CPSC 4411 Wireless TCP Performance Issues CPSC 441

2 Example #1 r 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

CPSC 4413 Example #1 (Cont’d) r Solution: “wireless-aware TCP” (I-TCP, ProxyTCP, Snoop-TCP, split connections...)

CPSC 4414 Example #2 r Wireless TCP Fairness Problems Wired Internet Wireless Bottleneck DATA ACK DATA D U AP Loss of ACK = Loss of DATA

CPSC 4415 Example #3 r Multi-hop “ad hoc” networking Carey Kelly

CPSC 4416 Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC 4417 Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC 4418 Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC 4419 Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC Example #3 (Cont’d) r Multi-hop “ad hoc” networking Carey Kelly

CPSC Example #3 (Cont’d) r Two interesting subproblems: m 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? m 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?

CPSC Summary of Wireless TCP r TCP is the “four wheel drive” of TP’s r Wireless is a newly emerging technology with rapidly growing deployment popularity r “TCP” and “Wireless” don’t fit together all that well r Making TCP smarter about wireless helps!