Question
Suppose the correspondent in Figure 6.22 were mobile. Sketch the additional network-layer infrastructure that would be needed to route the datagram from the original mobile user to the (now mobile) correspondent. Show the struc- ture of the datagram(s) between the original mobile user and the (now mobile) correspondent, as in Figure 6.23.
Answer
If the correspondent is mobile, then any datagrams destined to the correspondent would
have to pass through the correspondent’s home agent. The foreign agent in the
network being visited would also need to be involved, since it is this foreign agent that
notifies the correspondent’s home agent of the location of the correspondent. Datagrams
received by the correspondent’s home agent would need to be encapsulated/tunneled
between the correspondent’s home agent and foreign agent, (as in the case of the
encapsulated diagram at the top of Figure 6.23.