TCP Wake-Up: Reducing Keep-Alive Traffic in Mobile IPv4 and IPsec NAT Traversal

Applications such as instant messaging and push email require long-lived connections between clients and servers. In the absence of other traffic, stateful firewalls and Network Address Translators (NATs) require “keep-alive” messages to maintain state for such persistent connections. We present new measurements analyzing the energy consumption of these keep-alive messages on a mobile phone in 2G (GSM), 3G (WCDMA), High-Speed Downlink Packet Access (HSDPA), and IEEE 802.11 Wireless LAN networks. The measurements confirm earlier results showing that frequent keep-alive messages consume significant amounts of energy in 2G and 3G networks, but suggest they are not a significant problem in Wireless LANs. To reduce energy consumption, we introduce TCP Wake-Up, an extension to Mobile IPv4 and IPsec NAT traversal mechanisms. This extension significantly reduces the need for keep-alive messages, while still avoiding complexity of IP-over-TCP tunneling. Our measurements show that TCP Wake-Up can extend battery lifetime by a factor of 2 to 7 in 2G/3G networks. The results also suggest guidelines for developers of future protocols: in particular, we claim that “always-on” applications that aim to be used in current 2G/3G networks cannot be solely based on UDP.