GB2354908A - Redirection of active communication from one radio network controller to another - Google Patents

Abstract

A mobile telecommunication system has a plurality of Radio Network Controllers (RNC). When user equipment (UE) moves from one region to another, active communication may need to be switched from one RNC to another. During the switch, data may be lost which may be problematic if the data contains critical messages. Usually data is transmitted from the user equipment in an unacknowledged form to reduce network bandwidth requirements. To prevent critical data loss, at least one predetermined class of traffic may be transmitted in an acknowledged mode when communication is switched between Radio Network Controllers. User equipment may be notified that RNC relocation is about to occur.

Description

2354908 MOBILE TELECOMMUNICATIONS The present invention relates to mobile

telecommunications systems and is particularly, but not exclusively, concerned with third generation UMTS systems.

In a mobile telecommunications system, particularly in present proposals for a UMTS system, switching from one Radio Network Controller (RNQ to another is necessary from time to time, for example as the mobile User Equipment moves from one coverage region to another. Switching of RNCs is normally controlled by the network and the User Equipment is not involved.

Pursuant to the invention, it has been appreciated that during switching between RNCs, data transmitted by the User Equipment (UE) may be lost. This may be particularly problematic if the data comprises critical messages. Usually, data transfer from the User Equipment (UE) is not acknowledged (to reduce network bandwidth required), so the failure of data transmission may not be apparent to the User Equipment.

The present invention addresses this problem.

According to a first aspect, the invention provides a method of operating a mobile telecommunications system having a plurality of Radio Network Controllers (RNCs) comprising: during redirection of active communication with User Equipment from one Radio Network Controller (RNQ to another, employing an Acknowledged Transfer Mode (AM) for at least one predetermined class of traffic for which an Unacknowledged Transfer 20 mode was employed prior to redirection.

In this way, during the critical time when data is most likely to be lost, reliability is assured, without requiring the Acknowledged mode to be used at other times.

Redirection will almost invariably be performed following a positive decision to redirect and the decision will normally be made by the network. Switching into the Acknowledged mode is preferably triggered following the decision, for example by sending a message to signify that redirection is about to be attempted (redirection may not be successful). Switching may, however be triggered independently of the network decision to switch, for example based on determination (whether in the UE or a part of the network) that redirection is occurring or based on a request sent by the UE to change RNC. In the latter case, although the request will normally be followed by a decision to switch RNC by the network, the switching may precede the decision to switch.

In the usual case, where there is a decision to redirect, the invention may provide, in closely related but independent aspects, a method of operating a telecommunications network or component thereof or User Equipment, the method comprising: in response to a decision to redirect active communication with User Equipment from one Radio Network Controller (RNQ to another, switching communication of at least one predetermined class of traffic from an Unacknowledged Transfer Mode (UAM) to an Acknowledged Transfer Mode (AM) or determining whether at least one predetermined class of traffic which may be in either an Unacknowledged or Acknowledged mode is in an Acknowledged Transfer Mode (AM) and, if not, switching to an Acknowledged mode.

For certain types of communication, the traffic may already be in the Acknowledged Mode, so no actual change in mode is required for that particular communication traffic; in such a case, the "switching" provided by the invention will merely comprise determining that the traffic is already in an Acknowledged mode. It will be noted that determination is only required if the mode prior to switching is unknown and switching of mode is only required if the mode is Unacknowledged.

Preferably, the method further comprises, following completion of RNC relocation (i.e.

redirection of communication), switching said traffic back to the transfer mode prior to redirection, which may be stored to facilitate this.

Preferably, the method comprises signalling to the User Equipment that RNC Relocation is about to occur or is in progress and preferably, the User Equipment is arranged to switch to an acknowledged mode for said traffic on receipt of said signal. Similarly, the method preferably comprises sending a context update signal to the User Equipment when relocation has occurred and preferably the User Equipment is arranged, on receipt of said signal, to return to the pre-existing or default mode for the predetermined class of traffic. Preferably the User Equipment is arranged to signal an acknowledgment that the context update signal has been received.

Signalling of an imminent redirection may in itself be useful, even when mode switching is not provided, as it may facilitate other precautionary action (for example simply delaying transmission of critical but not time-critical data). Thus, in a closely related independent aspect (addressing the same problem of coping with RNC redirection), the invention provides a method of operating a telecommunications network or component thereof, the method comprising: following a decision to redirect active communication with User Equipment from one Radio Network Controller (RNC) to another, signalling to the User Equipment that RNC Relocation is about to occur.

The at least one predetermined class of traffic preferably comprises at least critical control messages (c-plane) traffic sent from the User Equipment. The traffic may further comprise certain user data (u-plane) traffic. Preferably at least traffic on the uplink (from the UE to the UTRAN) is switched to an acknowledged mode. Traffic on the downlink may also be switched.

In a further aspect, the invention provides a method of operating User Equipment in a mobile telecommunications network comprising switching a predetermined class of communication traffic from an Unacknowledged Transfer mode to an Acknowledged Transfer mode during redirection of active communication (preferably following a decision to redirect) from one Radio Network Controller to another, or determining whether at least one predetermined class of traffic which may be in either an Unacknowledged or Acknowledged mode is in an Acknowledged Transfer Mode (AM) and, if not, switching to an Acknowledged mode.

The invention extends to User Equipment and network components embodying the methods and preferred features above. The invention further extends to signals for use in the above methods.

In this specification, terms of the art as defined in the UNITS specification are used for ease of understanding. However, these terms are not intended to be limited to any specific system but are intended to encompass any functional equivalents in other systems, for example based on second generation GSM systems or the like. In particular, the term Radio Network Controller is intended to encompass any radio access point (base station) or underlying control centre (which may control a plurality of base stations) of which the system has a plurality and between which communication is switched. It should be noted that in GSM type systems, the invention may be applied to handover between cells. The term User Equipment (UE) is intended to encompass any communication device, for example voice, fax, data, E-mail, video or any combination of these which can communicate with one of the RNCs. The term Acknowledged Mode is intended to encompass any communication mode in which receipt of data sent by the UE to the network can be signalled back to the UE. This may include modes in which a very simple acknowledgement is provided, for example a periodic count of packets received, possibly after a delay, possibly "bolted onto" an existing system which does not have direct provision for acknowledgement by means of general purpose messages, as well as modes with complex handshaking and error correcting.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing in which:

Fig. I illustrates proposed signalling associated with SRNC relocation.

The following description of an embodiment relates to application to a UMTS telecommunications system; as will be explained below, the invention is not so limited.

In a UMTS system, during SRNC Relocation the Radio Resource Control (RRC) terinination point is moved from the one RNC to another. In the UNITS standards specifications existing up to 30 June 1999, the UE has no involvement in the SRNC Relocation Procedure [Please give references, if relevant]. Therefore, as explained above, the uplink (UE->UTRAN) traffic stream (signalling or user data) will be unreliable and vulnerable in the SRNC Relocation Procedure. This may be particularly critical for messages (user data or signalling) sent in the unacknowledged transfer mode (UAM) of Radio Link Control (RLQ (such as UAM cell condition reports). Furthermore, in the case of roll-back when the SRNC Relocation Procedure fails, the Uplink (UL) Radio Resource Control (RRC) signalling and user data transfer will be lost.

According to the embodiment, a mechanism is provided to indicate to the Radio Link Control (RLQ layer in the UE that the acknowledged mode (AM) should be used (preferably) during the SRNC Relocation. Exemplary additional signalling messages are shown in Figure 1.

An RRC message called "SRNC RELOCATION INITIATED" is introduced. This message shall be sent by the SRNC as the relocation decision has been made. Upon reception of such message, the UE shall set the RLC layer to AM for c-plane and non-real- time (delay-insensitive) u-plane. When the SRNC Relocation Procedure is accomplished, the SRNC shall form an "RRC CONTEXT UPDATE" message and send it to the UE. This message could include information about the new RRC-related parameters (such as s-RNTI and SRNC-ID). Upon reception of such a message, the UE shall update its RRC context information and set the Radio Link Control (RLQ layer to the default operation mode, that is to whatever mode was in place before the SRNC Relocation - this will typically be an Unacknowledged mode.

The above embodiment is described in the context of a UNITS system. However, it will be appreciated that the invention may be applied to any telecommunications system possessing the following characteristics:

a plurality of base stations (corresponding to RNCs); mobile equipment (corresponding to UE); relocation of active base station from one RNC to another; an acknowledged or handshaking mode of communication, or the ability to implement one if not present in the basic system, so that receipt of a message sent from the mobile equipment can be signalled back to the mobile equipment.

There should also be some means of signalling to the mobile equipment that active base station relocation is taking place.

It will be appreciated that the invention can therefore be implemented in virtually all current and proposed telecommunications systems. To assist in appreciating how the invention may be extended, a glossary of some terms used in the art pertaining to UMTS systems is provided; any of the terms of art may be replaced by functionally equivalent components in a non-UMTS system. The following documents are incorporated herein by reference:

Draft-ETR/SMG-50102, Special Mobile Group (SMG) Vocabulary for the Universal Mobile Telecommunications System.

ETSI DTR/SMG-0225xxU, Universal Mobile Telecommunications System (UMTS); Vocabulary for the UTRAN, UMTS 25.XX Version 0. 1.0.

Tenris and definitions Radio access bearer The service that the access stratum provides to the non-access stratum for transfer of user data between UE and CN.

Radio link The set of (radio) physical channels comprised in a transmission path between a UE to one UTRAN access point.

Radio Network Temporary Identifier (RNTI) A Radio Network Temporary Identifier is an identifier for a UE when an RRC connection exists. It is e.g. used by the MAC protocol on common Transport Channels (RACH, FACH,PCH).

RRC connection A point-to-point bi-directional connection between RRC peer entities on the UE and the UTRAN sides, respectively. An UE has either zero or one RRC connection.

Signalling connection An acknowledged-mode link between the user equipment and the core network to transfer higher layer information between peer entities in the non-access stratum.

Signalling link Provides an acknowledged-mode link layer to transfer the UE-UTRAN signalling messages as well as UE - Core Network signalling messages (using the signalling connection).

URA updating URA updating is a family of procedures that updates the UTRAN registration area of a UE when a RRC connection exists and the position of the UE is known on URA level in the UTRAN.

UTRAN Registration Area (URA) The UTRAN Registration Area is an area covered by a number of cells. The URA is only internally known in the UTRAN.

UTRAN access point A conceptual point within the UTRAN performing radio transmission and reception. A UTRAN access point is associated with one specific cell, i.e. there exists one UTRAN access point for each cell. It is the UTRAN-side end point of a radio link.

Abbreviations BSS Base Station System BTS Base Transceiver Station C_ Control cc Call Control CN Core Network DL Downlink DRNC Drift Radio Network Controller ITU International Telecommunication Union kbps kilo-bits per second ksps kilo-symbols per second Ll Layer I (physical layer) L2 Layer 2 (data link layer) L3 Layer 3 (network layer) Mcps Mega-chips per second RLC Radio Link Control RNC Radio Network Controller RNS Radio Network Subsystem RNTI Radio Network Temporary Identity RRC Radio Resource Control SAP Service Access Point SRNC Serving Radio Network Controller SRNS Serving Radio Network Subsystem TFCI Transport Format Combination Indicator TF1 Transport Format Indicator TN Termination Node TRX Transmitter/Receiver U_ User- UE User Equipment UL Uplink UMTS Universal Mobile Telecommunications System URA UTRAN Registration Area UTRA UMTS Terrestrial Radio Access UTRAN UMTS Terrestrial Radio Access Network All features described herein can be independently provided unless otherwise stated; for example the signals and messages may be provided even if the switching is not implemented in a particular User Equipment, or for other purposes. The appended abstract is incorporated herein by reference.

Claims (29)

Claims:

1. A method of operating a mobile telecommunications system having a plurality of Radio Network Controllers (RNCs) comprising: during redirection of active communication with User Equipment from one Radio Network Controller (RNQ to another, employing an Acknowledged Transfer Mode (AM) for at least one predetermined class of traffic for which an Unacknowledged Transfer mode was employed prior to redirection.

2. A method according to Claim 1, further comprising taking a decision to redirect.

3. A method according to Claim 2, wherein switching into the Acknowledged mode is triggered following the decision.

4. A method of operating a telecommunications network or component thereof, the method comprising: in response to a decision to redirect active communication with User Equipment from one Radio Network Controller (RNQ to another, switching communication of at least one predetermined class of traffic from an Unacknowledged Transfer Mode (UAM) to an Acknowledged Transfer Mode (AM).

5. A method of operating a telecommunications network or component thereof, the method comprising: in response to a decision to redirect active communication with User Equipment from one Radio Network Controller (RNQ to another, determining whether at least one predetermined class of traffic which may be in either an Unacknowledged or Acknowledged mode is in an Acknowledged Transfer Mode (AM) and, if not, switching communication of said at least one predetermined class of traffic from an Unacknowledged Transfer Mode (UAM) to an Acknowledged Transfer Mode (AM).

6. A method according to any preceding claim further comprising signalling to the User Equipment that RNC Relocation is about to occur or is in progress.

7. A method according to any preceding claim, or Claim 20, further comprising signalling to the User Equipment that RNC Relocation has completed.

8. A method according to Claim 7, wherein said signalling comprises signalling an updated context to the User Equipment, identifying the new RNC.

9. A method of operating User Equipment in a mobile telecommunications network comprising determining that redirection of active communication from one Radio Network Controller to another is about to occur and, in response to the determination, switching a predetermined class of communication traffic from an Unacknowledged Transfer mode to an Acknowledged Transfer mode.

10 10. A method of operating User Equipment in a mobile telecommunications network comprising determining that redirection of active communication from one Radio Network Controller to another is about to occur and, in response to the determination, determining whether at least one predetermined class of traffic which may be in either an Unacknowledged or Acknowledged mode is in an Acknowledged Transfer Mode (AM) 15 and, if not, switching communication of said at least one predetermined class of traffic from an Unacknowledged Transfer Mode (UAM) to an Acknowledged Transfer Mode (AM).

11. A method according to Claim 9 or 10, comprising further determining that redirection is completed.

12. A method according to Claim 9, 10 or I I wherein said determining or said further determining is based on a received signal.

13. A method according to Claim 5 or 10, further comprising storing the transfer mode of said predetermined class of traffic prior to redirection.

14. A method according to any preceding claim, further comprising, following completion of redirection of communication, switching said predetermined class of traffic back to the transfer mode in place prior to said redirection.

15. A method according to any preceding claim wherein the User Equipment is arranged to signal acknowledgement of completion of redirection.

16. A method according to any preceding claim wherein said at least one predetermined class of traffic comprises critical control messages.

17. A method according to any preceding claim wherein said at least one predetermined class of traffic comprises user data.

18. A method according to any preceding claim wherein traffic on the uplink is 10 switched to an acknowledged mode.

19. A method according to Claim 18, wherein traffic on the downlink is also switched to an acknowledged mode.

20. A method of operating a telecommunications network or component thereof, the method comprising: following a decision to redirect active communication with User 115 Equipment from one Radio Network Controller (RNC) to another, signalling to the User Equipment that RNC Relocation is about to occur.

21. Apparatus for use in a mobile telecommunications system capable of communicating at least one class of traffic in either an Unacknowledged mode or an Acknowledged transfer mode, the apparatus comprising means for determining that 20 redirection of active communication from one Radio Network Controller to another is about to occur and, in response to the determination, switching a predetermined class of communication traffic from an Unacknowledged Transfer mode to an Acknowledged Transfer mode.

22. Apparatus for use in a mobile telecommunications system capable of communicating at least one class of traffic in either an Unacknowledged mode or an Acknowledged transfer mode, the apparatus comprising means for determining that redirection of active communication from one Radio Network Controller to another is about to occur and, in response to the determination, determining whether at least one predetermined class of traffic which may be in either an Unacknowledged or Acknowledged mode is in an Acknowledged Transfer Mode (AM) and, if not, switching communication of said at least one predetermined class of traffic from an Unacknowledged Transfer Mode (UAM) to an Acknowledged Transfer Mode (AM).

23. Apparatus according to Claim 21 or 22, including means for receiving and interpreting a signal signifying that redirection is about to occur.

24. Apparatus according to Claim 21, 22 or 23 further comprising means for switching said traffic back to the transfer mode in place prior to said redirection.

25. Apparatus according to any of Claims 21 to 24 comprising User Equipment for a UMTS mobile telecommunications system.

26. A signal in a mobile telecommunications system directed to User Equipment and signifying that relocation between Radio Network Controllers is imminent.

27. A method substantially as any one herein described, with reference to the accompanying drawing.

28. Apparatus substantially as herein described, with reference to the accompanying drawing.

29. A signal substantially as any one herein described, with reference to the accompanying drawing.