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TCP in Wireless Environments: Problems and Solutions

TCP in Wireless Environments: Problems and Solutions. Author: Ye Tian, Kai Xu, Nirwan Ansari Reporter: 任菊梅. Contents. 1. Abstract. 2. Introduction. 3. Challenges. 4. Approaches. Abstract. Dominance remarkable simplicity and reliability Design wired networks

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TCP in Wireless Environments: Problems and Solutions

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  1. TCP in Wireless Environments:Problems and Solutions Author: Ye Tian, Kai Xu, Nirwan Ansari Reporter: 任菊梅

  2. Contents 1 Abstract 2 Introduction 3 Challenges 4 Approaches 2

  3. Abstract • Dominance remarkable simplicity and reliability • Design wired networks assumption: packet losses are signals of network congestion. • Wireless Environment performs poorly high BER, unstable channel, user mobility 3

  4. Introduction • TCP • RFC793, in 1981,end to end, connection-oriented, reliable and ordered delivery of data • TCP Reno 4

  5. Challenges in Heterogeneous Network • Heterogeneous Network • consists of wired and wireless network • TCP exhibits weakness • degradation of throughput • inefficiency in network resource utilization • excessive interrupt of data transmissions • Why? • unique characteristics of wireless links • TCP’s design assumption 5

  6. Challenges in Heterogeneous Network • Unique characteristics of Wireless links • Transmission medium--open air • Uncontrollable quality-affecting factors: weather condition, urban obstacles, mobility of wireless end devices • High BER & multiple losses in one RTT • TCP sender reduce its sending rate Unnecessarily! 6

  7. Challenges in Heterogeneous Network • Unique characteristics of Wireless links • Limitations of radio coverage & user mobility • excessive interrupt 7

  8. Challenges in Heterogeneous Network • Unique characteristics of Wireless links • Link asymmetry • Packet losses in reverse channel • TCP sender think it happens on forward channel, and reduce sending rate • ACK compression effect • Break TCP’s self-clocking & possible congestive packet losses in forward channel 8

  9. Approaches to Improve Wireless TCP Performance 9

  10. Application-specific approach • TCP-Peach • Satellite network long propagation delay • Dummy • Copies of the last data packet • Low priority • new mechanisms • Sudden start: 2RTTs(tradition: 7RTTs) • Congestion avoidance • Rapid recovery: improve throughput in the presence of high link error rate • Fast retransmit 10

  11. Application-specific approach • ATCP • Ad hoc network: High error rate, frequent rout changes and network partitions • Thin layer between TCP & IP • Packet losses: • High BER: retransmits • Rout change: persist state • Congestion: normal control • Freeze-TCP • Cellular network: handoff & high BER • Receiver: sets the advertised window size to zero in ACK packets • Sender: persist mode 11

  12. Split Mode & End-to-End Approach • Split Mode • End-to-End Approach 12

  13. Reactive Approach • TCP New Reno • Partial ACK • Modification: fast recovery • Limitation: can’t distinguish the cause of packet loss • TCP SACK • Selective ACK option for TCP • Exact number of packet losses • Modification: sender & receiver sides • Limitation: congestion avoidance 13

  14. Proactive Approach • TCP-Vegas • Minimal RTT as a reference • Stable congestion window • TCP-Veno • Based on Vegas • differentiate the cause of the packet loss • TCP-Westwood • Measuring the averaging the rate of returning ACKs as reference • TCP-jesery • ABE & CW as refrence 14

  15. Q & A 15

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