Patent Publication Number: US-2007115885-A1

Title: Method and system for fast IP handoff of a mobile node

Description:
FIELD OF THE INVENTION The present invention relates to the field of mobile communication and more specifically, to fast IP handoffs of mobile nodes.  
     BACKGROUND  
      When an electronic device such as a mobile node (MN) using packet data connection moves from a first wireless network to a second wireless network, it may be handed over from the first wireless network to the second wireless network. This is known as IP handoff or Mobile/IP handoff. When IP handoff is performed in such a way that the end user does not notice the impact on quality of real time traffic during the critical path of handoff, the handoff is referred to as fast handoff of the MN. To support this handoff, each wireless network has an access router (AR) associated with it. For example, the first wireless network is associated with a first access router, and the second wireless network is associated with a second access router. The access router performs the function of a mobility agent, to support the mobility of the MN from the first wireless network to the second wireless network, which is known as network layer mobility. In the case of a fast IP handoff between the ARs, also called an inter-AR handoff, the mobility agent for the MN changes from a first AR to a second AR.  
      The inter-AR handoff of an MN requires the establishment of a wireless link layer connection between an MN and the second access router and the subsequent establishment of a bi directional edge tunnel between the second access router and the first access router over an existing wired link. The tunnel is established to avoid performing Mobile/IP registration during the critical path of handoff. The tunnel enables the transfer of data packets between the first wireless network and second wireless network. The first network receives data packets from the CN and forwards the packets to the second wireless access router that in turn are delivered to the MN over the newly established link layer connection of the second network, and vice versa.  
      The establishment of the bidirectional tunnel between access routers reduces packet loss as well as packet delay during IP layer handoff. However, the establishment of the tunnel also results in a non-optimal routing and poor utilization of the resources of the access router. The problem of non-optimal routing is introduced due to the addition of the routing segment between the first AR and the second AR. This requires the first AR and the second AR to process data packets originating at the MN and the CN.  
      Known methods for solving these problems are mentioned in a standard published by the 3 rd  Generation Partnership Project  2  entitled “CDMA2000 Wireless IP Network Standard: Simple IP and Mobile IP Services”, and in a memo published by the Network Working Group entitled “Low Latency Handoffs in Mobile IPv4”. These methods state ways of tearing down a tunnel after a period and renewing the tunnel prior to that period. However these methods do not specify any criteria for fast handoff tunnel teardown. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Various embodiments of the invention will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the invention, wherein like designations denote like elements, and in which:  
       FIG. 1  illustrates an exemplary environment, in accordance with some embodiments of the present invention;  
       FIG. 2  illustrates a block diagram of network architecture in a fast IP handoff, in accordance with some embodiments of the present invention;  
       FIG. 3  is a block diagram of an access router (AR), in accordance with some embodiments of the present invention;  
       FIGS. 4 and 5  show a flowchart illustrating a method of fast IP handoff of the MN, from the first wireless network b the second wireless network, in accordance with some embodiments of the present invention; and  
       FIG. 6  is a flow chart, illustrating a method of determining release of a tunnel established between a first access router and a second access router, in accordance with some embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Before describing in detail the particular fast mobile IP handoff method and system in accordance with the present invention, it should be observed that the present invention resides primarily in combinations of method steps and system components related to fast mobile IP handoff technique. Accordingly, the system components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.  
      Referring to  FIG. 1 , an exemplary wireless network environment is shown, in accordance with some embodiments of the present invention. A mobile node (MN)  102  is shown to be in communication with a correspondent node (CN)  104  via a first wireless network  106 . The present invention is explained with reference to voice over Internet Protocol (VolP) communication. However, it will be apparent to a person skilled in the art that the present invention is equally applicable to other types of communication. The CN  104  operates in an IP network that may be a wired IP network or a wireless IP network. The MN  102  is moving, as illustrated by arrow  112 , towards a second wireless network  108 . As shown in FIG. 1  the MN  102  is presently associated with the first wireless network  106 , but a fast handover will be necessary to associate the MN  102  with second wireless network  108  in order to maintain the voice over IP communication without interruption.  
      Referring to  FIG. 2 , a block diagram illustrates the network architecture in a fast IP handoff, in accordance with some embodiments of the present invention. The first wireless network  106  includes a radio network (RN)  202  and is connected to a first access router (AR)  204  that provides routing services to the MN  102  while it is connected with the first wireless network  106 . The first AR  204  performs the function of a mobility agent to support the network layer mobility of the MN  102  from the first wireless network  106  to the second wireless network  108 . In an embodiment of the present invention, the AR  204  is referred to as a Packet Data Serving Node (PDSN). In another embodiment of the present invention, the AR  204  is referred to as a foreign agent (FA). As explained earlier with reference to  FIG. 1 , the MN  102  is switched to the second wireless network  108 , using a fast IP handoff to maintain IP packet communication with the CN  104 . In such an event of a fast IP handoff from the first wireless network  106  to the second wireless network  108 , the mobility agent for the MN  102  will be changed from the first AR  204  to the second AR  206 , i.e., the MN  102  becomes associated with the second wireless network  108 . The second AR  206  provides routing services to the MN  102  while it is attached to the second wireless network  108 . In order to provide fast IP handoff, a bidirectional edge tunnel  212 , or tunnel  212  as it is referred to hereafter, is established between the first AR  204  and second AR  206 . The tunnel  212  provides for routing of the IP packets from the MN  102  to the CN  104  through the second AR  206 , the first AR  204  and the packet switched network  208 . The tunnel  212  provides for IP packet routing at least until the second AR  206  is registered with the packet switched network  208  as the mobility agent for the MN  102 . Embodiments of the present invention implement a tear down of the tunnel  212  and re-registration of the MN  102 , for which IP communications are then supported directly by the second AR  206 .  
      Referring to  FIG. 3 , a block diagram illustrates an AR  302  used for fast IP handoff of the MN  102 , from the first wireless network  106  to the second wireless network  108 , in accordance with some embodiments of the present invention. In an embodiment of the present invention, the AR  302  is the first AR  204 . In another embodiment of the present invention, the AR  302  is the second AR  206 . The AR  302  includes a decision module  304  and an initialization module  306 . Certain functions of the AR  302  are explained in conjunction with  FIGS. 4 and 5 .  
      Referring to  FIGS. 4 and 5 , a flowchart illustrates a method for fast IP handoff of the MN  102  from the first wireless network  106  to the second wireless network  108 , in accordance with some embodiments of the present invention. At step  402 , a communication connection is established between the MN  102  and the CN  104 . This signifies that there is a call in progress between MN and CN using a first wireless network. At step  404 , it is checked whether the first AR  204  has a link-layer binding with the MN  102 . If the first AR  204  has a link-layer binding with the MN  102 , step  402  is repeated. However, if the first AR  204  does not have sufficiently reliable link-layer binding with the MN  102 , the second AR  206  establishes a link-layer connection with the MN  102 , at step  406 . At step  408 , it is determined whether the first AR  204  is reachable from the second AR  206  that is associated with the second wireless network  108 . If the first AR  204  is not reachable from the second AR  206 , a mobile IP session is established between the MN  102  and the second AR  206 , at step  410  and no further action is taken In this situation, since no tunnel could be established between the first AR  204  and the second AR  206 , there may be interruption of audio or loss of the call in a voice IP call.  
      However, if the first AR  204  is reachable from the second AR  206 , the second AR  206  establishes a tunnel with the first AR  204 , at step  512 . The tunnel allows the transfer of data traffic between the first AR  204  and the second AR  206 . At step  514 , the tunnel between the first AR  204  and the second AR  206  is released based on predefined criteria. Thereafter, the first AR  204  signals the second AR  206  to initiate the setting up of a mobile IP session with the MN  102 , at step  416 . At step  418 , the second AR  206  initiates a mobile IP session with the MN  102 . At step  520 , the second AR  206  signals the first AR  204  to release the tunnel between the first AR  204  to the second AR  206 .  
      In some embodiments of the present invention, the predefined criterion is based on the traffic profile of data traffic exchanged between the first AR  204  and the second AR  206 . The first AR  204  and the second AR  206  are configured in these embodiments to identify real-time data traffic, based on the traffic profile. The pattern of the traffic is compared with the traffic profile of the real-time data traffic. If the pattern of the traffic does not match the traffic profile of the real-time data traffic, the tunnel between the first AR  204  and the second AR  206  is released.  
      In yet another embodiment of the present invention, the predefined criterion is based on CPU utilization at the first AR  204 . The CPU utilization at the first AR  204  is determined. If CPU utilization exceeds a configurable CPU utilization threshold value, the tunnel between the first AR  204  and the second AR  206  is released. In an embodiment of the present invention, the tunnel release is associated with lower-priority users.  
      In yet another embodiment of the present invention, the tunnel between the first AR  204  and the second AR  206  is released if the time for which the MN  102  has been registered with one of the first AR  204  and the second AR  206  exceeds a tunnel lifetime of the MN  102 . In an embodiment of the present invention, the tunnel lifetime is referred to as a visitor list lifetime. In another embodiment of the present invention, the tunnel lifetime is referred to as a binding cache lifetime.  
      In a case in which multiple IP sessions or flows associated with a mobile node MN  102  are anchored at the first AR  204 , an IP flow/session associated with non-real time traffic can also be selectively transferred from AR  204  to AR  206  without impacting remaining flows associated with the same mobile, in accordance with yet another embodiment of the present invention. The selective transfer of an IP flow associated with MN  102  from first AR  204  to second AR  206  requires support of flow based mobility management by the underlying mobility protocol.  
      In still another embodiment of the present invention, a tunnel associated with a lower-priority user is released, when buffer utilization at the first AR  204  exceeds a buffer utilization threshold value. The buffering delay is compared to a preconfigured time. Tunnel teardown may be initiated when the data packets are buffered beyond the preconfigured time.  
      When the tunnel between the first AR  204  and the second AR  206  is released, based on at least one of the predefined criteria discussed above, a mobile IP registration procedure is initialized with the second AR  206 , at step  404 . In an embodiment of the present invention, the initialization module  306  initializes the mobile IP registration procedure with the second AR  206 .  
      Referring to  FIG. 6 a  flow chart illustrates a method for determining release of a tunnel established between a first access router and a second access router, in accordance with some embodiments of the present invention. At step  602 , a check is made to determine whether data traffic is tunneled or detunneled. In an embodiment of the present invention, the first AR  204  and the second AR  206  perform simultaneous tunneling and de-tunneling of data traffic. In another embodiment of the present invention, the first AR  204  tunnels data traffic and the second AR  206  de-tunnels it This other embodiment can happen in case of a streaming application or when downlink traffic gets tunneled and uplink traffic is sent using an optimized route (MN—second AR—CN). In yet another embodiment of the present invention, the first AR  204  de-tunnels data traffic and the second AR  206  tunnels it. For any of these embodiments, a tunnel release criteria may be used that is based on tunnel inactivity. Tunnel inactivity may be measured using an inactivity timer. The tunnel inactivity timer is held in reset, or initialized, at step  604  while the tunnel is determined to be active during monitoring step  602  (packets are being tunneled or detunneled). When the tunnel is determined to be inactive at step  602 , the inactivity timer is no longer held in reset, and allowed to time the inactivity at step  605 . When the inactivity timer is determined not to have expired at step  606 , monitoring of the tunnel activity continues at step  602 . When the inactivity timer is determined to have expired at step  606 , release of the tunnel is initiated at step  608 .  
      It will be appreciated that the fast IP handoff described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement some, most, or all of the functions described herein; such as, releasing the tunnel between the first access router and the second access router. Alternatively, the same functions could be implemented by a state machine that has no stored program instructions, in which each function or some combinations of certain portions of the functions are implemented as custom logic. A combination of the two approaches could be used. Thus, methods and means for performing these functions have been described herein.  
      The method for fast IP handoff of a MN, described herein, can be applied to IEEE 802.16, IEEE 802.20, CDMA, HSDPA and other technologies using Mobile/IP Fast Handoff protocol.  
      In the foregoing specification, the present invention and its benefits and advantages have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims.  
      As used herein, the terms “comprises”, “comprising”, “includes”, “including” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.  
      The term “another”, as used herein, is defined as at least a second or more. The term “having”, as used herein, is defined as comprising. The term “coupled”, as used herein with reference to electro-optical technology, is defined as connected, although not necessarily directly, and not necessarily mechanically. The term “program”, as used herein, is defined as a sequence of instructions designed for execution on a computer system. A “program”, or “computer program”, may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system. It is further understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.