The performance of Mobile IP in the case of micro mobility where the mobile node moves between two BSs in the same area showed Mobile IP’s inability to support this type of mobility [CAM 02], [REI 03]. In order to do so, a large amount of work has produced other approaches such as hierarchical approaches (PAA), or the enhanced routing approach (LERS) [MAN 02]. In the first category, there are
hierarchical Mobile IP (HMIP) [CAS 00], [MAL 00b],Fast Handoff (FMIP) [MAL00a and c] and other improvements for Mobile IP [MAL 01]. Other micromobility working groups are active at the IETF, such as Netlmm [NETLMM] where Proxy Mobile IP and Netlmm approaches are ongoing and Mext [MEXT] where IP mobility extensions are proposed. In the second category, there are Cellular IP [CAM 00b], HAWAII [RAM 00] and other approaches based on the multicast and ad hoc routing (MANET) approach [MAN 02].
One of the proposed changes of Mobile IP is hierarchical Mobile IP [CAS 00] which tries to improve the performance of Mobile IP in micro mobility. An FA will be installed at the gateway of the visitednetwork forming a GFA (Gateway Foreign Agent), which it will be responsible for the regional registration procedure [GUS 01], [MAL 00 2], thus hiding from the HA all movements of the mobile node inside the same visited network covered by a GFA. The mobile node will, in addition to the permanent address (HA), have a temporary address CoA to be attached to the gateway GFA, and a local address CoA to be attached to the FA visited network.
Thus, the HA retains the correspondence between the permanent address (HA) and the gateway CoA (GFA); however, the GFA keeps correspondence between the local CoA and the gateway CoA (GFA). The registration procedure is identical to that of Mobile IP, the only difference being that registration with the HA is only
necessary if the mobile node changes its GFA,otherwise the registration within the visited network is done with the GFA, which plays the role of a local HA. Packets to the mobile node are redirectedby the HA to the GFA, which then transfers them to
the mobile node.
Another improvement of Mobile IP is Fast Handoff [MAL 00a and c] which attempted to improve further handover delay of HMIP in micro mobility. To do so, it proposes to improve the detection of movement of the mobile node by using information from the link layer on top of the layer 2 handover (link layer). This information is used to precisely predict the layer 3 handover and thus can use network resources in the new cell as soon as possible after completing the layer 2 handover. In order to do this, the mobile node will begin its registration procedure (layer 3 handover) with the new FA through the old FA before the layer 2 handover is completed. In addition, a tunnel will be established between the old FA and the
new FA to deliver packets that continued to arrive at the former FA during the handover.