TABLE OF CONTENTS Wireless is about freedom of movement. Managing the mobility of users is therefore one of the key technical challenges of wireless IP research. It would seem that a user should be able obtain some IP services no matter where the user is located. For example, you would like to be able to take your laptop with you to places other than where you normally use it, and still be able to obtain some IP services, even if not as rich a set of services as you might be used to.
One can divide the problem into two parts. First, there is the issue of selecting an appropriate point of attachment to the network and establishing the link through that attachment point. Second, after the low-level link has been established, higher-level services (such as network services like IP routing, transport layer services like TCP connections, and higher-layer concepts like SIP-based multimedia sessions) need to be made accessible at the new attachment point. When selecting an appropriate point of attachment to the network, various factors are typically considered, like signal strength of the alternative choices (whether they be base stations of cellular systems, or access points of WLAN). Many algorithms have been proposed, but this selection and the link establishment are mostly radio issues below the network layer and beyond the scope of this book [1] , [2] , although we have briefly introduced some of the ideas like soft handoff in Chapter 3. In this chapter, we instead focus...
