In conventional mobile cellular net

In conventional mobile cellular networks and wireless LANs handover can be defined as the mechanism
by which an ongoing connection between a mobile host (MH) and a corresponding terminal or host is
transferred from one point of access to the fixed network to another [46]1. When an MH moves away
from a BS, the signal level degrades and it needs to switch communications to another BS. It is very
important in any cellular-based wireless networks because ongoing connection should be maintained
during handover. In cellular voice telephony and mobile data networks, such points of attachment are
referred to as BSs and in wireless LANs, they are called access points (APs). In either case, such a point
of attachment serves a coverage area called a “cell”. Handover, in the case of cellular telephony, involves
the transfer of a voice call from one BS to another. In the case of WLANs, it involves transferring the
connection from one AP to another. In hybrid networks, it will involve the transfer of a connection from
one BS to another, from an AP to another, between a BS and an AP, or vice versa.
For a voice user, handover results in an audible click interrupting the conversation for each
handover; and because of handover, data users may lose packets and unnecessary congestion control
measures may come into play. Degradation of the signal level, however, is a random process, and simple
decision mechanisms such as those based on signal strength measurements result in the ping-pong effect.
The ping-pong effect refers to several handovers that occur back and forth between two BSs. This exerts
severe burden on both the user’s quality perception and the network load. In the first part of this chapter,
we discuss general handover-related issues, and handover procedures of representative conventional
wireless networks. For excellent surveys on handover issues, see [44],[45],[46].