Abstract:
A method and apparatus for session continuity using pre-registration tunneling procedure are disclosed. For session continuity, a tunnel is established between a multi-mode wireless transmit/receive unit (WTRU) and a core network of a target system via a source system while the WTRU is still connected with the source system. An access procedure is performed toward the target system using the tunnel. A handover is the performed from the source system to the target system once the access procedure is complete. The access procedure includes session initiation protocol (SIP) registration, authentication of the WTRU at the target system, and internet protocol (IP) configuration. The handover may be from a third generation partnership project (3GPP) system to a non-3GPP system, or vice versa.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/169,751, filed Jul. 9, 2008; which claims the benefit of U.S. Provisional Patent Application Nos. 60/948,587, filed Jul. 9, 2007, and 60/949,085, filed Jul. 11, 2007, the contents of which are hereby incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present application is related to wireless communication systems. 
       BACKGROUND 
       [0003]    A dual-mode or multi-mode wireless transmit/receive unit has dual or multiple radio transceivers, each designed to communicate on a particular radio access technology (RAT), such as 3rd Generation Partnership Project (3GPP) and non-3GPP systems. The handover process between 3GPP and non-3GPP systems may be slow due to the nature of the system configurations and operations. One problem occurs when a WTRU moves from one system to another as the WTRU is required to register and authenticate in the other system. A similar problem exists for session initiation protocol (SIP)-based Session Continuity processes between 3GPP and non-3GPP systems. When moving from one system to the other, the WTRU is required to register and authenticate in the other system before registering with internet protocol (IP) multimedia subsystem (IMS). 
         [0004]    Another problem may occur due to the 3GPP prohibition against simultaneous radio transceiver operation. A single WTRU cannot have a 3GPP radio transceiver and a non-3GPP radio transceiver active at the same time. In such cases, dual-mode or multi-mode radio transceivers need sophisticated control of the radio switching. 
       SUMMARY 
       [0005]    The present invention is related to a method and apparatus for session continuity using pre-registration tunneling procedure. For session continuity, a tunnel is established between a wireless transmit/receive unit (WTRU) and a core network of a target system via a source system while the WTRU is still connected with the source system. An access procedure is performed toward the target system using the tunnel. A handover is performed from the source system to the target system once the access procedure is complete. For session initiation protocol (SIP) based handover, the access procedure includes SIP registration, authentication of the WTRU at the target system, and internet protocol (IP) configuration. The handover may be from a third generation partnership project (3GPP) system to a non-3GPP system, or vice versa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0007]      FIG. 1  shows a block diagram of dual protocol stack configuration in a dual mode wireless transmit/receive unit (WTRU) in accordance with a first embodiment; 
           [0008]      FIG. 2  shows a block diagram of a dual protocol stack configuration in a dual mode WTRU supporting pre-registration SIP-based session continuity in accordance with a second embodiment; 
           [0009]      FIGS. 3A and 3B  show a signal diagram of a pre-registration procedure for a 3GPP to non-3GPP handover in accordance with the first embodiment; 
           [0010]      FIGS. 4A and 4B  show a signal diagram of a pre-registration procedure for a non-3GPP to 3GPP handover in accordance with the first embodiment; 
           [0011]      FIGS. 5A ,  5 B and  5 C show a signaling diagram of pre-registration procedures for 3GPP to non-3GPP handover in accordance with the second embodiment; 
           [0012]      FIGS. 6A ,  6 B and  6 C show a signaling diagram of pre-registration procedures for non-3GPP to 3GPP handover in accordance with the second embodiment; 
           [0013]      FIG. 7  shows dual stack operation in a multi-mode WTRU supporting pre-registration SIP-based session continuity for 3GPP to non-3GPP handover in accordance with the second embodiment; and 
           [0014]      FIG. 8  shows dual stack operation in a multi-mode WTRU supporting pre-registration SIP-based session continuity for non-3GPP to 3GPP handover in accordance with the second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    When referred to hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to a Node-B, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. 
         [0016]    By way of reference, as a WTRU moves from a system A to a system B, system A is defined as the handover source and system B is defined as the handover target. One mechanism to speed access procedures to a target system is to allow pre-registration and pre-authentication procedures to be performed by upper layers in a WTRU via the source system. The source system may identify the target system, establish a tunnel between the WTRU and the core target network, (e.g., Autonomous Registration (AR) or Access, Authentication and Accounting (AAA)), and instruct the WTRU to start access procedures for the target network. Upon successful completion of the access procedure, the source network may instruct the WTRU to switch, or handover, to the target network and turn off the radio connected to the source network. 
         [0017]      FIG. 1  is a block diagram of dual protocol layer stack in a dual mode WTRU  101  supporting pre-registration tunneling in accordance with a first embodiment. As shown in  FIG. 1 , the WTRU  101  includes a non-3GPP protocol layer stack comprising an application layer  110 , a mobility management (MM) layer  111 , a radio resource control (RRC) and media access control (MAC) layer  112 , and a physical (PHY) layer  113 . The application layer  110  is coupled to the MM layer  111  by path  115 . The MM layer  111  is coupled to the RRC/MAC layer  112  by path  116 . Path  117  couples the RRC/MAC layer  112  to the PHY layer  113 . Similarly, a 3GPP protocol layer stack comprises an application layer  120 , a multimedia (MM) layer  121 , a radio resource control (RRC) and media access control (MAC) layer  122 , and a physical (PHY) layer  123 . The application layer  120  is coupled to the MM layer  121  by path  125 . The MM layer  121  is coupled to the RRC/MAC layer  122  by path  126 . Path  127  couples the RRC/MAC layer  122  to the PHY layer  123 . 
         [0018]    The dual protocol layer stack is further configured to include a path  141 , which cross connects the non-3GPP PHY layer  113  to the 3GPP RRC/MAC layer  122 . A path  131  couples the 3GPP PHY layer  123  to the non-3GPP RRC/MAC layer  112 . These paths  131  and  141  are used to establish tunneling between 3GPP and non-3GPP systems to facilitate 3GPP to non-3GPP handover. A controller  151  controls the signaling for handover and access procedures executed at the protocol stack layers shown in  FIG. 1 . 
         [0019]      FIG. 2  is a block diagram of dual protocol layer stack in a dual mode WTRU  201  supporting pre-registration tunneling in accordance with a second embodiment. As shown in  FIG. 2 , the WTRU  201  includes a non-3GPP protocol layer stack comprising an application layer  210 , a session management (SM) and mobility management (MM) layer  211 , a radio resource control (RRC) and media access control (MAC) layer  212 , and a physical (PHY) layer  213 . The application layer  210  is coupled to the SM and MM layer  211  by path  215 . The SM and MM layer  211  is coupled to the RRC/MAC layer  212  by path  216 . Path  217  couples the RRC/MAC layer  212  to the PHY layer  213 . Similarly, a 3GPP protocol layer stack comprises an application layer  220 , a SM and MM layer  221 , a radio resource control (RRC) and media access control (MAC) layer  222 , and a physical (PHY) layer  223 . The application layer  220  is coupled to the SM and MM layer  221  by path  225 . The SM and MM layer  221  is coupled to the RRC/MAC layer  222  by path  226 . Path  227  couples the RRC/MAC layer  222  to the PHY layer  223 . 
         [0020]    The dual protocol layer stack is further configured to include a path  241 , which cross connects the non-3GPP PHY layer  213  to the 3GPP RRC/MAC layer  222 . A path  231  couples the 3GPP PHY layer  223  to the non-3GPP RRC/MAC layer  212 . These paths  231  and  241  are used to establish tunneling between 3GPP and non-3GPP systems to facilitate 3GPP to non-3GPP handover. A controller  251  controls the signaling for handover and access procedures executed at the protocol stack layers shown in  FIG. 2 . 
         [0021]      FIGS. 3A and 3B  show a signal diagram for pre-registration procedure for a handover of a WTRU  301  from a 3GPP handover source  304  to a non-3GPP handover target  305 . A WTRU  301  includes a 3GPP radio transceiver  302  and a non-3GPP radio transceiver  303  for communication with a 3GPP core network (CN)  304  and a non-3GPP CN  305 . For simplicity, a dual mode WTRU  301  is shown, however the signaling described herein is valid for a multi-mode WTRU having multiple 3GPP and non-3GPP radio transceivers. While shown as direct signals from the WTRU  301  and CNs  303 ,  304 , the signals may be relayed by a NodeB or a base station entity (not shown). 
         [0022]    The pre-registration begins with the 3GPP transceiver  302  receiving a 3GPP and non-3GPP measurement list  311  from 3GPP CN  304 . The measurement list  311  identifies the channel frequencies of candidate handover targets. At  312 , the WTRU  301  stores the list in an internal memory, and for periodically initiating channel measurements. The 3GPP transceiver  302  sends an initialization signal  313  to the non-3GPP transceiver  303 , along with a list of candidate non-3GPP handover targets  314 . At  315 , the non-3GPP transceiver  303  is activated for a period in order to perform measurement procedures, in which it monitors channels and performs measurements. The non-3GPP transceiver  303  sends measurement reports  316  of the monitored channels to the 3GPP transceiver  302 . When measurement procedures by the non-3GPP transceiver  303  are completed, it may be deactivated. 
         [0023]    At  317 , the 3GPP transceiver  302  combines the measurements it made with those made by the non-3GPP transceiver  303 , formulates combined measurement reports, and transmits the combined measurement reports to the 3GPP CN  304 . At  318 , the 3GPP CN  304  examines the combined measurement reports and handover (HO) criteria, and selects a handover target system for the WTRU  301 . The 3GPP CN  304  sends a signal  319  to the target non-3GPP CN  305  to initiate a handover direct tunnel, and the target non-3GPP CN  305  responds with a tunnel establishment acknowledgment signal  320 . The 3GPP CN  304  sends a signal  321  to the 3GPP transceiver  302  to initiate a handover direct tunnel. This signal  321  may include a non-3GPP tunnel endpoint identification (TEID). The 3GPP transceiver  302  sends the target ID  322  to the non-3GPP transceiver  303 . The non-3GPP transceiver sends its handover direct tunnel acknowledgment (ACK)  323  to the 3GPP transceiver  302 , which is then forwarded to the 3GPP CN  304  as signal  324 . The direct handover tunnel  325  is established between the non-3GPP target CN  305  and the non-3GPP transceiver  303 . The source 3GPP CN  304  sends a signal  326  to initiate a non-3GPP registration to the 3GPP transceiver  302  which is then forwarded as signal  327  to the non-3GPP transceiver  303 . The upper layers of the non-3GPP transceiver  303  perform pre-registration pre-authentication procedures, and send a non-3GPP registration request  328 ,  329  via the 3GPP transceiver  302  to the non-3GPP target CN  305 . 
         [0024]    The 3GPP radio transceiver  302  and the non-3GPP target CN  305  then conduct authentication procedures  330 . Handover triggers  331  are communicated directly between the 3GPP CN  304  and non-3GPP CN  305  and the 3GPP CN  304  initiates handover with a signal  332  to the 3GPP transceiver  302 . The 3GPP transceiver  302  instructs the non-3GPP radio transceiver  303  to turn ON as signal  333 . With the non-3GPP radio transceiver  303  turned ON, it makes initial contact with the non-3GPP CN  305  and commences radio contact procedures  334 . The 3GPP radio transceiver  302  is turned OFF at  335  and the 3GPP CN  304  and non-3GPP CN  305  exchange handover complete and tunnel release signals  336 . 
         [0025]      FIG. 4  is a signal diagram for pre-registration procedure for a handover of a WTRU  401  from a non-3GPP handover source  404  to a 3GPP handover target  405 . A WTRU  401  includes a non-3GPP radio transceiver  402  and a 3GPP radio transceiver  403  for communication with a non-3GPP core network (CN)  404  and a 3GPP CN  405 . For simplicity, a dual mode WTRU  401  is shown, however the signaling described herein is valid for a multi-mode WTRU having multiple 3GPP and non-3GPP radio transceivers. While shown as direct signals between the WTRU  401  and CNs  403 ,  404 , the signals may be relayed by a NodeB or a base station entity (not shown). The pre-registration begins with the non-3GPP transceiver  402  receiving a 3GPP and non-3GPP measurement list  411  from non-3GPP CN  404 . The measurement list  411  identifies the channel frequencies of candidate handover targets. At  412 , the WTRU  401  stores the list in an internal memory, and for periodically initiating channel measurements. The non-3GPP transceiver  402  sends an initialization signal  413  to the 3GPP transceiver  403 , along with a list of candidate 3GPP handover targets  414 . The 3GPP transceiver  403  is activated and monitors channels and performs measurements at  415 . 
         [0026]    The 3GPP transceiver  403  sends measurement reports  416  of the monitored channels to the non-3GPP transceiver  402 . The non-3GPP transceiver  402  combines the measurements it made with those made by the 3GPP transceiver  403 , formulates combined measurement reports, and transmits the combined measurement reports  417  to the non-3GPP CN  404 . At  418 , the non-3GPP CN  404  examines the combined measurement reports and selects a handover target system for the WTRU  401 . The non-3GPP CN  404  sends a signal  419  to the target 3GPP CN  405  to initiate a handover direct tunnel, and the target 3GPP CN  405  responds with a tunnel establishment acknowledgment signal  420 . The 3GPP non-CN  404  sends a signal  421  to the non-3GPP transceiver  402  to initiate a handover direct tunnel. This signal  421  may include a 3GPP tunnel endpoint identification (TEID). The non-3GPP transceiver  402  sends the target ID  422  to the 3GPP transceiver  403 . The 3GPP transceiver sends its handover direct tunnel acknowledgment (ACK)  423  to the non-3GPP transceiver  402 , which is then forwarded to the non-3GPP CN  404  as signal  424 . The direct handover tunnel  425  is established between the 3GPP target CN  405  and the 3GPP transceiver  403 . The source non-3GPP CN  404  sends a signal  426  to initiate a 3GPP registration to the non-3GPP transceiver  402  which is then forwarded as signal  427  to the 3GPP transceiver  403 . A 3GPP registration request  428 , 429  is sent from the 3GPP transceiver  403  via the non-3GPP transceiver  402  to the 3GPP target CN  405 . 
         [0027]    The non-3GPP radio transceiver  402  and the 3GPP target CN  405  then conduct authentication procedures  430 . Handover triggers  431  are communicated directly between the non-3GPP CN  404  and 3GPP CN  405  and the non-3GPP CN  404  initiates handover with a signal  432  to the non-3GPP transceiver  402 . The non-3GPP transceiver  402  instructs the non-3GPP radio transceiver  403  to turn ON with signal  433 . With the 3GPP radio transceiver  403  turned ON, it makes initial contact with the 3GPP CN  405  and commences radio contact procedures  434 . The non-3GPP radio transceiver  402  is turned OFF at  435  and the non-3GPP CN  404  and 3GPP CN  405  exchange handover complete and tunnel release signals  436 . 
         [0028]      FIGS. 5A ,  5 B and  5 C show a signaling diagram of an SIP-based handover of a dual-mode WTRU  501  from a 3GPP source system to a non-3GPP target system. In order to speed the access procedures and hence the handover to the target system, pre-registration and pre-authentication procedures are allowed to be performed by the upper layers in the WTRU  501  of the target technology via the source system, including the IP configuration and connectivity establishment, and the SIP registration and connectivity establishment. 
         [0029]    In  FIG. 5A , the WTRU  501  comprises a 3GPP radio transceiver  502  and a non-3GPP radio transceiver  503 . Also shown are a 3GPP source CN  504  and a non-3GPP target CN  505 . The core networks CN  504  and  505  may be implemented as an access router (AR), access service network (ASN), or authentication, authorization and accounting (AAA) entity. The non-3GPP target system may include for example 3GPP2, WiMAX, or WiFi. 
         [0030]    As shown in  FIG. 5A , SIP connectivity  511  is already established between the 3GPP transceiver  502  and the 3GPP CN  504  and SIP connectivity  512  is already established between the 3GPP CN  504  and the internet protocol (IP) multimedia server (IMS)  506 . The pre-registration begins with the 3GPP transceiver  502  receiving a 3GPP and non-3GPP measurement list  513  from 3GPP CN  504 . The measurement list  513  identifies the channel frequencies of candidate handover targets. At  514 , the WTRU  501  stores the list in an internal memory, and for use in periodically initiating channel measurements. The 3GPP transceiver  502  sends an initialization signal  515  to the non-3GPP transceiver  503 , along with a list of candidate non-3GPP handover targets  516 . At  517 , the non-3GPP transceiver  503  monitors channels and performs measurements. 
         [0031]    The non-3GPP transceiver  503  sends measurement reports  518  of the monitored channels to the 3GPP transceiver  502 . The 3GPP transceiver  502  combines the measurements it made with those made by the non-3GPP transceiver  503 , formulates combined measurement reports, and transmits the combined measurement reports  519  to the 3GPP CN  504 . At  520 , the 3GPP CN  504  examines the combined measurement reports and selects a handover target system for the WTRU  501 . The 3GPP CN  504  sends a signal  521  ( FIG. 5B ) to the target non-3GPP CN  505  to initiate a handover direct tunnel, and the target non-3GPP CN  505  responds with a tunnel establishment acknowledgment signal  522 . The 3GPP CN  504  sends a signal  523  to the 3GPP transceiver  502  to initiate a handover direct tunnel. This signal  523  may include a non-3GPP tunnel endpoint identification (TEID). The 3GPP transceiver  502  sends the target ID  524  to the non-3GPP transceiver  503 . The non-3GPP transceiver sends its handover direct tunnel acknowledgment (ACK)  525  to the 3GPP transceiver  502 , which is then forwarded to the 3GPP CN  504  as signal  526 . The direct handover tunnel  527  is established between the non-3GPP target CN  505  and the non-3GPP transceiver  503 . The source 3GPP CN  504  sends a signal  528  to initiate a non-3GPP registration to the 3GPP transceiver  502  which is then forwarded as signal  529  to the non-3GPP transceiver  503 . A non-3GPP registration request  529 A is sent from the non-3GPP transceiver  503  to the 3GPP transceiver  502 , and forwarded as signal  530  to the non-3GPP target CN  505 . The registration request  529 A,  530  may include the TEID of the target CN  505 . 
         [0032]    The 3GPP radio transceiver  502  and the non-3GPP target CN  505  then conduct authentication procedures  531 . Signaling  532  occurs between different protocol stack layers of the 3GPP radio transceiver  502  and the non-3GPP transceiver  503 , where authorization information is exchanged to update the status of the protocol. If successful, then the process of establishing IP connection commences at  533 . The signaling  534  between the WTRU radio transceivers  502 ,  503  for establishing IP connectivity is started by tunneling the non-3GPP IP configuration message to the 3GPP protocol stack along crossover path  241 . 
         [0033]    The 3GPP transceiver  502  establishes non-3GPP IP configuration procedures  535  with the non-3GPP CN  505 . IP configuration messages  536 ,  537  are exchanged between the 3GPP transceiver  502  and the non-3GPP transceiver  503 , which may include the IP address of the IP gateway, IP type (e.g., IPv4 or IPv6) and the corresponding quality of signal (QoS) parameters. Additional information may also be sent in the signals  536 ,  537 , including a list of Proxy Call State Control Function (P-CSCF) to support the non-3GPP radio transceiver  503  to configure its SIP connectivity. The IP configuration of the non-3GPP transceiver is complete at  538 . 
         [0034]    For a handover between a 3GPP system and a non-3GPP system, two different IP gateways are involved. One IP gateway is for 3GPP, which is connecting the IMS to the 3GPP transceiver  502 , and the other IP gateway is for establishing the IP connectivity over a non-3GPP system for the non-3GPP transceiver  503 . 
         [0035]    As shown in  FIG. 5C , the SIP based handover signaling continues at  540 , where the non-3GPP transceiver  503  commences SIP registration procedures. Signals  541 - 544  are used to exchange SIP addresses and to perform P-CSCF discovery for connecting the SIP layer in the non-3GPP transceiver  503  to the IMS  506  via the Non-3GPP Core network. Signal  541  is exchanged between the 3GPP transceiver  502  and the non-3GPP transceiver  503  using the crossover path  241 . Signal  542  is sent over the 3GPP air interface from the 3GPP transceiver  602  PHY layer. Signal  543  is exchanged between the 3GPP CN  504  and the non-3GPP CN  505  and signal  544  is exchanged between the non-3GPP CN  505  and the IMS  506 . Acknowledgment signals  545  and  546  are sent between the appropriate protocol layer in the Non-3GPP transceiver  503  and the 3GPP transceiver  502  upon successful SIP registration. 
         [0036]    With the SIP registration of the non-3GPP transceiver  503  complete at  547 , SIP connectivity  548  and  549  is established between the non-3GPP transceiver  503  and the non-3GPP CN  505 , and between the non-3GPP CN  505  and the IMS  506 , respectively. The non-3GPP CN  505  informs the 3GPP CN  504  that handover is complete with signal  550 . The 3GPP transceiver  502  then performs SIP deregistration and IP release procedures  551  with the IMS  506 . The 3GPP transceiver  502  receives signal  552  from the 3GPP CN  504  indicating a handover complete, a radio switch OFF command and a release 3GPP radio access bearer (RAB) command. The 3GPP transceiver  502  informs the non-3GPP transceiver  503  that the handover is complete with signal  553 , and the non-3GPP radio transceiver  503  is activated ON. At  554 , the non-3GPP transceiver  503  commences non-3GPP RF connectivity procedures with the non-3GPP CN  505 . 
         [0037]      FIGS. 6A ,  6 B and  6 C show a signaling diagram of an SIP-based handover of a dual-mode WTRU  601  from a non-3GPP source system to a 3GPP target system. In order to speed the access procedures and hence the handover to the target system, pre-registration and pre-authentication procedures are allowed to be performed by the upper layers in the WTRU  601  of the target technology via the source system, including the IP configuration and the SIP registration procedures. 
         [0038]    In  FIG. 6A , the WTRU  601  comprises a 3GPP radio transceiver  602  and a non-3GPP radio transceiver  603 . Also shown are a 3GPP target CN  604  and a non-3GPP source CN  605 . The core networks CN  604  and  605  may be implemented as an access router (AR), access service network (ASN), or authentication, authorization and accounting (AAA) entity. The non-3GPP target system may include for example 3GPP2, WiMAX, or WiFi. 
         [0039]    As shown in  FIG. 6A , SIP connectivity  611  is already established between the non-3GPP transceiver  603  and the non-3GPP CN  605  and SIP connectivity  612  is already established between the non-3GPP CN  604  and the IP multimedia server (IMS)  606 . The pre-registration begins with the 3GPP transceiver  603  receiving a 3GPP and non-3GPP measurement list  613  from non-3GPP CN  605 . The measurement list  613  identifies the channel frequencies of candidate handover targets. At  614 , the WTRU  601  stores the list in an internal memory, and for use in periodically initiating channel measurements. The non-3GPP transceiver  603  sends an initialization signal  615  to the 3GPP transceiver  602 , along with a list of candidate 3GPP handover targets  616 . At  617 , the 3GPP transceiver  602  monitors channels and performs measurements. 
         [0040]    The 3GPP transceiver  602  sends measurement reports  618  of the monitored channels to the non-3GPP transceiver  603 . The non-3GPP transceiver  603  combines the measurements it made with those made by the 3GPP transceiver  603 , formulates combined measurement reports, and transmits the combined measurement reports  619  to the non-3GPP CN  605 . At  620 , the non-3GPP CN  605  examines the combined measurement reports and selects a handover target system for the WTRU  601 . The non-3GPP CN  605  sends a signal  621  ( FIG. 6B ) to the target 3GPP CN  604  to initiate a handover direct tunnel, and the target 3GPP CN  604  responds with a tunnel establishment acknowledgment signal  622 . The non-3GPP CN  605  sends a signal  623  to the non-3GPP transceiver  603  to initiate a handover direct tunnel This signal  623  may include a 3GPP tunnel endpoint identification (TEID). The non-3GPP transceiver  603  sends the target ID  624  to the 3GPP transceiver  602 . The 3GPP transceiver  602  sends its handover direct tunnel acknowledgment (ACK)  625  to the non-3GPP transceiver  603 , which is then forwarded to the non-3GPP CN  605  as signal  626 . The direct handover tunnel  627  is established between the 3GPP target CN  604  and the 3GPP transceiver  602 . The source non-3GPP CN  605  sends a signal  628  to initiate a 3GPP registration to the non-3GPP transceiver  603  which is then forwarded as signal  629  to the 3GPP transceiver  602 . A 3GPP registration request  629 A is sent from the 3GPP transceiver  602  to the non-3GPP transceiver  603  and forwarded as signal  630  to the 3GPP target CN  604 . The registration request  629 A,  630  may include the TEID of the target CN  604 . 
         [0041]    The non-3GPP radio transceiver  603  and the 3GPP target CN  604  then conduct authentication procedures  631 . Signaling  632  occurs between different protocol stack layers of the 3GPP radio transceiver  602  and the non-3GPP transceiver  603 , where authorization information is exchanged to update the status of the protocol. If successful, then the process of establishing IP connection commences at  633 . The signaling  634  for IP connectivity is started by tunneling the 3GPP IP configuration message to the non-3GPP protocol stack along crossover path  231 . 
         [0042]    The non-3GPP transceiver  603  establishes 3GPP IP configuration procedures  635  with the 3GPP CN  604 . IP configuration messages  636 ,  637  are exchanged between the 3GPP transceiver  602  and the non-3GPP transceiver  603 , which may include the IP address of the IP gateway, IP type (e.g., IPv4 or IPv6) and the corresponding quality of signal (QoS) parameters. Additional information may also be sent in the signals  636 ,  637 , including a list of Proxy Call State Control Function (P-CSCF) to support the 3GPP radio transceiver  602  to configure its SIP connectivity. The IP configuration of the non-3GPP transceiver is complete at  638 . 
         [0043]    As shown in  FIG. 6C , the SIP based handover signaling continues at  640 , where the 3GPP transceiver  602  commences SIP registration procedures. Signals  641 - 644  are used to exchange SIP addresses and to perform P-CSCF discovery for connecting the SIP layer in the 3GPP transceiver  602  to the IMS  606  via the 3GPP core network  604 . Signal  641  is exchanged between the 3GPP transceiver  602  upper layers and the non-3GPP transceiver  603  PHY layer using the crossover path  231 . Signal  642  is sent over the non-3GPP air interface from the non-3GPP transceiver  603  PHY layer to the non-3GPP CN  605 . Signal  643  is exchanged between the non-3GPP CN  605  and the 3GPP CN  604  and signal  644  is exchanged between the 3GPP CN  604  and the IMS  606 . Acknowledgment signals  645  and  646  are sent between the appropriate protocol layer in the Non-3GPP transceiver  603  and the 3GPP transceiver  602  upon successful SIP registration. 
         [0044]    With the SIP registration of the 3GPP transceiver  602  complete at  647 , SIP connectivity  648  and  649  is established between the 3GPP transceiver  602  and the 3GPP CN  604 , and between the 3GPP CN  604  and the IMS  606 , respectively. The 3GPP CN  604  informs the non-3GPP CN  605  that handover is complete with signal  650 . The non-3GPP transceiver  603  then performs SIP deregistration and IP release procedures  651  with the IMS  606 . The non-3GPP transceiver  603  receives signal  652  from the non-3GPP CN  605  indicating a handover complete, a radio switch OFF command and a release non-3GPP radio access bearer (RAB) command. The non-3GPP transceiver  603  informs the 3GPP transceiver  602  that the handover is complete with signal  653 , and the 3GPP radio transceiver  602  is activated ON. At  654 , the 3GPP transceiver  602  commences 3GPP RF connectivity procedures with the 3GPP CN  604 . 
         [0045]      FIGS. 7 and 8  show systematic block diagrams for the SIP based handover method described above. In  FIG. 7 , communication links for a handover of WTRU  201  from a 3GPP source system to a non-3GPP target system is shown sequentially by signal paths  701 ,  702  and  703 . Initially, the WTRU  201  is connected to the 3GPP source system on signal path  701  via an IMS  711 , a 3GPP CN  721 , and a 3GPP eNodeB (eNB)  722  that is in a wireless communication with the 3GPP PHY layer  223 . In order to prepare for handover to a non-3GPP target, a make-before-break path  702  is established to the non-3GPP transceiver protocol stack (i.e., SIP application layer  210 , SM and MM layer  211 , RRC and MAC layer  212 ) via the crossover path  241  between the 3GPP PHY layer  223  and non-3GPP RRC and MAC layer  212 . The communication path  702  allows the non-3GPP protocol stack to receive target system information via the active 3GPP source system using the 3GPP eNB  722 , the 3GPP CN  721 , which exchanges information with the target non-3GPP CN  731 , gateway (GW)  712  and IMS  711 . The communication path  702  is established when the WTRU  201  receives instructions from the source 3GPP system to start the access procedures toward the target system and to perform the sequence of access specific procedures (e.g., Attach, IP configuration, and SIP Registration). Upon successful completion of the access specific procedures and the SIP registration, the SIP connectivity is established as shown by communication path  703  between the non-3GPP protocol stack (i.e. layers  210 ,  211 ,  212  and PHY layer  213 ) and the non-3GPP radio access network (RAN)  732 , the non-3GPP CN  731 , the gateway (GW)  712  and IMS  711 . The WTRU  201  receives instructions from the 3GPP source system to switch (or handover) to the non-3GPP target system and turn off the radio on the 3GPP source system (i.e., turn OFF the 3GPP transceiver of WTRU  201 ), which terminates the communication links  701  and  702 . This ensures that the SIP based session is established to the non-3GPP target system. A WTRU controller  251  executes the access procedures and the handover procedures responsive to the received instructions from the 3GPP source system. 
         [0046]    In  FIG. 8 , communication links for a handover of WTRU  201  from a non-3GPP source system to a 3GPP target system is shown sequentially by signal paths  801 ,  802  and  803 . Initially, the WTRU  201  is connected to the non-3GPP source system on signal path  801  via an IMS  711 , a gateway (GW)  712 , a non-3GPP CN  731 , and a non-3GPP RAN  732  that is in a wireless communication with the non-3GPP PHY layer  213 . In order to prepare for handover to a 3GPP target system, a make-before-break path  802  is established between 3GPP target system to the 3GPP transceiver protocol stack (i.e., SIP application layer  220 , SM and MM layer  221 , RRC and MAC layer  222 ) via the crossover path  231  between the non-3GPP PHY layer  213  and non-3GPP RRC and MAC layer  222 . The communication path  802  allows the 3GPP protocol stack to receive target system information via the active non-3GPP source system using the non-3GPP RAN  732 , the non-3GPP CN  731 , which exchanges information with the target 3GPP CN  721  and IMS  711 . The communication path  802  is established when the WTRU  201  receives instructions from the source non-3GPP system to start the access procedures toward the 3GPP target system and to perform the sequence of access specific procedures (e.g., Attach, IP configuration, and SIP Registration). Upon successful completion of the access specific procedures and the SIP registration, the SIP connectivity is established as shown by communication path  803  between the 3GPP protocol stack (i.e. layers  220 ,  221 ,  222  and PHY layer  223 ) and the non-3GPP RAN  732 , followed by the non-3GPP CN  731 , the 3GPP CN  721  and IMS  711 . The WTRU  201  receives instructions from the 3GPP source system to switch (or handover) to the non-3GPP target system and turn off the radio on the 3GPP source system (i.e., turn OFF the non-3GPP transceiver of WTRU  201 ), which terminates the communication links  801  and  802 . This ensures that the SIP based session is established to the non-3GPP target system. A WTRU controller  251  executes the access procedures and the handover procedures responsive to the received instructions from the 3GPP source system. 
         [0047]    Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. The methods or flow charts provided in the present invention may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0048]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0049]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) module.