Exploiting Wireless Broadcast By Opportunistic Packet Splaying

The IEEE 802.11 random access MAC suffers from expensive channel acquisition costs which are exacerbated by the use of TCP. This floor acquisition mechanism is primarily a way to fashion unicast “links” out of what is fundamentally a broadcast medium. The main thesis of this paper is that such unicast usage of the wireless channel is unnecessary, and that once the floor has been acquired, we can instead “splay” packets to as many potential receivers as possible using the fact that wireless is a broadcast medium. Splay is placed between the IP and MAC layers and reduces the expensive cost of channel acquisition by opportunistically combining packets intended for different receivers. Splay allows for the use of sophisticated coding approaches to augment the IEEE 802.11 stop-and-go ARQ. This also helps prevent IEEE 802.11 from incorrectly backing off exponentially in response to fading losses on intermediate quality links, which are quite common in practice. We are currently implementing Splay as a Linux kernel module.