Alternating Primary Subflow in MPTCP by External Program without Kernel Modification

When users's terminals with multiple wireless network interfaces such as Wi-Fi and LTE have access to the Internet, traffic congestion often occurs since many of them use the same Access Point (AP) of Wi-Fi network for example. To migigate this congestion, we consider a network configuration that can perform dynamic traffic shaing with special VPN servers communicating with users' terminal through Multipath TCP (MPTCP). These VPN servers have a function than can select a primary subflow for each terminal dynamically according to the current conditions of APS. However, implementation of this function into server program reduces software maintainability and increases implementation cost. In this paper, we propose a subflow switching method using an external program to solve these problems. With this program, the VPN server can switch the primary subflows without modification.