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TCP for Home Multimedia: Why you can’t teach an old dog new tricks

TCP for Home Multimedia: Why you can’t teach an old dog new tricks. Hariharan Rahul Szymon Chachulski , Kah Keng Tay , Dina Katabi. TCP’s shining moment. NSFnet backbone crum bled in 1986 Throughput dropped from 32 kbps to 40 bps. Congestion Control saved the day!.

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TCP for Home Multimedia: Why you can’t teach an old dog new tricks

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  1. TCP for Home Multimedia:Why you can’t teach an old dog new tricks HariharanRahul SzymonChachulski, KahKengTay, Dina Katabi

  2. TCP’s shining moment • NSFnet backbone crumbled in 1986 • Throughput dropped from 32 kbps to 40 bps

  3. Congestion Control saved the day!

  4. A thousand cuts since! • High-delay networks • Satellite links • High-bandwidth links • 100 Gbps to Terabit fibers • Real-time traffic • Gaming, IP TV • Datacenters and cloud computing

  5. TCP under siege You are an analog computer in a digital world!

  6. The last straw: Wireless Multimedia • Home Entertainment to grow to $12B by 2010 – Jupiter Research • Multimedia home networks growing at 46% compounded – Frost and Sullivan Why should TCP change?

  7. It’s not what TCP does; It’s how it does it! • Wireless is lossy Needs loss recovery • Wireless is a scarce shared resource  Needs congestion control But…

  8. TCP’s Architecture Is Too Rigid • Ignores the characteristics of the higher layer • Provides complete reliability regardless of what the application needs • Ignores the characteristics of the lower layer • Congestion control reacts to all losses, regardless of their cause

  9. Live Video Streaming TCP Video Packets Server Client TCP ACKs • Server and client using 802.11b • VLC for video streaming over TCP • Asymmetric links • Forward link good • Reverse link poor

  10. s 1 2 3 4

  11. Live Video Streaming TCP Video Packets Server Client TCP ignores higher layer needs and lower layer characteristics! TCP recovered, Video still frozen TCP ACKs Burst ACK Loss Video recovers

  12. TCP’s Architecture Is Too Rigid • Ignores the needs of the higher layer • Ignores the characteristics of the lower layer • Couples logical and physical packets

  13. Multicasting Video • Many popular applications • Mobile TV • Security videos in airports and train stations • Commercials or music videos in malls and nightclubs • But wireless multicast needs loss recovery!

  14. The Multicast Experiment • Lecture streamed via an access point • All nodes use 802.11b • Nodes simultaneously subscribe to lecture video

  15. Many Unicasts Congest the Medium Capacity ReTxUsr3 User 1 ReTxUsr1 User 2 ReTxUsr2 User 3 Wastes the fundamental broadcast advantage of wireless!

  16. Smarter Multicast Scales Better! Capacity ReTxUsr6 Common ReTxUsr1 ReTxUsr2 ReTxUsr3 ReTxUsr4 ReTxUsr5

  17. TCP’s coupling of physical and logical packets hinders wireless multicast!

  18. TCP’s Architecture Is Too Rigid • Ignores the needs of the higher layer • Ignores the characteristics of the lower layer • Couples Logical Connections with Physical Packets • Intertwines reliability and congestion control

  19. TCP Stifles Innovation • Mesh networks for a multistory home • Innovative opportunistic protocols for high throughput • But do not work with TCP! TCP Innovation Choice Low Throughput High Throughput

  20. Mesh Network Experiment • 2-hop mesh network running 802.11b • Determined throughput sustainable by • TCP • Opportunistic Routing Solutions • Encoded video at the corresponding rates • Transmitted encoded video over mesh network

  21. TCP’s intertwined reliability and congestion control stifles innovation

  22. Conclusion • We need TCP’s functions! • But TCP’s architecture shackles us! • Rigid layering does not understand application needs or medium behavior • Tight coupling of physical and logical packets not conducive to multicast • Intertwined reliability and congestion control stifle innovations for high throughput

  23. The time has come for a newer, nimbler alternative!

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