Tuesday, November 7, 1995:

Advanced Technology Seminar 1: Mobile-IP Protocols


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 seminar 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. If there is time, the speaker will recount some of the history of the mobile-IP working group within the Internet Engineering Task Force, and describe some of the competing proposals that have been considered by that working group.

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, the speaker 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 the speaker will describe the use of a new option for DHCP which allows the acquisition of IP addresses appropriately configured for use with the mobile-IP protocols.

If there is time, the speaker will also give a brief overview of the additional protocol improvements for mobility available using the new (128-bit) version of IP. Last, but perhaps not least, the speaker defines the terms and describes some technical approaches to achieving ad-hoc networking -- that is, the ability of mobile computers to initiate and maintain a connectivity framework among themselves automatically, without any help from existing Internet routers.