Using adaptive heartbeat rate on long-lived TCP connections

In this paper, we propose techniques for dynamically adjusting heartbeat or keep-alive interval of long-lived TCP connections, particularly the ones that are used in push notification service in mobile platforms. When a TCP connection between a client behind a NAT (or any other middle-box) and a server is idle for a long time, it may get torn down due to TCP binding timeout. In order to keep the connection alive, the client device needs to send keep-alive packets through the connection when it is otherwise idle. To reduce resource consumption, the keep-alive packet should preferably be sent at the farthest possible time within the NAT binding timeout. We refer to this interval as the Optimal Keep-alive Interval. Due to varied settings of different network equipments, optimal keepalive interval will not be identical in different networks. Hence, the heartbeat rate used in different networks should be changed dynamically. We propose a set of iterative probing techniques, namely binary, exponential and composite search, that detect optimal keep-alive interval with varying degree of accuracy; and in the process, keeps improving the keep-alive interval used by the client device. We also analytically derive performance bounds of these techniques. To the best of our knowledge, ours is the first work that systematically studies several techniques to dynamically improve keep-alive interval. To this end, we run experiments in simulation as well as make a real implementation on Android to demonstrate the proof-of-concept of the proposed schemes.