In this paper, we investigate TCP performance over a multipath routing protocol. Multipath routing can improve the path availability in mobile environment. Thus, it has a great potential to improve TCP performance in ad hoc networks under mobility. Previous research on multipath routing mostly used UDP traffic for performance evaluation. When TCP is used, we find that most times, using multiple paths simultaneously may actually degrade TCP performance. This is partly due to frequent

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... packet delivery via different paths. We then test another multipath routing strategy called backup path routing. Under the backup path routing scheme, TCP is able to gain improvements against mobility. We then further study related issues of backup path routing which can affect TCP performance. Some important discoveries are reported in the paper and simulation results show that by careful selection of the multipath routing strategies, we can improve TCP performance by more than 30% even under very high mobility.