Proliferation(增生) of mobile devices: PDAs, laptops, smart phones, …
As user moves, point-of-attachment(辅助箱) to network necessarily changes
Problem: IP address specifies point-of-attachment to Internet
Changing IP address involves terminating all connections & sessions
Mobile IP (RFC 2002): device can change point-of-attachment while retaining(保持) IP address and maintaining communications
Routing in Mobile IP
Home Agent (HA) keeps track of location of each Mobile Host (MH) in its network; HA periodically(定期) announces its presence
If an MH is in home network, e.g. MH#1, HA forwards packets directly to MH
When an MH moves to a Foreign network, e.g. MH#2, MH obtains a care-of-address(转交地址) from foreign agent (FA) and registers this new address with its HA
Routing in Mobile IP
Correspondent Host (CH) sends packets as usual (1)
Packets are intercepted by HA which then forwards to Foreign Agent (FA) (2)
FA forwards packets to the MH
MH sends packet to CH as usual (3)
How does HA send packets to MH in foreign network?
IP-to-IP Encapsulation
HA uses IP-to-IP encapsulation
IP packet has MH IP address
Outer IP header has HA’s address as source address and care-of-address as destination address
FA recovers IP packet and delivers to MH
Route Optimization
Going to HA inefficient if CH and MH are in same foreign network
When HA receives pkt from CH (1), it tunnels using care-of-address (2a); HA also sends care-of-address to CH (2b)
CH can then send packets directly to care-of-address (4)
