WiSE: A Novel Efficient Transport Protocol for Wireless Networks

1. WiSE: A Novel Efficient Transport Protocol for Wireless Networks Roberta Fracchia Joint work with C. Casetti, C. Chiasserini, M. Meo

2. Multihoming: one SCTP host can establish an association with another SCTP host over multiple interfaces, each identified by a separate IP address SCTP: Multihoming If one of these addresses fails, the destination host can be reached through a different interface • PrimaryDestination Address - normally used for the transmission of new packets • SecondaryDestination Address - to retransmitlost packets - to transmit new packets only if the primary interface is ‘inactive’

3. WiSE: Wireless SCTP Extension • Designed specifically for wireless networks • Discriminates losses due to congestion from those due to the wireless channel: • is based on the bandwidth estimation on the default path - allows different reduction of the congestion window • Usesefficiently multiple destination addresses: • transmits on the path with the largest available bandwidth

4. WiSE: Bandwidth Estimation On the primary path : • accurate estimate based on received ACKs • employs a time-varying low-pass filter (as TCP Westwood) On the secondary path : • based on the transmission of a 6-packets train • uses Heartbeats transmission • tradeoffs efficiency vs. accuracy HB: Heartbeat (40 bytes) 1500 bytes 1500 bytes HB HB HB HB time IHB IDATA

5. WiSE: Congestion Control • If ( generated traffic > estimated bandwidth ) the sender is causing congestion: (acts as SCTP) Timeout 3 dup-acks ssth=ssth/2 cwnd=ssth ssth=cwnd/2 cwnd=1 • Otherwise, losses are not due to congestion: Timeout 3 dup-acks ssth=BWE*RTT/pktsizecwnd=ssth ssth=BWE*RTT/pktsize cwnd=1 BWE:estimated bandwidth RTT:minimum measured RTT

6. WiSE: Path Management • Relaxes SCTP’s rigid “primary-secondary” path definition • Transmits new packets on the path that seems in better conditions, increasing the probabilities of a successful communication if (Timeout expiration) if (primarybandwith < secondarybandwidth) primary  secondary

7. Cross Traffic FTP | AP1 SCTP WiSE SCTP WiSE SCTP WiSE FTP | AP2 TCP TCP AP Results (ns-2) Topology: • Long-lived flows generated by a FTP source Packet Size: 1500 bytes

8. Results Errors due to the wireless channel Capacity: wired-links=55Mb/s wireless links=11Mb/s 4.0 3.5 3.0 2.5 Throughput (Mb/s) 2.0 1.5 WiSE(path #2 error-free) 1.0 SCTP(path #2 error-free) WiSE(path #2 = path #1) 0.5 SCTP(path #2 = path #1) TCP 0.0 0.1 0 0.05 0.15 0.2 0.25 0.3 Average loss probability on path #1

9. Results Errors due to the wireless channel Capacity: wired-links=55Mb/s wireless links=11Mb/s 0.12 WiSE(path #2 error-free) SCTP(path #2 error-free) 0.10 WiSE(path #2 = path #1) SCTP(path #2 = path #1) TCP 0.08 Energy per successful packet (J/pkt) 0.06 0.04 0.02 0.00 0.1 0 0.05 0.15 0.2 0.25 0.3 Average loss probability on path #1

10. Results Errors due to congestion Capacity: wired-links=10Mb/s wireless links=2Mb/s 1.6 0.20 1.4 tON=1s WiSE tON=5s 1.2 0.15 tON=20s 1.0 tON=1s SCTP tON=5s tON=20s Reordering Time (s) 0.8 0.10 Throughput (Mb/s) tON=1s 0.6 WiSE tON=5s tON=20s 0.4 0.05 tON=1s SCTP 0.2 tON=5s tON=20s 0.0 0.00 0.8 0.85 0.9 0.95 1 0.8 0.85 0.9 0.95 1 Average load Average load

11. Results Errors due to congestion Capacity: wired-links=10Mb/s wireless links=2Mb/s 0.18 0.16 tON=1s WiSE tON=5s 0.14 tON=20s tON=1s 0.12 SCTP tON=5s tON=20s Energy per successful packet (J/pkt) 0.10 0.08 0.06 0.04 0.02 0.8 0.85 0.9 0.95 1 Average load

12. Conclusions We proposed a protocol that: • is primarily designed for wireless networks • supersedes TCP and UDP being transparent to the application • outperforms both TCP and SCTP in a mixed wired/wireless environment • improves energy performance