HACK: Hierarchical ACKs for Efficient Wireless Medium Utilization

WiFi’s physical layer has increased in speed from 802.11b’s 11 Mbps to the Gbps rates of emerging 802.11ac. Despite these gains, WiFi’s inefficient MAC layer limits achievable end-to-end throughput. The culprit is 802.11’s mandatory idle period before each medium acquisition, which has come to dwarf the duration of a packet’s transmission. This overhead is especially punish ing for TCP traffic, whose every two data packets elicit a short TCP ACK. Even frame aggregation and block link-layer ACKs (introduced in 802.11n) leave significant medium acquisition overhead for TCP ACKs. In this paper, we propose TCP/HACK (Hierarchical AC-Knowledgment), a system that applies cross-layer opti-
mization to TCP traffic on WiFi networks by carrying…

Lynne Salameh, Astrit Zhushi, Mark Handley, Kyle Jamieson, Brad Karp. Usenix ATC (best paper). June 2014. Philadelphia, PA, USA