A network layer approach to enable TCP over multiple interfaces

The mobile Internet is set to become ubiquitous with the deployment of various wireless technologies. When heterogeneous wireless networks overlap in coverage, a mobile terminal can potentially use multiple wireless interfaces simultaneously. In this paper, we motivate the advantages of simultaneous use of multiple interfaces and present a network layer architecture that supports diverse multi-access services. Our main focus is on one such service provided by the architecture: Bandwidth Aggregation (BAG), specifically for TCP applications. While aggregating bandwidth across multiple interfaces can improve raw throughput, it introduces challenges in the form of packet reordering for TCP applications. When packets are reordered, TCP misinterprets the duplicate ACKS received as indicative of packet loss and invokes congestion control. This can significantly lower TCP throughput and counter any gains that can be had through bandwidth aggregation. To improve overall performance of TCP, we take a two-pronged approach: (1) We propose a scheduling algorithm that partitions traffic onto the different paths (corresponding to each interface) such that reordering is minimized. The algorithm estimates available bandwidth and thereby minimizes reordering by sending packet pairs on the path that introduces the least amount of delay. (2) A buffer management policy is introduced at the client to hide any residual reordering from TCP. We show through simulations that our network-layer approach can achieve good bandwidth aggregation under a variety of network conditions.