In order to balance the issue of limited resources and the
accuracy of handoff decisions, cost function based VHDA is
introduced for the handoffs initiated by attachment points.
The cost function is used to determine whether the MN
should keep staying in the current access network or handoff
to the target network. In this subsection, we further classify
the handoff decision criteria into positive metrics and
negative metrics. Suppose that m positive metrics and n
negative metrics are considered in the cost function based
VHDA. The cost function is given by (5):