Mobile IP Handover

In the previous sections, we looked at how move detection and Mobile IP handover policy initiate a Mobile IP handover. Before we look at the messaging that performs a Mobile IP handover, we look at the possible types of handover. Using the information in agent advertisements, the Mobile Node can determine one of the following, as illustrated in Figure 2-12:

• Did I leave my Home Network? This implies a Mobile IP handover from the Home Network to a Foreign Network. When a Mobile Node leaves its Home Network, it initiates a new Mobile IP registration to its Home Agent.

• Did I roam to a different Foreign Network than the one I was already visiting? This implies a Mobile IP handover from one FA to another. In this case, the Mobile Node determines from its CoA whether a Mobile IP reregistration is necessary. If the CoA has changed, the Mobile Node initiates a Mobile IP reregistration. (If two access networks are connected to the same FA, the Mobile Node can hear the same CoA and not need to reregister.)

• Did I come back to my Home Network? This implies a Mobile IP handover from a Foreign Network to the Home Network. When the Mobile Node returns to its Home Network, it performs a Mobile IP deregistration to ensure that the Home Agent no longer attempts to tunnel its traffic. Remember that when a Mobile Node is attached to its Home Network, Mobile IP is not used for forwarding, because the standard IGP routing already delivers traffic to the Home Network.

Figure 2-12. Types of Mobile IP Handovers