Abstract:
The present invention is directed to a system and method which mobile devices can be handed from one access point to another while maintaining continuous communication with a network and without changing the device&#39;s IP address. In an embodiment, when a device is leaving the air interface range of its home access point, it establishes a connection with an intermediary access point. In an embodiment, the communications from the network are directed to the original access point using the original IP address for the device, and forwarded to the device via the intermediary access point. Communications from the device are routed through the intermediary access point and then either directly to the network, or else through the home access point to the network. The IP address handoff is repeated between intermediary access points until the device either returns to the home access point or ceases communication with the network.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to and claims priority to Chinese Application No. 200610162364.5 filed Dec. 14, 2006, entitled “SYSTEMS AND METHODS FOR ALLOWING IP ADDRESS HANDOFF FOR MOBILE DEVICES”, the disclosure of which is hereby incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    This invention relates to wireless communication systems and more particularly to such systems that use IP addresses for data communication and even more particularly to systems and methods for achieving fast handoff in situations where IP addresses are handled on a dynamic basis. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wireless communication has come of age now where any number of devices are communicating with other devices over an air interface. Many of these communications use an address, such as an IP address, of the device in order to have the communications delivered properly. In cases where a device, for example, a computer, is wired into a network (such as the Internet) the device is assigned an IP address either permanently (static IP address) or more commonly via a dynamic allocation of the IP address on a temporary basis (dynamic IP address). In this regard, the Dynamic Host Configuration Protocol, (DHCP) is typically used for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. The DHCP supports a mix of static and dynamic IP addresses. 
         [0004]    As devices become portable, an air interface is established between the device and the network, usually via an access point located at a fixed physical location. In some situations the access point, using the DHCP, assigns an IP address to the portable device for the duration of a communication session. However, problems exist when the portable device is moved to a new location. In the simple situation, the user simply turns off the device (or leaves the area served by the air interface), moves the device to a new location and connects to a new access point via a new air interface and receives a new IP address. 
         [0005]    A more difficult scenario occurs when the device user desires to use the device as the device is being moved from one air interface to another. For example, assume a user is using a device in his/her home (or office) and then takes the device and walks a few blocks for a coffee. Also assume that the user desires to use the device continuously while walking those few blocks. Also assume that the original air interface in the user&#39;s home does not extend all the way to the coffee shop. This last scenario is only possible if there is an air interface available that spans the boundaries of the home and coffee shop&#39;s respective air interfaces. However, even if such a spanning air interface exists, maintaining a continuous communication connection to the network is difficult at best. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a system and method which mobile devices can be handed from one access point to another while maintaining continuous communication with a network by allowing the device to keep its assigned IP address for the duration of a communication session. In one embodiment, when a device is leaving the air interface range of its home base it establishes a new (temporary) air interface connection to an intermediary (neighbor) network access point and provides that access point with its existing IP address. The intermediary access point then uses the existing IP address to route communications to and from the device using the original IP address assigned to that device. In one embodiment the communications from the network are directed to the original access point and relayed from there to the intermediary access point while communications from the device are received by the intermediary access point and sent directly to the network. This IP address handoff is repeated between intermediary access points until the device is connected to the final destination access point, all the while keeping its original IP address. 
         [0007]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
           [0009]      FIG. 1  shows the assignment of IP addresses in accordance with the prior art; 
           [0010]      FIGS. 2A ,  2 B,  3 A and  3 B show embodiments of an arrangement for transferring access points while maintaining the IP address; 
           [0011]      FIGS. 4A ,  4 B and  4 C show embodiments of an arrangement for returning a mobile device back to a starting access point; and 
           [0012]      FIG. 5  illustrates one embodiment of a method for achieving the objectives of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  shows the assignment of IP addresses in accordance with the prior art such that access point  12  is connected to network  100  via bi-directional communication channel  14 . Typically, this channel would be a high speed channel which could be wireless or wireline which allows access point  12  to gain access to, for example, the Internet and to exchange information from other access points with respect to network  100  or other networks connected to network  100 . 
         [0014]    Mobile device  11  is in communication with access point  12  via air interface  13  which, for example, can be any one of a number of protocols, such as the 802.16e protocol. Access point  12  then assigns an IP address which may or may not be part of the subnet associated with the IP address of access point  12 . Thus, assuming an IP address of access point  12  as IP  123 - 120  then, for example, access point  12  could assign IP address of  123 - 121  to mobile device  11 . 
         [0015]    This IP address can be assigned, for example, using the DHCP protocol or may be static. It operates such that communications from any user on network  100  are directed to device  11  simply by using IP address  123 - 121  with respect to each communication. The network knows to send packets with the address  123 - 121  over communication link  14  to access point  12 , and access point  12  knows to use air interface  13  between itself and device  11  for the delivery of the data packet. Data from device  11  is transferred in the opposite direction via air interface  13 , access point  12  and communication link  14  to network  100 , and via network  100  to the destination associated with whatever IP address is associated with the data from device  11 . 
         [0016]      FIG. 2A  shows embodiment  20  which illustrates the first step in the transferring of device  11  from one access point to a next access point. Thus, we can assume device  11  is connected via air interface  13  to access point  12  as discussed with respect to  FIG. 1 . Assume now that device  11  begins to move out of the range of access point  12  and comes in range at access point  22 . Access point  22  is accessed from network  100  using IP address  234 - 220  over link  24 . While still in range of both access points, device  11  makes contact with access point  22  via air interface  23 . Device  11  then begins communication with access point  22  which realizes that device  11  already has an active IP address of  123 - 121 . Access point  22  then requests access point  12  to set up a tunnel between itself and access point  12  using link  25 . When the handover is completed, access point  22  sends a message to access point  12  that access point  22  is the host of device  11 . This then allows access point  12  to, as will be discussed, drop connection  13 . 
         [0017]      FIG. 2B  shows the completed connection where data packets from network  100  addressed to address  123 - 121  are routed over link  14  to access point  12 , through tunnel  26  to access point  22 , and then to device  11  via air interface  23 . Device  11  is connected only to device  22  via air interface  23  while still maintaining the IP address  123 - 121  as assigned by access point  12 . Note that while packets having address  123 - 121  were previously directed by network  100  over communications link  14  to access point  12  and then to device  11  via air interface  13 , they are now forwarded to access point  22  for delivery to device  11  via air interface  23 . 
         [0018]    Outgoing data packets from device  11  to network  100  may be routed from access point  22  through tunnel  26  to access point  12  and then through link  14  to network  100 , or may be routed from access point  22  directly to network  100  through link  24 . 
         [0019]      FIG. 3A  shows device  11  moving from access point  22  to access point  32  in a similar manner as device  11  moved from access point  12  to access point  22 . Access point  32  is accessed from network  100  using IP address  345 - 320  over link  34 . Access points  12  and  22  must be informed that packets intended for device  11  should now be forwarded to access point  32  instead of to access point  22 . Either access point  32  may inform both access points  12  and  22  of this change using link  35 , or else access  32  point may inform access point  22 , which in turn informs access point  12 , possibly using tunnel  26 . After a tunnel is set up between access points  12  and  32  access point  22  is then no longer a link in the connection from device  11  to network  100 . 
         [0020]      FIG. 3B  shows the completed connection where data packets from network  100  addressed to address  123 - 121  are routed over link  14  to access point  12 , through tunnel  36  to access point  32 , and then to device  11  via air interface  33 . Device  11  is connected only to device  32  via air interface  33  while still maintaining the IP address  123 - 121  as assigned by access point  12 . Note that while packets having address  123 - 121  were previously directed by network  100  over communications link  14  to access point  12  and then to device  11  via air interface  13 , they are now forwarded to access point  32  for delivery to device  11  via air interface  33 . Outgoing data packets are handled in a similar manner as discussed above for access point  22 . That is, outgoing packets may either be routed through tunnel  36  and access point  12 , or directly to network  100  through link  34 . 
         [0021]      FIGS. 4A and 4B  illustrate the situation where device  11  moves from access point  32  to access point  42  and from access point  42  back to access point  12 . Note that intermediate access point  42  communicates with network  100  via bi-directional channel  44  and communicates to device  11  over air interface  43 . Access point  42  is not necessarily the same as access point  22  illustrated in  FIG. 3A . Device  11  is not constrained to move back toward access point  12  using the reverse route as was taken when moving from access point  12  to access point  32 . 
         [0022]      FIG. 4B  shows the continued progress of device  11  back towards access point  12  and  FIG. 4C  shows device  11  back at original access point  12 . Note that during all of the movement of device  11  between access points, the IP address originally assigned for this session has continued to be the same. Thus, communications from network  100  have been delivered back and forth bi-directionally to/from device  11  using the same IP address without regard to which access point was serving the device. 
         [0023]      FIG. 5  illustrates one embodiment  50  of a method for achieving the objectives of the invention. Process  501  establishes the initial IP address with the home access point, which in the illustration is access point  12  of  FIGS. 1 through 4C . Process  502  determines whether the device is moving to another access point, or whether the home access point will continue serving the device. If the device is not moving away from the home access point, nothing is done. If it is, then a tunnel request from the new access point to the home access point is established via process  503 . 
         [0024]    In process  504 , the new access point informs the home access point that a new access point will serve the device. The home access point sets up a tunnel to forward data to the new access point. In process  505 , an optional confirmation is made between the new and home access points to confirm that the tunnel has been set up successfully. 
         [0025]    In process  506 , a determination is made, similarly as discussed above, as to whether the current access point will remain serving the device, or whether the device is moving to another access point. If the device remains with the current access point, no changes are made. If the device is moving, process  507  determines whether the device is returning to the home access point. If the device is returning to the home access point, the tunnel is released in process  508 . The home access point becomes the serving access point, which returns method  50  to process  502 . 
         [0026]    If, however, the device is moving to a new access point that is not the home access point, the data will need to be forwarded to the new access point. Method  50  then returns to process  503 . On this and subsequent returns to process  503 , process  503  optionally removes any previous access points that are not the home access point. 
         [0027]    Note that during any travel, device  11  will maintain the same IP address, regardless of its access point, and there need not be multiple intermediate access points for the system to operate. Also, note that while the handoffs and transfers from one access point to another have been described in the context of device  11  moving, transfer of access point control may be made based on access point availability. That is, device  11  may be transferred to a new access point without device  11  actually moving, but rather because the serving access point becomes overburdened or experiences a failure. 
         [0028]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.