Abstract:
A method and apparatus for improving handover in an IEEE 802.21 compliant communication network. A query is transmitted from a wireless transmit/receive unit (WTRU) to a media independent handover (MIH) server (MIHS). The WTRU includes a target point of attachment (PoA) and/or a preferred mobile inter protocol (MIP) method. The WTRU receives a response from the MIHS indicating the MIP method supported by the target PoA. Based on the received response, the WTRU may make an informed decision regarding handover.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application No. 60/910,494, filed Apr. 6, 2007 which is incorporated by reference as if fully set forth. 
     
    
     TECHNOLOGY FIELD 
       [0002]    This subject matter disclosed herein is generally related to wireless communication systems. 
       BACKGROUND 
       [0003]    The IEEE 802.21 standard defines mechanisms and procedures that aid in the execution and management of inter-system handovers. IEEE 802.21 defines three main services available to Mobility Management applications, such as Client Mobile Internet Protocol (Client MIP) or Proxy MIP. Referring to  FIG. 1 , these services are the Event Service  100 , the Information Service  105  and the Command Service  110 . These services aid in the management of handover operations, system discovery and system selection by providing information and triggers from lower layers  115  to upper layers  120  via a media independent handover (MIH) function  125 . 
         [0004]    Within the context of the command service  110 , functionality is defined for querying an MIH compatible node to determine the node&#39;s Internet Protocol (IP) capabilities. This is accomplished via the MIH_Network_Address_Information Request message sent from a wireless transmit/receive unit (WTRU) and the MIH_Network_Address_Information Response message sent from the MIH compatible node. 
         [0005]    Certain systems, such as the Third Generation Partnership Project Long Term Evolution (3GPP LTE) system, utilize a hybrid mobility schema where both client MIP and proxy MIP are used. Proxy MIP is preferred because of its well known advantages such as elimination of over-the-air (OTA) tunnelling overhead, greater flexibility, and reduced latency. However, in a roaming scenario it is highly likely that a WTRU will encounter networks that do not support proxy MIP. In this scenario, client MIP is used. 
         [0006]    Under the current IEEE 802.21 standard, a WTRU is unable to determine whether an accessible network provides support for localized mobility procedures (such as proxy MIP) or only conventional mobility procedures (such as client MIP). This information is an important criterion in network selection. Selection of a network with undesirable mobility management procedures will result in sub-optimal mobility scenarios. Furthermore, if a WTRU is able to determine the MIP characteristics of a network, the WTRU may trigger IEEE 802.21 procedures to improve mobility handling. 
       SUMMARY 
       [0007]    A method and apparatus for improving handover in IEEE 802.21 compliant communications. A query is transmitted from a WTRU to a MIH server (MIHS). The WTRU includes a target point of attachment (PoA) and/or a preferred MIP method. The WTRU receives a response from the MIHS indicating the MIP method supported by the target PoA. Based on the received response, the WTRU may make an informed decision regarding handover. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A more detailed understanding of the invention may be had from the following description, given by way of example and to be understood in conjunction with the accompanying drawings wherein: 
           [0009]      FIG. 1  is a block diagram of MIH services; 
           [0010]      FIG. 2  shows a wireless communication system in which a WTRU is unable to obtain mobility management information regarding diverse networks located therein; 
           [0011]      FIG. 3  shows an enhanced network of  FIG. 2 , in which a WTRU may query a MIH server and receive mobility management information regarding diverse networks located therein; 
           [0012]      FIG. 4  is a diagram of a MIH_Network_Address_Information Request message disclosed herein; 
           [0013]      FIG. 5  is a diagram of a MIH_Network_Address_Information Response message disclosed herein; and 
           [0014]      FIG. 6  is a block diagram of a WTRU and an access point configured to transmit and receive the messages of  FIG. 4  and  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    When referred to herein, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile node, mobile station (STA), 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 “access point” includes but is not limited to a Node-B, a site controller, a base station (BS), or any other type of interfacing device capable of operating in a wireless environment. 
         [0016]    A solution to the aforementioned problem is to provide a WTRU with information regarding the MIP capabilities of a network. The network is preferably a prospective network to which the WTRU is considering a handover to. In one embodiment, a request message includes an identifier of a network that is the target network for handover. An associated response message includes MIP capabilities of the identified network. 
         [0017]      FIG. 2  is a communication system  200  including two distinct networks  205  and  210  where mobility management information is not available to WTRU  215 . network  205  includes multiple network routers ( 220 ,  225 ) and three access points  230 ,  235 , and  240 . A server  245  of the first network  205  communicates with the network routers  220 ,  225  and servers of other networks via the Internet  250 , for example. The second network  210  also includes a server  255 , a network router  260 , and an access point  265 . It is noted that the first network  205  and second network  210  may be of the same or different type. 
         [0018]    In the communication system  200 , localized mobility management protocols, such as proxy MIP, are supported only in the first network  205 . When WTRU  215  is communicating with access points  230 ,  235 , and  240  (locations A, B, and C, respectively), localized mobility management is available for inter-access point handovers. However, second network  210  does not support localized mobility management protocols and instead supports only client MIP. When WTRU  215  is in communication with the second network  210  (position D) via access point  265 , WTRU  215  will perform client MIP procedures, including Client originated MIP Binding Update procedures. This client MIP procedure may potentially delay handover of the WTRU  215  to access point  265  in the second network  210 . 
         [0019]    Referring to  FIG. 3 , a wireless communication system  300  includes all of the elements identified above with respect to  FIG. 2  as well as an MIH server (MIHS)  305  accessible via the Internet  250 . The MIHS  305  controls various aspects of MIH and coordinates services between WTRUs and various networks. When WTRU  215  is associated with access point  240 , the WTRU  215  may query the MIHS  305  to determine the capabilities of surrounding networks. This may be achieved via the MIH_Network_Address_Information_Request message  310 , sent from the WTRU  215  to the MIHS  305 . The prospective point of attachment (PoA) in the prospective network (second network  210 ) may be identified in the message  310 , in this scenario access point  265 . In response, the MIHS  305  provides information regarding the characteristics of the prospective network (second network  210 ), such as whether proxy MIP is supported. The MIHS  305  responds to the MIH_Network_Address_Information_Request message  310  by sending a MIH_Network_Address_Information_Response message  315  including the requested information. 
         [0020]    Alternatively, the MIH_Network_Address_Information Request message  310  may simply indicate the MIP preferences of the WTRU  215 . In this scenario, the MIHS  305  will identify networks that are capable of supporting the WTRU&#39;s  215  MIP preference. Based on the information received from the MIHS  305  in the MIH_Network_Address_Information_Response message  315 , the WTRU  215  may choose access point  240  or access point  265 , depending on supported MIP services and preference. 
         [0021]    Referring to  FIG. 4 , the MIH_Network_Address_Information Request message  400  includes a Source ID field  405 , a Destination ID field  410 , a Current Link ID field  415 , a New PoA Identifier field  420 , a Target PoA Identifier List field  425 , a Current IP Configuration Method field  430 , a Current dynamic host control protocol (DHCP) Server Address field  435 , a Current Foreign Agent (FA) Address field  440 , a Current Access Router Address field  445 , and a Requested MIP Mobility Method field  450 . 
         [0022]    The Source ID field  405  indicates the originator of the message. The Destination ID field  410  indicates a remote MIH function that will be the destination of the request. The Current Link ID field  415  indicates the source link for handover. The New PoA Identifier field  420  indicates a new point of attachment identity. The Target PoA Identifier List field  425  includes a listing of potential points of attachment that the WTRU is considering for handover. Optionally, the list of potential points of attachment is sorted by preference, with most preferred points of attachment listed ahead of least preferred. The Current IP Configuration Method field  430  indicates current IP configuration methods. In one embodiment, this field is an optional field. The current DHCP Server Address field  435  indicates the IP address of a current DHCP Server. In one embodiment, this field is only included when the WTRU is using a dynamic address configuration. In another embodiment, this field is optional. The Current Foreign Agent (FA) Address field  440  indicates the IP address of a current FA. In one embodiment, this field is only included when the WTRU is using MIPv4. The Current Access Router Address field  445  indicates the IP address of a current access router. In one embodiment, this field is only included when the WTRU is using IPv6. In another embodiment, this field is optional. The Requested MIP Mobility Method field  450  identifies a WTRU preferred MIP mobility method. The MIH_Network_Address_Information Request message  400  may include all of the above described fields, or any sub-set of these fields, in any combination. 
         [0023]    In one embodiment, the Requested MIP Mobility Method field  450  includes a Proxy Mobile IPv6 indicator at bit  14 . Table 1 below illustrates one embodiment of the Requested MIP Mobility Method field  450 . 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Requested 
                 Bit 
                 Bits 0-31 
                 Bit 0: IPv4 static 
               
               
                 MIP Mobility 
                 map 
                   
                 Bit 1: IPv4 dynamic 
               
               
                 Method 
                   
                   
                 Bit 2: Mobile IPv4 with FA (FA- 
               
               
                   
                   
                   
                 CoA) 
               
               
                   
                   
                   
                 Bit 3: Mobile IPv4 without FA 
               
               
                   
                   
                   
                 (Co-located CoA) 
               
               
                   
                   
                   
                 Bits 4-10: Reserved for IPv4 
               
               
                   
                   
                   
                 address configuration 
               
               
                   
                   
                   
                 Bit 11: IPv6 stateless address 
               
               
                   
                   
                   
                 configuration 
               
               
                   
                   
                   
                 Bit 12: IPv6 stateful address 
               
               
                   
                   
                   
                 configuration 
               
               
                   
                   
                   
                 Bit 13: IPv6 manual 
               
               
                   
                   
                   
                 configuration 
               
               
                   
                   
                   
                 Bit 14: Proxy Mobile IPv6 
               
               
                   
               
             
          
         
       
     
         [0024]    Referring to  FIG. 5 , the MIH_Network_Address_Information Response message  500  includes a Source ID field  505 , a Destination ID field  510 , a Current Link ID field  515 , a New PoA Identifier field  520 , an IP Configuration Method field  525 , a DHCP Server Address field  530 , an Access Router Address field  535 , and a Result Code field  540 . 
         [0025]    The Source ID field  505  indicates the originator of the message. The Destination ID field  510  indicates a MIH function that will be the destination of the message (i.e., the WTRU MIH). The Current Link ID field  515  indicates the source link for handover. The New PoA Identifier field  520  indicates the point of attachment of a new access network to which handover initiation is considered. The IP Configuration Method field  525  indicates the IP configuration method of the point of attachment identified in the PoA Identifier field  510 . The DHCP Server Address field  530  indicates the DHCP server IP address of the point of attachment identified in the PoA Identifier field  510 . The Access RouterAddress field  535  indicates the IP address of the access router associated with the point of attachment identified in the PoA Identifier field  510 . The Result Code field  540  indicates a result code associated with the message. The MIH_Network_Address_Information Response message  500  may include all of the above described fields, or any sub-set of these fields, in any combination. 
         [0026]    In one embodiment, the IP Configuration Method field  525  includes a Proxy Mobile IPv6 indicator at bit  14 . Table 2 below illustrates one embodiment of the IP Configuration Method field  525 . 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 IP 
                 Bit 
                 Bits 0-31 
                 Bit 0: IPv4 static 
               
               
                 Configuration 
                 map 
                   
                 Bit 1: IPv4 dynamic 
               
               
                 Method 
                   
                   
                 Bit 2: Mobile IPv4 with FA (FA- 
               
               
                   
                   
                   
                 CoA) 
               
               
                   
                   
                   
                 Bit 3: Mobile IPv4 without FA 
               
               
                   
                   
                   
                 (Co-located CoA) 
               
               
                   
                   
                   
                 Bits 4-10: Reserved for IPv4 
               
               
                   
                   
                   
                 address configuration 
               
               
                   
                   
                   
                 Bit 11: IPv6 stateless address 
               
               
                   
                   
                   
                 configuration 
               
               
                   
                   
                   
                 Bit 12: IPv6 stateful address 
               
               
                   
                   
                   
                 configuration 
               
               
                   
                   
                   
                 Bit 13: IPv6 manual 
               
               
                   
                   
                   
                 configuration 
               
               
                   
                   
                   
                 Bit 14: Proxy Mobile IPv6 
               
               
                   
               
             
          
         
       
     
         [0027]    Proxy MIP is currently defined as Network-based Localized Mobility Management (NETLMM) support for internet protocol version 6 (IPv6) capable networks. However, the evolution of NETLMM will likely lead to support of legacy internet protocol version 4 (IPv4) networks. In another embodiment, support of IPv4 proxy MIP may be indicated in the messages described above. This would similarly allow a WTRU to select the best handover target during network selection. Additional reserved bits could be used to request and advertise IPv4 functionality. 
         [0028]      FIG. 6  is a WTRU  600  and access point  605  configured to transmit and receive MIH_Network_Address_Information Request and MIH_Network_Address_Information Response messages, as described above. WTRU  600  includes a processor  610 , an MIH function  615 , and a plurality of transceivers  620   a  . . .  620   n . The processor  610  and MIH function  615  are configured to generate and process a MIH_Network_Address_Information Request message as described above. The plurality of transceivers  620   a  . . .  620   n  are configured to communicate in a plurality of different types of wireless communication systems using various radio access technologies, and to transmit a MIH_Network_Address_Information Request message as described above. 
         [0029]    Access point  605  includes a processor  625 , an MIH function  630 , and a transceiver  635 . The access point  605  communicates with WTRU  600  via air interface  640 . The processor  625  of the access point  605  processes received MIH_Network_Address_Information Request message from WTRU  600  via air interface  640  and transceiver  635 . The processor  625 , in combination with the MIH function  630 , of access point  605  forwards received MIH_Network_Address_Information Request message to MIHS  645  and receives MIH_Network_Address_Information Response messages from the MIHS  645 . Received MIH_Network_Address_Information_Response messages are forwarded to the WTRU  600  via air interface  640 . 
         [0030]    Although the features and elements of the present invention are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the 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). 
         [0031]    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. 
         [0032]    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.