1 / 32

MCP: Mobile-host-centric transport protocol

MCP: Mobile-host-centric transport protocol. Enhancing TCP throughput in WLAN Mobile-host-centric transport protocol -- MCP Enhancing TCP throughput in WLAN with multi-hop ?. TCP Problem over Wireless Networks. In TCP Packet Loss <=> Congestion But in Mobile Networks

dennis-delacruz
Download Presentation

MCP: Mobile-host-centric transport protocol

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MCP: Mobile-host-centric transport protocol • Enhancing TCP throughput in WLAN • Mobile-host-centric transport protocol -- MCP • Enhancing TCP throughput in WLAN with multi-hop ?

  2. TCP Problem over Wireless Networks • In TCP • Packet Loss <=> Congestion • But in Mobile Networks • Packet Loss <=> Congestion (Net) ??? • high bit error rate (Phy) - No • access contention (MAC) - ? • disconnection (Net) - No • handoff (Net) - No • The TCP end-to-end performance is degraded seriously in wireless networks

  3. Our solution – cross layer • Proposed a mobile-host-centric transport protocol called MCP • TCP-RCP integrated / hybrid • Shifts the transport layer control schema to the mobile host side under all cases (mobile host is a sender or receiver) • Mobile stations can make better transport layer control based on the status of wireless link (cross layer)

  4. Styles of handshake • DATA-ACK handshaking • When mobile station is the sender • Sender sends data, receiver sends ACK to acknowledge correct receive of that data • REQ-DATA handshaking • When mobile station is the receiver • Receiver sends REQ to request data, and sender sends data accordingly • Receiver sends pull REQ to request retransmit

  5. Congestion control • Maintains the congestion window (cwnd) at the mobile station under all cases (mobile host is a sender or receiver) • “Slow-start” • The window is increased exponentially • “Congestion avoidance” • Increase its window size by 1/cwnd every time

  6. Congestion control • Fast retransmit (- cumulative acks) • Detect loss • 3 dup ACKs or 3 out-order data packets • Retransmission • send data packet or pull request • Fast recovery • After a fast-retransmit set cwnd to ssthresh/2 • i.e., don’t reset cwnd to 1 • But when RTO expires still do cwnd = 1

  7. Cross-layer method • Track information at MAC layer • distinguish packet loss under MAC layer • Feedback these information to transport layer congestion control • Modify the fast retransmit and fast recovery schema according to these information

  8. Cross-layer implementation • Record packets that fail to send within limit times at the MAC layer of the mobile station • Notify the transport layer if the packet loss is caused by MAC layer • Fast retransmitimmediately if the packet loss is caused by MAC layer • Fast recoverywithout reducing congestion window if the packet loss is caused by MAC layer reason

  9. Simulation scenario Ⅰ • WS - Wireless Station • AP - Access point • FH - Fixed Host • 1 flow

  10. WS – as sender WS – as receiver Throughput (1 flow)

  11. Experiment result: Throughput • WS – as sender

  12. Simulation scenario Ⅱ • 5 flows

  13. WS – as sender WS – as receiver Throughput (5 flows)

  14. 业务加载 T(1- pW) T MCP控制 子模型 无线丢包 子模型 网络子模型 (M/M/1/B) p pB pW p=pB+(1- )pW 考虑无线丢包区分度的MCP模型 • 模型组成：MCP控制子模型、网络子模型、无线丢包子模型 • T:传输层吞吐率 • pB:队列丢包概率 • pW:无线丢包概率 • p:总丢包率 • :无线丢包区分因子，两种情况 • =0 不区分无线丢包，则有： • p=pB+pW (两种丢包独立) • =1 区分无线丢包 ，则有： • p=pB • 0<<1 实验确定最佳值 • 目的：建立MCP吞吐率随无线丢包率的变化曲线

  15. MCP控制子模型 • 作用 • 计算MCP的吞吐率，加载到网络子模型和丢包子模型 • 方法 • MCP以发送端为中心和以接收端为中心的控制方法都与TCP类似，借鉴TCP的吞吐率分析方法 • 参数 • 丢包率（p） • 往返时间（RTT ） • 数据包长度（MSS） • 假设条件 • RTT固定 • 不采用延迟 ACKs 或 REQs策略 • 只考虑拥塞避免阶段 • 周期性丢包，每个周期丢一个包

  16. Window +1 per RTT a loss event W W/2 Time W/2 RTT 简单的MCP控制模型 • 稳态情形下MCP拥塞窗口的变化规律

  17. 简单的MCP控制模型 • 稳态情形下，MCP的吞吐率计算 • T = MSS / (RTT * sqrt (2p/3)) • 下一步考虑用更精确的模型[Padhye sigcom98]进行分析 T

  18. Customers Server µ Queue (B-1) 网络子模型 • 我们将网络子模型视为一个M/M/1/B 排队模型 • 包到达速率为λ • 缓冲区容量为B个包 • 服务规则为FIFO • 缓冲区满时丢包（drop tail） • 缓冲区中的包通过速率为µ的瓶颈链路发送

  19. M/M/1/B 模型 • 排队论（L.Klanloc Queuing System Vol I pp.104 ，公式3.43），队列中有k个包的概率为： • 队列丢包概率：

  20. 无线丢包子模型 • 研究不同的无线丢包方式对MCP协议性能的影响 • 两种丢包模型：文献 [H. Balakrishnan, V. Padmanabhan, S. Seshan, and R. Katz, A Comparison of Mechanisms for ImprovingTCP Performance over Wireless Links, IEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 5, NO. 6, DECEMBER 1997] • 指数丢包模型 • 突发丢包模型 • 其他丢包模型（?）

  21. fT(t)  t 指数丢包模型 • 丢包由无线链路错误引起 • 无线链路连续两次发生错误的间隔时间T遵从参数为的指数分布

  22. 突发丢包模型 • 丢包由无线链路错误引起 • 丢包以突发方式产生 • 丢包的数据间隔是随机的，均值为64KB • 每64KB数据发生1次突发丢包 • 每次突发丢包时的丢包数 • 2 packets • 4 packets • 6 packets

  23. Using Cross-layer Info to Improve MCP Performance in Multi-hop WLAN • Cross-Layer info • Packet-loss info of MAC • Packet drop info of Interface Queue between IP layer and MAC layer • MCP Head • Between IP Head and TCP Head • Include sequence number and drop styles (MAC or IFQ )

  24. MCP Head MCP Head Drop reason Drop reason 1001 1001 Seqno Seqno 1002 1002 Process of info transfer (WS – as sender) • No. reason • MAC MAC Seqno=1001

  25. MCP Head MCP Head MAC MAC 1002 1002 Seqno=1001 Seqno=1001

  26. 1002 1002 1002 buffer No. Drop reason 1001 MAC

  27. Main Process (WS – as sender) • The collection and transmission of Packet Loss/Drop Info (PLDI ) • The source node mainly collects the PLDI from ACK and local MAC & IFQ • The intermediate nodes buffer the PLDI from local MAC and IFQ; and then piggyback it onto next packet • The destination node pack the PLDI of relays into ACKand send it back to the source node • The disposal of the source node when a PLDI received

  28. Three cases to confirm the packet loss in MCP MAC packet-loss info and IFQ packet-drop info received When MAC packet-loss info received, the source retransmit the lost packet and not reduce CW When IFQ packet drop info received, the source retransmit the drop packet and reduce the CW to 90% Adjust CW according to MCP ACK (WS – as sender)

  29. Adjust CW according to MCP ACK (WS – as sender) • Three cases to confirm the packet loss in MCP • Three Duplicate ACKs • If the MAC PLDI of the packet that triggers the duplicate ACKs is already recorded in the buffer, the source node retransmit the packet and not reduce CW • If the IFQ PLDI of the packet is already recorded in the buffer, the CW will be reduced to 90% again and retransmit the packet

  30. Three cases to confirm the packet loss in MCP Timeout If the MAC PLDI is in buffer, the source node initialize a retransmission process and not reduce CW If the IFQ PLDI is in buffer, the CW will be set to 1 and half the threshold Adjust CW according to MCP ACK (WS – as sender)

  31. Simulation scenario

  32. Throughput VS. Packet Error Rate WS – as sender WS – as receiver

More Related