1. Cellular IP: A New Approach to Internet Host Mobility
Shyam Seshadri
Zaheer Ahmed
ECE 4605
Fall 2005

2. Need for Cellular IP
Competing requirements of IP addresses in wireless networks?
Host IP address (as a unique host identifier) must be constant regardless of host mobility
Host IP address (as a location identifier) must change according to changes in host’s location
Mobile IP supports two addresses – becomes inefficient in case of frequent migrations

3. Cellular IP- Development motivation
Easy global migration
Cheap Passive Connectivity
Flexible handoff support
Efficient location management
Simple memory-less mobile host behavior

4. Cellular IP - Design Compatible with IP, needs no extra address space
Uses performance scalability, i.e. use same protocol in distinct environments
No centralized data bases
Complexity of network elements does not increase with increasing coverage area
Have a general idea of location, zoom in when needed

5. Paging and Routing Mappings – Mobile IP
Routing is done on hop-by-hop basis
Each node requires to know specific ports to forward packets
Mapping: The routing information which maps mobile host identifiers to node ports
Mappings are assigned timers to clear outdated mappings after handoff

6. Wireless Network Topography

7. Paging and Routing Mappings – Mobile IP
Issues:
Path to old station remains till mappings are cleared
Small timeout – too much control messaging
Idle mobile hosts must transmit dummy packets resulting in significant load
Large timeout – slow updating of mappings

8. Paging and Routing Mappings – Cellular IP
Two parallel mapping structures:
Paging Cache
Set of mappings for idle mobile hosts
Timeout = Migration frequency (approx. sec, min)
Routing Cache
Set of mappings for active mobile hosts or hosts expecting to receive
Timeout = Packet time scale
Adv: Wireless networks can have large number of mobile hosts – Why?

9. Paging and Routing

10. Paging
Paging-update packets: Short control packets generated by idle mobile hosts
If no up to date information is available, a paging packet is generated
Paging packets are used to find the location of the unknown host
Route-update packets: Created by base station after receiving a paging packet response

11. Paging for Idle Hosts
Paging for Moving Hosts

12. Routing
Packets addressed to a mobile host are routed along the reverse path by RC
RC is updated as soon as there is a migration

13. Handoffs Handoff in Cellular IP is always initiated by the mobile host
The first of the redirected packets will automatically configure a new path of RC mappings for the host
During timeout, packets delivered at both the old and new base stations
After timeout, old mapping is cleared

14. Handoffs
Flags
Route to be taken
During timeout
Route update

15. Protocol Design Addressing & Migration Control Packet types
Mobile host needs to communicate local GW’s address to home agent
Home agent sends packets to GW, which is forwarded to host
Control Packet types
All three contain the mobile host identifier only
Control packets are IP compatible
Implemented by a new IP option - regular routers need not know of this. Why?

16. Protocol Design Node configuration Cellular IP is plug and play
But node must know which port to use to reach the GW

17. Protocol Design Node Algorithms
Nodes without PC’s and RC’s forward packets through all ports
When a paging packet arrives, the PC is checked
If valid mapping exists, packet is forward; else discarded
RC routes data packets arriving from the uplink ports

18. Protocol Design
Mobile Host Algorithm

19. Issues Timers Cache Paging
Higher timeout decreases control messages and increases validity of unused paths
Performance sensitive to RC timeout
Cache
More PC’s result in less paging load in exchange for increased hardware costs
Paging
Long time taken to page a mobile host may be unacceptable to IP

20. Conclusions Backward compatibility with Mobile IP
Can be scaled to a large extent easily
Simple and extremely robust nature
Highly optimized for wireless access networks to improve mobile connectivity

21. Questions?