A CS395T Course Project MobileComputing &

WirelessNetworks

Spring 2001C

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Key Design/Approach A mode includes cwnd, ssthresh, rtt, srtt,

rttvar, rtxcur, etc. Generally, save the current mode and load

a new mode for a vertical handoff Schedule a handoff timer for a downward

handoff to avoid fast retransmission caused by out-of-order delivery

Reset mode for an upward handoff to an unvisited overlay network

An extension to New-reno TCP

New Ideas TCP manages multiple modes A mode is a subset of entire TCP state

– corresponds to an overlay network– dynamic

TCP is notified of the handoff events TCP switches between modes when the

mobile host vertical handoffs between different overlay networks

Different actions for upward and downward handoffs

Multi-Mode TCP for Wireless Overlay Networks

Results/Lesson Learned Implemented in ns2 Simulation results in ns2

–Eliminate unnecessary retransmissions caused by timeouts or duplicate acks

–TCP goodput improved (> 7%) Lesson learned:

– Implementation of TCP stack– Limitation of the simulation– Need of more realistic experiments

Project team: Fengfeng Tu, Hongxia TianURL: http://www.cs.utexas.edu/users/ftu//project.html

Motivation TCP has been tuned to traditional

networks comprising wired links and stationary hosts

Wireless overlay networks– Heterogeneous overlays– User mobility: vertical handoffs– Sudden, frequent, and significant changes in

bandwidth and delay Study TCP behavior over wireless overlay

networks and improve its performance