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ATCP : TCP for Mobile Ad Hoc Networks

ATCP : TCP for Mobile Ad Hoc Networks. By Jian Liu and Suresh Singh Presented By Harkirat Singh. Motivation. WireLess Network is Different from WireLine Network Ad Hoc Network - Node Mobility - Network Partition. Mobility Example:. s. s. a. a. d. d. b. b.

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ATCP : TCP for Mobile Ad Hoc Networks

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  1. ATCP : TCP for Mobile Ad Hoc Networks By Jian Liu and Suresh Singh Presented By Harkirat Singh CS 510 Internet Routing

  2. Motivation • WireLess Network is Different from WireLine Network • Ad Hoc Network - Node Mobility - Network Partition CS 510 Internet Routing

  3. Mobility Example: s s a a d d b b s s s T+5 T+20 d d d CS 510 Internet Routing

  4. Explicit Congestion Notification • By S.Floyd and Team • Active queue management with RED • RED can drop a packet or set a bit ECN-Echo flg 1, CWR flg 1 (SYN) ECN-Echo flg 0, CWR flg 1 ECT 1 CE 1 ECN-Echo flg 1 CS 510 Internet Routing

  5. Dynamic Source Routing <1,3,5,7> <1,2> 7 7 <1> Dest 2 2 5 5 Dest. <1,3,5> Src 8 8 Src <1> 1 3 1 3 <1,3> <1,4,6> 6 6 <1,4,6> 4 4 <1> <1,4,6> <1,4> <1,4,6> Route Discover – Route Record Propagation of Route Reply with Route Record CS 510 Internet Routing

  6. TORA-Route Creation (0,1) (0,3) (-,-) (-,-) 7 Dst 7 2 (0,0) Dst 2 5 5 8 (0,0) (0,3) (0,2) 8 . Src (-,-) (-,-) Src. 1 3 1 3 (0,3) (-,-) 6 6 4 (0,1) 4 (-,-) (0,2) (-,-) QRY packet UPD pkt – height updates CS 510 Internet Routing

  7. TCP in Ad Hoc Network • High Bit Error Rate (BER) • Route Recomputation • Network Partition • Multipath Routing CS 510 Internet Routing

  8. Goal • High BER – retransmit lost pkt • Route Recomputation & Transient Partition - stop transmitting • Multipath Routing – No congestion control • Maintain TCP’s congestion control CS 510 Internet Routing

  9. ATCP Functioning • States – Normal, congested, loss and disconnected • Lossy Channel – ATCP loss state and TCP Persist state • Disconnected – ICMP destination unreachable, TCP in persist state and ATCP in disconnected state • Congested – ECN flag, ATCP in congested state and do nothing! CS 510 Internet Routing

  10. State transition diagram Receive “Destination Unreachable” ICMP, CWND 1 Receive dup ACK or pkt from receiver TCP sender put in persist state Receive ECN New Ack RTO About to Expire OR 3 dup ACKs ATCP Retransmits segments in TCP’s buffer TCP transmits a pkt CS 510 Internet Routing

  11. Data flow - TCP/ATCP/IP stack data TCP_input() TCP_output() ATCP_input() ATCP_output() ipintr() ip_output() data CS 510 Internet Routing

  12. Flowchart for function atcp_input() CS 510 Internet Routing

  13. Flowchart for function atcp_output() CS 510 Internet Routing

  14. Performance study • Five Pentium PCs, each with two Ethernet cards • Emulate wireless in IP, 32 Kbps channel • Bit error rate 10(-5) • Random hop-by-hop delay • Network congestion – 5sec • Partition – 5 minutes and last for 1 min. • Packet reordering – 25 seconds CS 510 Internet Routing

  15. Bit Error - Performance Sequence number Time (seconds) Time (seconds) CS 510 Internet Routing

  16. Bit Error, Congestion Window Congestion Window Size Index Index CS 510 Internet Routing

  17. Congestion and Partition Performance Transfer time (second) hop by hop delay(ms) hop by hop delay(ms) Congestion Partition CS 510 Internet Routing

  18. Overall Performance CS 510 Internet Routing

  19. Conclusion • End-to-End TCP semantics are maintained • ATCP is transparent • ATCP does not interfere with TCP’s congestion control behavior • ATCP improves performance by one-third • ECN as standard - WIP CS 510 Internet Routing

  20. References • RFC 2481 • http://www-nrg.ee.lbl.gov/floyd/ecn.html • draft-ietf-manet-tora-spec-02.txt draft-ietf-manet-tora-spec-02.txt CS 510 Internet Routing

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