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Transferring Internet Data on Wireless Networks

Transferring Internet Data on Wireless Networks. Presented by : Mohamed Gamal Presented to : Prof. Dr. Mohab Mangoud. The Internet. It is the largest network where users share resources: Web pages File transfers Voice communication Video Streaming. The OSI model. TCP.

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Transferring Internet Data on Wireless Networks

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  1. Transferring Internet Data on Wireless Networks Presented by : Mohamed Gamal Presented to : Prof. Dr. Mohab Mangoud

  2. The Internet • It is the largest network where users share resources: • Web pages • File transfers • Voice communication • Video Streaming

  3. The OSI model

  4. TCP • Transmission Control Protocol is a reliable protocol • Flow control • Windowing • Congestion Control • Transmission Control Protocol is designed for Wired networks

  5. TCP Congestion control • AIMD (additive increase multiplicative decrease) • Affected by • RTT (round Trip Time) • Retransmit timeout • Packet losses • Assumes packet losses are due to congestion

  6. Wired vs. Wireless links • Wired • Constant delay • Almost constant bandwidth • Packet losses due to congestion • Wireless • Varying delay • Asymmetric variable bandwidth • Loss of connectivity and high bit error rate • Packet losses due to corruption

  7. Types of Wireless links used • We have three main types of links • Cellular • WLAN • Satellite

  8. Cellular Links • Coverage radius of cell varies 200m-30km • In GPRS downlink • 40kbps bandwidth and 400ms delay • In GPRS upnlink • 10kbps bandwidth and 200ms delay • Protected by FEC and retransmits which cause delay • Acquiring channel access causes excessive delay

  9. WLANs • Small coverage area • Low Latency 3-100ms • High BW 2-108Mbps • Uplink and downlink channels are not independent • Shared bandwidth

  10. Satellite links • Very Large coverage area • High Latency 50-300ms • Bandwidth 0.01-50Mbps • GEO sats have latency 270ms, dowlink bandwidth of 40Mbps, uplink bandwidth of 1Mbps • LEO sats have 100ms latency, 1Mbps bandwidth but handover interval of 4 seconds

  11. Topologies • Performance is affected by number and locations of wireless links in the path • General topologies • Bus • Ring • Mesh • Star • Common wireless topologies • Wireless link as last hop • Wireless link in the middle • 2 wireless links at the end (mobile and laptop) • Wireless links at both ends (VoIP) • Mobile users transfer more data downlink than uplink • WAP (Wireless Application Protocol)

  12. Performance metrics • Throughput • Delay • Fairness • Dynamics • Goodput • High Goodput = lower power and reduced expenses

  13. 1 Mbps duplex link1Mbps WLAN

  14. Wireless Link characteristics • Error Losses and Corruption • Delay Variation • Packet Reordering • On-Demand Resource Allocation • Bandwidth variation • Asymmetry in Bandwidth and Latency

  15. Error Loss and Corruption • Effect on TCP • Reduce sending rate • Burst losses trigger lengthy retransmission timeouts • Presence in wireless links • Handovers and mobility cause lots of packet losses • Losses have been decreased due to use of FEC and link layer retransmissions

  16. Delay Variation • Effect on TCP • Abrupt delay trigger spurious timeouts that cause unnecessary retransmissions and false congestion control • Persistent delay variation can inflate the retransmission timeout • Presence in wireless links • Occur due to link-layer error recovery and handovers • Sudden change in radio conditions (entering a tunnel) • Delay can occur in one direction if a path is asymmetric

  17. Packet Reordering • Effect on TCP • Triggers packet retransmissions • Presence in wireless links • WLAN do not introduce reordering • Cellular links include an option for out of order delivery • Reordering on satellite links with a high bandwidth-delay product is attractive because it reduces the per-packet delay for other traffic on the link

  18. On-Demand Resource allocation • Effect on TCP • Causes delay variation that depends on traffic patterns • Presence in wireless links • GPRS requires 200ms to allocate a channel for uplink and 80ms delay for downlink • For WLAN and satellite links a new data burst triggers MAC contention • Subsequent data can often be transmitted without delay

  19. Bandwidth variation • Effect on TCP • Periods of low link bandwidth can result in congestion • Periods of high link bandwidth could result in underutilization of that link • Presence in wireless links • Bandwidth oscillation can occur in CDMA2000 and UMTS (with High Speed Downlink Packet Access) links for certain configurations* • *M. Yavuz and F. Khafizov. TCP over wireless links with variable bandwidth.

  20. Asymmetry in Bandwidth and latency • Effect on TCP • Causes congestion for TCP ACKs • Presence in wireless links • Cellular links have moderate bandwidth asymmetry with factors of 2 to 5 • Satellite Links are often asymmetric in bandwidth and in latency

  21. Improving TCP or wireless ?

  22. Improving TCP performance over wireless • There are three categories • End-to-end protocols, where sender is aware of the wireless link • Link-layer protocols, that provide local reliability • Split-connection protocols, that break the end to end connection into two parts at the base station

  23. New Technologies made available by wireless links • Wireless VoIP • Mobile TV • Mobile Holograms

  24. Summary • During the last years, both internet and mobile systems grew extremely fast. • Nowadays these two worlds are converging. • Wired Links are still ahead of wireless links but wireless links progressed quickly.

  25. The END

  26. References • A. Gurtov and S. Floyd. Modeling Wireless Links for Transport Protocols. In ACM CCR, 34(2):85-96, April 2004 • Bernd Girod, Mark Kalman, Yi J. Liang, Rui Zhang. Advances in Channel Adaptive Video Streaming. In proc of IEEE Intern. Conf. Image Processing (ICIP’02) Sept. 2002 • Qian Zhang, Wenwu Zhu, and Ya-Qin Zhang. Network-adaptive Scalable Video Streaming Over 3G Wireless Network. In IEEE International Conference on Image Processing(ICIP’01), Oct., 2001 • Lin Cai, Xuemin Sherman, Jon W. Mark and Jianping Pan, Performance Analysis of AIMD-Controlled Multimedia Flows in Wireless IP Networks • Ramon Caceres and Liviu Iftode. Improving the performance of reliable Transport Protocols in Mobile Computing Environments. In IEEE Journal on Selected Areas in Communications, Vol. 13, No. 5, June 1995 • Trista Pei-chun Chen and Tsuhan Chen. Fine-Grained Rate Shaping for Video Streaming Over Wireless Networks. In EURASIP JASP 2004

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