) - a group of UEs are receivers Broadcast - all UEs are receivers

With connectionless D2D communication, data can be sent from one terminal device to another terminal device without prior arrangement, thereby reducing the overhead and increasing the communication capacity which is crucial in emergency situations. The source terminal device transmits data to one (unicast) or more (multicast/groupcast/broadcast) other terminal devices, without first ensuring that the recipients are available and ready to receive the data. Connectionless communication may be used for one-to-one or one-to-many communication, but it is particularly effective for multicast and broadcast transmissions and thus well-suited for broadcast and group communication. The connectionless communication may be realized, e.g., via PHY (physical) unicast/multicast/groupcast/broadcast transmissions; with PHY broadcast transmissions, the transmissions may still be turned into unicast/groupcast/multicast at higher layers. For example, in the medium access control, MAC, layer, multicast or even unicast addresses may be used. Alternatively, if using broadcast on both PHY and MAC, multicast or unicast Internet Protocol, IP, addresses may be used at the IP layer.

For D2D communication, a set of new channels have been defined. The physical layer offers the ProSe Communication Channel (PSCH) to the MAC layer. The PSCH is used to transmit and receive data directly between UEs, using one of the transmission modes (unicast, multicast or broadcast). MAC in turn offers the ProSe Traffic Channel (PTCH) to higher layers. The PTCH is mapped by MAC on the PSCH. In MAC there are addressing functions, which is by the receiver used to filter received packets. When there is an address match, MAC forwards the received data (the MAC service data unit, SDU) to the higher layer, which is RLC (radio link control). Each MAC protocol data unit, PDU, for D2D communication contains a source and a destination identifier, ID. The source ID is set locally by the transmitting UE and this ID is either preconfigured or assigned by another node (such as a network node). The destination ID is set to a group address in case of multicast and to a fixed broadcast address in case of broadcast. For unicast the destination ID is set to the identity of the receiving UE.

When a UE is has coverage from the network, any D2D communication is controlled by the network nodes (such as the eNB). Since the radio resources in a cell (especially the uplink resources) are shared between traditional cellular communication and D2D communication, the eNB should divide and assign the radio resources for D2D communication.

For D2D communication, the concept of relaying between a UE and the eNB or another UE, using a relay UE has been defined. This illustrated in Figure 1 . Figure 1 is also found in 3GPP TS 23.303 v12.3.0, section 4.4.3. For example, a UE 2 that is outside the coverage of the network 4 (which is also defined as a remote UE 2) may use a relay UE 6 (which has coverage from the network 4 via an eNB 8) to be able to use the traditional, non-D2D, services provided by the EPC (Evolved Packet Core) 10 (including a public safety address system 12, since the relay UE 6 forwards packets between the remote UE 2 and the eNB 8. Conceptually, also a relay UE 6 may forward packets between two remote UEs 2, without eNB 8 involvement. In addition to the concept in Figure 1 , methods for UE-to-UE relay have been disclosed.

Lately, the concept of isolated evolved, UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network (E-UTRAN) operation has been defined in 3GPP. This is illustrated in Figure 2, which is also found in 3GPP TR 22.897, v13.0.0, section 4. For example, when there is an outage where one, multiple or all eNBs in the network totally or partly looses the connectivity with the core network (as indicated by section 14 of the E-UTRAN that has lost connectivity with other parts 16 of the E- UTRAN that are still in contact with the core network (EPC) 10 and application servers 18), public safety users may still enjoy limited network connectivity. For example, the eNBs in E-UTRAN 14 may still control the radio resources for these services, and even the data may be locally routed via the eNBs. This local routing is illustrated in Figure 3, which is also found in 3GPP TR 22.803 v12.2.0, section 4.1 .2. In this figure, two UEs 20 (UE1 and UE2) communicate via local routing through an eNB 22. In addition to eNB 22, this figure also shows another eNB 24 and a core network node 26, such as a serving gateway (SGW) or packet data network gateway (PGW).

ProSe Direct Communication is defined as using a direct link between two UEs, or possibly communicating via a relay UE. A UE may enjoy the evolved packet system (EPS) network services when outside coverage of the network by using ProSe Direct Communication to a relay UE which then communicates with the network.

In this document, the term ProSe Direct Communication with selective routing is used for any communication which is capable of using either D2D transmission, i.e. transmission directly between UEs, which is herein referred to as "D2D mode" (although it will be noted that one of the UEs may be a relay UE), or being locally routed, i.e. transmitted via one or several network nodes. In this document the term "local routing (mode)", or "routing via the network?' refers to a routing mode other than the D2D mode, e.g. the intra-eNB mode. Typically transmission directly between UEs is supported by a limited set of applications in the UE, for example those application(s) categorized as Mission Critical Push To Talk (MCPTT) or Public Safety applications. The ProSe Direct Communication packets may either be exchanged directly between UEs (using D2D mode), or be locally routed via the network. Summary

In order for communication packets from a first UE to a second UE to be locally routed via one or more eNBs, it is necessary for the identity of the second UE to be known to the first UE and/or the eNB(s). However, existing techniques do not provide ways for the first UE and/or eNBs to determine this identifier. Thus, the techniques described herein provide ways to establish information about the identifier of the UE that is the target for a locally routed communication (although it will be appreciated that knowledge of the identifier of the UE can be used for other purposes than establishing local routing. According to a first aspect, there is provided a method of operating a first terminal device in a telecommunication network, with the first terminal device having a direct communication link with a second terminal device. The method comprises sending a request for an identifier for the second terminal device to the second terminal device via the direct communication link; receiving the identifier for the second terminal device from the second terminal device via the direct communication link; and sending the identifier for the second terminal device to a first network node in the telecommunication network.

According to a second aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein. The computer readable code is configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method described above. According to a third aspect, there is provided a first terminal device for use in a telecommunication network. The first terminal device is capable of communication with a second terminal device via a direct communication link with the second terminal device. The first terminal device is also adapted to send a request for an identifier for the second terminal device to the second terminal device via the direct communication link; receive the identifier for the second terminal device from the second terminal device via the direct communication link; and send the identifier for the second terminal device to a first network node in the telecommunication network.

According to a fourth aspect, there is provided a method of operating a network node in a telecommunication network. The method comprises receiving an identifier for a second terminal device from a first terminal device, the first terminal device having a direct communication link with the second terminal device.

According to a fifth aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein. The computer readable code is configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method defined above. According to a sixth aspect, there is provided a network node for use in a telecommunication network. The network node is adapted to receive an identifier for a second terminal device from a first terminal device, the first terminal device having a direct communication link with the second terminal device. According to a seventh aspect, there is provided a method of operating a second terminal device in a telecommunication network. The second terminal device has a direct communication link with a first terminal device and the method comprises receiving a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and sending the identifier for the second terminal device to the first terminal device via the direct communication link.

According to an eighth aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein. The computer readable code is configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method defined above.

According to a ninth aspect, there is provided a second terminal device for use in a telecommunication network. The second terminal device is capable of communication with a first terminal device via a direct communication link with the first terminal device, and the second terminal device adapted to receive a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and send the identifier for the second terminal device to the first terminal device via the direct communication link. According to a tenth aspect, there is provided a first terminal device for use in a telecommunication network, the first terminal device being capable of communication with a second terminal device via a direct communication link with the second terminal device. The first terminal device comprising a processor and a memory, the memory containing instructions executable by said processor whereby said first terminal device is operative to send a request for an identifier for the second terminal device to the second terminal device via the direct communication link; receive the identifier for the second terminal device from the second terminal device via the direct communication link; and send the identifier for the second terminal device to a first network node in the telecommunication network.

According to an eleventh aspect, there is provided a network node for use in a telecommunication network. The network node comprising a processor and a memory, the memory containing instructions executable by said processor whereby said network node is operative to receive an identifier for a second terminal device from a first terminal device, the first terminal device having a direct communication link with the second terminal device.

According to a twelfth aspect, there is provided a second terminal device for use in a telecommunication network, the second terminal device being capable of communication with a first terminal device via a direct communication link with the first terminal device. The second terminal device comprising a processor and a memory, the memory containing instructions executable by said processor whereby said second terminal device is operative to receive a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and send the identifier for the second terminal device to the first terminal device via the direct communication link.

Brief Description of the Drawings

Exemplary embodiments of the techniques introduced in this document are described below with reference to the following figures, in which: Figure 1 illustrates a UE-to-network relay;

Figure 2 illustrates isolated E-UTRAN operation; Figure 3 illustrates local routing between two UEs served by the same eNB;

Figure 4 is a non-limiting example block diagram of an LTE cellular communications network; Figure 5 is a block diagram of a terminal device according to an embodiment; Figure 6 is a block diagram of a network node according to an embodiment; Figure 7 is a signalling diagram according to a first embodiment;

Figure 8 is a flow chart illustrating a method of operating a first terminal device according to the first embodiment;

Figure 9 is a flow chart illustrating a method of operating a network node according to the first embodiment;

Figure 10 is a flow chart illustrating a method of operating a second terminal device according to the first embodiment; Figure 1 1 is a signalling diagram according to a second embodiment;

Figure 12 is a signalling diagram according to a third embodiment; and

Figure 13 is a signalling diagram according to a fourth embodiment.

Detailed Description

The following sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. But it will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. In some instances, detailed descriptions of well known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understood to comprise one or more processors, one or more processing modules or one or more controllers, and the terms computer, processor, processing module and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed. Moreover, the term "processor" or "controller" also refers to other hardware capable of performing such functions and/or executing software, such as the example hardware recited above.

Although the description is given for user equipment (UE), it should be understood by the skilled in the art that "UE" is a non-limiting term comprising any mobile or wireless device or node equipped with a radio interface allowing for at least one of: transmitting signals in uplink (UL), receiving and/or measuring signals in downlink (DL), and transmitting and/or receiving signals to/from another wireless device in a D2D mode. A UE herein may comprise a UE (in its general sense) capable of operating or at least performing measurements in one or more frequencies, carrier frequencies, component carriers or frequency bands. It may be a "UE" operating in single- or multi-radio access technology (RAT) or multi-standard mode. As well as "UE", the terms "mobile device" and "terminal device" may be used interchangeably in the following description, and it will be appreciated that such a device does not necessarily have to be 'mobile' in the sense that it is carried by a user. Instead, the term "mobile device" encompasses any device that is capable of communicating with communication networks that operate according to one or more mobile communication standards, such as the Global System for Mobile communications, GSM, UMTS, Long-Term Evolution, LTE, etc.

A cell is associated with a base station, where a base station comprises in a general sense any network node transmitting radio signals in the downlink (DL) and/or receiving radio signals in the uplink (UL). Some example base stations, or terms used for describing base stations, are eNodeB, eNB, NodeB, macro/micro/pico/femto radio base station, home eNodeB (also known as femto base station), relay, repeater, sensor, transmitting-only radio nodes or receiving-only radio nodes. A base station may operate or at least perform measurements in one or more frequencies, carrier frequencies or frequency bands and may be capable of carrier aggregation. It may also be a single-radio access technology (RAT), multi-RAT, or multi-standard node, e.g., using the same or different base band modules for different RATs. It should be noted that use of the term "network node" as used herein can refer to a base station, such as an eNodeB, a network node in the radio access network (RAN) responsible for resource management, such as a radio network controller (RNC), or, in some cases, a core network node, such as a mobility management entity (MME). Unless otherwise indicated herein, the signalling described is either via direct links or logical links (e.g. via higher layer protocols and/or via one or more network nodes).

Figure 4 shows an example diagram of an E-UTRAN architecture as part of an LTE- based communications system 32. Nodes in the core network 34 include one or more Mobility Management Entities (MMEs) 36, a key control node for the LTE access network, and one or more Serving Gateways (SGWs) 38 which route and forward user data packets while acting as a mobility anchor. They communicate with base stations 40 referred to in LTE as eNBs, over an interface, for example an S1 interface. The eNBs 40 can include the same or different categories of eNBs, e.g. macro eNBs, and/or micro/pico/femto eNBs. The eNBs 40 communicate with each other over an interface, for example an X2 interface. The S1 interface and X2 interface are defined in the LTE standard. Two UEs 42 are shown, and a UE 42 can receive downlink data from and send uplink data to one of the base stations 40 with that base station 40 being referred to as the serving base station of the UE 42. In various embodiments, the UEs 42 are configured or adapted to be able to communicate with each other in D2D mode (i.e. communicate directly with each other without routing the communications via one or more eNBs 40), and in local routing mode (i.e. communicate with each other via one or more eNBs 40). In this case, the eNBs are configured or adapted to enable local routing between UEs 40.

Figure 5 shows a terminal device (UE) 42 that can be adapted or configured to operate according to one or more of the non-limiting example embodiments described. The UE 42 comprises a processor or processing module 50 that controls the operation of the UE 42. The processing module 50 is connected to a transceiver module 52 (which comprises a receiver and a transmitter) with associated antenna(s) 54 which are used to receive signals from or both transmit signals to and receive signals from a base station 40 in the network 32. The processing module 50 and the transceiver module 52 are also configured or adapted to enable the UE 42 to operate in D2D mode or local routing mode.

The UE 42 also comprises a memory or memory module 56 that is connected to the processing module 50 and that contains instructions or computer code executable by the processor 50 and other information or data required for the operation of the UE 42. Figure 6 shows a base station 40 (for example a NodeB or an eNodeB) that can be adapted or configured to operate according to the example embodiments described. The base station 40 comprises a processor or processing module 60 that controls the operation of the base station 40. The processing module 60 is connected to a transceiver module 62 (which comprises a receiver and a transmitter) with associated antenna(s) 64 which are used to transmit signals to, and receive signals from, UEs 42 in the network 32. The base station 40 also comprises a memory or memory module 66 that is connected to the processing module 60 and that contains instructions or computer code executable by the processor 60 and other information or data required for the operation of the base station 50. The base station 40 also includes components and/or circuitry 68 for allowing the base station 40 to exchange information with other base stations 40 (for example via an X2 interface) and components and/or circuitry 69 for allowing the base station 40 to exchange information with nodes in the core network 34 (for example via the S1 interface). It will be appreciated that base stations for use in other types of network (e.g. UTRAN or Wideband Code Division Multiple Access (WCDMA) RAN) will include similar components to those shown in Figure 6 and appropriate interface circuitry 68, 69 for enabling communications with the other network nodes in those types of networks (e.g. other base stations, mobility management nodes and/or nodes in the core network).

It will be appreciated that only the components of the UE 42 and base station 40 required to explain the embodiments presented herein are illustrated in Figures 5 and 6.

Although it is possible for two UEs to communicate directly using D2D, it may be desirable to make use of local routing via a network node instead. This may be because D2D is not particularly efficient and can only make use of resources in the uplink. To establish the local routing connection from one UE to another UE, it is useful for the network node to know the identifier of the target or destination UE. The techniques described herein enable the network node to determine the identifier. It will be appreciated that there may be other reasons than establishing local routing for a network node to want or need to know the identifier for a UE engaged in D2D communications with a UE that is being served by the network node, and the techniques described herein can also be used in those situations.

The identifier for a terminal device (UE) is also referred to herein as an endpoint identifier. In some embodiments, the endpoint identifier for a UE is or includes an identifier provided by the network when the UE connects to a network node.

In some embodiments the endpoint identifier can comprise a first part that identifies the network node (e.g. eNB) that is serving the UE, and a second part that identifies the UE to the network node that is serving the UE. For example, the first part can be an Evolved Cell Global Identifier (ECGI), see e.g. 3GPP 36.331 V.8.20.0, Section 6.3.4, and the second part can be a local UE identifier, such as a Cell Radio Network Temporary Identifier (C-RNTI), see e.g. 3GPP 36.300 V.8.12.0, Section 8.1 .

As known in the art, the local UE identifier is typically assigned to a UE as part of a random access procedure conducted during connection establishment. In E-UTRAN, the UE receives a temporary C-RNTI in a response message from the eNB, and once the procedure has confirmed the subscription identity of the UE, the temporary C-RNTI becomes the C-RNTI of the connection.

Alternatively, a UE can be provided with a local identity to be used as an endpoint identifier via enhanced radio resource control (RRC) signalling. A UE can typically obtain the identifier of its serving cell via system information broadcast or by RRC signalling.

In some embodiments, the first part can be one of a Cell Global identifier; an Evolved Cell Global Identifier, ECGI; a Medium Access Control, MAC, address; an Internet Protocol, IP, address; an IP address and power number; and a Universally unique identity, UUID; and the second part is one of a Cell Radio Network Temporary Identifier, C-RNTI; an International Mobile Subscriber Identity, IMSI; an International Mobile Equipment Identity, IMEI; or another device identity that is unique to the network node.

The signaling diagram shown in Figure 7 and the flow charts shown in Figures 8, 9 and 10 illustrate exemplary embodiments of the techniques described herein. Figure 7 shows the signaling between a first UE (UE1 ), a second UE (UE2) and a network node (eNB1 ). Figure 8 illustrates a method of operating a terminal device that corresponds to UE1 in Figure 7. Figure 9 illustrates a method of operating a network node that corresponds to eNB1 . Figure 10 illustrates a method of operating a terminal device that corresponds to UE2 in Figure 7. UE1 and UE2 are operating in D2D mode and are communicating directly with each other, as indicated by signal 700 and optional steps 801 in Figure 8 and step 1001 in Figure 10. D2D communication is also known as 'sidelink' (in contrast to uplink and downlink). In some places UE2 is also referred to as the 'peer UE' for UE1 . UE1 sends a request for UE2's identifier to UE2 via the direct communication link between UE1 and UE2 (request 710 and step 803).

UE2 receives the request 710 (step 1003) and sends its endpoint identifier to UE1 via the direct communication link (response 720 and step 1005). UE1 receives response 720 that contains the endpoint identifier for UE2 (step 805) and sends the identifier for UE2 to eNB1 (Peer UE endpoint information signal 730 and step 807). eNB1 therefore receives the endpoint identifier for UE2 from UE1 (step 901 ). It will be noted that the proposed techniques provide for efficient signalling between the UEs and eNB, but do not require eNB1 to have a connection with the terminal device whose endpoint identifier is required, and also do not require any involvement by the core network 34 (which means that the techniques can be used when eNB1 is isolated from the rest of the E-UTRAN or when the E-UTRAN is isolated from the core network 34).

Figure 1 1 illustrates the signalling in a second embodiment of the techniques described herein. In Figure 1 1 , signals 1 100, 1 130, 1 140 and 1 160 respectively correspond to signals 700, 710, 720 and 730 in Figure 7. In this embodiment, the establishment of the connection between UE1 and eNB1 is shown (step 1 1 10). UE1 may initiate the establishment of the connection with eNB1 . Connection establishment can be according to conventional techniques (for example including the assignment of the C- RNTI described above) and results in eNB1 becoming the serving RAN node of UE1 . As part of the connection establishment, or once the connection is established, eNB1 provides an endpoint identifier or part of an endpoint identifier (e.g. C-RNTI) for UE1 to UE1 (signal 1 120). The endpoint identifier for UE1 can be of the same or a different type as the endpoint identifier of UE2. In some embodiments, the receipt of the endpoint identifier for UE1 (signal 1 120) can trigger the sending of the endpoint identifier request 1 130 to UE2.

In Figure 1 1 , signal 1 140 (which is the response signal from UE2 that contains the endpoint identifier for UE2) is shown as a dashed line to represent the situation where UE2 may not have an endpoint identifier assigned to it or otherwise available, such as where the UE2 does not have a connection to a network node (e.g. eNB1 or another eNB in the RAN). In this case, the response signal 1 140 may indicate to UE1 that no endpoint identifier is available, or UE2 may refrain from sending a response signal 1 140, in which case UE1 can interpret the lack of response signal from UE2 as an indication that no endpoint identifier is available for UE2. Signal 1 160 (the signal in which the endpoint identifier for UE2 is sent to eNB1 by UE1 ) is therefore also shown using a dashed arrow to indicate that this signal may not be sent if no endpoint identifier for UE2 is received by UE1 (although it is possible that UE1 could send signal 1 160 with an indication that no endpoint identifier for UE2 is available). Figure 1 1 also shows a step 1 150 in which UE1 evaluates one or more criteria after receiving the response signal 1 140 from UE2 and before sending the endpoint identifier for UE2 to eNB1 . Possible criteria to be evaluated in step 1 150 are described in more detail after Figures 12 and 13. Figure 12 illustrates the signalling in a third embodiment of the techniques described herein. In Figure 12, D2D mode direct communications 1200, signals 1220, 1230, 1240, 1260 and steps 1210, 1250 respectively correspond to D2D mode direct communications 1 100, signals 1 120, 1 130, 1 140, 1 160 and steps 1 1 10, 1 150 in Figure 1 1 .

In this embodiment, to avoid unnecessary signalling of the endpoint request 1230 and endpoint response 1240 signals between UE1 and UE2, additional signalling between UE1 and UE2 based on network connection indications can be provided. In particular, when UE1 has established a connection with the network (i.e. eNB1 ), UE1 can send a network connection indication signal (signal 1223) via the direct communication link to UE2 to indicate this. Signal 1223 therefore informs UE2 about the change in network connection status of UE1 .

In response to receiving network connection indication signal 1223, UE2 can send a network connection indication (signal 1226) via the direct communication link to UE1 if UE2 has a network connection established with the network (e.g. with eNB1 or another network node). This signal 1226 can be sent either directly in response to receiving the network connection indication signal 1223 from UE1 , or at a later time, for example once UE2 has established a connection to the network.

It will be appreciated that signals 1223 and 1226 could occur in the opposite order to that shown in Figure 12, i.e. UE2 could send a network connection indication 1226 when it establishes a connection to the network, and UE1 could send network connection indication 1223 in response to receiving the indication from UE2, or, if UE1 does not have a network connection at that time, after UE1 establishes a connection with the network. In some embodiments, if UE2 does not have a connection to the network, then on receipt of the network connection indication signal 1223 from UE1 , UE2 can send a signal to UE1 indicating that it does not have a connection. In some embodiments, on receipt of a signal from UE2 indicating that it does not have a network connection, rather than send the endpoint identifier for UE2, peer UE endpoint information signal 1360 may indicate that UE2 does not have a network connection, or that UE1 did not otherwise receive any information from UE2 regarding its network connection status. Although not shown in Figure 12, in some embodiments, UE1 and/or UE2 can also send network connection indications to the other UE indicating that they have disconnected from the network. In some embodiments, the signalling format of the network connection indication signal 1223, 1226 can be that the network connection indicator is set to true when a network connection has been established, and set to false when a network connection has been discontinued. Those skilled in the art will appreciate that other encoding alternatives could be used.

In some embodiments, the network connection indications 1 123, 1226 described above are only sent when there has been a change in connection status (e.g. disconnected to connected, connected to disconnected), or in response to receiving a network connection indication from another UE.

In some embodiments, the network connection indication signal 1223 and endpoint information request signal 1230 can be combined into a single signal. That is UE1 can send network connection indication signal 1223 to indicate that it has a connection to the network, and UE2 can interpret this signal 1223 as a request for its endpoint identifier. UE2 can therefore respond to signal 1223 by sending the endpoint identifier for UE2 to UE1 (signal 1240). Alternatively, UE1 may send endpoint information request 1230 if it has established a connection with the network, and UE2 can interpret the receipt of signal 1230 as a request for its endpoint identifier and an indication that UE1 has a connection to the network.

Figure 13 illustrates the signalling in a fourth embodiment of the techniques described herein. In Figure 13, D2D mode direct communications 1300, signals 1320, 1330, 1340, 1360 and steps 1310, 1350 respectively correspond to D2D mode direct communications 1 100, signals 1 120, 1 130, 1 140, 1 160 and steps 1 1 10, 1 150 in Figure 1 1 .

In this embodiment, UE1 sends the endpoint information request 1330 to UE2 in response to receiving a command from eNB1 that requests endpoint identifier information. Thus, after a connection has been established between UE1 and eNB1 , eNB1 sends a command 1322 to UE1 instructing UE1 to request endpoint identifiers from one or more UEs that UE1 is in direct communication with. UE1 sends endpoint information request 1330 in response to receiving command 1322.

In some embodiments, command 1322 can be received together with the endpoint identifier information for UE1 in signal 1320. In other embodiments, command 1322 can be received in a message configuring the connection between UE1 and eNB1 , such as an RRC Connection Setup message, an RRC Connection Re-establishment message, an RRC Connection Reconfiguration message etc., or some other message or signal sent as part of the connection establishment procedure 1310 or a subsequent connection reconfiguration procedure.

In some embodiments, command 1322 contains an indication that UE1 should retrieve endpoint identifier information from its direct communication (D2D) peers. In further embodiments, command 1322 can be sent by eNB1 in response to UE1 indicating to eNB1 that it has ongoing D2D mode communications with one or more other UEs. This indication from UE1 can be sent as part of the connection establishment procedure 1310, or in a separate signal (not shown in Figure 13).

Where UE1 receives command 1322 from eNB1 , peer UE endpoint information signal 1360 can be seen as the response to that command 1322.

In some embodiments, command 1322 is sent by eNB1 once it becomes aware that UE1 is engaged in direct communications with another UE. eNB1 may become aware of this by, for example, a scheduling assignment request from UE1 , or by some other signalling.

In any of the above embodiments, D2D mode signals between the UEs (e.g. request signal 710, 1 130, 1230 and 1330, response signal 720, 1 140, 1240 and 1340) can be conveyed in the MAC header. Where the signals are just an indicator (e.g. network connection indications 1223 and 1226), then these indicators can be associated with a specific bit in the MAC header. In alternative embodiments, the signals can be sent via a specific control plane between UEs. One example of such a control plane is a frame protocol with control elements embedded with user plane data.

In some embodiments, the endpoint identifier request sent by UE1 (signal 710, 1 130, 1230 and 1330) can also contain the endpoint identifier for UE1 . In this way UE2 can be informed of the endpoint identifier for UE1 without having to perform steps 803 and 805 in Figure 8. In other embodiments endpoint identifier request sent by UE1 (signal 710, 1 130, 1230 and 1330) does not contain the endpoint identifier for UE1 in order to minimise signalling overhead in the direct communication link.

Where an endpoint identifier is sent between the UEs (e.g. in the endpoint identifier response signal 720, 1 140, 1240 and 1340 and endpoint identifier request signal 710, 1 130, 1230 and 1330 in the above embodiment), the endpoint identifier can be encoded in those signals in the same way as an endpoint identifier is encoded when signalled between a serving eNB and a UE. As noted above, in some embodiments, the endpoint identifier in the response signal 720, 1 140, 1240 and 1340 includes information obtained from UE2's serving cell, such as the cell identifier (e.g. which can be found in a cell global identity (CGI), which can include a public land mobile network (PLMN) ID, an eNB identifier in the PLMN, and a cell identifier for the eNB), which allows UE1 to retrieve the identifier of UE2 in its serving cell.

As described above, after receiving an endpoint identifier response containing an endpoint identifier for UE2, UE1 can send the endpoint identifier for UE2 to eNB1 . However, in other embodiments, after receiving an endpoint identifier response 1 140, 1240 or 1340, UE1 evaluates one or more criteria before sending the peer UE endpoint information signal 1 160, 1260 or 1360 to eNB1 . In some of these embodiments, the criteria in step 1 150, 1250 or 1350 is met if the endpoint information response signal 1 140, 1240 or 1340 has been received. In other embodiments the criteria in step 1 150, 1250 or 1350 is met if the endpoint information response signal 1 140, 1240 or 1340 contains an endpoint identifier for UE2. In other embodiments, the criteria in step 1350 is met if UE1 has previously received a command 1322 from eNB1 to send the endpoint information request signal 1330. As noted above, on receipt of the endpoint identifier request 710, 1 130, 1230, 1330, UE2 responds by sending its endpoint identifier to UE1 . However, UE2 may not have an assigned endpoint identifier when request 710, 1 130, 1230, 1330 is received. Thus in some embodiments, directly on receipt of the request, UE2 sends response signal 720, 1 140, 1240, 1340 indicating to UE1 that no endpoint identifier is available and/or that UE2 does not have a connection to the network. In alternative embodiments, UE2 refrains from sending response signal 720, 1 140 1240, 1340 until it establishes a connection to the network and obtains an endpoint identifier (or obtains an endpoint identifier by other means).

In some embodiments, eNB1 relies on UE1 to provide information about whether a peer UE of UE1 has a network connection (and therefore is potentially available for local routing of the direct communications). In this case eNB1 therefore only needs to rely on the reception of a peer UE endpoint information signal 730, 1 160, 1260, 1360 from UE1 concerning the endpoint identifier of a peer UE. In alternative embodiments, eNB1 may probe whether the peer UE (e.g. UE2) has a network connection, and in some embodiments this probing is initiated via command message 1322 sent to UE1 . This will lead to eNB1 receiving information from UE1 regarding the endpoint information of the peer UE (for example the endpoint identifier of the peer UE, or an indication that the peer UE does not have a network connection.

There is therefore provided techniques for a network node to establish information about the identifiers of UEs engaged in direct communication. Modifications and other variants of the described embodiment(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiment(s) is/are not to be limited to the specific examples disclosed and that modifications and other variants are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Various exemplary embodiments are set out in the following statements:

1 . A method of operating a first terminal device in a telecommunication network, the first terminal device having a direct communication link with a second terminal device, the method comprising: sending a request for an identifier for the second terminal device to the second terminal device via the direct communication link;

receiving the identifier for the second terminal device from the second terminal device via the direct communication link; and

sending the identifier for the second terminal device to a first network node in the telecommunication network.

2. A method as defined in statement 1 , wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

3. A method as defined in statement 1 or 2, wherein the step of sending a request for an identifier for the second terminal device is performed in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network.

4. A method as defined in any of statements 1 -3, the method further comprising the step of:

sending a signal to the second terminal device via the direct communication link that indicates that the first terminal device has a connection to the telecommunication network.

5. A method as defined in statement 4, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

6. A method as defined in any of statements 1 -5, the method further comprising the step of:

sending an identifier for the first terminal device to the second terminal device via the direct communication link.

7. A method as defined in statement 6, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device. 8. A method as defined in any of statements 6 or 7, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

9. A method as defined in any of statements 1 -8, wherein the request for an identifier for the second terminal device is sent in response to the first terminal device receiving an identifier for the first terminal device from the first network node. 10. A method as defined in any of statements 1 -8, wherein the request for an identifier for the second terminal device is sent in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

1 1 . A method as defined in any of statements 1 -10, wherein the step of sending the identifier for the second terminal device to a first network node is performed if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

12. A method as defined in any of statements 1 -1 1 , the method further comprising the step of:

sending a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available. 13. A method as defined in any of statements 1 -12, wherein the first network node is a network node that is serving the first terminal device.

14. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of statements 1 -13.

15. A first terminal device for use in a telecommunication network, the first terminal device being capable of communication with a second terminal device via a direct communication link with the second terminal device, and the first terminal device adapted to: send a request for an identifier for the second terminal device to the second terminal device via the direct communication link;

receive the identifier for the second terminal device from the second terminal device via the direct communication link; and

send the identifier for the second terminal device to a first network node in the telecommunication network.

16. A first terminal device as defined in statement 15, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

17. A first terminal device as defined in statement 15 or 16, wherein the first terminal device is adapted to send the request for an identifier for the second terminal device in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network.

18. A first terminal device as defined in any of statements 15-17, wherein the first terminal device is further adapted to send a signal to the second terminal device via the direct communication link that indicates that the first terminal device has a connection to the telecommunication network.

19. A first terminal device as defined in statement 18, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

20. A first terminal device as defined in any of statements 15-19, wherein the first terminal device is further adapted to send an identifier for the first terminal device to the second terminal device via the direct communication link.

21 . A first terminal device as defined in statement 20, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device. 22. A first terminal device as defined in any of statements 20 or 21 , wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

23. A first terminal device as defined in any of statements 15-22, wherein the first terminal device is adapted to send the request for the identifier for the second terminal device in response to the first terminal device receiving an identifier for the first terminal device from the first network node.

24. A first terminal device as defined in any of statements 15-22, wherein the first terminal device is adapted to send the request for the identifier for the second terminal device in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

25. A first terminal device as defined in any of statements 15-24, wherein the first terminal device is adapted to send the identifier for the second terminal device to the first network node if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

26. A first terminal device as defined in any of statements 15-25, wherein the first terminal device is further adapted to send a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available.

27. A first terminal device as defined in any of statements 15-26, wherein the first network node is a network node that is serving the first terminal device.

28. A method of operating a network node in a telecommunication network, the method comprising:

receiving an identifier for a second terminal device from a first terminal device, the first terminal device having a direct communication link with the second terminal device.

29. A method as defined in statement 28, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device. 30. A method as defined in statement 28 or 29, the method further comprising the step of:

on or during establishment of a connection with the first terminal device, sending an identifier for the first terminal device to the first terminal device.

31 . A method as defined in any of statements 28-30, the method further comprising the step of sending a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device.

32. A method as defined in statement 31 , wherein the step of sending a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device is performed in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device.

33. A method as defined in any of statements 28-32, the method further comprising the step of:

receiving a signal from the first terminal device indicating that no identifier for the second terminal device is available.

34. A method as defined in any of statements 28-33, wherein the network node is serving the first terminal device. 35. A method as defined in any of statements 28-34, the method further comprising the step of:

using the received identifier for the second terminal device to establish a connection between the first terminal device and the second terminal device via the network node.

36. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of statements 28-35. 37. A network node for use in a telecommunication network, the network node adapted to:

receive an identifier for a second terminal device from a first terminal device, the first terminal device having a direct communication link with the second terminal device.

38. A network node as defined in statement 37, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

39. A network node as defined in statement 37 or 38, wherein the network node is further adapted to send an identifier for the first terminal device to the first terminal device on or during establishment of a connection with the first terminal device.

40. A network node as defined in any of statements 37-39, wherein the network node is further adapted to send a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device. 41 . A network node as defined in statement 40, wherein the network node is adapted to send the signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device.

42. A network node as defined in any of statements 37-41 , wherein the network node is further adapted to receive a signal from the first terminal device indicating that no identifier for the second terminal device is available. 43. A network node as defined in any of statements 37-42, wherein the network node is serving the first terminal device.

44. A network node as defined in any of statements 37-43, wherein the network node is further adapted to use the received identifier for the second terminal device to establish a connection between the first terminal device and the second terminal device via the network node. 45. A method of operating a second terminal device in a telecommunication network, the second terminal device having a direct communication link with a first terminal device, the method comprising:

receiving a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and

sending the identifier for the second terminal device to the first terminal device via the direct communication link. 46. A method as defined in statement 45, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device. 47. A method as defined in statement 45 or 46, the method further comprising the step of sending a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network. 48. A method as defined in statement 47, wherein the step of sending a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network is performed in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

49. A method as defined in statement 48, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network. 50. A method as defined in any of statements 45-49, wherein the step of sending the identifier for the second terminal device to the first terminal device via the direct communication link is performed when the second terminal device has a connection to the telecommunication network. 51 . A method as defined in any of statements 45-50, the method further comprising the step of: receiving an identifier for the first terminal device via the direct communication link.

52. A method as defined in statement 51 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device.

53. A method as defined in any of statements 45-52, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

54. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of statements 45-53.

55. A second terminal device for use in a telecommunication network, the second terminal device being capable of communication with a first terminal device via a direct communication link with the first terminal device, and the second terminal device adapted to:

receive a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and

send the identifier for the second terminal device to the first terminal device via the direct communication link.

56. A second terminal device as defined in statement 55, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

57. A second terminal device as defined in statement 55 or 56, wherein the second terminal device is further adapted to send a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network. 58. A second terminal device as defined in statement 57, wherein the second terminal device is adapted to send the signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

59. A second terminal device as defined in statement 58, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

60. A second terminal device as defined in any of statements 55-59, wherein the second terminal device is adapted to send the identifier for the second terminal device to the first terminal device via the direct communication link when the second terminal device has a connection to the telecommunication network.

61 . A second terminal device as defined in any of statements 55-60, wherein the second terminal device is further adapted to receive an identifier for the first terminal device via the direct communication link.

62. A second terminal device as defined in statement 61 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device. 63. A second terminal device as defined in any of statements 55-62, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device. 64. A first terminal device for use in a telecommunication network, the first terminal device being capable of communication with a second terminal device via a direct communication link with the second terminal device, and the first terminal device comprising a processor and a memory, said memory containing instructions executable by said processor whereby said first terminal device is operative to:

send a request for an identifier for the second terminal device to the second terminal device via the direct communication link; receive the identifier for the second terminal device from the second terminal device via the direct communication link; and

65. A first terminal device as defined in statement 64, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

66. A first terminal device as defined in statement 64 or 65, wherein the first terminal device is operative to send the request for an identifier for the second terminal device in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network.

67. A first terminal device as defined in any of statements 64-66, wherein the first terminal device is further operative to send a signal to the second terminal device via the direct communication link that indicates that the first terminal device has a connection to the telecommunication network.

68. A first terminal device as defined in statement 67, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network. 69. A first terminal device as defined in any of statements 64-68, wherein the first terminal device is further operative to send an identifier for the first terminal device to the second terminal device via the direct communication link.

70. A first terminal device as defined in statement 69, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device.

71 . A first terminal device as defined in any of statements 69 or 70, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device. 72. A first terminal device as defined in any of statements 64-71 , wherein the first terminal device is operative to send the request for the identifier for the second terminal device in response to the first terminal device receiving an identifier for the first terminal device from the first network node.

73. A first terminal device as defined in any of statements 64-71 , wherein the first terminal device is operative to send the request for the identifier for the second terminal device in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

74. A first terminal device as defined in any of statements 64-73, wherein the first terminal device is operative to send the identifier for the second terminal device to the first network node if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

75. A first terminal device as defined in any of statements 64-74, wherein the first terminal device is further operative to send a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available.

76. A first terminal device as defined in any of statements 64-75, wherein the first network node is a network node that is serving the first terminal device. 77. A network node for use in a telecommunication network, the network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to:

78. A network node as defined in statement 77, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device. 79. A network node as defined in statement 77 or 78, wherein the network node is further operative to send an identifier for the first terminal device to the first terminal device on or during establishment of a connection with the first terminal device. 80. A network node as defined in any of statements 77-79, wherein the network node is further operative to send a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device.

81 . A network node as defined in statement 80, wherein the network node is operative to send the signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device. 82. A network node as defined in any of statements 77-81 , wherein the network node is further operative to receive a signal from the first terminal device indicating that no identifier for the second terminal device is available.

83. A network node as defined in any of statements 77-82, wherein the network node is serving the first terminal device.

84. A network node as defined in any of statements 77-83, wherein the network node is further operative to use the received identifier for the second terminal device to establish a connection between the first terminal device and the second terminal device via the network node.

85. A second terminal device for use in a telecommunication network, the second terminal device being capable of communication with a first terminal device via a direct communication link with the first terminal device, and the second terminal device comprising a processor and a memory, said memory containing instructions executable by said processor whereby said second terminal device is operative to:

send the identifier for the second terminal device to the first terminal device via the direct communication link. 86. A second terminal device as defined in statement 85, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

87. A second terminal device as defined in statement 85 or 86, wherein the second terminal device is further operative to send a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network.

88. A second terminal device as defined in statement 87, wherein the second terminal device is operative to send the signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

89. A second terminal device as defined in statement 88, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

90. A second terminal device as defined in any of statements 85-89, wherein the second terminal device is operative to send the identifier for the second terminal device to the first terminal device via the direct communication link when the second terminal device has a connection to the telecommunication network.

91 . A second terminal device as defined in any of statements 85-90, wherein the second terminal device is further operative to receive an identifier for the first terminal device via the direct communication link.

92. A second terminal device as defined in statement 91 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device. 93. A second terminal device as defined in any of statements 85-92, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

94. A first terminal device for use in a telecommunication network, the first terminal device being capable of communication with a second terminal device via a direct communication link with the second terminal device, and the first terminal device comprises:

a first module configured to send a request for an identifier for the second terminal device to the second terminal device via the direct communication link;

a second module configured to receive the identifier for the second terminal device from the second terminal device via the direct communication link; and

a third module configured to send the identifier for the second terminal device to a first network node in the telecommunication network. 95. A first terminal device as defined in statement 94, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device. 96. A first terminal device as defined in statement 94 or 95, wherein the first module is configured to send the request for an identifier for the second terminal device in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network. 97. A first terminal device as defined in any of statements 94-96, wherein the first module is further configured to send a signal to the second terminal device via the direct communication link that indicates that the first terminal device has a connection to the telecommunication network. 98. A first terminal device as defined in statement 97, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

99. A first terminal device as defined in any of statements 94-98, wherein the first module is further configured to send an identifier for the first terminal device to the second terminal device via the direct communication link. 100. A first terminal device as defined in statement 99, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device.

101 . A first terminal device as defined in any of statements 99 or 100, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

102. A first terminal device as defined in any of statements 94-101 , wherein the first module is configured to send the request for the identifier for the second terminal device in response to the first terminal device receiving an identifier for the first terminal device from the first network node.

103. A first terminal device as defined in any of statements 94-101 , wherein the first module is configured to send the request for the identifier for the second terminal device in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

104. A first terminal device as defined in any of statements 94-103, wherein the third module is configured to send the identifier for the second terminal device to the first network node if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

105. A first terminal device as defined in any of statements 94-104, wherein the first terminal device further comprises a fourth module configured to send a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available.

106. A first terminal device as defined in any of statements 94-105, wherein the first network node is a network node that is serving the first terminal device.

107. A network node for use in a telecommunication network, the network node comprising: a first module configured to receive an identifier for a second terminal device from a first terminal device, the first terminal device having a direct communication link with the second terminal device. 108. A network node as defined in statement 107, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device. 109. A network node as defined in statement 107 or 108, wherein the network node further comprises a second module configured to send an identifier for the first terminal device to the first terminal device on or during establishment of a connection with the first terminal device. 1 10. A network node as defined in any of statements 107-108, wherein the network node further comprises a second module configured to send a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device. 1 1 1 . A network node as defined in statement 1 10, wherein the second module is further configured to send a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device.

1 12. A network node as defined in any of statements 107-1 1 1 , wherein the first module is further configured to receive a signal from the first terminal device indicating that no identifier for the second terminal device is available. 1 13. A network node as defined in any of statements 107-1 12, wherein the network node is serving the first terminal device.

1 14. A network node as defined in any of statements 107-1 13, wherein the network node further comprises a third module configured to use the received identifier for the second terminal device to establish a connection between the first terminal device and the second terminal device via the network node. 1 15. A second terminal device for use in a telecommunication network, the second terminal device being capable of communication with a first terminal device via a direct communication link with the first terminal device, the second terminal device comprising:

a first module configured to receive a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and a second module configured to send the identifier for the second terminal device to the first terminal device via the direct communication link.

1 16. A second terminal device as defined in statement 1 15, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

1 17. A second terminal device as defined in statement 1 15 or 1 16, wherein the second module is further configured to send a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network.

1 18. A second terminal device as defined in statement 1 17, wherein the second module is configured to send the signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

1 19. A second terminal device as defined in statement 1 18, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

120. A second terminal device as defined in any of statements 1 15-1 19, wherein the second module is configured to send the identifier for the second terminal device to the first terminal device via the direct communication link when the second terminal device has a connection to the telecommunication network. 121 . A second terminal device as defined in any of statements 1 15-120, wherein the first module is further configured to receive an identifier for the first terminal device via the direct communication link. 122. A second terminal device as defined in statement 121 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device.

123. A second terminal device as defined in any of statements 1 15-122, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

The modules of the first and second terminal devices defined above, as well as the module(s) of the network node defined above may in some embodiments be implemented as computer programs stored in memory (e.g. in the memory modules in Figures 5 and 6 respectively) for execution by processors (e.g. the processing modules of Figures 5 and 6 respectively).

Claims

1 . A method of operating a first terminal device (42) in a telecommunication network (32), the first terminal device (42) having a direct communication link with a second terminal device (42), the method comprising:

sending (803) a request for an identifier for the second terminal device to the second terminal device via the direct communication link;

receiving (805) the identifier for the second terminal device from the second terminal device via the direct communication link; and

sending (807) the identifier for the second terminal device to a first network node in the telecommunication network.

2. A method as claimed in claim 1 , wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

3. A method as claimed in claim 1 or 2, wherein the step of sending a request for an identifier for the second terminal device is performed in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network.

4. A method as claimed in any of claims 1 -3, the method further comprising the step of:

5. A method as claimed in claim 4, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

6. A method as claimed in any of claims 1 -5, the method further comprising the step of:

7. A method as claimed in claim 6, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device.

8. A method as claimed in any of claims 6 or 7, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

9. A method as claimed in any of claims 1 -8, wherein the request for an identifier for the second terminal device is sent in response to the first terminal device receiving an identifier for the first terminal device from the first network node.

10. A method as claimed in any of claims 1 -8, wherein the request for an identifier for the second terminal device is sent in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

1 1 . A method as claimed in any of claims 1 -10, wherein the step of sending the identifier for the second terminal device to a first network node is performed if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

12. A method as claimed in any of claims 1 -1 1 , the method further comprising the step of:

sending a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available.

13. A method as claimed in any of claims 1 -12, wherein the first network node is a network node that is serving the first terminal device.

14. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 1 -13.

15. A first terminal device (42) for use in a telecommunication network (32), the first terminal device being capable of communication with a second terminal device (42) via a direct communication link with the second terminal device, and the first terminal device adapted to:

send a request for an identifier for the second terminal device to the second terminal device via the direct communication link;

send the identifier for the second terminal device to a first network node (40) in the telecommunication network.

16. A first terminal device as claimed in claim 15, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

17. A first terminal device as claimed in claim 15 or 16, wherein the first terminal device is adapted to send the request for an identifier for the second terminal device in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network.

18. A first terminal device as claimed in any of claims 15-17, wherein the first terminal device is further adapted to send a signal to the second terminal device via the direct communication link that indicates that the first terminal device has a connection to the telecommunication network.

19. A first terminal device as claimed in claim 18, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

20. A first terminal device as claimed in any of claims 15-19, wherein the first terminal device is further adapted to send an identifier for the first terminal device to the second terminal device via the direct communication link.

21 . A first terminal device as claimed in claim 20, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device.

22. A first terminal device as claimed in any of claims 20 or 21 , wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

23. A first terminal device as claimed in any of claims 15-22, wherein the first terminal device is adapted to send the request for the identifier for the second terminal device in response to the first terminal device receiving an identifier for the first terminal device from the first network node.

24. A first terminal device as claimed in any of claims 15-22, wherein the first terminal device is adapted to send the request for the identifier for the second terminal device in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

25. A first terminal device as claimed in any of claims 15-24, wherein the first terminal device is adapted to send the identifier for the second terminal device to the first network node if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

26. A first terminal device as claimed in any of claims 15-25, wherein the first terminal device is further adapted to send a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available.

27. A first terminal device as claimed in any of claims 15-26, wherein the first network node is a network node that is serving the first terminal device.

28. A method of operating a network node (40) in a telecommunication network (32), the method comprising:

receiving (901 ) an identifier for a second terminal device (42) from a first terminal device (42), the first terminal device having a direct communication link with the second terminal device.

29. A method as claimed in claim 28, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

30. A method as claimed in claim 28 or 29, the method further comprising the step of: on or during establishment of a connection with the first terminal device, sending an identifier for the first terminal device to the first terminal device.

31 . A method as claimed in any of claims 28-30, the method further comprising the step of sending a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device.

32. A method as claimed in claim 31 , wherein the step of sending a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device is performed in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device.

33. A method as claimed in any of claims 28-32, the method further comprising the step of:

34. A method as claimed in any of claims 28-33, wherein the network node is serving the first terminal device.

35. A method as claimed in any of claims 28-34, the method further comprising the step of:

36. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 28-35.

37. A network node (40) for use in a telecommunication network (32), the network node adapted to:

receive an identifier for a second terminal device (42) from a first terminal device (42), the first terminal device having a direct communication link with the second terminal device.

38. A network node as claimed in claim 37, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

39. A network node as claimed in claim 37 or 38, wherein the network node is further adapted to send an identifier for the first terminal device to the first terminal device on or during establishment of a connection with the first terminal device.

40. A network node as claimed in any of claims 37-39, wherein the network node is further adapted to send a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device.

41 . A network node as claimed in claim 40, wherein the network node is adapted to send the signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device.

42. A network node as claimed in any of claims 37-41 , wherein the network node is further adapted to receive a signal from the first terminal device indicating that no identifier for the second terminal device is available.

43. A network node as claimed in any of claims 37-42, wherein the network node is serving the first terminal device.

44. A network node as claimed in any of claims 37-43, wherein the network node is further adapted to use the received identifier for the second terminal device to establish a connection between the first terminal device and the second terminal device via the network node.

45. A method of operating a second terminal device (42) in a telecommunication network (32), the second terminal device having a direct communication link with a first terminal device (42), the method comprising:

receiving (1003) a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and

sending (1005) the identifier for the second terminal device to the first terminal device via the direct communication link.

46. A method as claimed in claim 45, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

47. A method as claimed in claim 45 or 46, the method further comprising the step of sending a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network.

48. A method as claimed in claim 47, wherein the step of sending a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network is performed in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

49. A method as claimed in claim 48, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

50. A method as claimed in any of claims 45-49, wherein the step of sending the identifier for the second terminal device to the first terminal device via the direct communication link is performed when the second terminal device has a connection to the telecommunication network.

51 . A method as claimed in any of claims 45-50, the method further comprising the step of:

receiving an identifier for the first terminal device via the direct communication link.

52. A method as claimed in claim 51 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device.

53. A method as claimed in any of claims 45-52, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

54. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 45-53.

55. A second terminal device (42) for use in a telecommunication network (32), the second terminal device being capable of communication with a first terminal device

(42) via a direct communication link with the first terminal device, and the second terminal device adapted to:

56. A second terminal device as claimed in claim 55, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

57. A second terminal device as claimed in claim 55 or 56, wherein the second terminal device is further adapted to send a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network.

58. A second terminal device as claimed in claim 57, wherein the second terminal device is adapted to send the signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

59. A second terminal device as claimed in claim 58, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

60. A second terminal device as claimed in any of claims 55-59, wherein the second terminal device is adapted to send the identifier for the second terminal device to the first terminal device via the direct communication link when the second terminal device has a connection to the telecommunication network.

61 . A second terminal device as claimed in any of claims 55-60, wherein the second terminal device is further adapted to receive an identifier for the first terminal device via the direct communication link.

62. A second terminal device as claimed in claim 61 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device.

63. A second terminal device as claimed in any of claims 55-62, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

64. A first terminal device for use in a telecommunication network, the first terminal device being capable of communication with a second terminal device via a direct communication link with the second terminal device, and the first terminal device comprising a processor and a memory, said memory containing instructions executable by said processor whereby said first terminal device is operative to: send a request for an identifier for the second terminal device to the second terminal device via the direct communication link;

65. A first terminal device as claimed in claim 64, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

66. A first terminal device as claimed in claim 64 or 65, wherein the first terminal device is operative to send the request for an identifier for the second terminal device in response to receiving a signal indicating that the second terminal device has a connection with the telecommunication network.

67. A first terminal device as claimed in any of claims 64-66, wherein the first terminal device is further operative to send a signal to the second terminal device via the direct communication link that indicates that the first terminal device has a connection to the telecommunication network.

68. A first terminal device as claimed in claim 67, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

69. A first terminal device as claimed in any of claims 64-68, wherein the first terminal device is further operative to send an identifier for the first terminal device to the second terminal device via the direct communication link.

70. A first terminal device as claimed in claim 69, wherein the identifier for the first terminal device is sent with the request for an identifier for the second terminal device.

71 . A first terminal device as claimed in any of claims 69 or 70, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.

72. A first terminal device as claimed in any of claims 64-71 , wherein the first terminal device is operative to send the request for the identifier for the second terminal device in response to the first terminal device receiving an identifier for the first terminal device from the first network node.

73. A first terminal device as claimed in any of claims 64-71 , wherein the first terminal device is operative to send the request for the identifier for the second terminal device in response to receiving a request from the first network node to obtain an identifier for the second terminal device.

74. A first terminal device as claimed in any of claims 64-73, wherein the first terminal device is operative to send the identifier for the second terminal device to the first network node if the first terminal device has received a request from the first network node to obtain an identifier for the second terminal device.

75. A first terminal device as claimed in any of claims 64-74, wherein the first terminal device is further operative to send a signal to the first network node if no identifier for the second terminal device is received, the signal indicating that no identifier for the second terminal is available.

76. A first terminal device as claimed in any of claims 64-75, wherein the first network node is a network node that is serving the first terminal device.

77. A network node for use in a telecommunication network, the network node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said network node is operative to:

78. A network node as claimed in claim 77, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

79. A network node as claimed in claim 77 or 78, wherein the network node is further operative to send an identifier for the first terminal device to the first terminal device on or during establishment of a connection with the first terminal device.

80. A network node as claimed in any of claims 77-79, wherein the network node is further operative to send a signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device.

81 . A network node as claimed in claim 80, wherein the network node is operative to send the signal to the first terminal device indicating that the first terminal device is to obtain an identifier for the second terminal device in response to receiving an indication from the first terminal device that it has a direct communication link with a second terminal device.

82. A network node as claimed in any of claims 77-81 , wherein the network node is further operative to receive a signal from the first terminal device indicating that no identifier for the second terminal device is available.

83. A network node as claimed in any of claims 77-82, wherein the network node is serving the first terminal device.

84. A network node as claimed in any of claims 77-83, wherein the network node is further operative to use the received identifier for the second terminal device to establish a connection between the first terminal device and the second terminal device via the network node.

receive a request for an identifier for the second terminal device from the first terminal device via the direct communication link; and send the identifier for the second terminal device to the first terminal device via the direct communication link.

86. A second terminal device as claimed in claim 85, wherein the identifier comprises a first part that identifies a network node that is serving the second terminal device, and a second part that identifies the second terminal device to the network node that is serving the second terminal device.

87. A second terminal device as claimed in claim 85 or 86, wherein the second terminal device is further operative to send a signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network.

88. A second terminal device as claimed in claim 87, wherein the second terminal device is operative to send the signal to the first terminal device via the direct communication link indicating that the second terminal device has a connection with the telecommunication network in response to receiving a signal from the first terminal device that indicates that the first terminal device has a connection to the telecommunication network.

89. A second terminal device as claimed in claim 88, wherein the request for an identifier for the second terminal device is the signal that indicates that the first terminal device has a connection to the telecommunication network.

90. A second terminal device as claimed in any of claims 85-89, wherein the second terminal device is operative to send the identifier for the second terminal device to the first terminal device via the direct communication link when the second terminal device has a connection to the telecommunication network.

91 . A second terminal device as claimed in any of claims 85-90, wherein the second terminal device is further operative to receive an identifier for the first terminal device via the direct communication link.

92. A second terminal device as claimed in claim 91 , wherein the identifier for the first terminal device is received with the request for an identifier for the second terminal device.

93. A second terminal device as claimed in any of claims 85-92, wherein the identifier for the first terminal device comprises a first part that identifies a network node that is serving the first terminal device, and a second part that identifies the first terminal device to the network node that is serving the first terminal device.