Patent Publication Number: US-2010111040-A1

Title: Method and apparatus for fast break-before-make media independent handover

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Nos. 61/109,616 filed on Oct. 30, 2008 and 61/232,217 filed on Aug. 7, 2009, which are hereby incorporated by reference. 
    
    
     TECHNOLOGY FIELD 
     The present disclosure relates to wireless communications. 
     BACKGROUND 
     Typical radio access technologies may have defined mechanisms to control Network Discovery and Selection (NWDS). However, few mechanisms have been defined for heterogeneous network environments, where several different radio access technologies are available for a wireless transmit/receive unit (WTRU). Instead, it has typically been left to the WTRU and a user of the WTRU to handle network discovery and selection. 
     For example, Media Independent Handover (MIH) Services is a standard developed by Institute of Electrical and Electronics Engineers (IEEE) in the 802 family of standards. The MIH standard (IEEE 802.21) specifies access-independent mechanisms that optimize handovers between heterogeneous access networks, both wired and wireless. MIH mechanisms may be used for handovers between 802 networks and non-802 networks. 
     The purpose of the MIH client may be to allow efficient software implementations of handover between different technologies, for example, Wireless Broadband (WiBro) and Universal Mobile Telecommunications System (UMTS). Additional purposes of the MIH client may include enabling any of the following: automatic inter-technology mobility at both Layer 2 and Layer 3; reduced handover interruption time; and provide quality of service (QoS) optimization across technologies. 
       FIG. 1  depicts an intermediary node, such as an MIH server, configured to control handover  100 . According to the handover procedure as shown in  FIG. 1 , handover may be assisted by WTRU  105  as well as Mobile Internet Protocol (MIP) registration. As shown in  FIG. 1 , an MIH client  110  and MIP client  111  may be provided on the WTRU  105 . A binding entry  125  for the WTRU  105  may also exist at a source node such as a Home Agent (HA)  130 . The HA may be a router, or any other type of device, on a WTRU&#39;s home network that may tunnel data for delivery to the WTRU when it is away from home. The HA may maintain a current location for the WTRU, such as an IP address. The HA may be used with one or more target nodes, such as a Foreign Agent (FA). A FA may be a router, or any other type of device, that stores information about WTRUs visiting its network. FAs may also advertise care-of-addresses (CoAs) which may be used by MIP. A CoA of a WTRU may be a physical IP address of the device when operating in a foreign network. 
     When link quality degrades  135 , the MIH client may communicate a LinkGoingDown (low confidence) message  136  to the MIH server  137 . The MIH client  110  may also communicate a measurement report  138  and a LinkGoingDown (high confidence) message  139  to the MIH server  137 . The MIH server  137  then may decide to initiate a handover  140 . The MIH server  137  may communicate a handover request message  141  to the MIH client  110 . 
     The WTRU  105  may then turn down its current link on Network A  142 , resulting in connectivity being interrupted. The WTRU  105  may begin to establish Layer 2 connectivity on Network B  143 . The WTRU  105  may trigger MIP registration  144 . The MIP client  111  may transmit a Router Solicitation message  145  to a target node, such as a FA  120  in Network B. The FA  120  may respond with an Agent Advertisement (List of CoAs) message  146 . The MIP client  111  may send an MIP Register (WRTU+COA) message  147  to the FA  120 . The FA  120  then may send an MIP Register (WTRU+CoA) message  148  to the HA  130 . The HA  130  then may update its binding entry  125  with the new CoA (not shown). 
     After the HA  130  updates its binding entry  125 , Layer 3 connectivity may be resumed. The HA  130  may transmit an MIP Register Response message  150  to the FA  120 . The FA  120  may transmit an MIP Register Response message  155  to the MIP client  111 . The MIH client  110  then may send a Handover Completed message  160  to the MIH server  137 . The HA  130  may then forward data from the correspondent peer to the WTRU  105  using the new CoA  165 . 
     In typical break-before-make (BBM) approaches to MIH handover, a current link is torn down before a new connection is established on the target network. According to this approach, only one transmitter may be enabled at a time. Using a make-before-break approach (MBB), a new connection may be established on the targeted network before terminating the current connection. According to this approach, two or more transmitters may be enabled at the same time. The disadvantages of current MBB approaches, however, may include power consumption and radio interference issues when two or more transmitters are enabled at the same time in a single device. 
     In typical BBM approaches, an interruption period may occur following the current connection being torn down and prior to a new connection being established on the new network. This may have the undesirable effect of creating data loss during the interruption period. Interruption periods may not be of uniform length. Many steps may be performed before connectivity is resumed. For example, one step may be obtaining Layer 2 connectivity on the targeted network. Obtaining Layer 2 connectivity may depend on the technology that is used on the targeted network. For example, when connecting to a UMTS target network, the WTRU may camp on a cell, attach to the network, and activate a Packet Data Protocol (PDP) context. A second step may be updating the MIP registration/CoA allocation/FA discovery with the Home Agent (HA). This may involve sending a Router Solicitation message, waiting for an Agent Advertisement, and sending an MIP registration request to the HA. 
     SUMMARY 
     A method and apparatus may be used to perform a Media Independent Handover. Data may be received from a source node in a source network serving a WTRU via an intermediate node. The WTRU may transmit a first message to an intermediary node and receive a second message in response. The WTRU may establish connectivity on a target network and receive data from a target node. 
     The WTRU may receive data from a source node in a source network serving the WTRU. The WTRU may transmit a first message to an intermediary node, the first message including an indication of a location of the WTRU and an indication of a target network. In response, the WTRU may receive a second message from the intermediary node, the second message including an indication of an internet protocol (IP) address of a target node. The WTRU may then establish connectivity on the target network and receive data from the target node. 
     A target node may receive a first message from a source node and transmit a second message to the source node. The target node may also receive a third message from the source node indicating a WTRU to be registered and transmit a fourth message to the source node before forwarding data to the WTRU. 
     An intermediary node may transmit a first message to a source node, the first message indicating a dual MIP binding for a WTRU. In response, the intermediary node may receive a second message from the source node. The intermediary node may perform a determination to initiate handover of the WTRU; and transmit a Handover Request. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a diagram of a typical method for Media Independent Handover (MIH)-based handover; 
         FIGS. 2A and 2B  are a diagram of an example method for MIH-based handover that may include the use of Media Independent Information Services (MIIS); 
         FIGS. 3A and 3B  are a diagram of an example method for MIH-based handover that may not include the use of Media Independent Information Services (MIIS); and 
         FIGS. 4A and 4B  are a diagram of an example method for MIH-based handover that may include the use of Proxy Mobile Internet Protocol (PMIP); 
         FIGS. 5A and 5B  are a diagram of an example method for MIH handover where the MIP pre-registration may be performed by the MIH client; 
         FIGS. 6A and 6B  are a diagram of an example method for MIH handover where PMIP may be triggered by the MIH client; 
         FIG. 7  is a diagram of an example method where the MIH server may send an Agent Solicitation message. 
         FIG. 8  shows a wireless communication system/access network; and 
         FIG. 9  is an example block diagram of the wireless communication system/access network of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     When referred to herein, the terminology “wireless transmit/receive unit (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 herein, 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. The embodiments described herein may be configured to operate using MIP, Fast Mobile IP (FMIP), Hierarchical Mobile IP (HMIP), and other mobility technologies. 
     For purposes of explanation, the various embodiments are described in an 802.xx context, but the various embodiments may be implemented using any handover technology that supports inter-network handover. For example, in a Third Generation Partnership Project (3GPP) scenario, an Access Network Discovery and Selection Function (ANDSF) may be used to assist WTRUs in discovering and selecting heterogeneous access networks. The ANDSF may be used for the Interworking of 3GPP and non-3GPP networks. Other types of handover technologies may be applied to any type of network, for example Worldwide Interoperability for Microwave Access (WiMAX), Wireless Local Area Network (WLAN), Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA2000), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), or any future technology. 
     A wireless network may include an inter-technology handover server, for example as an MIH server, an ANDSF server, or any other device or intermediary node that may be used to assist WTRUs in discovering and in deciding which network to access. These types of devices may be used to centralize decisions regarding the handover of sessions among multiple access points and multiple access technologies, either alone or in combination with other functions. Such devices may allow a wireless network operator to balance the traffic load so as to alleviate congestion on specific access points, and deliver sufficient QoS to all users. 
     In an 802.xx scenario, for example, the MIH server may be in communication with an MIH client and a source node such as an HA. The MIH server and HA may be co-located or may be in communication with each other. An MIH server may be in communication with an intermediary node such as a Media Independent Information Services (MIIS). The MIH server and MIIS may be co-located. The MIIS may be able to determine which FA in a targeted network is reachable from a WTRU after the handover of the WTRU to the targeted network is completed. The HA may be able to send an MIP registration to the FA on behalf of the WTRU. The WTRU may include an MIP client. The MIP client may be used by the WTRU when connecting to the targeted network during handover. The FA IP address may be obtained based on the targeted network and/or current WTRU location. 
     A method and apparatus may be used to reduce the interruption interval resulting from a BBM handover by performing an MIP pre-registration on a targeted network before tearing down a current link. To perform the pre-registration, the MIIS and HA may obtain the Care of Address (CoA) of the target FA and communicate the CoA to the WTRU. The target FA&#39;s CoA may be obtained before terminating the connection on the source network (Network A). The MIP binding entry for the target network (Network B) may be added on the HA for simultaneous binding using the targeted CoA and may be created on the targeted FA (MIP pre-registration) before terminating the connection on Network A. 
     The MIH server may initiate the MIP pre-registration with the HA and the HA may send the MIP pre-registration to the FA on behalf of the WTRU. A Proxy Mobile Internet Protocol (PMIP) node on the current network may send an MIP pre-registration to the targeted FA on behalf of the WTRU. The MIH client on the WTRU may trigger MIP pre-registration to the targeted FA while still connected on the current Network A. As a result, since the MIP binding has been updated, the data from the correspondent node may reach the WTRU upon establishing Layer 2 connectivity. 
       FIGS. 2A and 2B  are a diagram of a method for handover  200 . As shown in  FIG. 2A , the WTRU  105  may initiate an acquisition of a targeted MIP CoA, and the MIH server  237  may initiate an MIP pre-registration with the HA  130  and the targeted FA  210 . 
     As shown in  FIG. 2A , the MIH client  110  and MIP client  111  may be present on a WTRU  105  in a memory unit, or a processor, etc. In the examples detailed below, the network currently serving the WTRU  105  is referred to as Network A and the target network is referred to as Network B. The MIH server  237 , MIIS  238 , and HA  130  may be communicating on Network A. In this example, the WTRU  105  may be registered on Network A, and an MIP binding entry  115 ,  125  may exist for the WTRU  105  on the FA  120  on Network A and the HA  130 . 
     When the WTRU  105  detects that its link quality is degrading  135 , it may transmit a LinkGoingDown (low confidence) message  136  and a measurement report  138  to the MIH Server  237 . The MIH client  110  then may send a GetInformationReq message  215  to the MIIS  238 . Other triggers for transmitting the GetInformationReq message may include, for example, an internal decision by the MIH client based on internal policies, a trigger from applications running on the WTRU, etc. The MIIS  238  may be co-located with the MIH server  237 . The WTRU&#39;s location and targeted network may be specified in the GetInformationReq message  215 . The targeted network may be, for example, a UMTS network. The MIIS  238  may transmit a message  220  to the HA  130  to obtain the CoA of the targeted FA  210 . The HA  130  may send an Agent Solicitation Message  225  to the target FA  210  to obtain the target FA&#39;s CoA. The target FA  210  may respond to the HA  130  with an Agent Advertisement Message  230  that may include the FA&#39;s CoA. The HA  130  may transmit the FA&#39;s CoA  235  to the MIIS  238 , which then may transmit a GetInformationResp message  240  to the MIH client  110  that includes the FA&#39;s CoA. The CoA may be the target address that the WTRU will register to during handover. The targeted CoA may be obtained using an alternative method as described in  FIG. 7 . 
     The MIH client  110  may transmit a LinkGoingDown (high confidence) message  139  to the MIH server  237 , when link quality is poor. The MIH server  237  may decide to initiate a handover. Before handover, the MIH server  237  may trigger registration of the WTRU  105  with the target FA  210 , and may create a dual CoA entry in the HA  130 . 
     The MIH server  237  may send a registration (dual/simultaneous binding) message  245  to the HA  130 . The HA  130  may update the WTRU binding entry  125  to include two bindings, a first binding for Network A and a second binding for Network B. The HA  130  may pre-register the WTRU  105  on Network B by sending an MIP registration message  250  to the target FA  210 . The data destined to the WTRU  105  may be forwarded to both FAs  120 ,  210 . Since the WTRU  105  may still be connected to Network A, it may continue to receive the data forwarded from the FA  120 . The FA  210  may buffer packets  267  until the WTRU  105  establishes Layer 2 connectivity with the FA  210 . In this example, there is no need for a tunnel between the two FAs  120 ,  210 . 
     The FA  210  may respond to the HA  130  by sending an MIP Rsp message  255 . The MIP Rsp message  255  may include a new CoA. The HA  130  may add the new CoA(B) to the binding entry while keeping the previous CoA(A). Data may be forwarded  260  from the HA  130  to the FA  120  on Network A as well as the target FA  210 . The FAs  120 ,  210  may forward the data to the WTRU  105 . Duplicated data sent from Network B may be lost. The HA  130  may send a Registration Rsp message  265  to the MIH server  237  to indicate that MIP registration is complete. In response, the MIH server  237  may send a Handover Request message  141  to the WTRU  105 . 
     The WTRU  105  may turn down  270  its current link on Network A and turn on a modem to connect to Network B. When the WTRU  105  turns down its current link on Network A, connectivity may be interrupted. The WTRU  105  then may establish Layer 2 connectivity on Network B  275 . Layer 3 connectivity may be resumed since the MIP registration was performed prior to initiating the handover. The FA  210  may forward the buffered packets  277  to the WTRU  105  and stop buffering. The MIH client  110  may trigger MIP registration using the previously-received CoA. The MIH client  110  may send an MIP Register message  279  to the FA  210  on Network B. The MIP Register message  279  may include a home IP address, i.e. the IP address assigned by the HA to the WTRU and a CoA, together referred to as (WTRU+CoA). The home IP address may not change when the WTRU moves to another FA. The CoA may change as the WTRU moves to another FA and may be allocated by the FA. The binding entry at the FA and HA may include the WTRU home address and a current CoA. The FA  210  on Network B sends an MIP register message  280  to the HA  130 . The MIP register message  280  may include (WTRU+CoA). The HA  130  may remove the duplicate binding entries, retaining only the new CoA for the WTRU  105 . The HA  130  may respond to the FA  210  by sending an MIP Register Rsp message  282 . The FA  210  in Network B may send an MIP Register Rsp message  284  to the WTRU  105 . The WTRU  105  may send a Handover Completed message  286  to the MIH server  237 . The HA  130  may forward data  288  to the WTRU via the Network B using the new CoA. 
       FIGS. 3A and 3B  are a diagram of another method for MIH handover  300 . As compared to the method of  FIGS. 2A and 2B , the method of  FIGS. 3A and 3B  does not include the use of the MIIS. Additionally, the method of  FIGS. 3A and 3B  differs from the method of  FIGS. 2A and 2B  in the following ways: indications of the WTRU&#39;s location and targeted network may be sent in the LinkGoingDown message; the Agent Solicitation and Agent Advertisement messages may be sent only when the decision to trigger handover is made; and the FA&#39;s CoA may be forwarded to the MIH client with the Handover Request instead of with the GetInformationRsp message. Efficiencies provided by the method of  FIGS. 3A and 3B  include: fewer messages may be communicated between the WTRU and the MIH server; the MIH server may receive an update of the WTRU&#39;s location before triggering handover since two LinkGoingDown messages may be sent, resulting in more efficient detection of the targeted FA; and Agent Solicitation and Advertisement messages may be sent only if the decision to trigger handover is made. Additional aspects of the method of  FIGS. 3A and 3B  may include the MIH server initiating the acquisition of the targeted CoA, the MIH server initiating the MIP re-registration with the HA and the targeted FA, and the WTRU receiving the targeted CoA with the Handover Request message. 
     As shown in  FIG. 3A , the WTRU  105  may include an MIH client  110  and an MIP Client  111 . The WTRU  105  may be registered to Network A, and a binding entry  115 ,  125  may exist for the WTRU at the FA  120  in Network A and at the HA  130 . When the WTRU  105  detects that its link quality is degrading  135 , it may send a LinkGoingDown (low confidence) message  336  to the MIH server. The LinkGoingDown (low confidence) message  336  may include the WTRU&#39;s location and an identifier of the targeted network. The WTRU  105  may send a measurement report  338  to the MIH server  137 . The WTRU  105  may send a LinkGoingDown (high confidence) message  339  to the MIH server  137 , including the WTRU&#39;s location and an identifier of the targeted network. The MIH server  137  may decide to initiate handover. 
     The MIH server  137  may send a Registration (simultaneous binding) message  345  to the HA  130 . The HA  130  may send an Agent Solicitation message  350  to the target FA  310 , which is in Network B. The target FA  310  may send an Agent Advertisement message  355  to the HA  130 , including the target FA&#39;s CoA. This is how the HA  130  may obtain the target FA&#39;s CoA while the WTRU  105  is still on Network A. The HA  130  may send an MIP Registration message  360  to the target FA  310 . The target FA  310  may send an MIP Rsp message  365  to the HA  130 . The HA  130  may add the new CoA(B) binding entry for the WTRU while retaining the previous CoA(A) entry. At this point, MIP data may be forwarded  370  to both the target FA  310  and the FA  120  on Network A. Both FAs may forward the data to the WTRU  105 . The HA  130  may send a Registration Rsp message  375  to the MIH server  137 , which may include the target FA&#39;s CoA. The FA  310  may buffer packets  380  until the WTRU  105  establishes Layer 2 connectivity with the FA  310 . 
     The MIH server  137  may send a Handover Request message  382  to the WTRU  105 . The Handover Request message  382  may include the targeted FA&#39;s CoA. The WTRU  105  may turn down  384  its current link on Network A, causing an interruption of connectivity, and establish Layer 2 connectivity  386  on Network B. Layer 3 connectivity may be resumed since the MIP registration was performed prior to initiating the handover. The FA  310  may forward the buffered packets  388  to the WTRU  105  and stop buffering. The MIH client  110  may trigger MIP registration using the previously-received CoA. It may send an MIP Register message  390  including (WTRU+CoA) to the FA  310  on Network B. The FA  310  on Network B may send an MIP register message  392  including (WTRU+CoA) to the HA  130 . The HA  130  may remove the duplicate binding entries, retaining only the new CoA for the WTRU  105 . The HA  130  may respond to the FA  310  by sending an MIP Register Rsp message  394 . The FA  310  in Network B may send an MIP Register Rsp message  396  to the WTRU  105 . The WTRU  105  may send a Handover Completed message  398  to the MIH server  137 . The HA  130  may forward data  399  from the Network B using the new CoA. 
       FIGS. 4A and 4B  are a diagram of a method for MIH handover  400  where Proxy MIP (PMIP) may be used. As PMIP is used in this method, it may not be required that the CoA is transmitted to the WTRU. As compared to the methods of  FIG. 2  and  FIG. 3 , the MIP pre-registration may be performed by the HA on the targeted network (Network B). The method of  FIGS. 4A and 4B  differs from the methods of FIGS.  2 A/ 2 B and FIGS.  3 A/ 3 B in the following ways: when the WTRU connects to the target network, PMIP may trigger the FA for MIP registration; since a binding entry may already exist on the FA resulting from the previously performed MIP pre-registration, the same CoA may be used on the MIP registration sent to the HA; and the HA may receive the MIP registration and overwrite the existing binding entry, removing the simultaneous bindings that may result in the loss of the Network A binding. Other aspects of the method of  FIGS. 4A and 4B  may include: the MIH server initiating the acquisition of the targeted CoA; the MIH server initiating the MIP pre-registration with the HA and the targeted FA; and the WTRU may not be involved in MIP registration or pre-registration. 
     As shown in  FIG. 4A , the WTRU  105  may include an MIH client  110  and may be registered on Network A. A binding entry  115 ,  125  may exist for the WTRU  105  at the FA  120  on Network A and at the HA  130 . When the WTRU  105  detects that its link quality is degrading  135 , it may send a LinkGoingDown (low confidence) message  436  to the MIH server  137 . The WTRU  105  may send a measurement report  438  to the MIH server  137 . The WTRU  105  may send a LinkGoingDown (high confidence) message  439  to the MIH server. The LinkGoingDown (high confidence) message  439  may include the WTRU location and the targeted network. The MIH server  137  may decide to initiate handover  140 . 
     The MIH server  137  may send a Registration (simultaneous binding) message  445  to the HA  130 . The HA  130  may send an Agent Solicitation message  450  to the target PMIP/FA  410 , which is in Network B. The target PMIP/FA  410  may send an Agent Advertisement message  455  to the HA  130 , including the target FA&#39;s CoA. This is how the HA  130  may obtain the target FA&#39;s CoA while the WTRU  105  is still on Network A. The HA  130  may send an MIP Registration message  460  to the target PMIP/FA  410 . The target PMIP/FA  410  may send an MIP Rsp message  465  to the HA  130 . The HA  130  may add the new CoA(B) binding entry for the WTRU while retaining the previous CoA(A) entry. At this point, MIP data may be forwarded  470  to both the target PMIP/FA  410  and the FA  120  on Network A. Both FAs may forward the data to the WTRU  105 . The HA  130  may send a Registration Rsp message  475  to the MIH server  137 , which may include the target FA&#39;s CoA. The FA  410  may buffer packets  480  until the WTRU  105  establishes Layer 2 connectivity with the FA  410 . 
     The MIH server  137  may send a Handover Request message  482  to the WTRU  105 . The Handover Request message  482  may include the targeted FA&#39;s CoA. The WTRU  105  may turn down  484  its current link on Network A, causing an interruption of connectivity, and establish Layer 2 connectivity  486  on Network B. Layer 3 connectivity may be resumed since the MIP registration was performed prior to initiating the handover. The FA  410  may forward the buffered packets  488  to the WTRU  105  and stop buffering. The PMIP/FA  410  may trigger MIP registration  490  via the FA on Network B. The FA on Network B may determine that a binding entry already exists for the WTRU  105 . The FA may send an MIP Register message  492  including (WTRU+registered CoA) to the HA  130 , using the same CoA that may be used for the MIP registration update. The HA  130  may retain only the new CoA. The HA  130  may send an MIP Register Rsp message  494  to the FA in Network B. The WTRU  105  may send a Handover Completed message  496  to the MIH server  137 . The HA  130  may forward data  498  from the correspondent peer to the WTRU using the new CoA. 
       FIGS. 5A and 5B  are a diagram of a method for MIH handover  500  where the MIP pre-registration may be performed by the MIH client. The MIH server may not be involved in this exchange. Additionally, the HA may not have to trigger the MIP registration with the FA, as compared to the method of FIGS.  2 A/ 2 B. As shown in  FIGS. 5A and 5B , the MIH client  110  may initiate the acquisition of the targeted MIP Care of Address (CoA), and the MIH client  110  may initiate the MIP pre-registration with the HA  130  and the targeted FA  210 . 
     As shown in  FIG. 5A , the MIH client  110  and MIP client  111  may be present on a WTRU  105 . The WTRU  105  may be registered on Network A, and an MIP binding entry  115 ,  125  may exist for the WTRU  105  on the FA  120  on Network A and the HA  130 . 
     When the WTRU  105  detects that its link quality is degrading  135 , it may transmit a LinkGoingDown (low confidence) message  136  and a measurement report  138  to the MIH Server  537 . The MIH client  110  then may send a GetInformationReq message  215  to the MIIS  538 . The MIIS  538  may be co-located with the MIH server  537 . The WTRU&#39;s location and the targeted network may be specified in the GetInformationReq message  215 . The targeted network may be, for example, a UMTS network. The MIIS  538  may transmit a message  220  to the HA  130  to obtain the Care of Address (CoA) of the FA  210 . The HA  130  may send an Agent Solicitation Message  225  to the target FA  210  to obtain the target FA&#39;s CoA. The target FA  210  may respond to the HA  130  with an Agent Advertisement Message  230  which may include the FA&#39;s CoA. The HA  130  may transmit the FA&#39;s CoA  235  to the MIIS  538 , which then may transmit a GetInformationResp message  240  to the MIH client  110  that may include the FA&#39;s CoA. The CoA is the target address that the WTRU may register to during handover. 
     The MIH client  110  may transmit a LinkGoingDown (high confidence) message  139  to the MIH server  537  if link quality is poor. The MIH server  537  may decide to initiate a handover. The MIH client  110  may trigger the MIP client  111  when a handover should be performed and when the targeted CoA is known. The targeted CoA may be obtained using an alternative method as described in  FIG. 7 . The current link (Network A) may be used to carry the MIP pre-registration destined for the FA on the targeted network. This may be performed by sending an MIP Register message  540  including (WTRU+CoA(B)+simultaneous binding) to the targeted FA  210 . The FA  210  may then send an MIP Register message  545  including (WTRU+CoA(B)+simultaneous binding) to the HA  130 . In response, the HA  130  may add the new CoA(B) binding entry for the WTRU while retaining the previous CoA(A) entry and may send an MIP Register Rsp message  550  to the target FA  210 . The FA  210  then may send an MIP Register Rsp message  555  over the current link (Network A) to the MIH client  110 . The targeted FA  210  may buffer the packets destined to the WTRU  105  until the WTRU  105  is detected on the targeted network. 
     The WTRU  105  may turn down  570  its current link on Network A and turn on a modem to connect to Network B. This is where connectivity may be interrupted. The WTRU  105  then may establish Layer 2 connectivity on Network B  575 . Layer 3 connectivity may be resumed since the MIP registration was performed prior to initiating the handover. The FA  210  may forward the buffered packets  577  to the WTRU  105  and stop buffering. The MIH client  110  may trigger MIP registration using the previously-received CoA. It may send an MIP Register message  579  including (WTRU+CoA) to the FA  210  on Network B. The FA  210  on Network B may send an MIP register message  580  including (WTRU+CoA) to the HA  130 . The HA  130  may remove the duplicate binding entries, retaining only the new CoA for the WTRU  105 . The HA  130  may respond to the FA  210  by sending an MIP Register Rsp message  582 . The FA  210  in Network B may send an MIP Register Rsp message  584  to the WTRU  105 . The WTRU  105  may send a Handover Completed message  586  to the MIH server  537 . The HA  130  may forward data  588  from the Network B using the new CoA. 
       FIGS. 6A and 6B  are a diagram of a method for MIH handover  600  where PMIP may be triggered by the MIH client. As PMIP is used in this method, an MIP client may not be required on the WTRU. 
     As shown in  FIG. 6A , the WTRU  105  may include an MIH client  110  and may be registered on Network A. A binding entry  115 ,  125  may exist for the WTRU  105  at the FA  120  on Network A and at the HA  130 . When the WTRU  105  detects that its link quality is degrading  135 , it may send a LinkGoingDown (low confidence) message  636  to the MIH server  637 . The WTRU  105  may send a measurement report  638  to the MIH server  637 . The WTRU  105  may send a LinkGoingDown (high confidence) message  639  to the MIH server  637 . The LinkGoingDown (high confidence) message  639  may include the WTRU location and the targeted network. 
     The MIH client  110  may obtain  640  the targeted PMIP/FA IP address using MIH Information Services, for example a Push Information from the MIH server  637  or a Get Information from the MIH client  110 . The MIH client  110  may obtain the targeted CoA and trigger the MIP pre-registration with the targeted PMIP/FA  610  and the HA  130  by sending an Agent Solicitation message  642 . In response, the PMIP/FA  610  may send an Agent Advertisement CoA  644 . The MIH client  110  may then trigger the MIP pre-registration on the targeted Network B by sending a modified Agent Solicitation message  646  with a selected CoA to the PMIP/FA  610 . The MIP pre-registration at the HA  130  may be performed by the targeted PMIP/FA  610  by sending an MIP Registration message  648  to the HA  130 . This may be performed by keeping simultaneous bindings at the HA  130  and buffering packets on the targeted network until the WTRU  105  is attached to the targeted network. The HA  130  may then send an MIP Rsp message  650  to the PMIP/FA  610  in response. The PMIP/FA  610  may then send an Agent Advertisement message  652  to the MIH client  110 . The Agent Solicitation message  646  and the Agent Advertisement message  652  may be modified to specify that MIP pre-registration is required to exchange these messages using unicast IP addresses. It is noted that the WTRU  105  sending these messages to the PMIP/FA  610  on the targeted Network B may still be connected to Network A. The HA  130  may forward  654  data to the FAs  120 ,  610  on Network A and Network B simultaneously while the PMIP/FA  610  buffers packets  656 . 
     The MIH server  637  may then decide to initiate  660  a handover by sending a handover request message  665 . The WTRU  105  may turn down  684  its current link on Network A, causing an interruption of connectivity, and establish Layer 2 connectivity  686  on Network B. Layer 3 connectivity may be resumed since the MIP registration was performed prior to initiating the handover. The PMIP/FA  610  may forward the buffered packets  688  to the WTRU  105  and stop buffering. The PMIP/FA  610  may trigger MIP registration  690  on Network B. The PMIP/FA  610  on Network B may determine that a binding entry already exists for the WTRU  105 . The PMIP/FA  610  may send an MIP Register message  692  including (WTRU+registered CoA) to the HA  130 , using the same CoA as used for the MIP registration update. The HA  130  may retain only the new CoA. The HA  130  may send an MIP Register Rsp message  694  to the PMIP/FA  610  in Network B. The WTRU  105  may send a Handover Completed message  696  to the MIH server  637 . The HA  130  may forward data  698  from the correspondent peer to the WTRU using the new CoA. 
     As described in the methods above, the targeted CoA may be acquired via an exchange of Agent Solicitation and Agent Advertisement messages with the targeted FA. The Agent Solicitation may be sent by the HA, as shown in  FIGS. 2  through  5 . In one alternative, the MIH client may send the Agent Solicitation message instead of the HA, as shown in  FIG. 6 . Another alternative may be for the MIH server to send the Agent Solicitation message, as shown in  FIG. 7 . 
     As shown in  FIG. 7 , the MIH server  737  may initiate an acquisition of the targeted CoA by sending an Agent Solicitation message  750 . The targeted CoA may then be forwarded to the MIH client  110  using a GetInformationRsp message  755 . The acquisition of the targeted CoA alternatives shown in  FIG. 7  may apply to other methods including those shown in  FIGS. 2-6 . 
       FIG. 8  is a diagram of an example wireless communication system/access network  800  that includes an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN)  805 . The E-UTRAN  805  may include a WTRU  810  and several evolved Node Bs, (eNBs)  820 . The WTRU  810  may be in communication with an eNB  820 . The eNBs  820  may interface with each other using an X2 interface. Each of the eNBs  820  may interface with a Mobility Management Entity (MME)/Serving GateWay (S-GW)  830  through an S1 interface. An MIH server  835  may be in communication with the MME/S-GW  830 . Although a single WTRU  810  and three eNBs  820  are shown in  FIG. 8 , it should be apparent that any combination of wireless and wired devices may be included in the wireless communication system access network  800 . 
       FIG. 9  is a block diagram of an example wireless communication system  900  including the WTRU  910 , the eNB  920 , and the MME/S-GW  930 . As shown in  FIG. 9 , the WTRU  910 , the eNB  920  and the MME/S-GW  930  may be configured to perform a BBM MIH in accordance with the examples provided above. 
     In addition to the components that may be found in a typical WTRU, the WTRU  910  may include a processor  916  with an optional linked memory  922 , at least one transceiver  914 , an optional battery  920 , and an antenna  918 . The processor  916  may be configured to perform a break-before-make media independent handover in accordance with the examples provided above. The transceiver  914  may be in communication with the processor  916  and the antenna  918  to facilitate the transmission and reception of wireless communications. A battery  920  may be used in the WTRU  910  to power the transceiver  914  and the processor  316 . 
     In addition to the components that may be found in a typical eNB, the eNB  920  may include a processor  917  with an optional linked memory  915 , transceivers  919 , and antennas  921 . The processor  917  may be configured to perform a break-before-make media independent handover in accordance with the examples provided above. The transceivers  919  may be in communication with the processor  917  and antennas  921  to facilitate the transmission and reception of wireless communications. The eNB  920  may be connected to the Mobility Management Entity/Serving GateWay (MME/S-GW)  930  which may include a processor  933  with an optional linked memory  934 . 
     The GetInformation messages described above may be used to carry a WTRU&#39;s location, an indication of the targeted network, and an indication of the targeted FA&#39;s CoA. Additionally, a LinkGoingDown message may include an indication of a WTRU&#39;s location. Further, a Handover Request message may include a target FA&#39;s CoA. 
     In the examples described above, an MIH server may request the creation of a new simultaneous binding entry for a WTRU in the HA. The methods may include a new message from the HA to the FA to register the WTRU during MIP pre-registration. Additionally, a Router Solicitation message may include a Mobility Agent extension. A Router Solicitation message may include a Mobility Agent Advertisement Extension. The HA may send an Agent Solicitation to the FA with the H bit set to indicate that the HA which originated the message. When the FA receives an Agent Solicitation message with the H bit set, it may respond with an Agent Advertisement (containing the CoAs) unicast to the HA. 
     An HA may send an MIP registration on behalf of the WTRU to the targeted FA. In such a case, the lifetime may not be equal to zero. If the source IP address is the same as the HA IP address included in the message, the FA may send the response to the HA. In such a case, the FA may not be required to forward the registration request to the HA. 
     Data destined to a WTRU may be tunneled to the target IP address as soon as the Layer 2 connection is established on the target network, thus reducing interruption time. The methods and apparatus may utilize MIH to facilitate inter-technology MIP re-registration at a targeted FA. By allowing the MIH server to trigger MIP pre-registration on behalf of a WTRU, the network may control WTRU operation. The methods and apparatus may be applicable to contexts where handover is triggered based on criteria other than link quality. For example, the methods and apparatus may be applicable where an MIH server triggers a handover even where link quality is acceptable in order to achieve load balancing. 
     When simultaneous bindings are used at the HA during handover, data may be sent from the HA to both FAs. When simultaneous bindings are used, there may be no need for data to be buffered at the current FA and the target FA. There may also be no need to reserve memory for buffering or tunnel data between the current FA and the target FA. 
     The acquisition of the target CoA in the examples above may be transparent to the WTRU. In addition, the MIP re-registration with the targeted network may be transparent to the WTRU and no additional network nodes may be required. 
     Although the above methods are described with reference to 802.21 and an MIH server, they may also be applied using any technology that supports heterogeneous access technology handover. For example, an ANDSF server, among other types of devices in other mobility technologies may be implemented using the methods described above. 
     Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated 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). 
     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. 
     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) or Ultra Wide Band (UWB) module.