GB2445389A - Providing control and user information in an access request message for intersystem handover - Google Patents

Abstract

A method for performing an inter-system change (intersystem handover) from a first communication system 100 to a second communication system 102, where a user session exists between the first communication system 100 and a user terminal 104, and user data related to the user session (i.e. data context) is handled and managed within the first communications system 100. The method includes receiving an access request message 108 in the second communications system 102 for a data transmission from the user terminal 104, establishing, in the second communications system 102, communications resources (e.g. control channel, signaling resources and/or traffic channel) in relation to the user's data transmission, and transmitting a notification message 110 in relation to the communications resources, to enable the user terminal 104 to proceed with the data transmission to the second communication system 102.

Description

2445389

1

MOBILE COMMUNICATION

FIELD OF THE INVENTION

The present invention relates to mobile communications systems and in particular 5 to providing communications resources to user terminals moving between multiple communications systems. More explicitly the invention relates to providing control and user information in an access request message for establishing the necessary communications resources when users require an inter-system change from one communication system to another communication system 10 in which the full range of required communication resources is provided.

BACKGROUND

Standard second generation (2G) and third generation (3G) communication 15 systems are, for example, Global Systeme Mobile/GPRS (GSM/GPRS) and Universal Mobile Telecommunications System (UMTS). Research and development of future communications systems, telecommunications equipment and standards, such as the fourth generation (4G) communications systems and beyond is ongoing. It is only now that signalling procedures are being designed to 20 allow a user terminal (also called user equipment) to perform an inter-system change between 2G/3G and 4G and beyond communications systems.

Typically, during an inter-system change in which a user terminal requires a data transmission, the Control-Plane and the User-Plane are required to be set up 25 before the user's data transmission can commence. The Control-Plane (C-Plane) includes communication resources that are, but are not limited to, the control channel and signalling resources required for data transmission from a user terminal. The User-Plane (U-Plane) includes communication resources that are, but are not limited to, the user traffic channel resources required for data 30 transmission from a user terminal.

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A subscriber or user can use a user terminal or user equipment (UE), these terms may be used interchangeably though this specification. Examples of user terminals or UEs are a mobile terminal (also known as a terminal), a mobile terminal with a Subscriber Identity Module (SIM) or Universal SIM (USIM) or 5 UICC, a computer terminal or other forms of equipment capable of being used in at least one communications system including 2G/3G/4G and beyond communication systems.

Currently, the 2G and 3G communications systems signalling procedures are 10 designed to allow a UE, in an inter-system change, to not inform the target communication system (also referred to as target system) of the UE's move to that system until such a time that the UE requires to send uplink data i.e. perform a data transmission.

15 This allowance is provided for only in the case where the inter-system change does not involve a Routing Area (RA) change and where the UE will send uplink data before the expiry of any periodic update timers. For example, if a update timer period expires before the uplink data is sent, the UE will update its location in the normal (periodic) procedure/way towards the target system. If a period 20 update timer does not expire prior to uplink data being sent, the UE will undertake a Routing Area Update (RAU) and other signalling procedures relevant to the target system before sending the uplink data.

In another example, if UMTS is the target system, then, when the UE has uplink 25 data to send, it will first perform a RAU and followed by a Service Request (SR). The RAU signalling indicates that the Mobility Management or GSM Mobility Management (MM/GMM) context of the UE is now to be moved to the target system that the RAU is sent to, and the SR is to establish the User-Plane (U-plane) for the uplink data and as a result, along with it flagging the Session Management 30 (SM) contexts to the target system. If GSM/GPRS is the target system, then the UE will first perform a RAU before sending uplink data in Logic Link Control Protocol Data Units (LLC-PDUs).

Other solutions covering such signalling procedures are described in "3GPP TS 23.060 - General Packet Radio Service (GPRS); Service description; Stage 2", see sub-clause 6.13.1.3, and in "3GPP TS 24.008 - Mobile radio interface Layer 3 specification; Core network protocols; Stage 2", see sub-clause of 4.7.1.7, bullet point (b). These references describe signalling procedures that are commonly termed Selective Routing Area Updates, as the RAU is selectively performed depending on (i) whether the target system that the UE ends up in at the point of sending uplink data is the same system the UE was in when the UE last sent some uplink data, (ii) if the Routing Area Identity (RAI) has not changed and (iii) whether and if guard timers are running.

There are however, some shortcomings of the Selective RAU signalling procedures particularly for the Long Term Evolution/System Architecture Evolution (LTE/SAE) type communication systems (e.g. 4G communication systems and beyond). It is understood that the present selective RAU procedure is basically two separate sequential and distinct procedures, these are: a) a procedure is performed to establish the C-Plane and then followed by b) a procedure is run to establish the U-Plane.

The term idle state (or IDLE), refers to when a user's data context (i.e. at least the data in relation to the user's profile etc.,) or user's session (i.e. an ongoing communication between user terminal and the network/communications system) is inactive, but still kept alive, on both sides of the communication link (between user terminal and the communications system) e.g. no bandwidth resources (i.e. no C-Plane and/or U-Plane) have been allocated/re-allocated to the user terminal. The term active state (or ACTIVE) refers to the user's data context or user's session being ACTIVE on both sides of the communications link, e.g. the user terminal has actively been given bandwidth resources (e.g. C-Plane and/or U-Plane have been set up) and/or is actively using the bandwidth resources, that is there is U-Plane activity (data transmission) over the communications link.

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In LTE/SAE, one of the key requirements is that the UE must be able to move from the SAE idle state, i.e. SAEIDLE, to the SAE active state, i.e. SAE_ACTrVE, within 100ms. So if a UE is in UMTS when it drops from ACTIVE to IDLE keeping still all its data contexts, then that UE when it arrives 5 in SAE and wishes to send uplink data, it has to fulfill the 100ms requirement that further takes in the necessity to perform an Inter-System change. This encompasses performing the RAU procedure and the SR procedure within this time limit. This tends to be a challenging proposition.

10 Figures 1, 2, and 3 provide an illustration of a present day Selective RA Update. All the information provided in relation to Figures 1, 2 and 3 are with respect to the target and serving communications systems in which the UE moves from and to but having the same Routing Area Identity (RAI). Additionally, it is understood that the UE has been properly registered with the serving communication system 15 and currently has a user session in the serving system. That is the serving system has stored the user's data information in relation to the session or data contexts, but such data contexts are currently idle (i.e. the data contexts are alive on UE side and the Core Network side but there is no data activity for some period of time and so no radio resources have been kept up for the UE).

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The illustrations below shows that the procedure performed in the target system at the time the UE wishes to send data is related to where (what the system was) the last time the UE last sent data.

25 Referring now to Figure 1, an inter-system change is illustrated between a 2G and 3G communications system. The following points, with reference to the corresponding references in Figure 1, describe the pertinent details of the inter-system change.

1. The UE is registered to the 2G system, hence a data context exists. 30 The UE wishes to send uplink data and initiate a GPRS LLC

procedure. The UE is within the 2G system coverage, which is indicated by the large solid circle.

2. Once the U-Plane is set up, the UE and 2G Core Network can exchange data. The U-Plane is only there for as long as there is data activity.

3. Upon completing the data transmission the UE moves towards 3G communications system coverage, which is indicated by the large dashed circle.

4. As the UE enters 3G coverage, the RAI of 3G communications system is the same as the RAI of the 2G communications system, thus the UE does no signalling.

5. The UE within the 3G communications system coverage with the same RAI as the 2G system wishes to send some data uplink.

6. UE initiates the RAU procedure with the 3G system. This also establishes the C-Plane.

7. After completion of RAU, the UE initiates a Service Request procedure.

8. With the U-plane up, the UE can now send uplink data.

This procedure results in multiple messages sent between the UE and the 3G system, resulting in an inefficient use of available communications resources and delay before data can be sent etc,.

Referring now to Figure 2, an inter-system change is illustrated from 2G to 3G back to a 2G communications system. The following points, with reference to the corresponding references in Figure 2, describe the pertinent details of the resulting inter-system change.

1. The UE is initially registered to the 2G system, hence a Data Context exists in the 2G system. The UE wishes to send uplink data and initiate a GPRS LLC procedure. The UE is in the 2G system coverage area, which is indicated by the large solid circle.

2. With the U-plane up, the UE and 2G CN can exchange data. The U-plane is only there for as long as there is data activity.

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3. Upon completing data transmission the UE moves towards 3G coverage.

4. UE enters 3G coverage, which is indicated by the large dashed circle, and it so happens that the RAI of 3 G is same as RAI of 2G,

5 hence the UE does not perform any signalling.

5. While in 3G the UE has no data activity and moves back to 2G coverage - indicated by the solid circle.

6. UE now wishes to send uplink data.

7. The UE needs to contact the 2G system and corresponding network

10 elements through GPRS procedures and following the establishment of the U-plane, UE can send its data.

Referring now to Figure 3, an inter-system change is illustrated from a 3G to 2G back to a 3G communications system. The following points, with reference to the

15 corresponding references in Figure 3, describe the pertinent details of the resulting inter-system change.

1. The UE is initially registered to the 3G system, and hence a Data Context exists in the 3G system. The UE wishes to send uplink data and initiates a Service Request procedure to get the U-Plane

20 up. The UE is in the 3G coverage area, which is indicated by the large solid circle.

2. With the U-plane up, the UE and 3G CN can exchange data. After data sending if there is no data activity, the CN will release the U-plane.

25 3. The UE moves towards 2G coverage.

4. When UE enters 2G coverage, which is indicated by the large dashed circle, and it so happens that the RAI of 2 G is same as RAI of 3G and as the UE has no specific need to send data at this point in time, no signalling takes place.

30 5. While in 2G the UE has no data activity and so moves back to 3G

coverage

6. The UE now wishes to send uplink data.

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7. The UE initiates a Service Request procedure and upon establishment of the U-plane the UE sends its data.

There are significant problems with the current implementation of routing Access 5 Update procedures. These procedures result in user terminals and communications systems not being able to make the 100ms requirement of the standard for setting up the C-Plane and U-Plane in relation to inter-system changes and thus resulting in failed data transmissions or sessions, and poor use of the communications resources.

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SUMMARY OF THE INVENTION

The Applicant has found that to overcome the above-mentioned problems when a user equipment or subscriber has an inter-system change the control information 15 and user information, and/or corresponding communications channels, and other resources that may be necessary and have to be allocated for the inter-system change are simultaneously sent in the access request message and once the C-Plane and U-Plane have been set up, the communications system simultaneously notifies the user equipment.

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The user equipment can then, in response to the completion of inter-system change as well as the provision of communication resources, acknowledge the completion of the inter-system change and use the resources accordingly. The Applicant has realised that simultaneous request for access including control and 25 user information and simultaneous notification of set up of the C-Plane and U-Plane through further control and user information. This is provided through various network entities or elements and channels etc., and significantly decreases the necessary time, messaging, and bandwidth used during inter-system changes.

30 An aspect of the invention provides a method for performing an inter-system change from a first communication system to a second communication system, wherein a user session is in progress in the first communication system on a user

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terminal, and user data related to the user session and/or data context is handled within the first communications system, the method includes receiving an access request message in the second communications system for a data transmission from the user terminal; establishing, in the second communications system, 5 communications resources in relation to the user's data transmission; and transmitting a notification message in relation to the communications resources, to enable the user to proceed with the data transmission to the second communication system.

10 Advantages of the invention provide optimised signalling in the UE's inter-system change from the first communication system to the second communication system. The signalling for setting up the communication resource is more efficient and has reduced latency compared to the current two stage approach used in current and legacy communications systems and networks.

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In a preferred embodiment of the present invention, the communications resources include control channel and signalling resources, in which all necessary control information is provided in the access request message to enable the second communications system to proceed with the set up of the control channel and 20 signalling resources without further control information. In a further embodiment of the invention, all necessary further control information is provided in the notification message to enable the user terminal to proceed with the data transmission without further control information. This further improves the signalling involved in the inter-system change and for setting up the required 25 communication resources resulting in a reduced latency due to the marked decrease in signalling.

In another preferred embodiment of the present invention, the required communications resources include user traffic channel resources and all necessary 30 user traffic information are provided in the access request message to enable the second communications system to proceed with the set up of the user traffic channel resources without need for providing further user traffic information. In a

further embodiment of the invention, in which all necessary further user traffic channel information is provided in the notification message to enable the user terminal to proceed with the data transmission without further control or user information.

A further embodiment of the invention provides the first communications system providing the second communications system with the user data related to the user session. This enables the second communications system to efficiently use any useful user data already present in the communications systems, hence there is no need to request further information from the user terminal.

In another embodiment of the present invention, a network element or entity in relation to either the first or second communications system sends/relays the access request message to the second communication system.

In a further embodiment of the invention provides the user terminal's mode is changed from an idle mode to an active mode in responsse to receiving the notification message from the second communication system.

An embodiment of the invention provides the first communication system and the second communication system having at least a portion of overlapping coverage area. In a further embodiment, the portion of the overlapping coverage area for the first communication system and the second communication system has the same routing area identity (RAI) and/or tracking area identity (TAI).

In a preferred embodiment of the invention, the user terminal moves to a location within at least the portion of the overlapping coverage area. In another preferred embodiment, the user terminal within the overlapping coverage area performs the inter-system change depending on, but not limited to, the condition of radio channel, user preferences, or operator preferences and network services and communications resources available in the first and/or second communications system. An advantage is that if the UE's location or the Routing Area

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Identity/Tracking Area Identity (RAI/TAI) has not changed then less signalling is required.

Further advantages are for example in an LTE/SAE communications system and 5 inter-system change between LTE/SAE system and UMTS system would be more signalling efficient and have reduced latency compared to the current two stage approach used in legacy communications systems and networks.

Additionally, even if the target system is a UMTS system, the invention as 10 defined in the claims provides a solution for LTE/SAE systems and justifiably for UMTS systems, and perhaps legacy systems, as well, as the signalling has been optimised over the need to run two separate procedures.

Further embodiments of the invention can apply to inter-system changes from 15 UMTS to SAE/LTE systems, inter-system changes from SAE/LTE systems to UMTS or any other appropriate or suitable inter-system change. These types of inter-system changes benefit registered terminals/users/subscribers that need to send uplink data in situations where the location of the terminal/users/subscribers (mobile) has not changed or where the change of location has not resulted in a 20 change of the Routing Area Identity (RAI) or Tracking Area Identity (TAI).

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features and embodiments of the invention will now be described, 25 purely by way of example, with reference to the accompanying drawings, in which: -

Figure 1 illustrates the present day selective RAU procedures in a 2G to 3G inter-system change.

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Figure 2 illustrates the present day selective RAU procedures in a 2G to 3G back to 2G inter-system change.

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Figure 3 illustrates the present day selective RAU procedures in a 3G to 2G back to 3G inter-system change.

5 Figure 4 illustrates a preferred embodiment of the invention in relation to an inter-system change from a serving communication system to a target communication system.

Figure 5 illustrates a preferred embodiment of the invention in a combined radio 10 access plus C-Plane, U-Plane initiation by the UE and completion by an SAE/LTE system.

Figure 6 illustrates another preferred embodiment of the invention showing a further optimization in which SAE MME/UPE response incorporates the 15 synchronization between the Evolved RAN.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, a description is given for a preferred embodiment of the invention for 20 performing an inter-system changes from a serving communication system 100 to a target communication system 102. This is followed by a description of further preferred embodiments for performing an inter-system change in a similar manner, in relation to, but not limited by, 2G/3G/4G and beyond type communications networks.

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Referring to Figure 4, an illustration of an inter-system change from a serving communications system 100 to a target communications system 102 is shown. The serving communications system 100 includes one or more network entities or elements (some of which are not shown) for providing user terminals 104 and 106 30 each with a user session and data handling and management (e.g. storage and forwarding)_ means 120 (included in one or more of the network elements) for handling user data related to the user sessions, i.e. a user's data context. The

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serving communications system 100 provides an area of coverage 114 to user terminals 104 and 106 for using the communications resources provided by the serving communications system 100.

Similarly, a target communications system 102 also provides data handling and management means 122 to handle (when appropriate) user data in relation to the user sessions (i.e. data context) of the user terminals 104 and 106. The target communications system 102 provides an area of coverage 116 to the user terminals 104 and 106. An portion of an area of coverage 124 is shown for a further communications system (not shown) that user terminal 106 may involve in an inter-system change.

It can be seen that user terminal 104 is in a location of an overlapping area of coverage from the serving and target communications systems 100 and 102, respectively. User terminal 106 is in another location of overlapping area of coverage from the serving communications system 100 and a further target communications system (not shown). This description will focus on user terminal 104 involving the serving communications system 100 and the target communications systems 102 in an inter-system change. User terminal 106 may involve its serving communications system 100 and the further target communication system (not shown) in an inter-system change in a similar manner.

In order to perform an inter-system change from a serving communication system 100 to a target communication system 102, a user session should be in progress at the serving communication system 100 on user terminal 104. The user data related to the user session (i.e. data context) can be stored within data handling and management means 122 as part of the serving communications system 100. The inter-system change may involve the user terminal 104 requiring a communications resource or network service from the target communications system 102 that is not available in the serving communications system 100. As such the user terminal 104 may send an access request message 108 to the target communications system 102. The target communications system 102 receives the

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access request message 108, which indicates that user terminal 104 requires communications resources for a data transmission.

The target communications system 102 establishes, within its corresponding 5 network elements (some specific examples are discussed with reference to Figure 5), communications resources in relation to the user terminal's data transmission. The target communication system 102, in response to establishing the communications resources transmits a notification message 110 in relation to the communications resources to the user terminal 104. This enables the user 10 terminal to proceed with the data transmission and user the communications resources of the target communication system 102.

In particular, the communications resources include control channel and signalling resources, hence the user terminal 104 may provide all the necessary control 15 information in the access request message 108 to enable the target communications system 102 to proceed with the set up of the control channel and signalling resources without further control information sent in further signalling messages. This minimises the signalling traffic between the user terminal 104 and the target communications system 102. In addition, the target communications 20 system 102 provides all necessary control information in the notification message 110 to enable the user terminal 104 to proceed with the data transmission without further control information.

Alternatively, the communications resources can instead include user traffic 25 channel resources, in which the user terminal 104 provides all necessary user traffic information in the access request message 108 to enable the target communications system 102 to proceed with the set up of the user traffic channel resources without further user traffic information send in further signalling messages. The target communications system 102 provides all necessary user 30 traffic channel information in the notification message 110 to enable the user terminal 104 to proceed with the data transmission without further user traffic channel information.

In a further alternative, the user terminal 104 can provide both all the necessary user traffic channel information and control channel and signalling information required to enable the target communications system 102 to proceed with the set up of the control channel and signalling resources and the user traffic channel resources. In essence, these resources correspond to the Control-Plane and User Plane, respectively. Hence, in one access request message 108, the user terminal 104 provides the target communications system 102 with all the necessary information for setting up the C-Plane and U-Plane required for the user terminal's data transmission to proceed.

When the target communications system 102 is setting up the necessary communications resources (typically in the target communications system's 102 Core Network) it may exchange signalling messages 112 to transfer the user data and data contexts related to the user session (i.e. the data context of user terminal 104) from the serving communications system's 100 data handling and management means 120 to the target communication system's data handling and management means 122. The signalling messages etc, can be provided for by the network elements within the Core Network (not shown) of each communications system 100 and 102.

Initially, to establish a user session the user terminal 104 registers with the serving communications network 100, which sets up a User-Plane and Control-Plane, for the user terminal 104 to perform data transmissions to the serving communications system 100. The user terminal 104 and the user session and data related to the user session (e.g. data context) are considered ACTIVE. But, during the user session the user terminal 104 may not be required to perform further data transmissions hence the user terminal 104 becomes IDLE, in turn the user session and data related to the user session (e.g. data context) also becomes IDLE in the serving communications system 100. Once this occurs, the U-Plane and C-Plane communications resources are relinquished. But the user session and data

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contexts etc are still kept alive, i.e. the user's session is considered IDLE but the data contexts (in the user terminal and communications system) are still there.

As discussed above and will be discussed below in more detail, the user terminal 5 104 can move into a portion of an area of coverage that both the serving and target communications systems 100 and 104 cover - an overlapping area of coverage. This is shown in Figure 4 in which user terminal 104 is in the portion of overlapping area of coverage 118. The serving and target communications systems may have the same identification, i.e. the same routing area or routing 10 area identifier, which provides additional advantages in the inter-system change.

In this location, the user terminal 104 may take advantage of the additional communications resources, improved channel conditions, network services, and application sessions and the like that the target communications system 102 may 15 provide. As part of the inter-system change, the user terminal 104 needs to transition to ACTIVE in order to transmit data, btu can only do this if appropriate communications resources (i.e. the C-Plane and/or the U-Plane) have been allocated. Typically, prior to transitioning to ACTIVE the target communications system 102 receives an access request message 108 (as discussed above, and 20 below in more detail) from the user terminal 104 in which an inter-system change is performed between the serving and target communications systems 100 and 102 in order to allocate the appropriate communications resources for the user terminal 104.

25 The following description illustrates additional preferred embodiments of the invention. These embodiments relate to methods to improve the transition of a user terminal or user equipment (UE) performing an inter-system change. In such cases, examples are given such that the UE changes states by going from an IDLE state (IDLE) to an ACTIVE state (ACTIVE) involving an inter-system change. 30 Similarly, the user's data context and user's session transitions from IDLE to ACTIVE and is synchronised between the serving and the target communications systems 100 and 102, respectively.

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The following examples show how to optimise the UE's transition from IDLE to ACTIVE.

5 1.1 The UE in its radio access procedure with the target communication system will in parallel initiate the necessary Non-Access Stratum (NAS) procedures to establish the Control (or signalling) Plane. The NAS is commonly understood to extend above the Access Stratum (AS) right up to the interface with the application level. This is disclosed in 3GPP TS 24.008 encompassing the 10 MM, GMM, CC, SMS, SM, SS.

1.2 The UE in its radio access procedure with the target system will in parallel initiate the necessary User Plane procedures to establish the U-Plane.

15 1.3 The UE in its radio access procedure with the target system will in parallel initiate necessary NAS and User-Plane procedures to establish both the C-Plane and U-Plane.

1.4. The target Core Network will synchronise the UE and its data context with 20 the last serving Core Network and the HSS in parallel with updating the target

Radio Access Network (RAN) of all necessary RAN-related information. This allows the target Core Network and target RAN to initiate and complete the establishment of the U-Plane at the same time as completing the C-Plane establishment. Hence, notification to the UE to transmit data is provided in one 25 notification message, which encompasses all the required information for the UE's data transmission.

1.5. The target Core Network if architecturally separated with the C-Plane part and the U-Plane part is handled and managed by the MME and UPE respectively,

30 will nevertheless provide a combined and co-ordinated response to the UE. This co-ordination can reside in either the MME, or ENB or even the UPE. This adheres to the concept of one fully combined radio access plus C-Plane and U-

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Plane initiation from the UE responded to by the CN in one fully combined process.

1.6. Regardless of the target Core Network architecture (i.e. of whether there is 5 MME/UPE split or MME/UPE be combined), while the UE adheres to the one fully combined radio access plus C-Plane and U-Plane initiation, the target CN can respond separately with the establishment of the C-Plane and U-Plane so long as the establishment of C-Plane and U-Plane, even in separate process step, is completed within the SAE/LTE requirement of 100ms to transit from IDLE to 10 ACTIVE.

Referring to Figure 5, an illustration is provided of the signalling flows of at least one of the preferred embodiments of the invention. This figure does not cover all the alternatives described below. It is left to specific detailing of the methods (as 15 discussed below hereafter) to further capture the embodiments of the invention. Figure 5 is an illustration of a combined radio access plus C-Plane, U-Plane initiation (by UE) and completion (by SAE/LTE system).

As illustrated, there are multiple communications systems, e.g. there is a 2G/3G 20 system and an SAE/LTE System. These systems comprise numerous network entities or elements such as the 2G/3G Access network element and the Evolved RAN network element. In this embodiment, these elements are in the same Routing Area (RA) /Tracking Area (TA). Further network elements are the 2G/3G Mobility Management Entity/User Plane Entity (UPE/MME) network 25 elements in relation to the 2G/3G system and the SAE MME/UPE network elements in relation to the SAE/LTE system. Also included is a Home Subscriber Service (HSS) network element. As illustrated, it is assumed that the UE is in 3G (UMTS) system in which a user session, (i.e. it can use multiple application sessions in the user session), is currently in progress. This implies that the 3G 30 system has stored a user data context, i.e. user information in relation to the user session etc,.

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The dark dotted lines indicate User-Plane activity, e.g. the UE is performing data transmissions on the uplink of the 3G system and hence the UE is considered to be in an ACTIVE state (or ACTIVE). The user data context and/or the user session in the 3 G system is also considered ACTIVE. After a period of inactivity, 5 the UE changes from the ACTIVE to an IDLE state (or IDLE), similarly, the user data context in the 3G (UMTS) system changes to IDLE. This may be because the UE does not transmit any more data.

The UE then "drifts" or moves into an SAE/LTE system, this may be caused by 10 the UE moving position or location or simply a logical or hardware move is made to the SAE/LTE system because of say, better radio conditions have been detected or additional network services and/or communications resources are available. A logical or hardware move is, but is not limited to, one in which either software (e.g. a computer program or other function) or hardware (e.g. the user terminal or 15 other portion of the system) makes a decision to perform an inter-system change from one communications system to the other. Reasons for the logical or hardware move are based on conditions of the radio channel, resources available, user preferences or operator preferences and the like. An example of a logical or hardware move may be that the user's preferences are set to automatically 20 perform an inter-system change when the user terminal detects it is within the coverage area of an SAE/LTE while being registered in a UMTS communication system. The SAE/LTE system is considered to have the same Routing Access Identifier as that of the 2G/3G system, i.e. the RA/TA remain unchanged. The UE still performs no signalling as it is still IDLE.

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The UE is now in a position to use the communications resources available in the SAE/LTE system. That is, the UE may use in the current user session another application session that requires network services specific to the SAE/LTE system. In any event, the UE may need to send further uplink data, i.e. make 30 another data transmission, to the SAE/LTE system. In this embodiment, the UE sends an access request message to the Evolved RAN network element, e.g. Radio Access Request, containing further information for the SAE/LTE system

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to set up the C-Plane and/or the U-Plane. This further information can be, but is not limited to, all the necessary the user traffic channel information and/or control channel and signalling information required to allow the SAE/LTE system set up the C-Plane and U-Planes.

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In this embodiment, RA/TA_Update_Request information is included (e.g. embedded in an Information Element or in a field) in the Radio_Access_Request message. In addition, Service Request information is also included (or embedded in a further Information Element or field) in the Radio Access Request message. 10 This information is received in the access request message in the SAE/LTE system, i.e. by the Evolved RAN network element.

This is the point in which the SAE/LTE system proceeds to set up the C-Plane and the U-Planes. It can be seen that Core network signalling messages are exchanged in the between the network elements of the Core Network of the SAE/LTE system and also between the Core Networks of the 3G system and SAE/LTE system. In this example, the Evolved RAN network element sends a signalling message containing the required user and control information in a UL_L3 Message (Uplink_Layer3_Message).

The user data context is exchanged/transferred by signalling messages from the 2G/3G MME/UPE to the SAE MME/UPE network elements. This provides the synchronisation of the user data context between the 3G system and the SAE/LTE system. That is, the UE context is transferred to the SAE MME/UPE network elements and to the Evolved RAN network elements. The U-Plane and C-Planes are also established.

In response to the U-Plane and C-Plane being established, the SAE MME/UPE sends an "internal" notification signalling message (e.g. the DL_L3 Message -30 Downlink_Layer3_Message) to the Evolved RAN. This signalling message includes further user and control information (e.g. RA/TA_Update_Accept, and Service_Accept), without which the UE is not able to begin data transmission to

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the LTE/SAE system. The Evolved RAN in response to receiving this "internal" notification signalling message considers the C-Plane and U-Plane to have been set up and hence the UE is notified accordingly by the 3G system. That is, the Evolved RAN notifies the UE through a notification signalling message (e.g. the 5 Radio Access Accept message) containing all the necessary information (RA/TA_Update_Accept and Service_Accept) to enable the UE to proceed with the data transmission.

The UE responds to the notification signalling message by sending an 10 acknowledgement signalling message to the 3G system, i.e. the SAE MME/UPE in a RA/TA_Update_Complete signalling message. The UE and the corresponding network elements of the 3G system can then proceed with the UE's data transmission, i.e. U-Plane activity occurs as indicated by the exchange of information in the dotted dark lines.

15

Further features of the embodiments of the invention are now provided.

2.1 Combining the RAU and Service Request

The RAU signalling message in addition to perform the RAU procedure will 20 piggyback the Service Request. Thus the information to set up both the Control Plane the User Plane are provided in one single signalling transition and can be completed thus in one single Over-The-Air (OTA) signalling exchange.

2.2 Expanding the RAU

25 The RAU message is expanded with additional Information Elements or expanded with additional fields within existing Information Elements to carry the required contents of a Service Request. With this expanded RAU message carrying the necessary information of a Service Request the CN can run procedures for both the C-Plane and the U-Plane.

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2.3 Signalling wherein C-Plane procedures piggybacks U-Plane procedures

21

Although the embodiments and examples disclosed herein make explicit references to 2G GSM/GPRS systems and 3G UMTS systems signalling messages, these embodiments of the invention are not limited to only these communications systems even though the evolution of current and future 5 standards, i.e. SAE/LTE systems may require different definitions of the 2G GSM/GPRS system and 3G UMTS system signalling messages. Hence the invention as defined by the claims is not limited to only the definitions for the signalling messages so far discussed.

10 In another embodiment, the signalling messages to establish the C-Plane, will "piggyback" the signalling messages to establish the U-Plane. Thus all necessary information in relation to the Control Plane and the User Plane are inserted into the signalling message, i.e. the access request message, when the user terminal or user equipment (UE) changes to ACTIVE and performs an inter-system change 15 by requesting access to a target communications system for transmission of data.

2.4 Signalling wherein the C-Plane procedures incorporates establishing the U-plane.

20 Although the embodiments and examples disclosed herein make explicit references to 2G GSM/GPRS systems and 3G UMTS systems signalling messages, these embodiments of the invention are not limited to only these communications systems even though SAE/LTE type systems might not evolve in a way that these 2G GSM/GPRS systems and 3G UMTS system signalling 25 messages are so named.

In another embodiment, the signalling messages to establish the C-Plane is so designed to incorporate all information necessary to allow establishment of the U-plane. Thus all the necessary control information also includes all the necessary 30 user information to establish both the C-Plane and the U-Plane in order to the user terminal or user equipment to proceed with a data transmission to the target communication system after the inter-system change.

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2.5 Combination of Radio Access with C-Plane and U-plane.

In a further embodiment of the present invention, the radio access procedure (which by analogy can be the RRC Connection Request procedure of the UMTS 5 system), shall combine with it the embodiments or methods as described herein such that the one single Over-The-Air (OTA) radio access or radio establishment procedure carries with it the initiation procedures for the C-Plane and the U-Plane.

2.6 CN and Evolved RAN synchronizing through single signalling step.

10

Referring back to Figure 5, as illustrated the SAE MME/UPE network elements respond to the Evolved RAN network element after the synchronization of the UE context between SAE MME/UPE and Evolved RAN network elements is completed.

15

Referring now to Figure 6, an illustration of a preferred embodiment of the invention is shown incorporating a further optimisation, where an SAE MME/UPE network element response can incorporate the synchronization between the Evolved RAN network element. This is illustrated in Figure 6.

20

The procedure for the UE requesting access to the 3G system is the same as set out in relation to Figure 5. The primary difference being that the Core network signalling procedures are performed by the SAE MME/UPE, HSS and 2G/3G MME/UPE network elements. Thus the user data context is transferred and the C-25 Plane and U-Planes are set up using these network elements. In response to the set up of the C-Plane and U-Planes, the SAE MME/UPE network element sends an acknowledgement to the Evolved RAN to proceed with the completion of the synchronisation of the user context, e.g. a DL acknowledgement is sent by the DL L3 Message, along with further information such as RA/TA_Update_Accept 30 and Service_Accept. The Evolved RAN then notifies the UE as described with reference to Figure 5.

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2.7 Coordinated response in an architecturally split SAE CN.

In another embodiment of the invention, even though the final architecture of the SAE/LTE system is yet to be decided, a method of a combined response to the UE can be achieved even in an architecturally split SAE/LTE system by having a co-5 ordination function reside in either MME or Evolved RAN or even UPE or even partly in any combination of these 3 SAE/LTE network elements or entities. The resulting effect - even for a split SAE/LTE architecture - is that the response back to the UE is a single OTA combined response to the radio access procedures, the C-plane initiation and establishment procedures and the U-Plane initiation and 10 establishment procedures.

As a further illustration of this embodiment, the MME whilst controlling the C-Plane establishment and associated procedures can have a co-ordination function coordinating with the UPE, which performs the U-Plane part (i.e. U-Plane set up) 15 and that the MME responds back to the UE through the Evolved-RAN. Thus the joint response to the UE can still be effected even if the UPE is to set up the U-Plane independently of any MME control.

2.8 Combined initiation but separate responses

20

In another preferred embodiment, a further variation to the method described in the previous sub-section is that the response back to the UE may be not a single combined response process to the radio procedures, the C-Plane initiation and establishment procedures and the U-Plane initiation and establishment procedures, 25 but instead the response will be individual responses or a combined mixture of responses. So while the initiation from the UE side is one fully combined single OTA process, the response from the SAE/LTE Core Network and RAN may be in separate steps. The gain in combining the initiation may be that such separation is possible and still be within the SAE/LTE requirement of 100ms to transit from 30 IDLE to ACTIVE states in the UE and in the target communication system in relation to the users session and request for data transmission.

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2.9 Applicability of methods to legacy systems

The preferred embodiments of the invention are not limited to only the above examples, since while the above described embodiments are so derived to 5 facilitate a transition of a UE from SAE/LTE system IDLE to SAE/LTE system ACTIVE in an inter-system change where the RA/TA is the same for target and serving systems, these embodiments are not exclusive for the SAE/LTE systems. The 3G UMTS system and 2G GSM/GPRS system also can be optimised such that their respective inter-system changes that takes a UE from idle data context to 10 fully active data context by importing the above described methods and embodiments.

The inter-system change may be performed using multiple network elements and entities within both serving and target communications systems. In addition, 15 portions or all of steps required to perform the inter-system change can be implemented in computer code or instructions, which when executed in the corresponding network elements or user terminals, perform the inter-system change. Thus a computer program may be included in the user terminal that includes computer code means adapted to perform the user terminal's functions in 20 relation to the inter-system change, i.e. at least the functions of sending an access request message and receiving a notification message as described herein and proceeding appropriately, i.e. to transmit data accordingly.

In addition, a computer program may be included in the target communications 25 system or in portions of a computer program within the related network elements and entities of the target communications system, which each include computer code means adapted to perform the required functions in relation to the inter-system change, i.e. receiving an access request message and performing when the program or portions thereof are run or executed on the respective elements 30 performs at least the set up of the C-Plane, U-Plane, synchronization of the user's data context and notification to the user terminal.

25

Furthermore, the invention is not limited to only 2G/3G/4G types of communications systems, but other communication systems such as future standards towards 4G and beyond type systems and the like are applicable. Furthermore, the invention can also be applicable to legacy systems to improve their signalling and functionality in an inter-system change.

It will be apparent from the foregoing that many other embodiments or variants of the above are possible. The present invention extends to any and all such variants, and to any novel subject matter or combination thereof disclosed in the foregoing.

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Claims (19)

1. A method for performing an inter-system change from a first communication system to a second communication system, wherein a user session exists between the first communication system and a user terminal, and user data 5 related to the user session is handled and managed within the first communications system, the method comprising:

receiving an access request message in the second communications system for a data transmission from the user terminal;

establishing, in the second communications system, communications

10 resources in relation to the user's data transmission; and transmitting a notification message in relation to the communications resources, to enable the user to proceed with the data transmission to the second communication system.

15

2. The method of claim 1, wherein the communications resources comprise control channel and signalling resources, the method further comprising providing all necessary control information in the access request message to enable the second communications system to proceed with the set up of the control channel and signalling resources without need to provide further control information.

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3. The method of claim 2, further comprising providing all necessary control information in the notification message to enable the user terminal to proceed with the data transmission without further control information.

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4. The method of any preceding claim, wherein the communications resources comprises user traffic channel resources, the method further comprising providing all necessary user traffic information in the access request message to enable the second communications system to proceed with the set up of the user traffic channel resources without further user traffic information.

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5. The method of claim 4, further comprising providing all necessary user traffic channel information in the notification message to enable the user terminal to proceed with the data transmission without further user traffic channel information.

5

6. The method of any preceding claim, further comprising the first communications system providing the second communications system with the user data and contexts related to the user session.

10

7. The method of any preceding claim, further comprising changing the user terminal's state or user's session from an idle state to an active state in response to receiving the notification message in relation to the communications resources from the second communication system.

15

8. The method of any preceding claim, wherein the first communication system and the second communication system have at least a portion of a coverage area that is overlapping.

9. The method of claim 8, wherein the portion of the coverage area that is 20 overlapping for the first communication system and the second communication system has the same routing area identity or tracking area identity.

10. The method of claims 8 or 9, wherein the user terminal moves to a location within at least the overlapping portion of the coverage area.

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11. The method of any of claims 8 to 10, the method further comprising performing the inter-system change in response to the user terminal's location being within the portion of the coverage area that is overlapping.

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12. The method of any preceding claim, the method further comprising, performing the inter-system change in response to a logical or hardware decision based on user or operator related preferences, or detection of improved radio

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conditions, or additional communication resources and network services, in relation to the second communication system.

13. A user terminal adapted to implement the transmitting and receiving of the access request and notification messages, respectfully, of the method of any of claims 1 to 12.

14. A communications system adapted to implement the method of any of claims 1 to 12.

15. A user terminal substantially as hereinbefore described with reference to any of Figures 4 to 6 of the accompanying drawings.

16. A communications system substantially as hereinbefore described with reference to any of Figures 4 to 6 of the accompanying drawings.

17. A method for performing an inter-system change substantially as hereinbefore described with reference to any of Figures 4 to 6 of the accompanying drawings.

18. A computer program comprising computer code means adapted to perform the method of any of claims 1 to 12 in relation to the user terminal when said program is run on the user terminal.

19. A computer program comprising computer code means adapted to perform the method of any of claims 1 to 12 in relation to the first or second communications system when said program is run on at least a portion of the first or second communications systems.