6610-l16- - Click to edit Master subtitle style 11 TCP over...

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Unformatted text preview: Click to edit Master subtitle style 11 TCP over Wireless Networks Puzzle o You are blindfolded o There is a square table in front of you o Four bottles places one at each corner o Bottles can either be in UP or DOWN orientations o You can feel any two of the bottles at a time, switch their orientation however you want to you win if all bottles are oriented alike o The table will be rotated arbitrary number of turns after each of your moves o Can you guarantee that you will win? 33 Recap o TCP over wireless networks n Wireless losses n Other losses n Large and varying delay n Path asymmetry n Low bandwidths n Large bandwidth delay product n Slow start o Approaches to improve TCP performance 44 WTCP o Reliable transport protocol for wide-area wireless networks o Alternative to TCP (but completely different unlike the schemes we have seen so far) o End-to-end approach 55 Reliability o Selective acknowledgements n SACKs very useful in TCP when random losses occur n Better utilization of the network resources (no unnecessary retransmissions) 66 Reliability (contd.) o No retransmit timeouts n Since RTOs cannot be relied upon, WTCP does not use RTOs o Use probe packets to recover from suffix losses o ACK frequency tuned by sender based on factors such as (a) observed loss rate on reverse path, (b) round-trip time, (c ) half-duplex or full-duplex nature of channel 77 WTCP Algorithm o Congestion control n 3 phases: increase, decrease, and maintain Chosen based on long-term and short term averages in inter-packet separation n RTT computation (for probing) n Using loss profile n Increase, decrease, maintain phases 88 WTCP Reliability o SACK algorithm o Probe packets Click to edit Master subtitle style RFC 3481 (TCP over 2.5G/3G) 99 Modifications o Appropriate window size o Increased initial window o Limited transport o Larger than default IP MTU o Path MTU discovery o SACK o ECN o Disabled TCP header compression 1010 Click to edit Master subtitle style 1111 pTCP: A Transport Layer Approach for Achieving Aggregate Bandwidths on Multi-homed Mobile Hosts 1212 Introduction o A multitude of wireless access technologies Objective n Allow simultaneous use of multiple wireless access technologies (striping) n Design a transport layer protocol that provides reliable and sequenced delivery like in TCP, and achieves effective bandwidth aggregation...
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6610-l16- - Click to edit Master subtitle style 11 TCP over...

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