Hey people , i want to just suicide in these days. However, i have to deliver my thesis until the first day of June. Working on Mobile IPv4 and its issues. Moreover, i have some questions again my mind. There are some elements in Mobile IPv4 communication such as correspondent node, Mobile node,foreign agent,home agent(disgusting one) and care of addresses with home addresses. I wonder tunneling among home agent and foreign agent. questions 1- why is that tunneling(encapsulation) "just only" among home agent and foreign agent? i ask this since while correspondent node tries to communicate with Mobile node when it is away from home, i consider there have to be set up new tunnels for instance between correspondent node and home agent? 2- We build a tunnel between home agent and foreign agent but if NAT is used at these devices,how can end-to-end communication occur ? 3- There is also a "binding update" thing at that protocol(Mobile IPv4). After learning home agents and foreign agents in that networks, Mobile node has to be registered to home agent directly or through foreign agent. Though, after tunneling there exists a binding update event. So what is the difference between registration and binding update?