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The Effect of Mobile IP Handoffs on the Performance of TCP

The Effect of Mobile IP Handoffs on the Performance of TCP. by A. Fladenmuller and R. D. Silva, Mobile Networks and Applications, Vol. 4, 1999, pp. 131-135. Handoff Scenarios. Effect of TCP Re-transmission on Mobile IP. TCP retransmission:

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The Effect of Mobile IP Handoffs on the Performance of TCP

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  1. The Effect of Mobile IP Handoffs on the Performance of TCP by A. Fladenmuller and R. D. Silva, Mobile Networks and Applications, Vol. 4, 1999, pp. 131-135.

  2. Handoff Scenarios

  3. Effect of TCP Re-transmission on Mobile IP • TCP retransmission: • RTO = retransmission time out value = 3 x round_trip_time • If after a RTO, the ACK to a TCP packet is not received, then the TCP packet will be retransmitted. • To prevent congestion, the timeout value will be doubled. • This is known as exponential backoff. • After a packet is correctly ACKed, the timeout value will be resumed to RTO. • Effect on Mobile IP: • At handoff, the TCP will consider this as “congestion”, which is incorrect. • Thus, after the handoff, there will be a period of NO TRAFFIC, until a retransmission occurs.

  4. On wireless link: MH to Foreign is by wireless... fig. 4 On wired link: fig. 5 Simulation Result

  5. There is no much difference on the delay between wireless links and wired links. • So the problem is not on the wireless part. • Factors contributing to the delay: • registration advertisement (once per second) • about 1 sec. • registration delay • about 1 sec. • TCP retransmission • about 1 sec.

  6. Conclusions • Possible solutions on Foreign Agent side: • buffer the underliverable packets • then forward to the new Foreign Agent after the handoff • Problem: This is only effective for the packets that are NOT retransmission packets. • Future Solutions Needed: • Agent advertisement • Faster handoff processing • TCP should not regard handoff as “congestion”

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