TCP/IP In Cellular Networks

Transcription

1 TCP/IP In Cellular Networks Two Techniques To Improve TCP Performance In Cellular Networks UNC Wireless Networks November, John DeArmon M-TCP: TCP for Cellular Networks Improving TCP Performance over Wireless Links with Frequent Disconnection, Low Bit-rate Error and Changing Bandwidth Kevin Brown, Suresh Singh Adapting TCP Segment to Cellular Real-time Segment Size Adjustment Based on Frame Error Rates Jin-Hee Choi, Jin-Ghoo Choi, and Chuck Yoo 1

2 M-TCP: TCP for Cellular Networks Improving TCP Performance over Wireless Links with Frequent Disconnection, Low Bit-rate Error and Changing Bandwidth Kevin Brown, Suresh Singh Characteristics of Cellular Networks High-Speed Network SH SH Divided into cells, and users share cell bandwidth Smaller cells are preferred to provide higher bandwidth to users Smaller cells result in smaller cell latencies, that, in turn, cause frequent handoffs Handoff: the action that mobile host changes wireless cell 4 2

3 TCP Congestion Control Window size Slope: 1/round-trip time W W/2 On detecting packet loss, TCP sender assumes that network congestion has occurred On determining congestion, TCP sender drastically reduces the congestion window Reducing congestion window reduces amount of data that can be sent per RTT Time Rationale TCP In Cellular Network Problem Improperly Trigger Congestion Control Solution Provide Appropriate Congestion Control Methods for Cellular Networks 3

4 Serial Timeouts at the TCP Sender Can Cause M-TCP: Latency TCP of Minutes for Cellular Networks Thus Serial Timeouts at the TCP Sender are More Harmful to Throughput Than Bit Errors or Small Congestion Windows Improving TCP Performance over Wireless Links with Periodic Disconnection UNC: SPECIAL TOPICS: HIGH- PERFORMANCE NETWORKS April 4, 2002 Wan Gang Zeng, Judy Zhan, Zhiwen Lin 1 Problem with TCP over Cellular Networks Congestion Control May be Inappropriate in a Cellular Environment On a Cellular Network, Packet Loss Occurs Due to the Following Reasons: Congestion: It Is Appropriate to Reduce Congestion Window Transmission Error: It Is Not Appropriate to Reduce Congestion Window Handoff: It Is Not Appropriate To Reduce Congestion Window 4

5 Comparison With Conventional Approaches All Assume High BER Is Root Cause of TCP Issues M-TCP Approach to Improve TCP Performance Three-level Hierarchy of Architecture Introduce Gateways to Manage Cellular Networks High-Speed Network SH SH Supervisor Host Cell Mobile Support Station (MSS) Mobile Host (MH) 7 5

6 Comparison: TCP and M-TCP TCP SH TCP Fixed Host (Sender) Mobile Host (Receiver) Comparison: TCP and M-TCP Control Window Reduced TCP SH Fixed Host (Sender) Mobile Host (Receiver) If the MH disconnects to the network and RTO times out, congestion control is invoked at the sender. If the disconnection time is long, the connection may be lost. 6

7 Comparison: TCP and M-TCP TCP SH M-TCP Fixed Host (Sender) SH-TCP M-TCP Mobile Host (Receiver) ACK(n) ACK(n-1) At SH, TCP connection is split into SH-TCP and M-TCP Comparison: TCP and M-TCP Cwnd unchanged TCP SH Fixed Host (Sender) SH-TCP M-TCP Mobile Host (Receiver) ACK(n, 0) If the wireless link is broken, SH-TCP will send an ACK packet to acknowledge the nth byte with a receiver window 0. This forces the Sender into Persist Mode. 7

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9 M-TCP Characteristics * Be able to deal with the problems caused by lengthy disconnection or by frequent disconnection Transport protocol in mobile computing Maintain end-to-end TCP semantics Ensure that handoffs are efficient M-TCP Test Environment * Be able to deal with the problems caused by lengthy disconnection or by frequent disconnection Transport protocol in mobile computing Maintain end-to-end TCP semantics Ensure that handoffs are efficient 9

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15 Adapting TCP Segment to Cellular Real-time Segment Size Adjustment Based on Frame Error Rates Jin-Hee Choi, Jin-Ghoo Choi, and Chuck Yoo 15

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21 Q&A And Thank You! 21