CA2467292A1 - Method and apparatus for providing immediate ciphering after an inter-system utran-gsm handover - Google Patents

Method and apparatus for providing immediate ciphering after an inter-system utran-gsm handover Download PDF

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Publication number
CA2467292A1
CA2467292A1 CA002467292A CA2467292A CA2467292A1 CA 2467292 A1 CA2467292 A1 CA 2467292A1 CA 002467292 A CA002467292 A CA 002467292A CA 2467292 A CA2467292 A CA 2467292A CA 2467292 A1 CA2467292 A1 CA 2467292A1
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Prior art keywords
handover
command
utran
ciphering
gsm
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CA002467292A
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French (fr)
Inventor
Juha T. Timonen
Pasi P. Laitinen
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Nokia Oyj
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Individual
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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/0005Control or signalling for completing the hand-off
    • H04W36/0011Control or signalling for completing the hand-off for data sessions of end-to-end connection
    • H04W36/0033Control or signalling for completing the hand-off for data sessions of end-to-end connection with transfer of context information
    • H04W36/0038Control or signalling for completing the hand-off for data sessions of end-to-end connection with transfer of context information of security context information
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W12/00Security arrangements; Authentication; Protecting privacy or anonymity
    • H04W12/03Protecting confidentiality, e.g. by encryption
    • H04W12/033Protecting confidentiality, e.g. by encryption of the user plane, e.g. user's traffic
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/14Reselecting a network or an air interface
    • H04W36/144Reselecting a network or an air interface over a different radio air interface technology
    • H04W36/1443Reselecting a network or an air interface over a different radio air interface technology between licensed networks
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/14Reselecting a network or an air interface

Abstract

Disclosed is a method for performing an inter-system handover (Fig. 4). The method triggers the handover of a mobile station (100) from a UTRAN system t o a GSM system by sending a HANDOVER FROM UTRAN COMMAND message from the UTRAN system. For the case where a HANDOVER COMMAND is sent transparently with the HANDOVER FROM UTRAN COMMAND, where the HANDOVER COMMAND has an information element set for indicating that ciphering is to be started, the method begin s data ciphering immediately after handing over to the GSM system such that th e first data frame transmitted by the mobile station in the GSM system is a ciphered data frame. For the case where there is a pre-existing UTRAN system ciphered data connection when the HANDOVER FROM UTRAN COMMAND message is received, the method continues without interruption the use of data cipherin g with the data connection after handing over to the GSM system.

Description

METHOD AND APPARATUS FOR PROVIDING IMMEDIATE CIPHERING
AFTER AN INTER-SYSTEM UTRAN-GSM HANDOVER
TECHNICAL FIELD:
' These teachings relate generally to wireless communications systems and methods and, more specifically, relate to cellular wireless communications systems and to techniques for a mobile station (MS), also referred to herein as user equipment (UE), to transition from one cell to another.
to BACKGROUND:
The following abbreviations are herewith defined, at least some of which are referred to in the ensuing description of the prior art and the preferred embodiments.
3GPP Third Generation Partnership Project BSC Base Station Controller BSS Base Station System BTS Base Transceiver Station 2o CN Core Network CRS Cell Re-Selection CS Cellular System DL Down Link (to the MS) EDGE Enhanced Data rate for Global Evolution EGPRS Enhanced General Packet Radio Service GERAN GSM/EDGE Radio Access Network GPRS General Packet Radio Service GMM GPRS Mobility Management GSM Global System for Mobile Communications 3o GSN GPRS Support Node HO Handover IE Information Element MAC Medium Access Control MS Mobile Station, also referred to herein as User Equipment (UE) MSC Mobile Switching Center RLC Radio Link Control RNC Radio Network Controller RR Radio Resources RRC Radio Resource Control SGSN Serving GPRS Support Node TBF Temporary Block Flow UL Uplink (from the MS) UMTS Universal Mobile Telecommunications System URA User (or UTRAN) Registration Area 1o UTRAN Universal Terrestrial Radio Network Reference can also be made to 3GPP TR 21.905, V4.4.0 (2001-10), Third Generation Partnership Project; Technical Specification Group Services and System Aspects;
Vocabulary for 3GPP Specifications (Release 4), as well as to ETSI TR 101748, V8Ø0 (2000-OS), Digital cellular telecommunications system (Phase 2+);
Abbreviations and acronyms (GSM 01.04 version 8Ø0 release 1999).
By way of introduction, reference is made to Fig. 1 for the ensuing description of a conventional inter-system handover from UTRAN to GSM. The UE 1 receives the GSM
2o neighbor cell parameters from the RNC of the UTRAN 3 either in a SYSTEM
INFORMATION BLOCK or in a MEASUREMENT CONTROL message. These parameters are required in order to be able to measure candidate GSM cells.
Based on the measurement report from the UE 1, including GSM measurements, the RNC of the UTRAN 3 makes a handover decision. After resources have been reserved from the GSM
BSS 2, via MSC 4, the RNC 3 sends an Inter-System Handover Command message (now also referred to as a HANDOVER FROM UTRAN COMMAND, as shown in Fig. 2), that also carnes an embedded HANDOVER COMMAND of the GSM system. At this point, the GSM RR protocol in the UE 1 takes control and sends a GSM-specific HANDOVER ACCESS message to the GSM BSC. After a successful completion of the 3o handover procedure, the GSM BSS 2 initiates resource release from the UTRAN
3. In response, the UTRAN 3 releases the radio connection and removes all context information for the UE 1.

Referring to Fig. 2, a more detailed description of the inter-system UTRAN to GSM
handover is now provided, as specified in 3GPP TS 25.303, chapter 6.4.11. For CS
domain services the UTRAN to GSM inter-RAT Handover procedure is based on measurement reports from the UE 1, but initiated from the UTRAN 3. A HANDOVER
FROM UTRAN COMMAND is sent using acknowledged data transfer on the Dedicated Control Channel (DCCH). The UE transition from the UTRAN Connected Mode starts when the HANDOVER FROM UTRAN COMMAND is received. The transition to the GSM Dedicated mode, which may also be referred to as the GSM Connected mode, is finished when the HANDOVER COMPLETE message is sent from the UE 1.
The UTRAN 3 sends a RELOCATION REQUIRED to the CN/AS. This message contains information needed for the GSM system to be able to perform a handover (e.g.
serving cell, target cell). Some parts of this information (e.g., MS
classmark) are obtained at the setup of the RRC Connection and are stored in the CN.
The CN/AS sends a HANDOVER REQUEST message to BSC-RR 2 allocating the necessary resources to be able to receive the GSM UE 1, and acknowledges this by sending HANDOVER REQUEST ACKNOWLEDGE to the CN/AS. The HANDOVER
REQUEST ACKNOWLEDGE contains a GSM-RR message (HANDOVER
COMMAND) with all radio-related information that the UE 1 requires for the handover.
The CN/AS then sends a RELOCATION COMMAND (type UTRAN-to-BSS HARD
HANDOVER) to the UTRAN 3 to start the execution of the handover. This message contains a GSM-RR message (HANDOVER COMMAND) with all the information needed for the UE 1 to be able to switch to the GSM cell and perform a handover to GSM.
Upon receipt of the HANDOVER FROM UTRAN COMMAND message in the UE l, the UE-RRC entity forwards the GSM-RR message (HANDOVER COMMAND) to the MS-RR entity. To release the UTRAN resources the MS-RR entity requests the UE-RRC
entity to release the RRC connection locally. The UE-RRC entity then locally releases the resources on the RLC, MAC and physical layers of the UE 1.
After having switched to the assigned GSM channel received in the HANDOVER
FROM UTRAN COMMAND, the GSM MS sends HANDOVER ACCESS in successive layer 1 frames, just as it typically would have done for a conventional GSM
handover initiation.
When the BSC-RR 3 has received the HANDOVER ACCESS it indicates this to the CN/AS by sending a HANDOVER DETECT message. The BSC-RR sends a PHYSICAL INFORMATION message to the GSM MS in unacknowledged mode that contains various fields of physical layer -related information allowing a proper to transmission by the MS.
After layer 1 and 2 connections are successfully established, the GSM MS
returns the HANDOVER COMPLETE message. The CN/AS is then able to release the UTRAN
resources that were used for the UE 1 in the UTRAN Connected Mode. The CN/AS
send an IU RELEASE COMMAND to the UTRAN, after which UTRAN can release all network resources from the RLC, MAC and the physical layer. When the release operation is complete, a ICT RELEASE COMPLETE message is sent to the CN/AS.
The 3GPP 33.102 specification introduces the UMTS security context. The UMTS
2o security context is used in the Release 1999 (R99) and later UMTS and GSM
system releases. Chapter 4.3.2.a of 3GPP 24.008 describes a technique whereby ciphering keys for both GSM and UMTS systems are calculated during authentication.
Authentication in the UMTS system guarantees the presence of ciphering keys for both systems.
The inter-system handover (HO) between two cellular systems is described in 25.331, 04.18 and 05.08 specifications, and in 3GPP 25.303, chapter 6.4.11, Inter-RAT
Handover: UTRAN to GSM/BSS, CS domain services. The GSM-RR message that is discussed in the specification 3GPP 04.18, chapter 9.1.15 is the HANDOVER
COMMAND . This command is delivered within the HANDOVER FROM UTRAN
COMMAND, as is discussed in 3GPP 25.331, chapter 10.2.15.
In the UMTS to GSM inter-system handover the radio system changes from the UMTS
radio system to the GSM radio system while an already established user data connection or link, such as a voice data or a circuit-switched data connection, continues after the handover. During this type of inter-system handover it is important that data ciphering or encryption continues uninterrupted in order to guarantee the security goals of 3GPP
33.102. In order for this to occur the GSM ciphering must begin immediately with the 5 first transmitted data frame when handing over to the GSM system. However, the inventors have realized that the specification 3GPP 04.18, as currently written, makes it impossible to immediately initiate the use of GSM ciphering during an inter-system handover to the GSM system.
More specifically, 3GPP 04.18, chapter 3.4.4.1, states in part:
Optionally a cipher mode setting. In that case, this ciphering mode has to be applied on the new channel. If no such information is present, the ciphering mode is the same as on the previous channel. In either case the ciphering key shall not be changed. The HANDOVER COMMAND
message shall not contain a cipher mode setting IE that indicates "start ciphering" unless a CIPHERING MODE COMMAND message has been transmitted previously in this instance of the dedicated mode: if such a HANDOVER COMMAND message is received it shall be regarded as erroneous, a HANDOVER FAILURE message with cause "Protocol error unspecified" shall be returned immediately, and no further action taken.
In the case of UTRAN to GSM handover, the HANDOVER COMMAND
message, which is sent transparently via RNC from BSS to the mobile station, shall always contain the cipher mode setting IE. In the case of CDMA2000 to GSM handover, the HANDOVER COMMAND message, which is sent transparently via RNC from BSS to the mobile station, shall always contain the cipher mode setting IE.
That is, the GSM system does not permit the use of ciphering without first receiving a 3o CIPHERING MODE COMMAND. However, the CIPHERING MODE COMMAND
cannot be sent before the HANDOVER COMMAND, as no GSM connection yet exists.
Stated another way, in the case where there is an inter-system handover from UTRAN
to GSM, it is not possible to send any commands before the HANDOVER COMMAND, as no GSM connection exists prior to the HANDOVER COMMAND. This being the case, ciphering cannot continue in an uninterrupted fashion during the inter-system handover to GSM, and the potential thus exists for a third party to receive a voice or data transmission that is being sent unciphered.
It is noted that it is possible to send other commands within the UTRAN
specific messages. At first glance it might appear that one could readily send both the CIPHERING MODE COMMAND and the HANDOVER COMMAND transparently.
However, this would be a complex approach, and would also require that a significant amount of changes be made to the specification and to the network.
It should further be noted that the current specification states that in case of a UTRAN
to GSM handover the HANDOVER COMMAND shall always contain the cipher mode setting IE, but at the same time it is said that IE shall not contain a "start ciphering"
indication.
SUMMARY OF THE PREFERRED EMBODIMENTS
The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings.
Disclosed is a mobile station and a mobile station executed method for handing over from a current system to a target system. The method includes triggering the handover of the mobile station from the current system to the target system by receiving a current system-specific handover command from the current system, where the target system is one that requires the mobile station to initiate the use of data ciphering only in response to receiving a specific command from the target system to initiate the use of data ciphering. A further step starts the use of data ciphering after handing over to the target system in response to receiving a target system-specific handover command that was sent transparently to the mobile station with the current system-specific handover command, where the target system-specific handover command has an information element set for indicating that ciphering is to be started. In the preferred embodiment the current system-specific handover command is a HANDOVER FROM UTRAN COMMAND, and the target system-specific handover command is a HANDOVER COMMAND with a cipher mode settings IE that indicates "start ciphering".
Stated another way, what is disclosed is a method for performing an inter-system handover. The method triggers the handover of the mobile station from a UTRAN
system to a GSM system by sending a HANDOVER FROM UTRAN COMMAND message from the UTRAN system and, for the case where a HANDOVER COMMAND is sent transparently with the HANDOVER FROM UTRAN COMMAND, where the HANDOVER COMMAND has a cipher mode settings information element set for indicating that ciphering is to be started, beginning data ciphering immediately after handing over to the GSM system such that the first data frame transmitted by the mobile station in the GSM system is a ciphered data frame. For the case where there is a pre-existing UTRAN system ciphered data connection when the HANDOVER FROM
UTRAN COMMAND message is received, continuing without interruption the use of data ciphering with the data connection after handing over to the GSM system.
The use of the teachings of this invention does not require any modifications to be made to the presently specified HANDOVER COMMAND, and thus has a minimal impact on 2o already defined messaging and signaling formats and protocols.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein:
Fig. 1 is simplified process flow diagram for an inter-system UTRAN to GSM
handover;
Figs. 2A, 2B and 2C, collectively referred to as Fig. 2, are a more detailed process flow diagram of the inter-system UTRAN to GSM handover;
Fig. 3 is a simplified block diagram of an embodiment of a wireless communications system that is suitable for practicing this invention; and Fig. 4 is a logic flow diagram that is descriptive of a method in accordance with this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Refernng to Fig. 3, there is illustrated a simplified block diagram of an embodiment of a wireless communications system 5 that is suitable for practicing this invention. The 1o wireless communications system 5 includes at least one mobile station (MS) 100, also referred to herein as User Equipment (UE). Fig. 3 also shows an exemplary network operator having, for example, a Serving GPRS Support Node (SGSN) 30 for connecting to a telecommunications network, such as a Public Packet Data Network or PDN, at least one base station controller (BSC) 40, and a plurality of base transceiver stations (BTS) 50 that transmit in a forward or downlink direction both physical and logical channels to the mobile station 100 in accordance with a predetermined air interface standard. A
reverse or uplink communication path also exists from the mobile station 100 to the network operator, which conveys mobile originated access requests and traffic.
The air interface standard can may enable both voice and data traffic, such as data traffic enabling Internet 70 access and web page downloads.
Each BTS 50 supports a cell, such as a serving cell that is currently servicing the MS
100, and at least one neighbor cell. In this exemplary system the BSC 40 and BTSs 50 are assumed to be associated with a UTRAN cellular system, while a second BSC

and at least one BTS 50A are assumed to be associated with a GSM cellular system. As such, a handover from the BTS 50 and BSC 40 to the BTS SOA and BSC 40A is an inter-system UTRAN to GSM handover.
The network operator may also include a suitable type of Message Center (MC) 60 that 3o receives and forwards messages for the mobile stations 100. Other types of messaging service may include Supplementary Data Services and possibly Multimedia Messaging Service (MMS), wherein image messages, video messages, audio messages, text messages, executables and the like, and combinations thereof, can be transferred between the network and the mobile station 100.
The mobile station 100 may be a handheld radiotelephone, such as a cellular telephone or a personal communicator. The mobile station 100 could also be contained within a card or module that is connected during use to another device. For example, the mobile station 10 could be contained within a PCMCIA or similar type of card or module that is installed during use within a portable data processor, such as a laptop or notebook computer, or even a computer that is wearable by the user.
The user equipment or mobile station 100 typically includes a data processor such as a microcontrol unit (MCU) 120 having an output coupled to an input of a display 140 and an input coupled to an output of a keyboard or keypad 160. The MCU 120 is assumed to include or be coupled to some type of a memory 130, including a read-only memory (ROM) for storing an operating program, as well as a random access memory (RAM) for temporarily storing required data, scratchpad memory, received packet data, packet data to be transmitted, and the like. A separate, removable SIM (not shown) can be provided as well, the SIM storing, for example, a preferred Public Land Mobile Network (PLMN) list and other subscriber-related information. The ROM is assumed, for the purposes of this invention, to store a program enabling the MCU 120 to execute the software routines, layers and protocols required to implement the inter-system UTRAN to GSM
handover, and related methods, in accordance with these teachings.
The ROM of the MS 100 also typically stores a program that provides a suitable user interface (IJn, via display 140 and keypad 160. Although not shown, a microphone and speaker are typically provided for enabling the user to conduct voice calls in a conventional manner.
The mobile station 100 also contains a wireless section that includes a digital signal processor (DSP) 180, or equivalent high speed processor or logic, as well as a wireless 3o transceiver that includes a transmitter 200 and a receiver 220, both of which are coupled to an antenna 240 for communication with the network operator. At least one local oscillator (LO) 260, such as a frequency synthesizer, is provided for tuning the transceiver. Data, such as digitized voice and packet data, is transmitted and received through the antenna 240.
The ROM of the MS 100 is assumed to store a program that enables the MS 100 to receive and process a HANDOVER FROM UTRAN COMMAND message, as defined 5 in 3GPP TS 25.331, v4.2.0, chapter 10.2.15. This message includes a number of information elements (IEs), shown in the following Table, and is used for handover of the MS 100 from UMTS to another system, such as to a GSM system. One or several messages from the other system can be included within the Inter-RAT message information element in this message. Note, for example, that one or a plurality of GSM
10 messages can be embedded into this message, as could cdma2000 messages if handing off to a cdma2000 system. The other-system message or messages are structured and coded according to that systems' specification.
Information Element/GroupNeed MultiType and Semantics description I name reference S

Message Type MP Message Type UE information elements RRC transaction MP RRC transaction identifier identifier 10.3.3.36 Integrity check CH Integrity info check info 10.3.3.16 Activation time MD Activation Default value time is "now"

10.3.3.1 1RB information elements RAB information OP 1 For each ItAB
list to to be <max handed over.
In this ltABs version, the maximum etup> size of the list of 1 shall be applied for all system es.

>ItAB info MP RAB info 10.3.4.8 Other information elements CHOICE System type MP This IE indicates which specification to apply, to decode the transported messa es >GSM

Frequency band MP Enumerated (GSM/DCS

band used), band used) GSM message 30 >Single GSM messageMP Bit string Formatted and (no coded explicit according to size GSM

constraint) specifications The first bit of the bit string contains the first bit of the GSM messa e.

>GSM message List MP l.to.<Bit string Formatted and (1..512) coded maxln according to GSM

terSys specifications.
The first Messa bit of the bit string ges> contains the first bit of the GSM messa e.

>cdma2000 cdma2000MessageListMP l.to.<

maxln l terSys Messa es>

>MSG_TYPE(s) MP Bit string Formatted and (8) coded according to cdma2000 specifications.
The MSG TYPE bits are numbered b0 to b7, where b0 is the least si ificant bit.

35 >cdma2000Messagepayload(s)MP Bit string Formatted and (1..512) coded according to cdma2000 specifications.
The first bit of the bit string contains the first bit of the cdma2000 messa e.

In accordance with the teachings of this invention, an exception is added to the currently specified procedure of 3GPP 04.18 to enable the MS 100 to immediatelybegin ciphering, when entering the GSM connected mode after handing over from a UTRAN system, 4o without first having to receive a CIPHERING MODE COMMAND.
The preferred implementation of this invention is to change the above quoted 04.18, chapter 3.4.4.1, so that it reads, in part (or can be interpreted to mean that):
The HANDOVER COMMAND message shall not contain a cipher mode setting IE that indicates "start ciphering" unless a CIPHERING MODE
COMMAND message has been transmitted previously in this instance of the dedicated mode, or unless the HANDOVER COMMAND message is sent transparently via RNC from BSS to the mobile station (emphasis added).
As employed herein, the phrase "unless the HANDOVER COMMAND message is sent transparently" means that the GSM-specific HANDOVER COMMAND is sent from the to BSC-RR entity to the UE-RR entity encapsulated within the UTRAN/LJMTS-specific command (HANDOVER FROM UTRAN COMMAND). By so encapsulating the GSM
specific command the UTRAN network elements that handle the UTRAN/LTMTS
specific command need not handle or understand the encapsulated GSM-specific command, i.e., the GSM-specific command is "transparent" from the perspective of the UTRAN network.
The wireless network is assumed to include a suitable controller or control elements) for causing the HANDOVER COMMAND message to be sent transparently to the mobile station 100, with the IE set for indicating "start ciphering".
In accordance with the conventional procedure discussed above, the HANDOVER
COMMAND received with the cipher mode settings IE that indicated "start ciphering"
would have been treated as an error condition and ignored. The teachings of this invention overcome this problem by recognizing the reception of the HANDOVER
COMMAND with the cipher mode settings IE that indicate "start ciphering", that is sent transparently with the UTRAN specific message, as a special case wherein the cipher mode settings IE that indicate "start ciphering" are to be interpreted and acted upon.
Referring to Fig. 4, at Step A it is assumed that the MS 100 is in the process of executing 3o an inter-system handover. In the preferred embodiment the inter-system handover is a UTRAN to GSM handover, but in other embodiments of this invention other types of system handovers could occur, so long as the system being handed over to is one that does not permit the use of ciphering without the MS 100 receiving a command that expressly instructs the MS 100 to begin the use of ciphering.
At Step B a determination is made if the HANDOVER COMMAND has been received transparently, as described above. Assuming that it has, at Step C a determination is made if the transparently received HANDOVER COMMAND has an IE that indicates that ciphering should be started. If it does, control passes to Step D to start ciphering, and then to Step E to terminate the HANDOVER COMMAND processing, else control passes from Step C to Step E to terminate the HANDOVER COMMAND processing.
1o The tests made at Steps B and C can be made by the MCU 120 checking the state of appropriate software flags stored in a register or in the memory 130.
The end result is that ciphering may be started whether or not ciphering was in effect when the inter-system handover was initiated. If ciphering was already in effect, as will typically be the case in the UTRAN system, then ciphering continues without interruption in the GSM system when performing the inter-system handover. If ciphering was not in effect in the UTRAN system, then it can be started immediately in the GSM
system after the handover by programming the cipher mode setting IE
appropriately in the GSM-specific HANDOVER COMMAND message that is sent transparently to the 2o MS 100.
While described in the context of various specific messages a functions, those having skill in the art should appreciate that the teachings of this invention are not intended to be limited to only the presently preferred embodiments. The foregoing method is applicable to a number of wireless networks that allow user mobility, as well as an ability for the user to transition between different types of systems. The disclosed method clearly improves the UTRAN to GSM inter-system handover procedure by preserving the immediate use of ciphering after the handover, as well as conserving network resources by not requiring that additional messages be sent. While the disclosed method 3o is especially applicable for the UTRAN to GSM handover situation, it is not limited for use with only these network types.

Claims (12)

What is claimed is:
1. A mobile station executed method for handing over from a current system to a target system, comprising:
triggering the handover of the mobile station from the current system to the target system by receiving a current system-specific handover command from the current system, where the target system is one that requires the mobile station to initiate the use of ciphering only in response to receiving a specific command from the target system to initiate the use of ciphering; and starting the use of ciphering after handing over to the target system in response to receiving a target system-specific handover command that is sent transparently with the current system-specific handover command, where the target system-specific handover command has an information element set for indicating that ciphering is to be started.
2. A method as in claim 1, wherein the target system is a GSM system.
3. A method as in claim 1, wherein the current system is a UTRAN system.
4. A method as in claim 1, wherein the current system-specific handover command is a HANDOVER FROM UTRAN COMMAND, and where the target system-specific handover command is a HANDOVER COMMAND with a cipher mode settings information element that indicates "start ciphering".
5. A mobile station operable for being handed over from a current system to a target system, comprising an RF transceiver coupled to a data processor, said data processor being responsive to a receipt through said RF transceiver of a current system-specific handover command from the current system for triggering the handover of the mobile station from the current system to the target system, where the target system is one that requires the mobile station to initiate the use of ciphering only in response to receiving a specific command from the target system to initiate the use of ciphering, said data processor operating to immediately start the use of ciphering after handing over to the target system in response to receiving a target system-specific handover command that is sent transparently with the current system-specific handover command, where the target system-specific handover command has an information element set for indicating that ciphering is to be started.
6. A mobile station as in claim 5, wherein the target system is a GSM system.
7. A mobile station as in claim 5, wherein the current system is a UTRAN
system.
8. A mobile station as in claim S, wherein the current system-specific handover command is a HANDOVER FROM UTRAN COMMAND, and where the target system-specific handover command is a HANDOVER COMMAND with a cipher mode settings information element that indicates "start ciphering".
9. A method for performing an inter-system handover, comprising:
triggering the handover of the mobile station from a UTRAN system to a GSM
system by sending a HANDOVER FROM UTRAN COMMAND message from the UTRAN system; and for the case where a HANDOVER COMMAND is sent transparently with the HANDOVER FROM UTRAN COMMAND, where the HANDOVER
COMMAND has an information element set for indicating that ciphering is to be started, beginning ciphering immediately after handing over to the GSM system such that a first data frame transmitted by the mobile station in the GSM
system is a ciphered data frame.
10. A method as in claim 9, where for the case where there is a pre-existing UTRAN
system ciphered connection when the HANDOVER FROM UTRAN COMMAND
message is received, continuing without interruption the use of ciphering with the connection after handing over to the GSM system.
11. A wireless mobile communications system operable for performing an inter-system handover, comprising:
wireless network means for triggering the handover of a mobile station from a UTRAN system to a GSM system by sending a predetermined command message from the UTRAN system, the predetermined command comprising a HANDOVER FROM UTRAN COMMAND message with a HANDOVER
COMMAND that is sent transparently with the HANDOVER FROM UTRAN
COMMAND, the HANDOVER COMMAND comprising an information element set for indicating that ciphering is to begin; and mobile station means, responsive to a receipt of the predetermined command, for beginning ciphering immediately after handing over to the GSM system.
12. A system as in claim 11, where for the case where there is a pre-existing UTRAN
system ciphered connection when the HANDOVER FROM UTRAN COMMAND
message is received, continuing without interruption the use of ciphering with the connection after handing over to the GSM system.
CA002467292A 2001-11-15 2002-10-17 Method and apparatus for providing immediate ciphering after an inter-system utran-gsm handover Abandoned CA2467292A1 (en)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US33651001P 2001-11-15 2001-11-15
US60/336,510 2001-11-15
US10/241,276 2002-09-10
US10/241,276 US6643513B2 (en) 2001-11-15 2002-09-10 Method and apparatus for providing immediate ciphering after an inter-system UTRAN-GSM handover
PCT/IB2002/004286 WO2003043355A1 (en) 2001-11-15 2002-10-17 Method and apparatus for providing immediate ciphering after an inter-system utran-gsm handover

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