Interconnection Between UMTS and WLAN Based on Mobile IP

The interconnection architecture related to the mobile IP is presented in
Figure 2.22. Mobile IP is employed to restructure connections when an MS
roams from one network to another. Outside of its home network, the MS
is identified by a care of address (COA) associated with its point of attachment
and a colocated FA that manages deencapsulation and delivery of
packets. The MS registers its COA with an HA. The HA resides in the home
network of the MS and is responsible for intercepting datagrams addressed to
the MS’s home address as well as encapsulating them to the associated COA.
The datagrams to an MS are always routed through the HA. Datagrams from
the MS are relayed along an optimal path by the Internet routing system,
though it is possible to employ reverse tunneling through the HA.
The required dual-mode MS protocol stack is the same as in Figure
2.21. It is clear that both networks are peer networks and that the functionality
of the HA/FA exists at the IP layer.