WO2016048219A1

WO2016048219A1 - Establishing a dedicated control plane tunnel

Info

Publication number: WO2016048219A1
Application number: PCT/SE2015/050973
Authority: WO
Inventors: Icaro L. J. Da Silva; Mattias TAN BERGSTRÖM; Angelo Centonza; Oumer Teyeb
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2014-09-26
Filing date: 2015-09-17
Publication date: 2016-03-31

Abstract

A method is for use in a system comprising a first network node, a second network node, and a terminal device, in a case where the terminal device has a connection to the second network node over a radio interface and the first network node has a connection to the second network node over an inter-node interface. A dedicated control plane tunnel is established, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

Description

ESTABLISHING A DEDICATED CONTROL PLANE TUNNEL TECHNICAL FIELD

This relates to establishing a dedicated control plane tunnel between a network node and a terminal device, in particular in circumstances where the terminal device has relinquished a data plane connection with the network node.

BACKGROUND

The wireless local-area network (WLAN) technology known as "Wi-Fi" has been standardized by IEEE in the 802.1 1 series of specifications (i.e., as "IEEE Standard for Information technology— Telecommunications and information exchange between systems. Local and metropolitan area networks— Specific requirements. Part 1 1 : Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications").

Cellular operators that are currently serving mobile users with, for example, any of the technologies standardized by the 3rd-Generation Partnership Project (3GPP), including the radio-access technologies known as Long-Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS)/Wideband Code-Division Multiple Access (WCDMA), High Speed Packet Access (HSPA) and Global System for Mobile Communications (GSM), see Wi-Fi as a wireless technology that can provide good additional support for users in their regular cellular networks. There is interest around using the Wi-Fi technology as an extension, or alternative to cellular radio access network technologies to handle the always increasing wireless bandwidth demands. The term "operator-controlled Wi-Fi" points to a Wi-Fi deployment that on some level is integrated with a cellular network operator's existing network and where the 3GPP radio access networks and the Wi-Fi wireless access may even be connected to the same core network and provide the same services. However, most current Wi-Fi/WLAN deployments are totally separate from mobile cellular communication networks, and can be seen as non-integrated from the terminal device's perspective. Most operating systems (OSs) for UEs such as Android and iOS®, support a simple Wi-Fi offloading mechanism where a UE (user equipment - the term used to refer to terminal devices by 3GPP) immediately switches all its Internet Protocol (IP) traffic or Packet-Switched (PS) bearers to a Wi-Fi network upon a detection of a suitable network with a received signal strength above a certain level. Henceforth, the decision to offload to a Wi-Fi or not is referred to as access network selection and/or traffic steering and the term "Wi-Fi-if-coverage" is used to refer to the aforementioned strategy of selecting Wi-Fi whenever such a network is detected. There are several drawbacks of the "Wi-Fi-if-coverage" strategy and so 3GPP has been working on a feature/mechanism for WLAN/3GPP Radio interworking which improves operator control with respect to how a UE performs access selection and traffic steering between 3GPP and WLANs belonging to the operator or its partners (it may even be so that the mechanism can be used for other, non-operator, WLANs as well, even though this is not the main target), and a mechanism has been specified in Release 12 of the 3GPP specifications for LTE (TS 36.300 v12.2.0 (2014-06)). This mechanism supports Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) assisted UE based bi-directional traffic steering between E-UTRAN and WLAN for UEs in RRCJDLE and RRC_CONNECTED modes.

In this mechanism, the 3GPP radio access network (RAN) provides assistance parameters to the terminal devices (UEs) via broadcast and dedicated RRC (radio resource control) signalling that are used in the mechanism to decide whether the terminal device is to access and/or steer traffic to WLAN. The RAN assistance information or parameters may include, for example, threshold values (such as E- UTRAN signal strength and quality thresholds, WLAN channel utilization thresholds, WLAN backhaul data rate thresholds, WLAN signal strength and quality thresholds) and/or offloading preference indicator (OPI). E-UTRAN can also provide a list of WLAN identifiers to the UE via broadcast signalling. WLANs identified by the E- UTRAN may include an associated priority.

The UEs uses these RAN assistance parameters in the evaluation of traffic steering rules, which will be defined in TS 36.304, and ANDSF (Access Network Discovery and Selection Function) policies, which will be defined in TS 24.312, in order to make traffic steering decisions between E-UTRAN and WLAN. As an example, the rules/policies can indicate that the UE is to make measurements of one or more signal parameters in the 3GPP network (E-UTRAN) and/or WLAN and compare the measurements to the threshold values. Based on the evaluation of the rule, the UE will steer traffic to the appropriate one of E-UTRAN and WLAN. An example of a traffic steering rule is shown below (where RCPI is the Received Channel Power Indicator and RSRP is the reference signal received power):

If (RSRP < RSRPJhresholdJow) AND (RCPI > RCPI_threshold_high) AND (WLAN utilization < WLAN utilization thresholdjow) then

OFFLOAD FROM 3GPP TO WLAN

else

If (RSRP > RSRP_threshold_high) OR (RCPI < RCPIJhresholdJow) OR (WLAN utilization > WLAN utilization thresholdJow) then

OFFLOAD FROM WLAN TO 3GPP

Example 1

The OPI is only used in ANDSF policies. WLAN identifiers are only used in traffic steering rules [TS 36.304]. If the UE is provisioned with ANDSF policies it shall forward the received RAN assistance parameters to upper layers, otherwise it shall use them in the traffic steering rules [section 23.6.2, TS 36.304 v12.5.0]. The traffic steering rules are applied only to the WLANs of which identifiers are provided by the E-UTRAN.

According to the mechanism, a UE in RRC_CONNECTED shall apply the parameters obtained via dedicated signalling if such have been received from the serving cell; otherwise, the UE shall apply the parameters obtained via broadcast signalling.

A UE in RRCJDLE shall keep and apply the parameters obtained via dedicated signalling, until cell reselection or a timer has expired from when the UE entered RRCJDLE, upon which the UE shall apply the parameters obtained via broadcast signalling. In the case of radio access network (RAN) sharing, each PLMN (public land mobile network) sharing the RAN can provide independent sets of RAN assistance parameters.

Although 3GPP has introduced a network-assisted WLAN interworking mechanism for Release 12, it is possible that a fully network-controlled solution may be specified in future releases.

A fully network controlled WLAN/3GPP interworking solution follows principles similar to CONNECTED mode operations in 3GPP, where the three main steps are employed for traffic steering. The signalling between the UE and an eNB (the name used for a radio base station in E-UTRAN) is illustrated in Figure 1 , and the signalling is explained below.

1 . Measurement control configuration: the RAN sends information to the UE that includes details like the target WLAN(s) to be measured (e.g. specific identities such as service set identifiers (SSIDs)/basic SSIDs (BSSIDs)/homogenous extended SSIDs (HESSIDs) or more general information like operating frequencies), events/thresholds for triggering measurement reports (e.g. when WLAN signal becomes better/worse than a certain threshold, WLAN signal becomes better/worse than a certain threshold and 3GPP signal becomes worse/better than another threshold, etc.).

2. Measurement reporting: When the conditions for triggering thresholds, as configured by signal 1 above, are fulfilled, the UE sends a measurement report to the 3GPP RAN.

3. Traffic steering: Based on the measurement report received in signal 2, the RAN evaluates the received measurements and other relevant information obtained in eNB/RNC (radio network controller) and as a result of this sends a traffic steering command to the UE, which can specify the traffic to be steered. This can be an explicit indication of each bearer to be moved (i.e. by specifying data radio bearer (DRB)/radio bearer (RB)-IDs) or more general like the Quality of Service (QoS) Class Identifier (QCI), which can apply to many bearers at once. It is intended that the UE acts on the received steering command and steers traffic to the indicated radio access technology (RAT).

4. UE ACK/Response: With this signal, the UE indicates to the RAN whether or not the action dictated by the traffic steering command was successfully performed or not.

UEs that are in IDLE mode can request the set-up of an RRC connection so that the UE can send measurement reports when the conditions of the measurement control configuration are satisfied. Alternatively, the solutions above in which the UE takes the steering decision on the basis of assistance parameters provided by the RAN, which are equally applicable to both IDLE and CONNECTED UEs, might be employed for handling IDLE UEs, while the fully-network controlled solution is used only for CONNECTED UEs.

In most E-UTRAN implementations, an inactivity timer (that can range from a few seconds to several hours) monitors how long the UE does not transmit any traffic through E-UTRAN. If the UE remains inactive in both uplink (UL) and downlink (DL) for a period longer than the timer value, the network will trigger RRC connection release and the UE goes into IDLE mode.

The following problem arises from this scenario: Once the UE notifies upper layers to steer the traffic to WLAN and the inactivity timer expires, the UE goes to RRCJDLE and is not able to receive dedicated control signalling from E-UTRAN any longer. In this case, the following RRC functionalities cannot be executed:

i) Measurement Control, including measurement configuration and measurement reporting;

ii) Mobility Management, including inter/intra E-UTRA mobility, mobility from E- UTRA and handover from E-UTRA;

iii) Connection control procedures, including RRC Connection Reconfiguration and UE capabilities transfer; and

iv) Transparent message transfer.

It might be beneficial for a given source eNodeB (eNB-1 ) to be able to execute these functionalities for UEs temporarily steering their traffic to WLAN (for example during some overloading period) but still under the coverage area of eNB-1 . The problem is illustrated in Figure 2. In Figure 2(a) a UE (UE-1 ) is connected to eNB-1 and is steering traffic to eNB-1 . There is an RRC connection between UE-1 and eNB-1 (UE-1 is in RRC_CONNECTED mode). Due to overload at eNB-1 , eNB-1 steers UEs in RRC_CONNECTED mode to WLAN (and in particular access point, AP-1 ) by setting appropriate thresholds via dedicated signalling. Thus, in Figure 2(b), UE-1 is connected to AP-1 , and after the timer expires, UE-1 is put into RRCJDLE mode and the RRC connection is released. However, if the load in eNB-1 decreases to a more acceptable level, eNB-1 cannot steer specific UEs (e.g. UE-1 ) back to E-UTRAN since no dedicated signalling to those UEs is possible. Since the thresholds used by UE-1 were received when UE-1 was in RRC_CONNECTED, UE-1 will use them as long as a pre-defined timer runs, after which UE-1 will read the thresholds broadcast by eNB-1 . Despite this possibility, it is not possible to bring back UEs to E-UTRAN one by one or by taking into account some specific UE characteristics. WO2013/091236 discloses a method for traffic offloading, in which an access point can establish a tunnel with another access point having a lo-located local gateway, in order to use the traffic offloading capabilities of the other access point. WO2007/143721 discloses a method of tunnelling packets between remote and serving access points for delivery to an access terminal.

SUMMARY

Future study of improvements in joint coordination between 3GPP-WLAN has been started, and it has been agreed to focus on non-integrated 3GPP/WLAN nodes since integrated nodes are a matter of implementation. Part of the study will examine potential enhancements of RAN interfaces and procedures to support the joint operation among different RATs, including WLAN, and this may involve specifying an inter-node interface between the E-UTRAN and WLAN.

The techniques and mechanisms described herein enable the setup of a dedicated connection (e.g. that can be used to carry E-UTRAN RRC signalling) associated with a first node over an inter-node interface to a second node (e.g. between a WLAN AP and an eNodeB). It will be appreciated from the details provided that although the techniques are described with reference to establishing a dedicated connection between an eNodeB and a WLAN AP, the techniques are more generally applicable to establishing a dedicated connection between two radio access nodes operating according to different radio access technologies (RATs) via an interface between the nodes.

According to an aspect, there is provided a method for use in a system comprising a first network node, a second network node, and a terminal device, wherein the terminal device has a connection to the second network node over a radio interface and the first network node has a connection to the second network node over an inter-node interface, the method comprising:

establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. According to an aspect, there is provided a method in a first network node of a network using a first radio access technology, comprising, in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a second radio access technology different from the first radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface:

establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

According to an aspect, there is provided a method in a first network node of a network using a first radio access technology, comprising,

in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a second radio access technology different from the first radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface:

sending a request to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. According to an aspect, there is provided a method in a first network node of a network, wherein the first network node has a radio interface, the method comprising:

receiving from a second network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

According to an aspect, there is provided a method in a second network node of a network, wherein a first network node has a connection to the second network node over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, the method comprising:

receiving from the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface; and

establishing said dedicated control plane tunnel. According to an aspect, there is provided a method in a second network node of a network, the method comprising: establishing a connection to a terminal device over a radio interface, receiving information from the terminal device identifying a first network node with which the terminal device has had a connection, wherein the first network node has a connection to the second network node over an inter-node interface; and

sending to the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

According to an aspect, there is provided a method in a system comprising a first network node, and a second network node, wherein the first network node has a connection to the second network node over an inter-node interface, the method comprising:

determining that a terminal device has replaced a traffic connection over a first radio interface with the first network node by a traffic connection over a second radio interface with the second network node; and

attempting to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the second radio interface. According to an aspect, there is provided a system comprising a first network node, a second network node, and a terminal device, wherein the terminal device has a connection to the second network node over a radio interface and the first network node has a connection to the second network node over an inter-node interface, the system being adapted for:

According to an aspect, there is provided a first network node for a network using a first radio access technology, being adapted for:

in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a second radio access technology different from the first radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. According to an aspect, there is provided a first network node for a network using a first radio access technology, being adapted for:

sending a request to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. According to an aspect, there is provided a second network node for a network, wherein a first network node has a connection to the second network node over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, being adapted for:

establishing said dedicated control plane tunnel.

According to an aspect, there is provided a second network node for a network, being adapted for:

establishing a connection to a terminal device over a radio interface,

receiving information from the terminal device identifying a first network node with which the terminal device has had a connection, wherein the first network node has a connection to the second network node over an inter-node interface; and

According to an aspect, there is provided a system comprising a first network node, and a second network node, wherein the first network node has a connection to the second network node over an inter-node interface, the system being adapted for: determining that a terminal device has replaced a traffic connection over a first radio interface with the first network node by a traffic connection over a second radio interface with the second network node; and

attempting to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the second radio interface.

According to an aspect, there is provided a method of operating a network node in a first network operating according to a first radio access technology, RAT, the method comprising:

establishing and/or maintaining a dedicated control plane tunnel to a terminal device that is connected to a network node in a second network that is operating according to a second RAT, the dedicated control plane tunnel being established through the network node in the second network;

establishing and/or maintaining a dedicated control plane connection directly with the terminal device while the dedicated control plane tunnel is established and/or maintained; and

communicating control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection.

According to an aspect, there is provided a network node for use in a first network operating according to a first radio access technology, RAT, the network node being adapted to:

establish and/or maintain a dedicated control plane tunnel to a terminal device that is connected to a network node in a second network that is operating according to a second RAT, the dedicated control plane tunnel being established through the network node in the second network;

establish and/or maintain a dedicated control plane connection directly with the terminal device while the dedicated control plane tunnel is established and/or maintained; and

communicate control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection.

According to an aspect, there is provided a method of operating a terminal device that is connected to a network node in a second network that is operating according to a second radio access technology, RAT, the method comprising: establishing and/or maintaining a dedicated control plane tunnel to a network node in a first network that is operating according to a first RAT, the dedicated control plane tunnel being established through the network node in the second network;

establishing and/or maintaining a dedicated control plane connection directly with the network node in the first network while the dedicated control plane tunnel is established and/or maintained; and

communicating control plane information with the network node in the first network via the dedicated control plane tunnel and/or the dedicated control plane connection.

According to an aspect, there is provided a terminal device for use in a first network operating according to a first radio access technology, RAT, and a second network operating according to a second RAT different from the first RAT, the terminal device being adapted to:

establish and/or maintain a dedicated control plane tunnel to a network node in a first network that is operating according to a first RAT, the dedicated control plane tunnel being established through the network node in the second network;

establish and/or maintain a dedicated control plane connection directly with the network node in the first network while the dedicated control plane tunnel is established and/or maintained; and

communicate control plane information with the network node in the first network via the dedicated control plane tunnel and/or the dedicated control plane connection. According to an aspect, there is provided 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 any of the method embodiments described above.

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 is a signalling diagram illustrating a fully network-controlled interworking mechanism;

Figure 2 is a diagram illustrating problems with UEs going to IDLE mode when connected to a WLAN;

Figure 3 is a non-limiting example block diagram of an LTE cellular communications network; Figure 4 is a block diagram of a terminal device according to an embodiment;

Figure 5 is a block diagram of a radio access network node according to an embodiment; Figure 6 is a block diagram of a core network node according to an embodiment; Figure 7 is a block diagram of a WLAN access point according to an embodiment; Figure 8 is a signalling diagram illustrating a method;

Figure 9 is a signalling diagram illustrating a method; Figure 10 is a signalling diagram illustrating a method; Figure 1 1 is a signalling diagram illustrating a method; Figure 12 is a signalling diagram illustrating a method; Figure 13 is a signalling diagram illustrating a method;

Figure 14 is a signalling diagram illustrating a method;

Figure 15 illustrates RRC diversity through LTE and an inter-node interface and WLAN; Figure 16 is a signalling diagram illustrating a method; and Figure 17 is a protocol stack diagram.

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 and also in some cases a receiver component and/or transmitter component 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 units, one or more processing modules or one or more controllers, and the terms computer, processor, processing unit, processing module and controller may be employed interchangeably. When provided by a computer, processor, processing unit, processing module or controller, the functions may be provided by a single dedicated computer, processor, processing unit, processing module or controller, by a single shared computer, processor, processing unit, processing module or controller, or by a plurality of individual computers, processors, processing units, processing modules or controllers, some of which may be shared or distributed. Moreover, the terms "processor", "processing unit", "processing module" or "controller" also refer 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 a terminal device or user equipment (UE), it should be understood by the skilled in the art that "terminal device" and "UE" are non-limiting terms comprising any mobile, non-mobile or wireless device or node equipped with a radio interface allowing for at least one of: transmitting signals in uplink (UL) and receiving and/or measuring signals in downlink (DL). 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" and "terminal device", the term "mobile device" is 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", as with "terminal device" encompasses any device that is capable of communicating with communication networks that operate according to one or more mobile communication standards, such as GSM, UMTS, LTE, WiFi, etc.

A cell is associated with a radio access network (RAN) node, where a RAN node comprises in a general sense any node transmitting radio signals in the downlink (DL) to a terminal device and/or receiving radio signals in the uplink (UL) from a terminal device. Some example RAN nodes, or terms used for describing RAN nodes, are base station, 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 RAN node 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 circuitry for different RATs.

It should be noted that unless otherwise indicated, the use of the general term "network node" as used herein refers to a RAN node, such as a base station, an eNodeB, a network node in the RAN responsible for resource management, such as a radio network controller (RNC), a core network node, such as a mobility management entity (MME) or SGW, or a WLAN Access Point (AP) or WLAN access controller (AC).

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). For example, signalling from a coordinating node may pass another network node, e.g., a radio node.

Figure 3 shows an example diagram of an evolved UMTS Terrestrial Radio Access Network (EUTRAN) architecture as part of an LTE-based communications system 2. Nodes in the core network 4 include one or more Mobility Management Entities (MMEs) 6, a key control node for the LTE access network, and one or more Serving Gateways (SGWs) 8 which route and forward user data packets while acting as a mobility anchor. They communicate with base stations 10 in the RAN referred to in LTE as eNBs or eNodeBs, over an interface, for example an S1 interface. The eNBs 10 can include the same or different categories of eNBs, e.g. macro eNBs, and/or micro/pico/femto eNBs. The eNBs 10 communicate with each other over an interface, for example an X2 interface. The S1 interface and X2 interface are defined in the LTE standard. A UE 12 can receive downlink data from and send uplink data to one of the base stations 10 with that base station 10 being referred to as the serving base station of the UE 12. An access point (AP) 14 that is part of a WLAN is also shown in Figure 3, although it will be appreciated that the WLAN and AP 14 are not part of the EUTRAN architecture.

In order to implement some of the various embodiments described herein, a communication path is established between the WLAN AP 14 and at least one of the nodes 10 in the LTE network 2 so that a dedicated connection can be established between the nodes. One such communication path/interface is shown as interface 16 in Figure 3, and it will be appreciated that this connection would typically be established via the WLAN AP's 14 broadband connection, rather than there being a direct (e.g. air interface) signalling connection between the AP 14 and eNB 10. Similar interfaces 16 may be established between one node 10 and multiple WLAN APs 14. It will also be appreciated that where the AP 14 is within the coverage area of several eNBs 10, the AP 14 may have separate interfaces 16 to each of those eNBs 10. Inter-node interfaces 16 between a pair of nodes 10, 14 may be a peer to peer interface, i.e. an interface that connects the two nodes directly. Alternatively, inter-node interfaces could connect the two nodes while passing through other network nodes. Figure 4 shows a terminal device 12 or user equipment (UE) that can be adapted for use in one or more of the non-limiting example embodiments described. The terminal device 12 comprises a processing unit 30 that controls the operation of the terminal device 12. The processing unit 30 is connected to a receiver or a transceiver 32 (which comprises a receiver and a transmitter) with associated antenna(s) 34 which are used to receive signals from or both transmit signals to and receive signals from two different types of radio access network (i.e. two radio access networks that are operating according to different radio access technologies, RATs), such as RAN node 10 in the LTE network 2 and access point (AP) 14 in a WLAN. The terminal device 12 also comprises a memory unit 36 that is connected to the processing unit 30 and that stores computer program code and other information and data required for the operation of the terminal device 12.

Specifically, modules for performing specified actions in certain embodiments may be implemented by means of a computer program running on the processing unit 30.

Figure 5 shows a RAN node 10 (for example a base station, NodeB or an eNodeB) that can be adapted for use in example embodiments described. The RAN node 10 comprises a processing unit 40 that controls the operation of the base station 10. The processing unit 40 is connected to a transmitter or a transceiver 42 (which comprises a receiver and a transmitter) with associated antenna(s) 44 which are used to transmit signals to, and receive signals from, terminal devices 12 in the network 2. The RAN node 10 also comprises a memory unit 46 that is connected to the processing unit 40 and that stores computer program code and other information and data required for the operation of the RAN node 10. The RAN node 10 also includes components and/or circuitry 48 for allowing the RAN node 10 to exchange information with other RAN nodes 10 (for example via an X2 interface) and components and/or circuitry 49 for allowing the RAN node 10 to exchange information with nodes in the core network 4 (for example via the S1 interface). The RAN node interface 48 can also be used to form an interface/connection 16 between the RAN node 10 and one or more WLAN APs 14 in the coverage area of the RAN node 10 and allow a dedicated connection to be established with the WLAN APs 14. It will be appreciated that RAN nodes for use in other types of network (e.g. UTRAN or WCDMA RAN) will include similar components to those shown in Figure 3 and appropriate interface circuitry 48, 49 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).

Specifically, modules for performing specified actions in certain embodiments may be implemented by means of a computer program running on the processing unit 40.

Figure 6 shows a core network node 6, 8 that can be used in the example embodiments described. The node 6, 8 comprises a processing unit 50 that controls the operation of the node 6, 8. The processing unit 50 is connected to components and/or circuitry 52 for allowing the node 6, 8 to exchange information with RAN nodes 10 with which it is associated (which is typically via the S1 interface). The node 6, 8 also comprises a memory unit 56 that is connected to the processing unit 50 and that stores computer program code and other information and data required for the operation of the node 6, 8.

Specifically, modules for performing specified actions in certain embodiments may be implemented by means of a computer program running on the processing unit 50.

Figure 7 shows a WLAN AP 14 that can be used in the example embodiments described. The AP 14 comprises a processing unit 60 that controls the operation of the AP 14. The processing unit 60 is connected to a transmitter or a transceiver 62 (which comprises a receiver and a transmitter) with associated antenna(s) 64 which are used to transmit signals to, and receive signals from, terminal devices 12. The AP 14 also comprises a memory unit 66 that is connected to the processing unit 60 and that stores computer program code and other information and data required for the operation of the AP 14. The AP 14 also includes components and/or circuitry 68 for connecting the AP 14 to a telephone line or other broadband connection. The processing unit 60 can be configured to establish the interface 16 between the AP 14 and one or more RAN nodes 10 and receive and send information from the RAN node 10.

Specifically, modules for performing specified actions in certain embodiments may be implemented by means of a computer program running on the processing unit 60. It will be appreciated that only the components of the terminal device 12, RAN node 10, core network node 6, 8 and AP 14 required to explain the embodiments presented herein are illustrated in Figures 4, 5, 6 and 7. Various exemplary aspects and embodiments of the techniques described herein are set out below. These techniques are a set of mechanisms between two radio access nodes and a mobile terminal capable of being connected to both of the radio access nodes. In some embodiments, these mechanisms enable the setup of a dedicated connection that can be used to carry signaling associated with a first node over an inter-node interface through the second node to the mobile terminal.

In one embodiment, there is provided a method for use in a system comprising a first network node, a second network node, and a terminal device, wherein the terminal device has a connection to the second network node over a radio interface and the first network node has a connection to the second network node over an inter-node interface, the method comprising: establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. The dedicated control plane tunnel may be established in response to detecting that the terminal device has a connection to the second network node over the radio interface. Specifically, the dedicated control plane tunnel may be established in response to the first network node detecting that the terminal device has a connection to the second network node over the radio interface, or in response to the second network node detecting that the terminal device has a connection to the second wireless access point over the radio interface.

Establishing the dedicated control plane tunnel may comprise the first network node sending a request to the second network node over the inter-node interface.

Establishing the dedicated control plane tunnel may comprise the second network node sending a request to the first network node over the inter-node interface in response to establishing a connection with the terminal device. A specific identifier may be used to map the tunnel to said terminal device. The identifier mapping the tunnel to the UE may indicate a UE class or group that identifies some or all of the UE characteristics. The dedicated control plane tunnel may comprise a first container through the inter- node interface and a second container through the radio interface.

The first network node and the second network node may use different radio access technologies. Specifically, the first network node and the second network node may use different 3GPP radio access technologies.

One of the first network node and the second network node may use a 3GPP radio access technology while the other of the first network node and the second network node uses a non-3GPP radio access technology.

The first network node may be a UTRAN radio access node, and the control plane tunnel may be an RRC tunnel. The second network node may then be a WLAN access point. The first network node may be a WLAN access point.

The second network node may be a UTRAN radio access node.

In one embodiment, a method for use in a first network node of a network, comprises, in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

The first network node may make said determination that the terminal device has established the connection to the second network node. Establishing the dedicated control plane tunnel may comprise sending a tunnel request to the second network node over the inter-node interface. The method may comprise maintaining a control plane connection to the terminal device over a radio interface of the first network node, after establishing said dedicated control plane tunnel.

The method may comprise releasing a control plane connection to the terminal device over a radio interface of the first network node, after establishing said dedicated control plane tunnel. The method may comprise exchanging with the second network node a specific identifier for mapping the tunnel to said terminal device. The identifier mapping the tunnel to the UE may indicate a UE class or group that identifies some or all of the UE characteristics. The dedicated control plane tunnel may comprise a first container through the inter- node interface and a second container through the radio interface.

In one embodiment, a method for use in a first network node of a network, comprises, in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: sending a request to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

The method may further comprise: in the event of receiving a message from the second network node rejecting said request to establish the dedicated control plane tunnel, maintaining a control plane connection to the terminal device over a radio interface of the first network node.

In one embodiment, a method for use in a first network node of a network, wherein the first network node has a radio interface, comprises: receiving from a second network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. The dedicated control plane tunnel may comprise a first container through the inter- node interface and a second container through the radio interface. In one embodiment, a method for use in a second network node of a network, wherein a first network node has a connection to the second network node over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, comprise: receiving from the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface; and establishing said dedicated control plane tunnel.

The method may comprise establishing said dedicated control plane tunnel only in response to determining that said first network node is a network node with which the terminal device has had a connection. The method may comprise establishing said dedicated control plane tunnel only in response to determining that said first network node is a network node with which the terminal device has most recently had a connection. The method may comprise determining that said first network node is a network node with which the terminal device has most recently had a connection from information known to the second network node. Alternatively, the method may comprise determining that said first network node is a network node with which the terminal device has most recently had a connection by sending a message to the terminal device requesting information regarding the network node with which the terminal device has most recently had a connection. Alternatively, the method may comprise determining that said first network node is a network node with which the terminal device has most recently had a connection by sending a message to the terminal device containing information regarding the network node from which it received the request to establish the dedicated control plane tunnel, and requesting confirmation that said network node is the network node with which the terminal device has most recently had a connection.

The method may comprise exchanging with the first network node a specific identifier for mapping the tunnel to said terminal device. The identifier mapping the tunnel to the UE indicates a UE class or group that identifies some or all of the UE characteristics. The dedicated control plane tunnel may comprise a first container through the inter- node interface and a second container through the radio interface. In one embodiment, a method for use in a second network node of a network comprises: establishing a connection to a terminal device over a radio interface, receiving information from the terminal device identifying a first network node with which the terminal device has had a connection, wherein the first network node has a connection to the second network node over an inter-node interface; and sending to the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

In one embodiment, a method for use in a system comprising a first network node, and a second network node, wherein the first network node has a connection to the second network node over an inter-node interface comprises: determining that a terminal device has replaced a traffic connection over a first radio interface with the first network node by a traffic connection over a second radio interface with the second network node; and attempting to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the second radio interface.

The dedicated control plane tunnel may comprise a first container over the inter-node interface and a second container over the second radio interface.

Determining that the terminal device has replaced the traffic connection over the first radio interface with the first network node by the traffic connection over the second radio interface with the second network node may comprise determining that the terminal device has performed traffic steering from the first network node to the second network node.

The first network node may be a 3GPP radio access node while the second network node is a WLAN access point. The dedicated control plane tunnel may be an RRC tunnel. In one embodiment, a system comprises a first network node, a second network node, and a terminal device, wherein the terminal device has a connection to the second network node over a radio interface and the first network node has a connection to the second network node over an inter-node interface, the system being adapted for: establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

The system may be configured for establishing the dedicated control plane tunnel in response to detecting that the terminal device has a connection to the second network node over the radio interface. Specifically, the dedicated control plane tunnel may be established in response to the first network node detecting that the terminal device has a connection to the second network node over the radio interface, or in response to the second network node detecting that the terminal device has a connection to the second wireless access point over the radio interface.

The system may be configured for establishing the dedicated control plane tunnel by the first network node sending a request to the second network node over the inter- node interface.

The system may be configured for establishing the dedicated control plane tunnel by the second network node sending a request to the first network node over the inter- node interface in response to establishing a connection with the terminal device. A specific identifier may be used to map the tunnel to said terminal device. The identifier mapping the tunnel to the UE may indicate a UE class or group that identifies some or all of the UE characteristics.

The dedicated control plane tunnel may comprise a first container through the inter- node interface and a second container through the radio interface.

The first network node and the second network node may use different radio access technologies. Specifically, the first network node and the second network node may use different 3GPP radio access technologies. One of the first network node and the second network node may use a 3GPP radio access technology while the other of the first network node and the second network node uses a non-3GPP radio access technology. The first network node may be a UTRAN radio access node, and the control plane tunnel may be an RRC tunnel. The second network node may then be a WLAN access point.

The first network node may be a WLAN access point.

The second network node may be a UTRAN radio access node.

In one embodiment, there is provided a system comprising: a first network node, a second network node, and a terminal device, wherein the terminal device has a connection to the second network node over a radio interface and the first network node has a connection to the second network node over an inter-node interface, the system further comprising an establishment module, for establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

In one embodiment, a first network node for a network is adapted for: in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

The first network node may be adapted to make said determination that the terminal device has established the connection to the second network node.

The first network node may be adapted to establish the dedicated control plane tunnel by sending a tunnel request to the second network node over the inter-node interface. The first network node may be adapted to maintain a control plane connection to the terminal device over a radio interface of the first network node, after establishing said dedicated control plane tunnel. The first network node may be adapted to release a control plane connection to the terminal device over a radio interface of the first network node, after establishing said dedicated control plane tunnel.

The first network node may be adapted to exchange with the second network node a specific identifier for mapping the tunnel to said terminal device. The identifier mapping the tunnel to the UE may indicate a UE class or group that identifies some or all of the UE characteristics.

In one embodiment, there is provide a first network node of a network, comprising: an establishment module for, in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface, establishing a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. In one embodiment, a first network node for a network is adapted for: in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: sending a request to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

The first network node may be further adapted for: in the event of receiving a message from the second network node rejecting said request to establish the dedicated control plane tunnel, maintaining a control plane connection to the terminal device over a radio interface of the first network node. In one embodiment, a first network node of a network comprises a sending module for, in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: sending a request to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

In one embodiment, a method for use in a first network node of a network, wherein the first network node has a radio interface, is configured for: receiving from a second network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

The dedicated control plane tunnel may comprise a first container through the inter- node interface and a second container through the radio interface. In one embodiment, a first network node of a network, wherein the first network node has a radio interface, comprises a receiving module, for receiving from a second network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

In one embodiment, a second network node for a network, wherein a first network node has a connection to the second network node over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, is adapted for: receiving from the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface; and establishing said dedicated control plane tunnel.

The second network node may be configured for establishing said dedicated control plane tunnel only in response to determining that said first network node is a network node with which the terminal device has had a connection. The second network node may be configured for establishing said dedicated control plane tunnel only in response to determining that said first network node is a network node with which the terminal device has most recently had a connection. The second network node may be configured for determining that said first network node is a network node with which the terminal device has most recently had a connection from information known to the second network node. Alternatively, the second network node may be configured for determining that said first network node is a network node with which the terminal device has most recently had a connection by sending a message to the terminal device requesting information regarding the network node with which the terminal device has most recently had a connection. Alternatively, the second network node may be configured for determining that said first network node is a network node with which the terminal device has most recently had a connection by sending a message to the terminal device containing information regarding the network node from which it received the request to establish the dedicated control plane tunnel, and requesting confirmation that said network node is the network node with which the terminal device has most recently had a connection.

The second network node may be configured for exchanging with the first network node a specific identifier for mapping the tunnel to said terminal device. The identifier mapping the tunnel to the UE indicates a UE class or group that identifies some or all of the UE characteristics.

In one embodiment, a second network node of a network, wherein a first network node has a connection to the second network node over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, comprises: a receiving module, for receiving from the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface; and an establishing module for establishing said dedicated control plane tunnel. In one embodiment, a second network node for a network is adapted for: establishing a connection to a terminal device over a radio interface, receiving information from the terminal device identifying a first network node with which the terminal device has had a connection, wherein the first network node has a connection to the second network node over an inter-node interface; and sending to the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. In one embodiment, a second network node of a network comprises: an establishing module, for establishing a connection to a terminal device over a radio interface; a receiving module, for receiving information from the terminal device identifying a first network node with which the terminal device has had a connection, wherein the first network node has a connection to the second network node over an inter-node interface; and a sending module, for sending to the first network node a request to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface. In one embodiment, a system comprises a first network node, and a second network node, wherein the first network node has a connection to the second network node over an inter-node interface, the system being adapted for: determining that a terminal device has replaced a traffic connection over a first radio interface with the first network node by a traffic connection over a second radio interface with the second network node; and attempting to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the second radio interface.

The system may be adapted for determining that the terminal device has replaced the traffic connection over the first radio interface with the first network node by the traffic connection over the second radio interface with the second network node by determining that the terminal device has performed traffic steering from the first network node to the second network node. The first network node may be a 3GPP radio access node while the second network node is a WLAN access point. The dedicated control plane tunnel may be an RRC tunnel.

In one embodiment, a system comprises: a first network node; a second network node, wherein the first network node has a connection to the second network node over an inter-node interface; a determining node, for determining that a terminal device has replaced a traffic connection over a first radio interface with the first network node by a traffic connection over a second radio interface with the second network node; and an attempting node, for attempting to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the second radio interface.

In one embodiment, a method of operating a network node in a first network operating according to a first radio access technology, RAT comprises: establishing and/or maintaining a dedicated control plane tunnel to a terminal device that is connected to a network node in a second network that is operating according to a second RAT, the dedicated control plane tunnel being established through the network node in the second network; establishing and/or maintaining a dedicated control plane connection directly with the terminal device while the dedicated control plane tunnel is established and/or maintained; and communicating control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection.

The control plane information may be communicated with the terminal device through both the dedicated control plane tunnel and the dedicated control plane connection. Control plane information received from the terminal device at the network node in the first network may be communicated via one of the dedicated control plane tunnel and the dedicated control plane connection, and control plane information sent to the terminal device from the network node in the first network is communicated via the other one of the dedicated control plane tunnel and the dedicated control plane connection. The method may further comprise determining whether to communicate control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection according to load conditions in the first network and/or second network. In some embodiments, the load conditions relate to the load distribution in the uplink and downlink in the first network and/or second network.

The step of establishing and/or maintaining a dedicated control plane connection directly with the network node in the first network may comprise establishing and/or maintaining the dedicated control plane connection through an air or radio interface between the terminal device and the network node in the first network.

The dedicated control plane tunnel may be a dedicated radio resource control, RRC, tunnel, while the dedicated control plane connection is an RRC connection. The first RAT may be a 3GPP-specified RAT while the second RAT is WLAN, for example Wi-Fi. The 3GPP-specified RAT may be Long Term Evolution, LTE, Universal Mobile Telecommunications System, UMTS, Wideband Code-Division Multiple Access, WCDMA, High Speed Packet Access, HSPA, or Global System for Mobile Communications, GSM.

In one embodiment, a network node for use in a first network operating according to a first radio access technology, RAT, is adapted to: establish and/or maintain a dedicated control plane tunnel to a terminal device that is connected to a network node in a second network that is operating according to a second RAT, the dedicated control plane tunnel being established through the network node in the second network; establish and/or maintain a dedicated control plane connection directly with the terminal device while the dedicated control plane tunnel is established and/or maintained; and communicate control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection.

The control plane information may be communicated with the terminal device through both the dedicated control plane tunnel and the dedicated control plane connection.

The network node may be further adapted to communicate control plane information received from the terminal device at the network node in the first network via one of the dedicated control plane tunnel and the dedicated control plane connection, and to communicate control plane information sent to the terminal device from the network node in the first network via the other one of the dedicated control plane tunnel and the dedicated control plane connection. The network node may be further adapted to determine whether to communicate control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection according to load conditions in the first network and/or second network. In some embodiments, the load conditions relate to the load distribution in the uplink and downlink in the first network and/or second network.

The network node may be further adapted to establish and/or maintain a dedicated control plane connection directly with the network node in the first network by establishing and/or maintaining the dedicated control plane connection through an air or radio interface between the terminal device and the network node in the first network.

The dedicated control plane tunnel may be a dedicated radio resource control, RRC, tunnel, while the dedicated control plane connection is an RRC connection.

The first RAT may be a 3GPP-specified RAT while the second RAT is WLAN, for example Wi-Fi. The 3GPP-specified RAT may be Long Term Evolution, LTE, Universal Mobile Telecommunications System, UMTS, Wideband Code-Division Multiple Access, WCDMA, High Speed Packet Access, HSPA, or Global System for Mobile Communications, GSM.

In one embodiment, a network node in a first network operating according to a first radio access technology, RAT comprises: a tunnel module, for establishing and/or maintaining a dedicated control plane tunnel to a terminal device that is connected to a network node in a second network that is operating according to a second RAT, the dedicated control plane tunnel being established through the network node in the second network; a connection module, for establishing and/or maintaining a dedicated control plane connection directly with the terminal device while the dedicated control plane tunnel is established and/or maintained; and a communication module, for communicating control plane information with the terminal device via the dedicated control plane tunnel and/or the dedicated control plane connection. In one embodiment, a method of operating a terminal device that is connected to a network node in a second network that is operating according to a second radio access technology, RAT, may comprise: establishing and/or maintaining a dedicated control plane tunnel to a network node in a first network that is operating according to a first RAT, the dedicated control plane tunnel being established through the network node in the second network; establishing and/or maintaining a dedicated control plane connection directly with the network node in the first network while the dedicated control plane tunnel is established and/or maintained; and communicating control plane information with the network node in the first network via the dedicated control plane tunnel and/or the dedicated control plane connection.

Control plane information may be communicated with the network node in the first network through both the dedicated control plane tunnel and the dedicated control plane connection.

Control plane information sent from the terminal device to the network node in the first network may be communicated via one of the dedicated control plane tunnel and the dedicated control plane connection, and control plane information received at the terminal device from the network node in the first network is communicated via the other one of the dedicated control plane tunnel and the dedicated control plane connection.

The first RAT may be a 3GPP-specified RAT while the second RAT is WLAN, for example Wi-Fi. The 3GPP-specified RAT may be Long Term Evolution, LTE, Universal Mobile Telecommunications System, UMTS, Wideband Code-Division Multiple Access, WCDMA, High Speed Packet Access, HSPA, or Global System for Mobile Communications, GSM. In one embodiment, a terminal device for use in a first network operating according to a first radio access technology, RAT, and a second network operating according to a second RAT, is adapted to: establish and/or maintain a dedicated control plane tunnel to a network node in a first network that is operating according to a first RAT, the dedicated control plane tunnel being established through the network node in the second network; establish and/or maintain a dedicated control plane connection directly with the network node in the first network while the dedicated control plane tunnel is established and/or maintained; and communicate control plane information with the network node in the first network via the dedicated control plane tunnel and/or the dedicated control plane connection.

The terminal device may be further adapted to communicate control plane information with the network node in the first network through both the dedicated control plane tunnel and the dedicated control plane connection.

The terminal device may be further adapted to communicate control plane information sent from the terminal device to the network node in the first network via one of the dedicated control plane tunnel and the dedicated control plane connection, and to communicate control plane information received at the terminal device from the network node in the first network via the other one of the dedicated control plane tunnel and the dedicated control plane connection.

The terminal device may be further adapted such that the step of establishing and/or maintaining a dedicated control plane connection directly with the network node in the first network comprises establishing and/or maintaining the dedicated control plane connection through an air or radio interface between the terminal device and the network node in the first network. The dedicated control plane tunnel may be a dedicated radio resource control, RRC, tunnel, while the dedicated control plane connection is an RRC connection.

In one embodiment, a terminal device that is connected to a network node in a second network that is operating according to a second radio access technology, RAT, comprises: a tunnel module, for establishing and/or maintaining a dedicated control plane tunnel to a network node in a first network that is operating according to a first RAT, the dedicated control plane tunnel being established through the network node in the second network; a connection module, for establishing and/or maintaining a dedicated control plane connection directly with the network node in the first network while the dedicated control plane tunnel is established and/or maintained; and a communicating module, for communicating control plane information with the network node in the first network via the dedicated control plane tunnel and/or the dedicated control plane connection.

In one embodiment, a computer program product comprises 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 any of the method embodiments described above.

In the illustrated embodiments, the two radio access nodes are an eNodeB and a WLAN AP respectively, and the mechanisms enable the setup of a dedicated connection that can be used to carry E-UTRAN Radio Resource Control (RRC) signaling associated with the eNodeB, even when the mobile terminal has a connection to the WLAN AP. To give one, purely illustrative example of a use of this, when a given UE performs traffic steering from the first node (eNodeB) to the second node (AP) and releases its control signaling connection with the first node (RRC Connection released with the eNodeB), the UE and the first node (eNodeB) may still be able to exchange dedicated control signaling through the inter-node interface. In another example, if the UE is able to transmit on both access nodes the mechanisms could enable a dual-RRC connection for diversity purposes. Thus, in this example, a UE that has performed traffic steering away from the eNodeB to WLAN can still exchange dedicated messages with the eNodeB. Typical dedicated control signaling can then be executed via a non-3GPP air interface and an inter-node interface. Although most of the description and examples in this document refer to the establishment of an RRC tunnel between 3GPP (LTE) and WLAN, the described mechanisms are applicable also to setting up Control plane tunnels between 3GPP and other non 3GPP networks other than WLAN, or between two different 3GPP RATs such as LTE and WCDMA/HSPA, or more generally between any two access nodes in circumstances where it is useful to be able to establish a dedicated control plane connection between an access node and a terminal device that has a wireless connection to a second access node.

The embodiments described herein relate to a method running at two radio access nodes (e.g. a 3GPP eNodeB-1 and a WLAN AP-1 ) and a mobile terminal where the two nodes have an inter-node interface between them (e.g. a suitable inter-node interface is referred to herein as an Xw interface). Initially, the first node (e.g. eNB-1 ) has a dedicated connection with the mobile terminal (e.g. UE-1 ) via their radio interfaces (e.g. an RRC Connection for control plane signaling). Upon the detection by either the first or second nodes (eNodeB-1 or AP-1 ) that a radio interface connection has been established between the UE-1 and the second node (e.g. AP-1 ), either the first or the second node triggers the setup of a dedicated tunnel through the inter-node interface between the mobile terminal (UE-1 ) and the first radio access node (e.g. the eNodeB-1 ) so that the first radio access node is able to exchange dedicated messages with the UE-1 via the radio interface of the second node.

Figure 8 illustrates an example in which the first node (eNB-1 ) initially has a dedicated connection with the mobile terminal (UE-1 ) via their radio interfaces (e.g. for RRC control plane signaling).

Then, in signaling step 81 in Figure 8, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). In signaling step 82, the first node (eNodeB-1 ) detects that UE-1 is connected to AP-1 for traffic steering. For example, the detection may be based on measurement reports, or on signaling from AP-1 .

Then, in signaling step 83 in Figure 8, a tunnel setup request is sent from eNodeB-1 to AP-1 . This consists of the first node (eNB-1 ) sending a DEDICATED TUNNEL REQUEST message (e.g. via Xw) to the second node (AP-1 ). This message contains a UE identity that makes the UE-1 identifiable at the second node. The identity can be permanent, or temporary and can be obtained via different methods. The UE-1 identity can either be an E-UTRAN identity (e.g. C-RNTI, IMSI, TSMI, etc.) made available at the WLAN, it can be a WLAN identity (WLAN MAC address) made available at the E-UTRAN or a common identity made available to both nodes. Upon the reception of this message, the second node (AP-1 ) checks (signaling step 84 in Figure 8) if the UE is associated and authenticated. If, as illustrated in Figure 8, the UE is not associated, the AP sends to the eNB a DEDICATED TUNNEL REJECT with a reject cause = "non-associated UE" (signaling step 85 in Figure 8). In signaling step 86 in Figure 8, the eNodeB-1 releases the UE context for this tunnel.

Figure 9 illustrates an alternative example in which the first node (eNB-1 ) initially has a dedicated connection with the mobile terminal (UE-1 ) via their radio interfaces (e.g. for RRC control plane signaling).

Then, in signaling step 91 in Figure 9, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). In signaling step 92, the first node (eNodeB-1 ) detects that UE-1 is connected to AP-1 for traffic steering. For example, the detection may be based on measurement reports, or on signaling from AP-1 .

Then, in signaling step 93 in Figure 9, a tunnel setup request is sent from eNodeB-1 to AP-1 . This consists of the first node (eNB-1 ) sending a DEDICATED TUNNEL REQUEST message (e.g. via Xw) to the second node (AP-1 ). This message contains a UE identity that makes the UE-1 identifiable at the second node. The identity can be permanent, or temporary and can be obtained via different methods. The UE-1 identity can either be an E-UTRAN identity (e.g. C-RNTI, IMSI, TSMI, etc.) made available at the WLAN, it can be a WLAN identity (WLAN MAC address) made available at the E-UTRAN or a common identity made available to both nodes.

In this case, upon the reception of this message, the second node (AP-1 ) checks (signaling step 94 in Figure 9) if the UE is associated and authenticated, and confirms that the UE is associated and authenticated. In signaling step 95 in Figure 9, AP-1 confirms that it has the latest eNodeB identity for UE-1 .

In signaling step 96, the AP-1 verifies if the eNodeB requesting the tunnel is the eNodeB associated to the 3GPP cell identity (e.g. E-CGI) associated to UE-1 (assumed to be known by the AP). In the embodiment shown in Figure 9, the AP-1 is aware of the latest cell the UE has been associated with (e.g. via some measurement report) so it can check the matching immediately. Having confirmed that the eNodeB requesting the tunnel is the eNodeB associated to the 3GPP cell identity associated to UE-1 , in signaling step 97 in Figure 9, AP-1 sends a dedicated tunnel confirmation to eNodeB-1 .

In signaling step 98, eNodeB-1 performs an RRC Establishment procedure with UE-1 through the WLAN. As shown in step 99, eNodeB-1 keeps a special UE context for the tunnel, with the UE identity in LTE (for example E-UTRAN identity C-RNTI) and/or the AP-1 MAC.

Figure 10 is a further alternative example, in which the first node (eNB-1 ) initially has a dedicated connection with the mobile terminal (UE-1 ) via their radio interfaces (e.g. for RRC control plane signaling).

Then, in signaling step 101 in Figure 10, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). In signaling step 102, the first node (eNodeB-1 ) detects that UE-1 is connected to AP-1 for traffic steering. For example, the detection may be based on measurement reports, or on signaling from AP-1 .

Then, in signaling step 103 in Figure 10, a tunnel setup request is sent from eNodeB-1 to AP-1 . This consists of the first node (eNB-1 ) sending a DEDICATED TUNNEL REQUEST message (e.g. via Xw) to the second node (AP-1 ). This message contains a UE identity that makes the UE-1 identifiable at the second node. The identity can be permanent, or temporary and can be obtained via different methods. The UE-1 identity can either be an E-UTRAN identity (e.g. C-RNTI, IMSI, TSMI, etc.) made available at the WLAN, it can be a WLAN identity (WLAN MAC address) made available at the E-UTRAN or a common identity made available to both nodes.

In this case, upon the reception of this message, the second node (AP-1 ) checks (signaling step 104 in Figure 10) if the UE is associated and authenticated, and confirms that the UE is associated and authenticated.

In this embodiment, in signaling step 105 in Figure 10, the AP-1 sends a message to the UE-1 (for example by sending a MAC management frame with a flag) requesting the identity of its associated cell, that is, the one that it has most recently been associated with. Upon the reception of the WLAN frame with the specific flag, in signaling step 106 in Figure 10, the UE sends the cell identity of the latest cell that it has been associated with. As shown in signaling step 107 in Figure 10, this may be sent by sending a MAC management frame with a flag, and containing the identity of its latest selected eNodeB. Upon reception, in signaling step 108 in Figure 10, the AP-1 can detect the matching.

Having confirmed that the eNodeB requesting the tunnel is the eNodeB associated to the 3GPP cell identity associated to UE-1 , in signaling step 109 in Figure 10, AP-1 sends a dedicated tunnel confirmation to eNodeB-1 .

In signaling step 109a, eNodeB-1 performs an RRC Establishment procedure with UE- 1 through the WLAN. As shown in step 109b, eNodeB-1 keeps a special UE context for the tunnel, with the UE identity in LTE (for example E-UTRAN identity C-RNTI) and/or the AP-1 MAC.

Figure 1 1 is a further alternative example, in which the first node (eNB-1 ) initially has a dedicated connection with the mobile terminal (UE-1 ) via their radio interfaces (e.g. for RRC control plane signaling).

Then, in signaling step 1 1 1 in Figure 1 1 , a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). In signaling step 1 12, the first node (eNodeB-1 ) detects that UE-1 is connected to AP-1 for traffic steering. For example, the detection may be based on measurement reports, or on signaling from AP-1 . Then, in signaling step 1 13 in Figure 1 1 , a tunnel setup request is sent from eNodeB-1 to AP-1 . This consists of the first node (eNB-1 ) sending a DEDICATED TUNNEL REQUEST message (e.g. via Xw) to the second node (AP-1 ). This message contains a UE identity that makes the UE-1 identifiable at the second node. The identity can be permanent, or temporary and can be obtained via different methods. The UE-1 identity can either be an E-UTRAN identity (e.g. C-RNTI, IMSI, TSMI, etc.) made available at the WLAN, it can be a WLAN identity (WLAN MAC address) made available at the E-UTRAN or a common identity made available to both nodes.

In this case, upon the reception of this message, the second node (AP-1 ) checks (signaling step 1 14 in Figure 1 1 ) if the UE is associated and authenticated, and confirms that the UE is associated and authenticated.

In this embodiment, in signaling step 1 15 in Figure 1 1 , the AP-1 sends a message to the UE-1 (for example by sending a MAC management frame with a flag) indicating that a tunnel request has been made, and containing a cell identity received from the eNodeB. Upon the reception of the WLAN frame with the specific flag, in signaling step 1 16 in Figure 1 1 , the UE checks whether this cell identity matches the cell identity of the latest cell that it has been associated with.

Figure 1 1 shows the case where the eNodeB identities match, and, in signaling step 1 17, the UE sends a MAC management frame with a flag, and confirming that the eNodeB identified by the AP-1 matches the identity of its latest selected eNodeB.

Having confirmed that the eNodeB requesting the tunnel is the eNodeB associated to the 3GPP cell identity associated to UE-1 , in signaling step 1 18 in Figure 1 1 , AP-1 sends a dedicated tunnel confirmation to eNodeB-1 .

In signaling step 1 19, eNodeB-1 performs an RRC Establishment procedure with UE-1 through the WLAN. As shown in step 1 19a, eNodeB-1 keeps a special UE context for the tunnel, with the UE identity in LTE (for example E-UTRAN identity C-RNTI) and/or the AP-1 MAC. Figure 12 is a further alternative example, in which the first node (eNB-1 ) initially has a dedicated connection with the mobile terminal (UE-1 ) via their radio interfaces (e.g. for RRC control plane signaling). Then, in signaling step 121 in Figure 12, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). In signaling step 122, the first node (eNodeB-1 ) detects that UE-1 is connected to AP-1 for traffic steering. For example, the detection may be based on measurement reports, or on signaling from AP-1 .

Then, in signaling step 123 in Figure 12, a tunnel setup request is sent from eNodeB-1 to AP-1 . This consists of the first node (eNB-1 ) sending a DEDICATED TUNNEL REQUEST message (e.g. via Xw) to the second node (AP-1 ). This message contains a UE identity that makes the UE-1 identifiable at the second node. The identity can be permanent, or temporary and can be obtained via different methods. The UE-1 identity can either be an E-UTRAN identity (e.g. C-RNTI, IMSI, TSMI, etc.) made available at the WLAN, it can be a WLAN identity (WLAN MAC address) made available at the E-UTRAN or a common identity made available to both nodes.

In this case, upon the reception of this message, the second node (AP-1 ) checks (signaling step 124 in Figure 12) if the UE is associated and authenticated, and confirms that the UE is associated and authenticated. In this embodiment, in signaling step 125 in Figure 12, the AP-1 sends a message to the UE-1 (for example by sending a MAC management frame with a flag) indicating that a tunnel request has been made, and containing a cell identity received from the eNodeB. Upon the reception of the WLAN frame with the specific flag, in signaling step 126 in Figure 12, the UE checks whether this cell identity matches the cell identity of the latest cell that it has been associated with.

Figure 12 shows the case where the eNodeB identities do not match. In this case, in signaling step 127, the UE sends a MAC management frame with a flag, indicating the non-matching. The message sent by the UE may also indicate the identity of its most recently selected eNodeB. If the AP-1 receives the message indicating non-matching (signaling step 128 in Figure 12), AP-1 sends a dedicated tunnel rejection message to eNodeB-1 (signaling step 129 in Figure 12) with the cause = "new eNB selected", or cause = "eNodeB-id-not- available" or cause = "resources not available in Xw interface",

In step 129a in Figure 12, the eNodeB-1 then releases the UE context for this tunnel.

In certain embodiments, the eNodeB-1 is a 3GPP eNodeB, and the dedicated connection is an RRC Connection. When the eNodeB-1 receives confirmation that the tunnel has been set up, it may allocate a special and/or new C-RNTI associated to the new tunneled dedicated connection. In another embodiment, the same C-RNTI as used for the UE during the initial connection is kept (i.e. reused). The AP-1 may also inform the UE that the dedicated tunnel has been established. In this case, the UE is able to initiate, for example, an RRC Connection Establishment procedure. The same C-RNTI can be used, in the case of a previously released RRC connection with the same eNodeB or another newly allocated C-RNTI informed to the UE during any of the previous steps.

In some scenarios, the RRC connection will be released after some time after the UE starts to transmit over WLAN. Therefore it may in some scenarios be beneficial to establish the RRC tunnel before terminating the RRC connection which is going over the 3GPP radio interface. This would ensure that, at any point in time, the terminal has an active RRC connection to the eNB. This could be achieved by the eNB maintaining the RRC connection to the terminal up until the RRC tunnel has been successfully been established (i.e. the "RRC tunnel confirmation" message has been received), even though a timer (like the inactivity timer described in the background section) has expired. In case the RRC tunnel setup procedure is unsuccessful (i.e. the "RRC tunnel reject" message has been received), the eNB may however anyway terminate the RRC connection even though the RRC tunnel has not been setup.

Thus, Figure 13 shows an embodiment in which the first node (eNB-1 ) initially has a dedicated RRC connection for control plane signaling with the mobile terminal (UE-1 ) via an LTE radio interface. Then, in signaling step 131 in Figure 13, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). As shown in signaling step 132, the UE maintains its RRC connection with eNB-1 even if its timer expires, until it receives an explicit RRC connection release message from eNB-1 .

In signaling step 133, the first node (eNodeB-1 ) is notified that UE-1 is connected to AP-1 for traffic steering. The eNodeB-1 holds the UE context.

Then, as shown at step 134 in Figure 13, the initial steps for tunnel setup are performed, as described previously.

In this example, the process is successful, and, in signaling step 135 in Figure 13, AP-1 sends a dedicated tunnel confirmation to eNodeB-1 . As shown at 136, eNodeB-1 performs an RRC Establishment procedure with UE-1 through the WLAN.

As shown in step 137, eNodeB-1 releases the UE context for the connection over the LTE interface and, in signaling step 138, sends an RRC connection release message to the UE. In response, in step 139, the UE goes to RRCJDLE, and starts to use the RRC connection over the WLAN interface.

Figure 14 shows an alternative embodiment in which the first node (eNB-1 ) initially has a dedicated RRC connection for control plane signaling with the mobile terminal (UE-1 ) via an LTE radio interface. Then, in signaling step 141 in Figure 14, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). As shown in signaling step 142, the UE maintains its RRC connection with eNB-1 even if its timer expires, until it receives an explicit RRC connection release message from eNB-1 . In signaling step 143, the first node (eNodeB-1 ) is notified that UE-1 is connected to AP-1 for traffic steering. The eNodeB-1 holds the UE context.

Then, as shown at step 144 in Figure 14, the initial steps for tunnel setup are performed, as described previously. In this example, the process is successful, and, in signaling step 145 in Figure 14, AP-1 sends a dedicated tunnel confirmation to eNodeB-1 . As shown at 146, eNodeB-1 performs an RRC Establishment procedure with UE-1 through the WLAN. In this example, as shown in step 147, eNodeB-1 keeps the UE context for the connection over the LTE interface as well as the UE context for the connection over the dedicated tunnel and over WLAN. Thus, eNodeB-1 keeps both RRC connections, one through the LTE interface and one using the tunnel via WLAN and the inter-node interface. This creates RRC diversity, which may be beneficial in certain scenarios.

This use of the dedicated control plane tunnel is shown in Figure 15. This figure illustrates RRC diversity through LTE and an inter-node interface and WLAN. Here, eNB 10 maintains the direct RRC connection to the UE 12 (i.e. through the radio interface between the eNB 10 and UE 12) and also establishes and maintains an RRC connection through the dedicated RRC tunnel through the WLAN AP 14 to the UE 12. The eNB 10/UE 12 can then communicate control plane (RRC) information through either or both of the RRC connections.

In some scenarios there could be some unbalanced downlink and uplink coverage, and it can be beneficial to have two RRC connections. RRC messages can be sent to/from the UE 12 via both the 3GPP (direct) RRC and the tunnelled RRC (i.e. the tunnel established via WLAN 14 for the UE 12), or in either the 3GPP RRC or the tunnelled RRC. For example, the 3GPP RRC connection can be used for RRC messages from the eNB to the UE, and the tunnelled RRC connection for RRC messages from the UE to the eNB, or vice versa. This distribution of RRC messages can be related to the load distribution in the downlink and uplink in LTE and WLAN.

Figure 16 shows an alternative embodiment in which the first node (eNB-1 ) initially has a dedicated RRC connection for control plane signaling with the mobile terminal (UE-1 ) via an LTE radio interface.

Then, in signaling step 161 in Figure 16, a radio interface connection is established between the UE-1 and the second node (e.g. AP-1 ). As shown in signaling step 162, the UE maintains its RRC connection with eNB-1 even if its timer expires, until it receives an explicit RRC connection release message from eNB-1 .

In signaling step 163, the first node (eNodeB-1 ) is notified that UE-1 is connected to AP-1 for traffic steering. The eNodeB-1 holds the UE context.

Then, as shown at step 164 in Figure 16, the initial steps for tunnel setup are performed, as described previously. In this example, the process is unsuccessful, and, in signaling step 165 in Figure 16, AP-1 sends a tunnel rejection message to eNodeB-1 . As shown at 166, eNodeB-1 keeps the UE context for the connection over the LTE interface, and does not trigger the inactivity timer. This ensures that the UE stays in RRC connected mode with eNodeB-1 as shown at 169, even though it has an active data plane connection to AP- 1 .

In another embodiment a specific identifier is used to map the tunnel to the specific UE. This identifier may be set after identification of the UE has occurred in the first node or in the second node or in both nodes. Such identification may have occurred by means of a specific UE identifier reported by the UE and used by either of the nodes to identify the UE. As part of signaling the RRC Tunnel Setup Request and RRC Tunnel Setup Response, a new RRC Tunnel identifier can be exchanged between the two nodes, which have the role of mapping the tunnel to the UE. Note that the UE may move to an idle state in any of the nodes, while being active in the other. For example, the UE may move to Idle in the connection with node 1 (e.g. eNB-1 ) while being active in node 2. It may also happen that the UE context at the node where the UE moved to Idle is in part or in full removed once the UE changes state. Therefore, the identifier mapping the tunnel to the UE may be used to point at a UE class or to a generic group that identifies part or all of the UE characteristics such as capabilities, services in use, configuration, and enabled bearers, etc. With such mapping it would be possible to avoid storing full UE contexts once the UE moves to idle mode.

As an enhancement deriving from the embodiment above, UEs that moved to idle in either of the nodes, e.g. in node 1 , may be classified in groups depending on their UE contexts. RRC messages from node 1 may be triggered for all UEs in the same group, namely a common RRC treatment can be enabled for all UEs in the same group, despite the tunnel may be setup for each of the UEs.

In embodiments described above, the tunnel request is sent by the first network node, that is, the node with which the terminal had the original connection. In other embodiments, the RRC Tunnel Request may be triggered by the second network node, which in the illustrated embodiments is the WLAN AP-1 , once the UE connects to it. In this case it is assumed that the UE will report information that would let AP-1 identify the eNB where the UE was or is connected. The second network node AP-1 can therefore trigger an RRC Tunnel Setup message towards eNB-1 and proceed with the methods described above.

Several of the embodiments described herein assume the existence of an interface between the two access nodes and a radio interface between the second node and the UE. In this case, the tunnel uses two containers, one through the inter-node interface and one through the radio interface. Where the second node is a WLAN access point, the second container is through WLAN. The application protocol running in the inter- node interface is adapted to the inter-node interface. For example, if the inter-node interface may be an Xw interface, Xw application protocol (XwAP) can be used as the application protocol running in the inter-node interface. Each inter-node interface may be a peer to peer interface, i.e. an interface that connects the two nodes directly, or may connect the two nodes while passing through other network nodes.

A new flag may be defined in the management MAC frames in WLAN to indicate the signaling messages as the payload in both Uplink and Downlink directions so the UE (and/or the AP) are able to identify that the payload has to be transferred to the control layer. Similarly, the AP may be informed that a given MAC frame should be encapsulated into Xw containers with the proper identities and flags indicating these are RRC messages.

As mentioned previously, any access technologies can be used. For example, while the first radio access node may be an eNB and the second may be a WLAN AP, it is equally possible for the first radio access node to be a WLAN AP while the second is an eNB. In this latter case, the dedicated control plane tunnel can be used to carry any required control messages. Figure 17 shows a protocol stack in the case of a first network node being an eNodeB with an E-UTRAN air interface and the second network node being a WLAN access point. In this example, the inter-node interface is described as an Xw interface, but any suitable inter-node interface may be used.

When the RRC tunnel is setup the eNB may exchange RRC messages with the UE through the RRC tunnel.

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.

Claims

1 . A method for use in a first network node of a network using a first radio access technology, comprising,

in response to a determination (92; 102; 1 12) that a terminal device has established a connection to a second network node over a radio interface using a second radio access technology different from the first radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface:

establishing (93, 97; 103, 109; 1 13, 1 18) a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

2. A method as in claim 1 , wherein the first network node makes said determination (92; 102; 1 12) that the terminal device has established the connection to the second network node.

3. A method as in claim 1 , wherein establishing the dedicated control plane tunnel comprises sending a tunnel request (93; 103; 1 13) to the second network node over the inter-node interface.

4. A method as in claim 1 , comprising exchanging with the second network node a specific identifier for mapping the tunnel to said terminal device.

5. A method as in any of claims 1 to 4, wherein the dedicated control plane tunnel comprises a first container through the inter-node interface and a second container through the radio interface.

6. A method in a first network node of a network using a first radio access technology, comprising,

in response to a determination (92; 102; 1 12) that a terminal device has established a connection to a second network node over a radio interface using a second radio access technology different from the first radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface: sending a request (93; 103; 1 13) to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

7. A method as in claim 6, further comprising:

in the event of receiving a message from the second network node rejecting said request to establish the dedicated control plane tunnel, maintaining a control plane connection to the terminal device over a radio interface of the first network node.

8. A method in a first network node of a network, wherein the first network node has a radio interface, the method comprising:

9. A method as in any preceding claim, wherein the dedicated control plane tunnel comprises a first container through the inter-node interface and a second container through the radio interface.

10. A method in a second network node of a network, wherein a first network node has a connection to the second network node over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, the method comprising:

receiving from the first network node a request (93; 103; 1 13) to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface; and

establishing said dedicated control plane tunnel (97; 109; 1 18).

1 1 . A method as in claim 10, comprising establishing said dedicated control plane tunnel in response to determining (96; 108; 1 17) that said first network node is a network node with which the terminal device has had a connection.

12. A method as in claim 1 1 , comprising establishing said dedicated control plane tunnel in response to determining (108; 1 17) that said first network node is a network node with which the terminal device has most recently had a connection.

13. A method as in claim 1 1 or 12, comprising determining that said first network node is a network node with which the terminal device has most recently had a connection by sending a message (105) to the terminal device requesting information regarding the network node with which the terminal device has most recently had a connection.

14. A method as in claim 1 1 or 12, comprising determining that said first network node is a network node with which the terminal device has most recently had a connection by sending a message (1 15) to the terminal device containing information regarding the network node from which it received the request to establish the dedicated control plane tunnel, and requesting confirmation (1 17) that said network node is the network node with which the terminal device has most recently had a connection.

15. A method as in one of claims 10 to 13 , comprising exchanging with the first network node a specific identifier for mapping the tunnel to said terminal device.

16. A method as in one of claims 10 to 15, wherein the dedicated control plane tunnel comprises a first container through the inter-node interface and a second container through the radio interface.

17. A method in a second network node of a network, the method comprising:

establishing a connection to a terminal device over a radio interface,

18. A first network node for a network, being adapted for: in response to a determination that a terminal device has established a connection to a second network node over a radio interface using a different radio access technology, wherein the first network node has a connection to the second network node over an inter-node interface:

19. A node as in claim 18, being further adapted for performing the method as in one of claims 2 to 5.

20. A first network node for a network operating according to a first radio access technology, being adapted for:

sending a request to the second network node to establish a dedicated control plane tunnel, for sending dedicated messages, between the first network node and the terminal device over the inter-node interface and the radio interface.

21 . A node as in claim 20, being further adapted for performing the method as in one of claims 7 to 9.

22. A second network node for a network operating according to a first radio access technology, wherein a first network node has a connection to the second network node operating according to a second radio access technology different from the first over an inter-node interface, and wherein a terminal device has a connection to the second network node over a radio interface, being adapted for:

establishing said dedicated control plane tunnel.

23. A node as in claim 22, being further adapted for performing the method as in one of claims 1 1 to 16.

24. A second network node for a network, being adapted for:

establishing a connection to a terminal device over a radio interface,

25. A method of operating a terminal device that is connected to a network node in a second network that is operating according to a second radio access technology, RAT, the method comprising:

establishing and/or maintaining a dedicated control plane tunnel to a network node in a first network that is operating according to a first RAT, the dedicated control plane tunnel being established through the network node in the second network;

26. A method as in claim 25, in which the control plane information is communicated with the network node in the first network through both the dedicated control plane tunnel and the dedicated control plane connection.

27. A method as in claim 25 or 26, in which control plane information sent from the terminal device to the network node in the first network is communicated via one of the dedicated control plane tunnel and the dedicated control plane connection, and control plane information received at the terminal device from the network node in the first network is communicated via the other one of the dedicated control plane tunnel and the dedicated control plane connection.

28. A method as in claims 25 to 27, in which the dedicated control plane tunnel is a dedicated radio resource control, RRC, tunnel, and the dedicated control plane connection is an RRC connection.

29. A method as in claims 25 to 28, in which the first RAT is a 3GPP-specified RAT and the second RAT is WLAN.

30. A method as in claims 25 to 28, in which the 3GPP-specified RAT is Long Term Evolution, LTE, Universal Mobile Telecommunications System, UMTS, Wideband Code-Division Multiple Access, WCDMA, High Speed Packet Access, HSPA, or Global System for Mobile Communications, GSM.

31 . A terminal device for use in a first network operating according to a first radio access technology, RAT, and a second network operating according to a second RAT, the terminal device being adapted to:

communicate control plane information with the network node in the first network via the dedicated control plane tunnel and/or the dedicated control plane connection.

32. A terminal device as in claim 31 , in which the terminal device is further adapted to operate according to one of the claims 25 to 30.

33. 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 any of the claims 1 to 17 or 25 to 30.