1. Wireless TCP Performance Issues Carey Williamson Department of Computer Science University of Calgary

2. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20112 Example #1 Wireless TCP Performance Problems Wired Internet Wireless Access High capacity, low error rate Low capacity, high error rate Hard to distinguish losses here from losses here

3. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20113 Example #1 (Cont’d) Solution: “wireless-aware TCP” (I-TCP, ProxyTCP, Snoop-TCP, split connections...)

4. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20114 Example #2 Wireless TCP Fairness Problems Wired Internet Wireless Bottleneck DATA ACK DATA D U AP Loss of ACK = Loss of DATA

5. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20115 Example #3 Multi-hop “ad hoc” networking Carey You

6. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20116 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

7. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20117 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

8. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20118 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

9. Copyright © 2005 Department of Computer Science CPSC 641 Winter 20119 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

10. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201110 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

11. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201111 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

12. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201112 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

13. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201113 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

14. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201114 Example #3 (Cont’d) Multi-hop “ad hoc” networking Carey You

15. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201115 Example #3 (Cont’d) Two interesting subproblems: –Dynamic ad hoc routing: node movement can disrupt the IP routing path at any time, disrupting TCP connection; yet another way to lose packets!!!; possible solution: Explicit Loss Notification (ELN)? Handoff? Route prediction? –TCP flow control: the bursty nature of TCP packet transmissions can create contention for the shared wireless channel among forwarding nodes; collisions between DATA and ACKs possible solution: rate-based flow control? Burst mode? Spatial reuse of channels?

16. Copyright © 2005 Department of Computer Science CPSC 641 Winter 201116 Summary of Wireless TCP TCP is the “four wheel drive” of TLPs Wireless is a newly emerging technology with rapidly growing deployment popularity “TCP” and “Wireless” don’t fit together well Making TCP smarter about wireless helps!