MobiCom '95 Tutorials

Mobile IP

Charlie Perkins
IBM T. J. Watson Research, U.S.A

Mobile-IP is a means by which mobile computers can use Internet protocols (IP) to communicate data with network resources transparently to application software. The mobile client supplies information to a router, called its home agent, about its current whereabouts using a simple registration protocol. The mobile client uses the same IP address as it moves from place to place, and the problem of enabling mobility for IP clients is translated into the problem of allowing a home agent to determine a current path to the unchanging destination address of its mobile client. Subsequently, the home agent delivers data to the mobile client at its current location by a tunneling mechanism. Since the mobile-IP protocol does not depend on the characteristics of any particular subnetwork protocol, the same mechanism works for every wireless medium, as well as existing wired media like Ethernet. The tutorial will explain the details of the mobile-IP model, as well as the registration protocols and tunneling mechanisms. Once the basic operation has been shown, additional mechanisms will be described to avoid the need for routing packets through the (possibly distant) home agent, providing an faster route between mobile clients and their correspondents.

The Dynamic Host Configuration Protocol (DHCP) will also be introduced and its usefulness for mobile users explained. After describing the basic DHCP client/server model, We will apply it in some likely scenarios for mobile computing, and show the advantages and the disadvantages of using DHCP. Perhaps even more than static computers, mobile computers will be used by people uninterested in performing administrative duties, and We will describe the use of a new option for DHCP which allows the acquisition of IP addresses appropriately configure for use with the mobile-IP protocols.

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