TCP Fairness in Multipath Transport Protocols

Multipath transfers are a promising technique for enhancing the reliability of Internet connections, making better use of multihoming, and using spare network capacity. However, näıve designs and implementations of multipath transfer protocols risk substantial unfairness to well-behaved TCP flows. In this thesis, I propose two novel definitions of multipath TCP-fairness, and will show that multipath transport can compete fairly with traditional TCP flows even on a single bottleneck. I describe three possible approaches that achieves multipath TCP-fair transfers, with congestion control performed independently on each of many subflows over which data are striped. In addition, two promising, novel approaches were implemented and evaluated in NS-2: a multi-priority based scheme that rapidly backs off on congested paths, and a bi-level scheme that performs an additional level of congestion control on top of its multiple subflows. Examination of each schemes ability to adhere to the proposed definitions of multipath TCP-fairness was performed, and evaluation shows that both approaches meet the definition of multipath TCP-fairness while readily consuming spare bandwidth. Comparisons to previous multipath approaches demonstrate scenarios in which they exhibit unfairness to traditional TCP flows. Thesis Supervisor: John H. Jannotti Title: Assistant Professor of Computer Science