Page 75 - Mobile Computing

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o A mobile node has to change its IP address whenever it changes its
point of attachment, so that packets destined to the node are routed

correctly.
o To maintain existing TCP connections, the mobile node its IP
address the same. Changing the IP address will cause the connection
to be disrupted and lost.
 computer mobility in heterogenic networks
 relocation between different IP-subnets
 Goal: transparent migration and localization, compatibility to IP, no

changes of existing routers
 Idea: introduction of temporary/ actual IP-addresses (also “care-of
o Mobile IP is a proposed standard protocol that builds on the Internet
Protocol for packet routing and delivery by making mobility
transparent to applications and higher-level protocols like TCP.

o Changed perceptions of the Internet due to large variety of wireless
devices offering IP connectivity, such as PDAs, handhelds, and
digital cellular phones.

Routing

 Based on IP destination address, network prefix (e.g. 129.13.42)

 Determines physical subnet
 Change of physical subnet implies change of IP address to have a
topological correct address (standard IP) or needs special entries in the
routing tables.

Specific routes to end-systems?

 Change of all routing table entries to forward packets to the Right
Destination Does not scale with the number of mobile hosts and frequent
 Changes in the location, security problems

Changing the IP-address?

 Adjust the host IP address depending on the current location
 Almost impossible to find a mobile system, DNS updates take to long time
 TCP connections break, security problems

 Without specific support, delivery not possible for mobile nodes away
from its home IP subnet (because routing based on the network prefix and
dents IP add).
 Cannot change IP address on moving to new IP-subnet (because cannot
maintain tpt/higher level connections).