Mobile and cellular IP CS 215 W 01

Mobile IP Mobile IP allows a computer to roam freely on the Internet while being reachable at the same IP address Each Mobile Host (MH) is associated with a unique home network as indicated by its IP address When a MH is away a special host (the Home Agent or HA) is designated on this network for intercepting and forwarding its packets

Mobile IP The MH uses a special registration protocol to keep its HA informed about its current location Whenever a MH moves to a foreign network, it chooses a foreign agent (FA) on the new network Packets for the MH are intercepted and tunneled by its HA and sent to its FA Tunneling: Refers to the process of enclosing the original datagram inside another datagram with a new IP header Called tunneling since the intermediate routers remain oblivious of the inner (original) IP header On receiving the tunneled packet, the FA forwards the original datagram to the MH

Three-way registration Process Home Agent Foreign Agent Mobile host Home Agent Foreign Agent Mobile host Home Agent Foreign Agent Mobile host Mobile Host registers with Foreign Agent Foreign Agent informs Home Agent about Mobile Host’s registration Home Agent starts interception and tunneling of packets for Mobile Host. Sends Confirmation to Foreign Agent

Interception and Tunneling Home Agent Foreign Agent Mobile host Old location of Mobile host Sender Tunneled Packet Interception: Lookup a table containing ‘currently away’ Mobile Hosts from the Agent’s network Tunneling: Encapsulate the packet within another IP packet

A typical cellular IP environment Base station 2 Base station 3 / Gateway Base station 1 Mobile Host Internet

Cellular IP & Mobile IP A B Gwy M.A. MIP tunnel Cellular IP Internet & Mobile IP

Cellular IP basic rules Every packet directed to a mobile host must go through the gateway Every packet that comes from a mobile host must come from the gateway The base-station wired subnet is reponsible to dynamically reroute packets to mobile host (via Cellular IP) Mobile hosts are responsible for handing off.

Cellular IP routing Each base station keeps a list of mappings (host IP address, interface) indicating on which interface to send a packet directed to each mobile host (ie, like forwarding in a bridged LAN; except, we use IP istead of MAC addresses). Routing is source-tree routing from the gateway (i.e. packets are routed on a tree rooted at the gateway) Each time a base station receives a packet from a host, it checks the validity of its routing table, and updates it if necessary (ie, backward learning). To handoff, a host simply sends a packet through the new base station. It cannot receive packets from its former base station after it has handed off (hard handhoff)

Cellular IP (hard) handoff A host monitors the power received from its base station. When power drops below a threshold, the host changes base station by sending a packet to its new base station (on a new frequency)

Packet loss in Cellular IP Packets may be lost due to handoff: Gwy

The simulation environment Simulation using GloMoSim GloMoSim was extended so that a hybrid environment (wired/wireless) could be simulated Implementation of cellular IP

Simulation topology Wired BS subnet Base station

Simulation parameters (cont ’d) 13 Base stations 39 Mobile hosts 20 min simulation runs Mixed traffic: real-time, ftp, telnet Random waypoint mobility

Results (cont ’d): Packet Loss

Simulation results: Handoff freq. vs mobility

Results (cont ’d): Succesful H/OFFs Speed(m.s -1 )