Exploring mobile/WiFi handover with multipath TCP

Abstract

Mobile Operators see an unending growth of data traffic generated by their customers on their mobile data networks. As the operators start to have a hard time carrying all this traffic over 3G or 4G networks, offloading to WiFi is being considered. Multipath TCP (MPTCP) is an evolution of TCP that allows the simultaneous use of multiple interfaces for a single connection while still presenting a standard TCP socket API to the application. The protocol specification of Multipath TCP has foreseen the different building blocks to allow transparent handover from WiFi to 3G back and forth.In this paper we experimentally prove the feasibility of using MPTCP for mobile/WiFi handover in the current Internet. Our experiments run over real WiFi/3G networks and use our Linux kernel implementation of MPTCP that we enhanced to better support handover.We analyze MPTCP's energy consumption and handover performance in various operational modes. We find that MPTCP enables smooth handovers offering reasonable performance even for very demanding applications such as VoIP.Finally, our experiments showed that lost MPTCP control signals can adversely affect handover performance; we implement and test a simple but effective solution to this issue.

Use Cases and Operational Experience with Multipath TCP

“…When the WiFi interface fails, a new subflow is established over the cellular interface in order to preserve the established Multipath TCP sessions. Compared to the backup mode described earlier, measurements reported in [Cellnet12] indicate that this mode of operation is characterized by a throughput drop while the cellular interface is brought up and the subflows are reestablished.…”

“…The first experimental analysis of Multipath TCP in a public wireless environment was presented in [Cellnet12]. These measurements explore the ability of Multipath TCP to use two wireless networks (real WiFi and 3G networks).…”

“…This implies that data flows only over the WiFi interface when both interfaces are considered to be active. If the WiFi interface fails, then the traffic switches quickly to the cellular interface, ensuring a smooth handover from the user's viewpoint [Cellnet12]. The cost of this approach is that the WiFi and cellular interfaces are likely to remain active all the time since all subflows are established over the two interfaces.…”

“…When an MPTCP session is established, a subflow is created over the WiFi interface. No packet is sent over the cellular interface as long as the WiFi interface remains up [Cellnet12]. This implies that the cellular interface can remain idle and battery capacity is preserved.…”

“…From a protocol viewpoint, [Cellnet12] discusses the problem posed by the unreliability of the REMOVE_ADDR option and proposes a small protocol extension to allow hosts to reliably exchange this option.…”