802.11n: A Survival Guide

Part II. The MAC

Before 802.11n, the 802.11 MAC was generally viewed as being about 50% efficient—take the operating data rate of the system during transmission, and cut it in half to account for the various forms of protocol overhead needed to coordinate transmissions between stations. When data rates were relatively low, the cost of inefficiency was manageable. Losing half of a one-megabit network is only 500 kbps. As transmission speeds continued to increase, the loss became more and more significant. 802.11n developed several protocol features to reclaim some of the inefficiently used airtime. Focus on efficiency has paid off: under many conditions, 802.11n can have an efficiency of 70%.