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Mobile IP protocols allow mobile hosts to send and receive packets addressed with their home network IP address, regardless of the IP address of their current point of attachment in the Internet.While some recent work in Mobile IP focuses on a couple of specific routing optimizations for sending packets to and from mobile hosts [Joh96] [Mon96], we show that a variety of different optimizations are appropriate in different circumstances. The best choice, which may vary on a connection-by-connection or even a packet-by-packet basis, depends on three factors: the characteristics the protocol should optimize, the permissiveness of the networks over which the packets travel and the level of mobile-awareness of the hosts with which the mobile host corresponds.Of the sixteen possible routing choices that we identify, we describe the seven that are most useful and discuss their benefits and limitations. These optimizations range from the most costly, which provides completely transparent mobility in all networks, to the most economical, which does not attempt to conceal location information. In particular, hosts should retain the option to communicate conventionally without using Mobile IP whenever appropriate.Further, we show that all optimizations can be described using a 4×4 grid of packet characteristics. This makes it easier for a mobile host, through a series of tests, to determine which of the currently available optimizations is the best to use for any given correspondent host. |
