1. TCP over Multipath Routing in Ad Hoc Networks Jiwei Chen, Matthew Azuma Tutor: Kaixin Xu

2. Motivation Standard TCP assumes one path Problems with Wireless TCP Low throughput(high BER) Route disconnection and rediscovery Interrelation with RTT and RTO Multihop wireless Hidden terminal: optimal window size Contention induced loss typically happens before congestion loss

3. Multipath TCP: Pros Rich connectivity Robustness and resilience Full use of network resources Load balancing

4. Multipath TCP: Cons Out-of-order problem different delays on paths-> packet reordering-> duplicate ACKs -> false congestion signals Need multipath routing protocol(network support) How to spread packets?

5. Previous work TCP over multipath routing Use multipath routing(DSR) TCP performance degraded by out-of-order delivery Use one primary path while with backup path Other transport layer approaches Parallel TCP Maintain and control a single send buffer for all the TCP-v pipes Individual congestion control and loss recovery Congestion window based data striping

6. Our approach Take advantage of multiple paths to improve TCP throughput Routing modifications(DSR) to discover, maintain multiple paths TCP modifications to spread the packets to multiple paths Use spreading ratio, more flexible! Address out-of-order problem

7. Multipath DSR Node will send duplicate RREQ Receiver will return two best paths maximally disjoint -> min hop number -> receiving time Sender will send packets on two paths according to TCP’s demand Keep path view consistent at sender and receiver

8. Routing Challenges Mobility Find new path whenever one path is unavailable? Provide more state info about path changes for TCP? Data packet salvage QOS provisioning

9. Multipath TCP Sender keeps packet path queue Sender uses spreading function Modified congestion window Duplicate TCP control block variables RTT variables Rtx timers Duplicate packet counter

10. Multipath TCP diagram

11. Out-of-order problem

13. Packet path queue

14. Spreading function P1+…+Pn = 1 Congestion Avoidance Pa = percentage for min RTT path Pa = ((RTTa / RTT1) + … + (RTTa / RTTn)) -1 Pi = (RTTa / RTTi) * Pa Slow Start / Fast Recovery Po = path in slow start / fast recovery Po = 1 / (new cwin) Pi = Pi * (old cwin / new cwin)

15. Congestion window modifications Timeout on path i --> Slow Start cwin = (cwin * (1 - Pi)) + 1 ssthresh = (cwin * (1 - (Pi / 2))) 3 dup ACK on path i --> Fast Recovery cwin = (cwin * (1 - (Pi / 2))) + 1 ssthresh = (cwin * (1 - (Pi / 2)))

16. Multiple TCP CB variables

17. Where are we now? Finished modifications to DSR Finished modifications to TCP Debugging and testing TCP modifications

18. Future work Run comparison tests to Backup Multipath Routing Eliminate modifications to TCP Receiver Try other spreading functions, such as ratio according to congestion level, bandwidth… Mobility issue: Routing support send duplicate packets over multiple paths Possibility to separate congestion control and reliability control

19. Reference Haejung Lim, Kaixin Xu, and Mario Gerla, " TCP Performance over Multipath Routing in Mobile Ad Hoc Networks, " In Proceedings of IEEE ICC 2003. H.Y. Hsieh, R. Sivakumar, “A Transport Layer Approach for Achieving Aggregate Bandwidths on Multi-homed Mobile Hosts”, ACM MobiCom’02, 2002, Atlanta, Georgia.