A Transport Protocol to Exploit Multipath Diversity in Wireless Networks

• Published in: IEEE/ACM transactions on networking Vol. 20; no. 4; pp. 1024 - 1039
• Main Authors: Sharma, Vicky, Kar, Koushik, Ramakrishnan, K. K., Kalyanaraman, Shivkumar
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2012; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aggregates; Bandwidth; Blocking; Congestion; Diversity gain; Encoding; Forward error correction; lossy environments; multihop wireless networks; multipath; Networks; Packets (communication); Receiving; Reliability; Studies; TCP; TCP (protocol); Transport; Transport protocols; Wireless networks
• ISSN: 1063-6692; 1558-2566
• DOI: 10.1109/TNET.2011.2181979

Wireless networks (including wireless mesh networks) provide opportunities for using multiple paths. Multihoming of hosts, possibly using different technologies and providers, also makes it attractive for end-to-end transport connections to exploit multiple paths. In this paper, we propose a multipath transport protocol, based on a carefully crafted set of enhancements to TCP, that effectively utilizes the available bandwidth and diversity provided by heterogeneous, lossy wireless paths. Our Multi-Path LOss-Tolerant (MPLOT) transport protocol can be used to obtain significant goodput gains in wireless networks, subject to bursty, correlated losses with average loss rates as high as 50%. MPLOT is built around the principle of separability of reliability and congestion control functions in an end-to-end transport protocol. Congestion control is performed separately on individual paths, and the reliability mechanism works over the aggregate set of paths available for an end-to-end session. MPLOT distinguishes between congestion and link losses through Explicit Congestion Notification (ECN), and uses Forward Error Correction (FEC) coding to recover from data losses. MPLOT uses a dynamic packet mapping based on the current path characteristics to choose a path for a packet. Use of erasure codes and block-level recovery ensures that in MPLOT the receiving transport entity can recover all data as long as a necessary number of packets in the block are received, irrespective of which packets are lost. We present a theoretical analysis of the different design choices of MPLOT and show that MPLOT chooses its policies and parameters such that a desirable tradeoff between goodput with data recovery delay is attained. We evaluate MPLOT, through simulations, under a variety of test scenarios and demonstrate that it effectively exploits path diversity in addition to efficiently aggregating path bandwidths while remaining fair to a conventional TCP flow on each path.