Seamless Handoffs in Wireless HetNets: Transport-Layer Challenges and Multi-Path TCP Solutions with Cross-Layer Awareness

Complications and performance issues resulting from handoffs have widely been overlooked by transport layer protocols. In mobile scenarios, layer 2 protocols begin to see issues, especially when multiple handoffs are imminent. Differentiating between delay caused by actual packet loss and congestion on the current link and delay simply caused by handoffs is an important distinction where transport layer protocols fall short. With current advancements in technology, traditional TCP reform is needed to accommodate a growing mobile culture. MPTCP is a new evolution of TCP that enables multiple paths or subflows and connections to be used transparently to applications. This is essential in a dynamically changing network as each subflow runs independently, allowing the connection to be maintained. In this article, we present our findings on transport layer handoff issues in currently deployed networks. We then discuss the use of MPTCP as a potential solution to address handoff-related and mobility-related service continuity issues. Finally, we propose cross-layer techniques for potential solutions to consider when designing a handoff-aware MPTCP protocol.