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

2. 2016-9-29 1 2 3 4 Contents Abstract Introduction Challenges Approaches 2

3. 2016-9-29 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. 2016-9-29 Introduction 4 TCP RFC793, in 1981,end to end, connection- oriented, reliable and ordered delivery of data TCP Reno

5. 2016-9-29 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

6. 2016-9-29 Challenges in Heterogeneous Network 6 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!

7. 2016-9-29 Challenges in Heterogeneous Network 7 Unique characteristics of Wireless links Limitations of radio coverage & user mobility excessive interrupt

8. 2016-9-29 Challenges in Heterogeneous Network 8 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

9. 2016-9-29 9 Approaches to Improve Wireless TCP Performance

10. 2016-9-29 Application-specific approach 10 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

11. 2016-9-29 Application-specific approach 11 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

12. 2016-9-29 Split Mode & End-to-End Approach 12 Split Mode End-to-End Approach

13. 2016-9-29 Reactive Approach 13 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

14. 2016-9-29 Proactive Approach 14 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

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