GB2453526A - Communicating between user equipment involved in first and second communication systems - Google Patents

Abstract

A method of communicating between user equipment, involved in an active communication with a first communications system, and a second communications system is disclosed. Communication between the user equipment and the first communications system uses a first communication protocol and communication between the second communications system and the user equipment uses a second, different communications protocol. The method comprises the steps of transmitting a signal from the user equipment to the first communications system, the signal comprising a signaling message, in accordance with said second protocol, and a protocol discriminator; receiving the signal in the first communications system, identifying in the received signal the presence of the protocol discriminator and forwarding the signaling message from the first communications system to the second communications system. A method of initiating a handing over of an active communication and corresponding communications apparatus are also disclosed.

Description

1 2453526 Communication Method and Apparatus

Field of the invention

The present invention relates in general to a method of communicating between user equipment, involved in an active communication with a first communications system, and a second communications system, where communication between user equipment and the first communications system uses a first communication protocol and communication between the second communications system and user equipment uses a second, different communicattons protocol. In particular, although not exclusively, the invention relates to a method of handing over an active communication transaction with a user from one communications system to another.

Backciround to the invention A number of abbreviations and terms will be used in this document. A list of those abbreviations and terms is provided at the end of the description to assist the reader.

There are a number of communications systems currently available, enabling a user to carry out wireless communication transactions (e.g. telephone calls, data transactions) using mobile equipment, such as mobile phones and PDAs. In general, different communication systems use different communication protocols for communicating with user devices (or user equipment, UE), and a signal sent from UE in a format according to a protocol of one system will in general not be understood by a different system. p S S...

In certain circumstances, although a communication transaction with a UE may be active and handled by one communications system, it may become desirable to hand over that transaction to another communications system (e.g. if the other communications system can provide better signal coverage, improved bandwidth, or lower cost). For example, in S...

.. : 30 SA2, RAN2, WiMax and 3GPP2 forums moves are ongoing to design functions to enable a user in an active call in an SAE system or WiMax system to be handed-over from one system to the other system. The system initially handling the call (or other communications transaction) may conveniently be described as the source system or network, and the system to which the call is to be transferred may be described as the target system or network.

Handover techniques have indeed been developed, and a general description of procedures for inter-3G MSC handovers (in particular for handover from UMTS to GSM) can be found in section 8 of document TS 23. 009 available from the 3GPP web site. An extract from 3GPP TS 23.009 is reproduced in Annex C to this document. In the described handover technique, there is no direct communication between mobile and target system until such time as after the inter-system change command has been issued and the mobile tunes into the target system and therein accesses the target system. Indeed, in the described technique and in the other prior art handover systems the source system is responsible for initiating the handover preparations between itself and the target system. Annex E provides details of another proposed handover technique for performing an Inter-System change in the SAE system. Again, in the proposed technique the source system (and in particular its MME) performs the tasks of initiating, requesting and negotiating a handover. Annex E also provides details of a further proposal for handover in which the UE may talk to the target system, but the proposal gives no information as to how this talking could be achieved. Source system controlled handovers have served well, for example as evidenced by current handovers within the GSM system and between GSM system and UMTS system However, source system controlled handovers require that the source system commands and controls the way the UE makes and reports these measurements. This is very processing intensive -a) designing means to inform a UE on what to measure, who to measure; b) designing spacing timing so that the UE can measure a second system; C) design ways that a UE can report and d) then processing the measurements and make decisions on handovers.

S *s*

::::* 25 As an alternative to these prior art handover techniques, a "Tunnel approach" has been proposed in which the UE would be able to talk" to the target network to prepare the resources in the target network ahead of a handover from the source system to the : target system. For the "Tunnel approach" the source system would not be involved in deciding the handover, in initiating the handover preparations between itself and the **55 : 30 target system, or in triggering the execution of a handover towards the UE. It has been proposed to adopt a "Tunnel approach" for mobility and handovers between LTE/SAE system and 3GPP2. However, how this tunnel approach between 3GPP2 and LTE/SAE systems would work (and, more precisely, how in this "Tunnel approach" the UE could tunnel a signalling message when in the source system through to the CN controller in the target system) has not previously been solved.

A proposed architecture for a system in which it would be desirable to implement a "Tunnel approach" for communicating from a LTE/SAE system to a WiMax system (and vice versa) is shown in fig. 1. Thus, fig.1 shows a possible architecture for "Tunnel approach" between LTE/SAE 3GPP access system and non-3GPP WiMax system. For the case of handover from LTE to WiMax, it has been recognised as desirable that for the WiMA)( Access Service Network GateWay, the UE should appear to be on a WiMAX basestation and for the case of handover from WiMax to LTE, then for the MME, the UE should appear to be on an LTE eNB. Clearly this means that UE even when in the LTEISAE system will need to run WiMax signalling protocol when talking' to the IWF function and WiMax ASN GW (in pursuit of the LIE to WiMax handover). This naturally implies the converse that is the UE in WiMax will need to run SAE signalling protocols when talking to the MME (in the EPC) of the SAE/LTE system Further details of the proposed tunnel approach, outlined above, are provided in Annex D. It will be appreciated from Annex 0 and the above description that in the proposed technique the mobile device itself (UE) should contact and negotiate with the target system to do the inter-system change. It will be appreciated from the following description that certain embodiments of the invention implement the proposed technique; they provide solutions to the problem of how to achieve the desired tunnelling.

in the previous absence (i.e. before the filing of the present application) of a solution to the problem of how to achieve the desired tunnelling, another proposed technique for performing a handover between SAE/LTE and 3GPP2 is taking the system architecture as shown in fig. 1 and introduce an IWF function, which then works as follows, Instead of a tunnel protocol or signalling, the IWF manipulates the signalling so that it "fit for purpose" for the target system. In this proposal, there is no suggestion that the UE, while in the source system, actually talks to the target system or that the target system :. considers the UE as being on a basestation subsystem of the same access technology as the target system. The point here is that the IWF needs to manipulate signalling * 30 messages so that the target system would see the network signalling protocol not just compatible to the target system but would expect network signalling protocol exactly as defined for the target system.

Another possible solution for communication between the UE and the target system would be an extension of methods used for transporting information between UE and target systems for the Inter-System Handovers defined by 3GPP for 3GPP systems.

Those methods involve use of a "container" in which the UE can place certain information, maybe even an entire message. This container is then shipped transparently through the source system to the target system. This container mechanism is also applied in the reverse direction (ie. from target system to UE). However, this container mechanism makes use of protocol signalling and messages of the source system, e.g. the RRC and MM and GMM messages of the UMTS system, and allows for a container in which information meant for target system or UE is placed. Thus, message containers have been used in past and lately have been used to realise PS Handovers in UMTS/GERAN. This method realised the "shipping" of messages from one system to another system by placing the intended message for the target entity in a container of a "carrier" message of e.g. a source system/entity. An important point to appreciate here is also that both source and target system here are running same 3GPP protocols. A further discussion of message containers can be found in Annex F

Summary of the invention

According to a first aspect of the invention, there is provided a method of communicating between user equipment, involved in an active communication with a first communications system, and a second communications system, communication between user equipment and the first communications system using a first communication protocol and communication between the second communications system and user equipment using a second, different communications protocol, the method comprising the steps of: transmitting a signal from the user equipment to the first communications system, S..

the signal comprising a signalling message, in accordance with said second protocol, S. .S and a protocol discriminator; ::::* receiving the signal in the first communications system; : identifying in the received signal the presence of the protocol discriminator; and forwarding the signalling message from the first communications system to the a : 30 second communications system. *5 a * S S *S

Thus, the signalling message tunnels out of the first (or source) system to the second (or target) system. This communication can be regarded as being in parallel with the active communication because the communication with the target system takes place while the communication transaction handled by the first system is ongoing. The communication with the second system may be for a variety of purposes For example, it may be for the purpose of handing over the active communication (e.g. call) from the first to the second system. With reference to the disadvantages identified above in relation to "source system controlled handovers, methods embodying the present invention are able to provide a new way of performing handovers (with the UE talking" directly to the target system) which may still require a), but provide an easier b), C) need not be done and d) is something thrust onto the UE.

In certain embodiments the step of forwarding further comprises forwarding the protocol discriminator from the first to the second communications system together with the signalling message.

The signal sent from the UE may comprise additional information / Content.

Alternatively, the transmitted signal may consist of the signalling message and the protocol discriminator.

In certain embodiments the protocol discriminator is a second protocol discriminator in a format understandable by the second communications system, and the transmitted signal further comprises a first protocol discriminator, the first protocol discriminator being in a format understandable by the first communications system.

The step of forwarding may then comprise omitting the first protocol discriminator from a signal forwarded to the second communications system, the forwarded signal comprising the signalling message and the second protocol discriminator.

S

S S..

In certain embodiments the method further comprises the steps of: the user equipment

SSIS

selecting the protocol discriminator from a plurality of protocol discriminators, each ::::* protocol discriminator corresponding to a respective one of a plurality of second : communications systems using a respective second communications protocol; and forwarding the signalling message to the second communication system associated with S...

30 the selected protocol discriminator in the signal from the user equipment. S* S S. S **

It will be appreciated that, in certain embodiments, the protocol discriminator is indicative of a protocol process within the target system for which the signalling message is intended Thus, in addition to the PD being used by the source system to tunnel the signalling message out of that source system to the target, the PD can then be used by the target system to direct the signalling message to the appropriate process within the target system Methods embodying the invention may be applied to communications involving a wide variety of communications systems. For example, the first and second systems may be systems from a list comprising: mobile equipment, LTE/SAE system, GSM system, GPRS system, UMTS system, 3GPP2, WiFi, WiMax, WiBro. However, it will be appreciated that this list is not exhaustive -the systems are merely examples.

Furthermore, methods embodying the invention may be employed with new communications systems, perhaps using new protocols, which may be developed in the future.

In certain embodiments the method further comprises the steps of: the second communications system responding to the forwarded signalling message by sending a response signal to the first communications system, the response signal comprising a response signal message and a response protocol discriminator; the first communications system identifying the presence in the response signal of the response protocol discriminator and forwarding the response signal message to the user equipment.

The response protocol discriminator may, in certain embodiments, be different from the PD used by the UE, although in alternative embodiments the response protocol discriminator is the same as the protocol discriminator transmitted by the user :. 25 equipment. The response PD may be indicative of a protocol process within the UE for which the response message is intended. *S.. *S.. * * *.S.

Another aspect of the invention provides a method of initiating (or requesting) a handing over of an active communication between user equipment and a first communications system from the first communications system to a second communications system, . : communication between the user equipment and the first communications system using * S. a first communication protocol and communication between the second communications system and user equipment using a second, different communications protocol, the method comprising communicating, while involved in the active communication with the first communications system, with the second communications system using a method in accordance with the first aspect of the invention, wherein the signalling message transmitted from the user equipment is a handover initiation message, or a message requesting a handover, to the second communications system.

Another aspect of the invention provides a method of handing over an active communication of a user using user equipment from a first communications system to a second communications system, communication between user equipment and the first communications system using a first communication protocol and communication between the second communications system and user equipment using a second, different communications protocol, the method comprising the steps of: sending at least one handover signal message from the user equipment to the second communications system via the first communications system using a method in accordance with the first aspect, each handover signal message being comprised in a respective signal transmitted from the user equipment to the first communications system message, whereby each transmitted signal is received in the first communications system and the respective handover signalling message is forwarded to the second communications system after the presence of the protocol discriminator is identified in each received signal.

Although the above paragraph mentions the sending of at least one handover signal message, it will be appreciated that in general a handover method embodying the invention may comprise the sending of a plurality of handover messages form the UE to the target system, and the sending of a plurality of handover messages from the target system to the UE.

: Another aspect of the invention provides communications apparatus comprising: S.. S *

* S.. user equipment; a first communications system adapted to communicate with the user equipment SSS.

using a first communication protocol, and * 30 a second communications system adapted to communicate with the user equipment using a second, different communications protocol, S.. the user equipment being adapted to transmit, while involved in a active communication with the first communication system, a signal to the first communications system, the signal comprising a signalling message, in accordance with said second protocol, and a protocol discriminator, the first communications system being adapted to receive the signal, identify in the received signal the presence of the protocol discriminator (meant for the second communications system); and forward the signalling message to the second communications system.

The UE may take a variety of forms. For example, it may be a mobile phone and the active communication may be an active voice call. Alternatively, it may be a PDA, with the active communication being a data transaction. Other forms of UE will be apparent to the skilled reader, and may be used in embodiments of the invention.

Another aspect of the invention provides user equipment for a telecommunications system, the user equipment being adapted to communicate with a first telecommunications system using a first protocol and with a second telecommunications system using a second different protocol, the user equipment being further adapted to communicate with the second communications system, while involved in an active communication with the first system, by transmitting a signal for reception by the first system the signal comprising a signalling message in accordance with said second protocol, and a protocol discriminator, Again, the UE may take a variety of forms, and the invention is not limited to any particular type of UE.

In certain embodiments the UE is adapted to initiate a handover of an active call from the first communications system to the second communications system by sending a handover initiation or handover request message to the second system by transmitting a : signal comprising the handover initiation or handover request message in accordance SI..

with the second protocol and a protocol discriminator for reception by the first system. S...

S S...

S

S.....

* 30 Brief description of the drawings

:. Embodiments of the invention will now be described (by way of example only) with reference to the accompanying drawings, of which: Fig. 1 is a possible architecture for a tunnel approach of communication embodying the invention, between communication systems; Fig. 2 is an illustration of a message flow and action sequence steps in a communication method embodying the invention; Fig. 3 illustrates the encapsulation of a signalling message in a method embodying the invention; Fig. 4 illustrates an alternative encapsulation of a signalling message in accordance with an embodiment: Figs. 5 and 6 are illustrations of SAE/LTE reference architecture as defined by 3GPP and in which methods embodying the invention can be used; Fig. 7 illustrates communication apparatus embodying the invention and in which methods embodying the invention may be used: Fig. 8 illustrates a protocol architecture of a mobile terminal; Fig. 9 illustrates a Basic UMTS to GSM Handover Procedure requiring a circuit connection; Fig. 10 illustrates the signalling flow of a proposed solution for performing an inter-system change from the PS only LTE/SAE system to the CS domain of a GERAN or UMTS system; Fig. 11 illustrates a detailed call flow for the HRPD VoIP-to-Ix circuit-switched voice : **. domain transfer procedure; *S.. S * *5. S

Fig. 12 illustrates an initial attachment when network based MM mechanism are used over S2b for non-roaming; 30 Fig. 13 illustrates a basic intra-3G MSC handover from UMTS to GSM procedure; and * Fig. 14 is an illustration of a message flow and action sequence steps in another communication method embodying the invention.

Detailed description of embodiments of the invention Referring again to fig.1, one can see that to tunnel signalling messages between UE and the IWF function (or indeed directly to the WiMax ASN GW), there must effectively be some means to channel those messages through the MME in the EPC without the EPC or MME or some other entity having to open, examine, repackage and send onward the contents of the messages to the WiMax system Certainly designs can be made such that the messages can be opened, examined, repackaged and manipulated, but then these would not be offering a tunnel approach and would not ease the work of the MME, the EPC and the SAE/LTE system: they would involve the MME.

Similarly when the UE is in the WiMax system (and involved in an active communication transaction handled by the WiMax system), and the UE needs to talk to the MME to negotiate a handover to the SAE/LTE system, the messages that the UE intends for the MME have to be effectively passed through the WiMax ASN GW and the IWF without these entities having to manipulate the messages so that they fit into the format expected by the MME.

Embodiments of the invention provide solutions to the problem of how to realise this tunnelling of messages, so that the MME (in the case of the UE in SAE/LTE system wanting to negotiate handover with the target WiMax system) and the WiMax ASN GW (in the case of the UE in the WiMax system wanting to negotiate handover with the target SAE/LTE system) controllers are not burdened by having to open, examine, repackage, manipulate and manage the signalling between the UE and the target : system. ***s * S S..

Before discussing how this tunnelling is achieved in more detail, it is important not to mix S * S... . , . . . tunnelling (the term used in connection with the concept of performing a inter-system ***...

* 30 change which involves the mobile, while in the source system, talking to the target system to "negotiate" the inter-system change) with the technique of message ". : containers within a "carrier" message, or even with encapsulation of a message. Annex F provides a brief discussion of differences between tunnelling and message containers within "carrier" messages, useful in understanding the invention.

Embodiments of the present invention provide methods which effectively allow tunnelling of inter-system signalling messages. One of the ways in which they achieve this is by use of a dedicated Protocol Discriminator. In certain embodiments, a new and dedicated Protocol Discriminator (PD) is used by the UE, the source system and the target system.

This PD can be the same whether it is on the WiMax side or the SAE/LTE side. For the sake of elaboration this PD can be, for instance, named as Inter-System Signalling Entity (ISSE) PD. It might just as well be partitioned in Inter-System Mobility Entity (ISME) and Inter-System Call Control Entity(ISCE) should it be more useful to have a specific PD for Mobility Management and one for Call Control or even Inter-System Radio Control protocol (ISRC).

The working of a method embodying the invention is as follows. The UE and that target system when signalling between peer entities (in the target system and the UE respectively) use the PD to indicate that the signalling message is a specific signalling protocol message not meant for the source system. The MME (of the source system) or the WiMax ASN GW (of the source system) will then channel this signalling message onwards thus achieving the required tunnelling.

To illustrate with an example, consider the case where the peer entity in WiMax ASN GW wishes to acknowledge the direct request for handover (eg REQUEST_HANDOVER TO YOUR SYSTEM) to the WiMax system from the UE in SAE/LTE with the message REQUEST_HANDO VER TO MY SYSTEM ACCEPT What the WiMax ASN GW peer entity does is send this message toward the MME in the SAE/LTE system with a PD = ISSE.

:. It should be noted that prior to this the UE (in the SAE/LTE) system has sent ***.

S..... REQUEST HANDOVER TO YOUR SYSTEM with a PD = ISSE to the MME. The MME, seeing the PD = ISSE (i.e. recognising the presence of the PD in the received signal),

S

then just channels the message onwards (i.e. sends the message to the target * * 30 network/system). *I*5

S S

Figure 2 provides a diagram showing message flow and action sequence steps to illustrate the inventive method idea here described. To further understand the method, one has to see the function of the DTAP (Direct Transfer Application Part). Further explanation of how this DTAP function fits into this method is given in the following description. DTAP has been in existence since the beginning of GSM, and is described in TS 08.06, later evolved into IS 48.006. DTAP happens to be a natural part of the MME's or EPC's message reception, handling and distribution function, and embodiments of the invention make use of it It will be appreciated that the method embodying the invention uses a Protocol Discriminator to realise tunnelling of peer-to-peer signalling messages from one system to another system (i.e. out of one system to another). This is in distinct contrast to prior uses of PDs; in those techniques the PDs were used to route signals to the appropriate destination within a single system. In embodiments of the invention, when the source system recognises the presence of the appropriate PD it forwards the associated message out of the source system to the target system. This expands beyond the present state-of-the-art use of PD where PD is used strictly within one single system.

Although fig. 2 does indicate the presence of the IWF in the system as a whole, it will be appreciated that an IWF is not essential; methods embodying the invention may be used in systems incorporating or not incorporating an IWF. If an IWF is present, it need not perform any processing on the signalling message forwarded from the source system to the target system, it can merely behave as a conduit for the forwarded signal (which therefore tunnels from the source to the target system after the PD has been noted by the source system).

In this regard, we refer also to fig. 14. This illustrates signal flow in another method and apparatus embodying the invention in which there is no IWF.

An advantage of a method as described above with reference to fig. 2 and fig 14. is that, by using a dedicated PD, the MME need not process the received message; the MME acts more like a relay of the message. By not processing the message, it means the MME need not open up the message, need not have to examine its contents, and not *.S.

S.... need to repackage or manipulate its contents. Communication between the UE and the target network or system is therefore facilitated.

S I...

*.S...

* * 30 Clearly, to implement the method it is essential that the UE is arranged (adapted) so as to be able to communicate using the protocols of both the source and target systems, . : and to add a suitable protocol discriminator to signals it sends out (transmits). The * protocol discriminator may, in general, take any form but necessarily in a form expected and understood by the target system but it is a requirement that the source system should be adapted so as to be able to identify at least the presence of the protocol discriminator in a received signal and forward the contained signal message to the external target system accordingly. In other words, the source system is adapted to identify the presence of a predetermined "indicator" in a message from the UE, and the UE is arranged to include that predetermined indicator in an outgoing signal intended for the target system.

Thus, use of a new PD in embodiments of the invention means that message discrimination functions and message distribution functions that work on PDs needs to be changed if not created. This does not represent a significant inconvenience in the newly designed SAE/LTE system as there is no need to be backward compatible to an older version of its protocol.

A clear advantage of the above-described method with reference to fig. 2 is that the source system need not open, examine, repackage or manipulate the signalling message to the target system. Furthermore, the source system is not required (and indeed is not involved) to manage the signalling between UE and target system; it simply forwards the signalling messages onwards.

In embodiments of the invention, the UE and the target system effectively signal and negotiate using the protocol of the target system, thereby doing away with (or at least minimising) protocol conversion and interworking entities and functions. Clearly, and as stated above, to implement the invention the UE needs to run the protocol of the target system, as well as that of the source system.

It is important to note the difference between this "tunnelling" of signalling messages directly from a source system to a target system in embodiments of the invention, and S..' using containers to transfer messages; using containers requires opening of a message S...

and repackaging what is in the container. This can be seen in many examples in 23.009 and is also indicated in Annex C. *S..

S

PSS

* 30 Further methods embodying the invention will now be described which involve the encapsulating of the signalling message. In these methods the signalling messages : between UE and the target system are encapsulated within either a new or existing protocol message of the source system. Two separate variants (one of adapting and existing GMM message and one of using a new GMM message) of this general method are described below. The difference between this general method and the prior art method of using containers within "carrier" messages, is that this method still utilises a Protocol Discriminator -PD understood in the target system. Using a PD means that there is no need (or much less need) for IWF to manipulate "carrier" messages to extract and work on the container message, thus reducing the amount of processing that the system as a whole needs to perform, facilitating communication.

Thus what stands out and needs to be appreciated of this embodiment is that two PDs are used, one PD pertaining to protocol communication use in source system and a second PD pertaining to protocol communication use in second system.

In a first variant, the method uses a technique of encapsulating within an existing GMM message. For instance the GMM INFORMATION message that exist in UMTS can be expanded to carry a PDU or an Information Element where in that PDU or IE is the actual signalling message the UE (or the target system) wishes to send to the target system (or UE) respectively, It should be noted that the existing GMM INFORMATION message is uni-directional and goes only from the CN to the UE. In the present embodiment the GMM INFORMATION message from the UE (in SAE/LTE system) is sent by the UE to the MME. Encapsulated within this GMM+INFORMATION message will be a PDU containing REQUEST_HANDOVER TO YOUR SYSTEM Figure 3 further illustrates this method.

In a second variant, the method uses a technique of encapsulating within an new GMM message. A new GMM message eg. INTER_SYS_SIG_INFO, is used, and with that message, a PDU carries the actually signalling message. For illustration by example, the UE in SAE/LTE system will send INTERSYS_SlG_INFQ which contains within it a PDU and that PDU will be the REQUEST HANDOVER TO YOUR SYSTEM Figure 4 provides a diagrammatic view of this proposal. *SS.

An advantage of these techniques is that, because an existing GMM message (or a new GMM message) is used the MME and the message processing functions of the MME will not change. However, precisely because the message processing functions are being used as it was designed to do, it means the MME will have to open the GMM message, ** examine the contents of the GMM message, extract and repack, and might even manipulate such contents before sending it onwards.

Further embodiments of the invention will now be described.

Referring now to fig. 5, extracted from 23.401, this gives an illustration of the SAE/LTE reference architecture as defined by 3GPP Highlighted in fig 5 is also the 2G GSM/GPRS system (GERAN + SGSN) and the 3G UMTS system (UTRAN + SGSN). By that one is able to the see the "link-up" from/to the 3GPP 2G and 3G system and 3GPP's SAE/LTE. Certain methods embodying the invention and described in this document refer to EPC and EPS and in particular refer to possible Interworking Functions within the EPC. To help visualize the scope of EPC, Fig. 6 is provided (from which it should be noted that EPC also encompasses the HSS). In the system architecture as shown in figs 5 and 6, methods embodying the invention are able to provide relay functions for direct transfer through the SlO interface. From the SAE/LTE Reference Network Architecture of figs 5 and 6 one will see an illustration of what is within the bounds of the EPC. One will also notice the SlO interface, which is the interface between MMEs. This Sb interface is the interface to the WiMax IWF (not shown in the figures) which appears to the MME as just another MME. So, when the Inter-System-Signalling protocol messages arrive at the MME, the MME can identify the presence of the PD, and accordingly can decide that that message is meant to be shipped out to through the Sb interface towards the other (target) system (be it 3GPP2 system or the WiMax system). To do this the MME can rely on a relay function equivalent to the Direct Transfer Application Part (DTAP) first publicised in TS 08.08 and now its 3GPP equivalent 48.008. As will be appreciated, the normal function of DTAP is to transfer call control and mobility management messages between the MSC and the MS. The DTAP function is further described in TS 48.006. Thus, by using essentially a DTAP function, methods embodying the invention, and in particular the method of applying a PD to Inter-System Signalling messages, can be made to work within the MME and EPC of the SAE/LTE system. S...

Referring now to fig. 7, this shows communications apparatus comprising a plurality of communication systems and in which an inter-system handover is being carried out in accordance with a method embodying the present invention. The method is implementing the above-described tunnel solution to the problem of achieving direct communication between the UE and the target system (network), i.e. in parallel with the :: : UE's communication with the source system (the active call or other communication transaction). The UE has sent a signal comprising a signalling message in the protocol of the target system and an indicator (PD). The Source system (in fact its MME) has recognised the presence of the indicator and is forwarding the signalling message directly to the target system (using tunnel S23). The UE and the target system are "talking" directly to one another, without an IWF. I. * 1 * S *5,* *5SS S * ** I. * S

S * S S. * S. * * . *.

Abbreviations, Terms and Definitions For the purpose of ease of elaboration and also for readers unfamiliar with terms and abbreviations within the 3GPP, some of the used abbreviation and terms used in this document are provided here. It must be clearly noted and understood by readers that whilst every attempt has been made to have the terms and abbreviations used in this paper to be an exact match with those terms and abbreviations used in 3GPP, the terms and abbreviations here listed are strictly only for the purpose of use relating to this document.

Abbreviations AS Access Stratum.

B2BUA Back-to-Back UA BCD Binary Coded Decimal CC Call Control CMIP Client MIP (also known as host-based mobility) (rlr I+t.,rirl, CS Circuit Switch CSI An abbreviation collectively grouping the CS and IMS Combined Services (CSICS) DL DownLink eNB Enhanced Node B EPC Enhanced Packet Core EPS Enhanced Packet System (For information: eNB + EPC = :. EPS) S *s* HPLMN Home PLMN * SS* IMS IP MultiMedia Subsystem

ISIS

ISUP ISDN User Part (an ITU No.7 Signalling Protocol) *** S. * IWF Inter-Working Function LTE Long Term Evolution (relate most to the Radio Access Network) . : MAP Mobile Application Part

S

MIP Mobile IP MM Mobility Management MME Mobility Management Entity NAS Non Access Stratum P-GW PDN Gateway PLMN Public Land Mobile Network PMIP Proxy MIP (also known as Network-based mobility) PS Packet Switched SAE System Architecture Evolution (relate most to the EPC) S-GW SAE Gateway SM Session Management SRSC Single Radio Service Continuity SRVCC Single Radio VCC SS Supplementary Service UA User Agent UE User Equipment UL UpLink UMTS Universal Mobile Telecommunications System UPE User Plane Entity VCC Voice Call Continuity VoIP Voice over IP VPLMN Visited PLMN GW Gateway ASN Access Service Network PDU Protocol Data Unit : DTAP Direct Transfer Application Part S...

****** PD Protocol Discriminator Note:For abbreviations relevant to 3GPP please refer to IS 21.905. Should there be a conflict between the abbreviations given here above and abbreviations given in TS 21.905, the abbreviations given in TS 21 905 have precedence if the abbreviations : 5 are for 3GPP related terms. S. S*

Terminologies WiMax Broadband Wireless Access System being defined under IEEE 802. 16e Further information on abbreviations used in this document can be found on the 3GPP website, and technical documents referred to in this specification, including the following annexes can be obtained from http://www.3gpp.org/ftp/Specs! S. * S * S.. a... * S * *.. a... * a a... a **aaS * S a... * S* a. a S. I a Sa S.

Annex A: Further information on SAE/LTE Reference Network Architecture can be found in document 23.401. It gives an illustration of the SAE/LTE reference architecture as defined by 3GPP. Figures 5 and 6 of this specification correspond to figures Al and A2 of that document respectively Annex B This gives further information on the prior art techniques of managing protocol signalling and messages through protocol discriminators. Document TS 24 007, clause 5 provides amongst other things a protocol architecture of a mobile station. In this clause the use of Protocol Discriminators in the managing and distributing of signaling protocol messages to intended protocol entities is explained and illustrated. Figure 8 of this specification is an extract from TS 24.007. Figure 8 illustrates a Protocol architecture of a mobile terminal, and it is clear that the PD is used to channel signaling messages to the intended protocol entities. ft ensures that messages not meant for a certain protocol entity never gets to that protocol entity thereby relieving extra message processing.

Annex C: This provides additional information on (current) Inter-System changes (i.e. handovers) where the source system initiates and controls the system change.

The following is extracted from document 23 009.

8 General Description of the procedures for inter -3G_MSC handovers 8.1 Handover UMTS to GSM The following clauses describe two options for the Basic and Subsequent UMTS to GSM Handover procedures. The first, as described in clauses 8 1.1 and 8.1.3 respectively, S.... provides for a circuit connection between 3G_MSC-A and 3QMSC-B. The second, as described in clauses 8.1.2 and 8.1.4 respectively, provides for a Basic and Subsequent *.S...

Handover without the provision of a circuit connection between 3G_MSC-A and 3G_MSC-B. 3G_MSC can also be a pure GSM MSC.

In all the above mentioned clauses, the following principles apply: a) during the handover resource allocation, except for the messages explicitly indicated in b and c below, only the handover related messages that are part of the applicable BSSAP subset -as defined in 3GPP TS 49 008 [7] -shall be transferred on the E-interface; b) the trace related messages that are part of the applicable BSSAP subset -as defined in 3GPP TS 49.008-can be sent by the 3G MSC-A on the E-interface after successful handover resource allocation. In the clauses 8.1.1 and 8.1 2, it is however allowed at basic handover initiation on the E-lnterface to transfer one trace related message that is part of the applicable BSSAP subset -as defined in 3GPP TS 49.008 [7] -together with the applicable handover related message The applicable handover related message shall always appear as the first message; C) during the handover resource allocation for subsequent inter-MSC inter-system handover according to subclauses 8.1.3 and 8.1.4, it is allowed to transfer either DTAP or RANAP Direct Transfer messages on the E-lnterface between 3G_MSC-A and 3G_MSC-B. RANAP Direct Transfer messages shall be used for this purpose if and only if the basic handover procedure was an inter MSC SRNS relocation; d) during the handover execution, i.e. while the UE/MS is not in communication with the network, the 3G_MSC-A shall queue all outgoing BSSAP or RANAP messages until the communication with the UE/MS is resumed; e) during the execution of a basic inter-system inter-MSC handover to MSC-B or a subsequent inter-system inter-MSC handover to a third MSC-B', only the handover related messages and the A-Clear-Request message that are part of the applicable BSSAP subset -as defined in 3GPP TS 49.008 [7] -may be sent by the target MSC on :.::: the E-interface; S...

"s. f) during a subsequent inter-system inter-MSC handover back to 3G_MSC-A or to a S...

third MSC-B', 3G_MSC-B may initiate either an lu-Release-Request procedure or an A-*..s..

* 30 Clear-Request procedure on the E-interface. An lu-Release-Request procedure shall be initiated only if the basic handover procedure was an inter-MSC SRNS relocation; S. S * S 5 * g) finally, during supervision, i.e. while the UE/MS is not in the area of 3G_MSC-A after a successful lnter-3G_MSC handover, the subset of BSSAP procedures and their related messages -as defined in 3GPP IS 49.008 [7] -shall apply on the E-lnterface.

As the only exception to this rule, in case of a subsequent inter-MSC SRNS relocation back to 3G_MSC-A or to a third 3G_MSC-B', during the relocation resource allocation, the relocation and trace related messages that are part of the applicable RANAP subset -as defined in 3GPP IS 29.108 [15] -shall be transferred on the E-interface (see subclause 8.3, a and b).

If a subsequent inter-MSC handover/relocation back to 3G_MSC-A or to a third 3G_MSC-B' is cancelled, then the supervision continues, and BSSAP procedures and their related messages shall apply on the E-interface.

NOTE: A subsequent inter-MSC SRNS relocation back to 3G_MSC-A or to a third 3G_MSC-B' can occur, e.g., if after the basic inter-MSC handover to 3G_MSC-B the MS performed a subsequent intra-3G MSC-B GSM to UMIS inter-system handover; h) during the intra-3G_MSC -B handover execution, if any, the 3G_MSC -B shall queue all outgoing BSSAP or RANAP messages until the communication with the UE/MS is resumed.

8.1.1 Basic Handover procedure requiring a circuit connection between 3G_MSC -A and MSC-B The procedure used for successful lnter- 3G_MSC UMTS to GSM Handover is shown in figure 18 (reproduced in this specification as fig. 9). Initiation of the UMTS to GSM handover procedure is described in clause 5. The procedure described in this clause makes use of messages from the 3GPP IS 08.08 and of the transport mechanism from the Mobile Application Part (MAP) (3GPP IS 29.002 [12]). After an lnter- 3G_MSC : .. relocation/handover, lntra-3G_MSC UMTS to GSM handover may occur on 3G_MSC -B, this handover will follow the procedures specified in a previous clause. S...

It should be noted that the signals shown in fig. 9 can be sent at any time after the *5SS*S * 30 reception of IAM.The above extract, although it does not document the handover of what :. is currently being designed as handover from LTEISAE system to UMST system, *: nevertheless shows an example of what may be the source system (in this extract the 3G system is the source system) and what may be the target system (in this extract the target system is the 2G).

Annex D: This provides additional information elaborating discussions on solutions to inter-system change (from LTE-SAE to non-3GPP access) A possible architecture for a Tunnel approach" between LTE/SAE 3GPP access system and non-3GPP WiMax system is shown in fig. 1. This tunnel approach has been proposed for mobility between LTE and 3GPP2 systems. In this approach the UE will talk to the target network to prepare the resources in the target network for handover. It is proposed to use the TMtunnel approach" for mobility to/from WiMAX for the following reasons:jLLess impact on source networksince most of the signalling related to the target RAT is handled transparently by the source RAT, there is less specification/ implementation effort required for the source RAT)Less impact on target network: Since the target network is receiving signalling "in its own language" as originating from the UE, there is less specification/implementation effort required for the target RAT.

Annex E This provides additional information comparing some other "talked about" solutions for inter-system change (i.e handover).

The following is an extract from S2-072102rev2. This extract shows the signalling flow of a proposed solution for doing inter-system change from the PS only LTE/SAE system to the CS domain of a GERAN or UMTS system, and the figure to which it relates is

reproduced in this specification as fig. 10:

: *... ============1 extract ==============-====--================== 1. Target measurements and handover trigger detection at the source eNB and the UE for initiation of handover to CS. * * S...

2. Handover Required message sent by the source eNB to source MME containing *:::: 30 required information such as source to target information.

3. Standard PS-PS handover procedure at the source eNB for initiation of Forward Relocation Request toward PCHCF.

4. PS handover request interworked with CS Inter MSC handover request to the target MSC at PCHCF associated with the target MME for initiation of Prepare Handover Request toward target MSC Its assumed that the CS Security context is available at the PCHCF: mechanisms for the discovery/retrieval of the CS security context at the PCHCF are FFS 5. Target GERAN preparation via the target MSC.

6 Handover Number returned in Prepare Handover Response by the target MSC for establishment of circuit connection between the target MSC and the MGW associated with the PCHCF End of first extract It is clear from the extract and message flow that the UE does not initiate communications towards the target system (ie. in the extracted figure that will be the MSC) to initiate, request or negotiate a handover. That task still rests solely with the MME (of the source system).

The following text, and fig 11 of this specification, are extracted from X.P0042-001- 0_vO.88. This X.P0042-001 -0 vO.88 is a 3GPP2 document and what is covered is the rr piuposau on now to nanoover a voice caii in me j.,ti-' i' system tie. me 3GPP2 HRPD) to the 3GPP2 CS system (ie. lx).

2d extract -===--================-_===-_==== Figure 8-4 (which is reproduced in this specification as fig. 11) illustrates a detailed call flow for the HRPD VoIP-to-1 x circuit-switched voice domain transfer procedure.

Pre-conditions: :... 25 It is assumed that initially there is an HRPD/IMS V0IP call setup between the UE and *.*.

the Other End Point (OEP). SIP call dialog 1 for this voice call is illustrated by a heavy dashed double arrow between the VCC AS and the OEP SIP call dialog 2 for this voice call is illustrated by a heavy dashed double arrow between the VCC AS * and the UE. The voice bearer path is illustrated by a heavy solid double arrow between the UE and the OEP. * ** ** * ** S * * * * S.

1. UE 1 and the HRPD AN interact to initiate a domain transfer'. See [10] & [11] for 1 The HRPD AN determines that UE 1 is close to the edge of HRPD coverage and sends an HRPD 3GlXServices message containing a lx Service Redirection Message to UE 1 UE 1 sends the HRPD 3GlXServicesAck message to the HRPD AN in acknowledgement.

signaling details.

2. UE 1 sends a lx call origination2 to the MSCNLR via the HRPD AN (and optionally, the lx BS) and includes the VCC AS E 164 number The specific messages and any acknowledgements are not shown for brevity See [10] & [11] for signaling details.

Note, steps 3-6 are optional, depending on whether the UE has previously been lx CS registered and authenticated.

3. The Visited MSCNLR may initiate a lx registration procedure on behalf of UE 1 The Visited MSC sends an MAP AUTHREQ message to UE l's HLR to authenticate UE 1 prior to allowing registration and prior to allocating a lx traffic channel to UE 1.

4. UE l's HLR responds by sending an MAP authreq message to the Visited MSC.

5. The Visited MSC sends an MAP REGNOT message to UE 1 S HLR.

6. UE l's HLR responds by sending an MAP regnot message to the Visited MSC 1 Note: Steos 7-8 are shown using the MAP ORREQ operation. Optionally, a post digit analysis trigger using the MAP ANLYZD operation may be used instead to obtain routing information for the domain transfer.

Note 2: If either origination triggers are not supported by the MSCNLR or origination triggers are not armed for this subscriber, proceed to Step 9.

7. Once the visited MSCNLR has obtained the service profile for the originating subscriber (i.e., by Step 4), the Visited MSCNLR invokes a call origination trigger to obtain routing information. The Visited MSCNLR sends a MAP ORREQ :... message to the WIN SCP (or to the HLR), containing the Calling Party Number *.S.

(MDN) of UE 1 (derived from the IMSI) and the Called Party Number from the call origination. The WIN SCP (or HLR) sends the ORREQ message on to the VCC AS. Optionally, the Visited MSCNLR may send the ORREQ message directly to *....

* * a VCC AS that has an integrated WIN SCP function.

:. 8. The VCC AS determines that this is a domain transfer scenario based on the ** * VCC AS E.164 number in the Called Party Number (and the Calling Party Number) in the ORREQ message, and then allocates an IMS Routing Number, which is an E.164 temporary routing number associated with this domain 2 The CSNA protocol is used to deliver a lx Call Origination message from UE 1 via the

HRPDAN

transfer The VCC AS then sends back orreq message to WIN SCP (or HLR), which returns the orreq message to the MSCNLR Optionally, the VCC AS has an integrated WIN SCP function and sends the orreq message directly to the MSCNLR..

9 The Called Party Number is either the dialed digit string in the lx call origination message (Step 2) or, in the event that origination triggering resulted in the allocation of an IMRN, the IMRN (Step 8). The translation of Called Party Number performed by the Visited MSCNLR results in an ISUP lAM message being routed to either an MGCF in the serving network or to the PSTN, based upon operator policy The Visited MSC includes the E.164 MDN of UE 1 in the

Calling Party Number field of the ISUP lAM.

10. Anytime after receipt of the lAM message, based on local policy the MGCF returns an ACM message to the MSC. The MGCF requests the MGW to create two terminations. The first termination is a TDM connection between the Visited MGW and the Visited MSC. The second termination is an RTP/UDPIIP ephemeral termination.

11. Anytime after Step 2, the MSCNLR sends a lx handoff initiation to UE 1 via the HRPD AN and the HRPD air interface. This indicates that UE 1 should acquire the lx traffic channel. See [101 & [1lJ for signaling details.

12. The lx BS acquires UE l's reverse traffic channel and the voice path is established with the MSC.

13. UE 1 responds by sending a lx handoff done (via the lx BS) to the MSCNLR.

See [10J & [11] for signaling details.

14. Anytime after Step 9, the Visited MGCF sends a SIP INVITE message via the I-*a*.

25 CSCF to the VCC AS containing the Request-URI, a P-Asserted-ID, and an SDP offer The Request-URI is based upon the lAM Called Party Number, the P-Asserted-ID is based upon the lAM Calling Party Number, and the SDP offer is * based upon the Visited MGW SDP information 15. The VCC AS examines the P-Asserted-ID header of the SIP INVITE to determine *. : 30 which subscriber is performing the HRPD VolP-to-lx circuit-switched voice domain transfer. Note that the VCC AS has already been put into the call flow signaling path during session setup.

CSNA protocol is used to deliver a lx Handoff Direction message to UE 1 via the HRPD AN Based upon the P-Asserted-ID, the VCC AS determines the OEP of the ongoing call. The VCC AS creates a SIP re- INVITE message with the Request-URI set to the OEP and an SDP offer based upon the Visited MGW SDP information. The VCC AS sends the SIP re-INVITE to the S-CSCF Editor's Note. The issue of how to deal with domain transfer of more than one voice call at a time is for further study 16. The S-CSCF forwards the re-INVITE to the far end network.

17 The Other End Point (OEP) (IMS user or PSTN MGCF/MGW) modifies its RTP bearer termination with the Visited MGW SOP and responds with a SIP 200 OK message to the S-CSCF containing an SDP answer with the OEP SDP 18 The S-CSCF forwards the 200 OK to the VCC AS.

19. The VCC AS sends a SIP 200 OK message via the I-CSCF to the Visited MGCF containing an SOP answer with the OEP SDP information.

20. The Visited MGCF requests modification of the Visited MGW ephemeral termination with the OEP SDP information and instructs the Visited MGW to reserve/commit Remote resources. The Visited MGCF sends an ISUP ANM message.

21. Anytime after the 200 OK is received, the Visited MGCF sends a SIP ACK message via the l-CSCF to the VCC AS This completes the establishment of SIP call dialog 3 between the MGCF and the VCC AS. The VCC AS records the location of UE 1 as present in the lx CS domain.

22. Anytime after the VCC AS receives the 200 OK, it sends a SIP ACK message to the S-CSCF. s..

23. The S-CSCF forwards the ACK to the OEP *** 25 24 Anytime after Step 18, the VCC AS sends a SIP BYE message to UE 1 via the S-CSCF to release SIP call dialog 2 between UE 1 and the VCC AS. Note that * since UE 1 is already on a lx traffic channel it will not respond to this SIP BYE. ****

*..* : Post-conditions: ** * * *: There is now voice call setup between the UE and the OEP via the lx circuit 3D switched network. SIP call dialog 1 for this voice call is illustrated by a heavy dashed double arrow between the VCC AS and the OEP. SIP call dialog 3 for this voice call is illustrated by a heavy dashed double arrow between the VCC AS and the MGCF The voice bearer path is illustrated by heavy solid double arrows connecting the UE, MSC, MGW and the OEP end of 2ndt extract ===========-==================--Here in this 3GPP2 proposal, it is seen in step 2 and its associated text that the UE should "talk" directly to the target system, ie the MSC. However, there is no information in 3GPP2 of how that direct "talking" is achieved.

Annex F Additional information on tunnelling and message container Tunnel and Tunnelling A tunnel is between two endpoints. It provides a virtual point-to-point between two peer entities communication with one another as a result of having set up that tunnel. The two end points communicate in a protocol language known to the two end points and any subsystem along that tunnel who serves to keep up that tunnel does not know or iiriirstnd or manipulate to allow the end-points to understand that communication. In other words there is no Inter-working needed.

Extracted here (1 extract) from 23.402, subclause 5.4 2.4. are some text which should reinforce the above paragraph.

l extract 5.4.2.4 Initial Attach on S2b 5.4.2 4 1 General This section is related to the case when the UE powers-on in an untrusted network via * S2b interface. S...

." 5.4 2.4.2 Initial Attach procedure with PMIPv6 for non-roaming In the non-roaming case, PMIPv6 [8] is used to setup a PMIPv6 tunnel between the ePDG and the PON GW. It is assumed that MAG is collocated with ePDG. The IPsec * .. . * 30 tunnel between the UE and the ePDG provides a virtual point-to-point link between the :. UE and the MAG functionality on the ePDG..

S.. Figure 5.4.2.4.2-1: Initial attachment when Network based MM mechanism are used over S2b for non-Roaming (reproduced in this specification as fig. 12 NOTE: Before the UE initiates the setup of an IPsec tunnel with the ePDG it configures an IP address from an untrusted non-3GPP access network This address is used for sending all lKEv2 [9] messages and as the source address on the outer header of the IPsec tunnel.

1) The IKEv2 tunnel establishment procedure is started by the UE The UE may indicate in a notification part of the lKEv2 authentication request that it supports MOBIKE. The ePDG IP address to which the UE needs to form IPsec tunnel is discovered via DNS query as specified in section 5 4.2 2.. After the UE is authenticated, UE is also authorized for access to the APN. The procedure is as described in 3GPP Is 33.234 [7] The PDN GW address is determined at this point as described in section 5 4.2 1 The PDN GW information is returned as part of the reply from the 3GPP AAA Server to the ePDG This may entail an additional name resolution step, issuing a request to a DNS Server.

2) The ePDG sends the Proxy Binding Update message to the PDN GW. The proxy binding update message shall be secured.

Ed!tor's note: H the Prnyy Rindina Update messaae is secured is FFS.

3) The selected PDN GW informs the 3GPP AAA Server of the PDN GW address.

Editor's note: it is FFS whether this step can be avoided, e g. if the PON GW address is already known by the AAA/HSS by other means.

4) The PDN GW processes the proxy binding update and creates a binding cache entry for the UE. The PDN GW allocates an IP address for the UE The PDN GW then sends a proxy binding ack to the ePDG, including the IP address allocated for theUE.

U

NOTE: If UE requests for both lPv4 and lPv6 addresses, both are allocated. If the UE requests for only lPv4 or lPv6 address only one address is allocated accordingly.

I..... * *

Editors note: It is FFS which entity stores the allocated PON GW IP Address. * S..

S S S 5.

5) After the BU is successful, the ePDG is authenticated by the UE. S Sq

6) The ePDG sends the final lKEv2 message with the IP address in IKEv2 Configuration payloads 7) IP connectivity from the UE to the PON GW is now setup Any packet in the uplink direction is tunnelled to the ePDG by the UE using the IPSec tunnel. The ePDG then tunnels the packet to the PDN GW. From the PDN GW normal IP based routing takes place. In the downlink direction, the packet for UE (HoA) arrives at the PDN GW The PDN GW tunnels the packet based on the binding cache entry to the ePDG. The ePDG then tunnels the packet to the UE via proper IPsec tunnel.

end of 151 extract So after step 7, there is a tunnel and it allows communication between PDN GW That tunnel make pass through a whole lot of subsystems eg. eNB, UPE but all those subsystems see are just bits of data, those subsystems do not need to interwork the signalling protocol.

The following is further information on message container and message encapsulation techniques: If a protocol message has designed within it a PDU that can carry anything that anything can be another signalling message. So if Protocol Entity A (PE-Al) is communicating with Prntocnl Entity A2 (PE-A2) has a message (just for eg.) HANDOVER_PREARATION_ACKNOWLEDGE that has a PDU where PE-Al has put in another message (eg. HANDOVER COMMAND) not meant for PE-A2 but meant for in fact a different subsystem, then when PE-A2 gets HANDOVER_PREPARATION_ACKNOWLEDGE, PE-A2 must work on that message takes out the PDU, redresses it in a protocol message that the final destined subsystem can understand and then send it along (and in the meantime it could be sent along not directly to the destined subsystem but to another intermediate subsystem by yet another :. 25 message container). * *** * *

This way of passing a signalling message does not in any way pertain to tunnelling of S...

* . messages. *. *....

* 30 This way of passing signalling message is already existing and can be well seen and -S..

: understood when one looks into 23.009 where it is clear that the final HANDOVER COMMMAND sent to the UE in the source system comes from the Base station of the target system, in which it was first place within a message (by the target BSS) to the target MSC which then extracted and placed in another message from target MSC to source MSC who extracts and repackages for the source BSC who finally extracts and send to UE. The following extract from 23 009 is given by example.

2 extract =========-====--============= 6 2 Procedure for lntra-3G_MSC Handovers 6 2.1 lntra-3G_MSC Handover from UMTS to GSM The procedure for a successful lntra-3G_MSC handover from UMTS to GSM is shown in figure 8. It is assumed that selection of a candidate UE/MS has already taken place within the RNS based upon the criteria presented in clause 5. The exact algorithm, in the RNS, for determining a candidate UE/MS is not addressed in the present document. The procedures discussed do not make use of the Mobile Application Part (MAP), represented by signalling function 4 in figures 4 and 6. The procedure described in this clause covers case ii).

Figure 8: Basic lntra-3G_MSC Handover from UMTS to GSM Procedure (reproduced as

fig 13 of this specification).

6.2.1 1 With no bearer or one bearer The successful operation of the procedure is as follows. When the RNS (RNS-A), currently supporting the UE/MS, determines that the UE/MS requires to be handed over to GSM it will send an lU-RELOCATION-REQUIRED message to the 3U_MSU (3G_MSC-A). The U-RELOCATION-REQUIRED message shall contain a single cell, to which the UE/MS can be handed over. When the 3G_MSC-A receives the lU-RELOCATION-REQUIRED message it shall begin the process of handing over the UE/MS to a BSS (BSS-B). The 3G_MSC-A shall generate an A-HANDOVER-REQUEST message to the selected BSS (BSS-B) When BSS-B receives the A-HANOOVER-REQUEST message it shall take the necessary action to allow the UE/MS to access the radio resource of BSS-B, this is detailed in 3GPP TS 48.058 [6] and in 3GPP TS 45.008 :. [4]. The switching of the radio resource through the necessary terrestrial resources is detailed in 3GPP TS 24.008 [10] and 3GPP TS 08.08 [5]. S... * . *. a

**S.S. * * S... * SS S. S *. S

S S S S.

Once resource allocation has been completed by BSS-B it shall return an A-HANDOVER-REQUEST-ACK. to 3G_MSC-A When this message is received by 3G_MSC-A it shall begin the process of instructing the U ElMS to tune to a new dedicated radio resource. An lU-RELOCATION-COMMAND will be sent by the 3G_MSC-A to RNS-A. On receipt of the lU-RELOCATION-COMMAND message RNS-A will send the radio resource control message RRC-HANDOVER-COMMAND, containing a Handover Reference number previously allocated by BSS-B, to the UE/MS The UE/MS will then access the new radio resource using the Handover Reference number contained in the RI-HANDOVER-ACCESS message. The number will be checked by BSS-B to ensure it is as expected and the correct UE/MS has been captured If this is the correct UE/MS then the BSS-B shall send an A-HANDOVER-DETECT to 3G_MSC-A. When the UE/MS is successfully communicating with the BSS-B a RI-HANDOVER-COMPLETE message will be sent by the UE/MS to BSS-B The BSS-B will then send an A-HANDOVER-COMPLETE message to 3G_MSC-A.

NOTE: The A-HANDOVER-REQUEST-ACK from BSS-B contains the complete radio resource control message that shall be sent by RNS-A to the UE/MS in the RRC-HANDOVER-COMMAND, 3G_MSC-A transparently passes this radio interface message onto RNS-A.

After 3G_MSC-A has received the A-HANDOVER-COMPLETE message from BSS-B it shall begin to release the resources allocated on RNS-A. In figure 8 the resource is released by using the lU-RELEASE-COMMAND sequence.

If a failure occurs during the handover attempt, for example A-HANDOVER-FAILURE returned from BSS-B, then 3G_MSC-A will terminate the handover to BSS-B and send an I U-RELOCATION-PREPARATION-FAILURE message to RNS-A.

If RNS-A has decided to cancel the handover, it sends lU-RELOCATION-CANCEL message to 3G_MSC-A. The 3G_MSC-A will then terminate the handover towards BSS-B (if initiated) and send lU-RELOCATION-CANCEL-ACKNOWLEDGE message to * .S.

RNS-A.

In all cases the existing connection to the UE/MS shall not be cleared except in the case of expiry of the timer for receipt of A-HANDOVER-COMPLETE.

During the period that the UE/MS is not in communication with the network 3G_MSC-A a..

shall queue all appropriate messages. All messages shall be delivered to the UE/MS once communication is resumed. In the case of an lntra-3G_MSC handover from UMTS to GSM on 3G_MSC-B then the messages shall be queued by 3G_MSC-B.

6.2.1.2 With multiple bearers (Optional functionality) If 3G_MSC-A supports the optional supplementary service Multicall (See 3GPP TS 23 135), 3G_MSC-A shall have the following functionality additionally to the

description in clause 6 2.1 1.

Upon receipt of the lU-RELOCATION-REQUIRED from RNS-A 3G_MSC-A shall select one bearer to be handed over if the UE is engaged with multiple bearers. After that, 3G_MSC-A generates an A-HO-REQUEST message for the selected bearer to BSS-B When an A-HO-REQUEST-ACK is received from BSS-B, 3G_MSC-A sends IU-RELOCATION-COMMAND, which indicates the bearers not to be handed over as bearers to be released, to RNS-A.

After 3G_MSC-A receives A-HO-COMPLETE message from BSS-B, 3G_MSC-A shall release calls via BSS-B, which has been carried by the bearers not to be handed over, and then sends lU-RELEASE-COMMAND to RNS-A.

end of 2ndt extract =================-=======--===== In certain fora and circles this way of transferring signalling messages between two destined protocol entities through intermediate protocol entities requiring intermediate entities to rework and repackage the signalling messages is a.K.a. message encapsulation. S. * S * S.. *... * S *.S. *SSS * S *SS5

S. SS SI * S 55.. * S. S S. 5

S S S I 55

Claims (19)

1. A method of communicating between user equipment, involved in an active communication with a first communications system, and a second communications system, communication between user equipment and the first communications system using a first communication protocol and communication between the second communications system and user equipment using a second, different communications protocol, the method comprising the steps of: transmitting a signal from the user equipment to the first communications system, the signal comprising a signalling message, in accordance with said second protocol, and a protocol discriminator; receiving the signal in the first communications system; identifying in the received signal the presence of the protocol discriminator; and forwarding the signalling message from the first communications system to the second communications system.

2. A method in accordance with claim 1, wherein the step of forwarding further comprises forwarding the protocol discriminator from the first to the second communications system together with the signalling message.

3. A method in accordance with claim 1 or claim 2, wherein the transmitted signal consists of the signalling message and the protocol discriminator.

4 A method in accordance with claim 1 or claim 2, wherein the protocol discriminator is a second protocol discriminator in a format understandable by the second communications system, and the transmitted signal further comprises a first protocol discriminator, the first protocol discriminator being in a format understandable by the first communications system. *S.. * . *S..

5. A method in accordance with claim 4, wherein the step of forwarding comprises *****.

* omitting the first protocol discriminator from a signal forwarded to the second *:::: communications system, the forwarded signal comprising the signalling message and *. : the second protocol discriminator. * S.

6. A method in accordance with any preceding claim, further comprising the steps of: the user equipment selecting the protocol discriminator from a plurality of protocol discriminators, each protocol discriminator corresponding to a respective one of a plurality of second communications systems using a respective second communications protocol; and forwarding the signalling message to the second communication system associated with the selected protocol discriminator in the signal from the user equipment

7. A method in accordance with any preceding claim, wherein the protocol discriminator is used by the equipment sending the signalling message to indicate the designated protocol process within the target system for which the signalling message carrying the said protocol discriminator is meant for.

8. A method in accordance with any preceding claim, wherein the first communications system is a system from a list comprising: mobile equipment, LTE/SAE system, GSM system, GPRS system, UMTS system, 3GPP2, WiFi, WiMax, WiBro.

9. A method in accordance with any preceding claim, wherein the second communications system is a system from a list comprising: mobile equipment, LTE/SAE system, GSM system, GPRS system, UMTS system, 3G11-'2, vviFi, vviMax, WiBro

10. A method in accordance with any preceding claim, further comprising the steps of: the second communications system responding to the forwarded signalling message by sending a response signal to the first communications system, the response signal comprising a response signal message and a response protocol discriminator; the first communications system identifying the presence in the response signal of the response protocol discriminator and forwarding the response signal message to the user equipment. S...

11. A method in accordance with claim 10, wherein the response protocol discriminator is the same as the protocol discriminator transmitted by the user equipment.

S. S... * S * 5* S. *

12. A method of initiating a handing over of an active communication between user S *5 * equipment and a first communications system from the first communications system to a second communications system, communication between the user equipment and the first communications system using a first communication protocol and communication between the second communications system and user equipment using a second, different communications protocol, the method comprising communicating, while involved in the active communication with the first communications system, with the second communications system using a method in accordance with any preceding claim, wherein the signalling message transmitted from the user equipment is a handover initiation message or a message requesting a handover to the second communications system.

13. A method of handing over an active communication of a user using user equipment from a first communications system to a second communications system, communication between user equipment and the first communications system using a first communication protocol and communication between the second communications system and user equipment using a second, different communications protocol, the method comprising the steps of: sending at least one handover signal message from the user equipment to the second communications system via the first communications system using a method in accordance with any one of claims 1 to 11, each handover signal message being comprised in a respective signal transmitted from the user equipment tu iiu ut communications system message, whereby each transmitted signal is received in the first communications system and the respective handover signalling message is forwarded to the second communications system after the presence of the protocol discriminator is identified in each received signal.

14. Communications apparatus comprising: user equipment; a first communications system adapted to communicate with the user equipment S....' using a first communication protocol, and ** a second communications system adapted to communicate with the user equipment using a second, different communications protocol, *.S..' * 1 the user equipment being adapted to transmit, while involved in a active communication with the first communication system, a signal to the first communications system, the signal comprising a signalling message, in accordance with said second * : protocol, and a protocol discriminator, the first communications system being adapted to receive the signal, identify in the received signal the presence of the protocol discriminator, and forward the signalling message to the second communications system.

15. User equipment for a telecommunications system, the user equipment being adapted to communicate with a first telecommunications system using a first protocol and with a second telecommunications system using a second, different protocol, the user equipment being further adapted to communicate with the second communications system, while involved in an active communication with the first system, by transmitting a signal for reception by the first system, the signal comprising a signalling message in accordance with said second protocol, and a protocol discriminator,

16. User equipment in accordance with claim 15 and adapted to initiate a handover of an active call from the first communications system to the second communications system by sending a handover initiation or handover request message to the second system by transmitting a signal comprising the handover initiation or handover request message in accordance with the second protocol and a protocol discriminator for reception by the first system.

17. A method of communicating substantially as hereiribefore described with reference to the accompanying drawings.

18. Communications apparatus substantially as hereinbefore described with reference to the accompanying drawings

19. User equipment substantially as hereinbefore described with reference to the : accompanying drawings. *.. S * S S... S... * S

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