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

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

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

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

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Mapping: The routing information which maps mobile host identifiers to node ports Mappings are assigned timers to clear outdated mappings after handoff

Wireless Network Topography

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

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?

Paging and Routing

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

Paging for Idle Hosts Paging for Moving Hosts

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

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

Handoffs Flags Route to be taken During timeout Route update

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?

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

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

Protocol Design Mobile Host Algorithm

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

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

Questions?