Cisco Cisco Catalyst 6000 Multilayer Switch Feature Card MSFC2 White Paper

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Are 802.11n Data Rates Dependable?

Today, many clients are 802.11n ready and this can provide throughput and efficiency increases in a high-density

deployment. Most WLANs, however, will support a mix of client protocols. Evaluating the historic average client

mix in a WLAN is possible by either looking at the WLAN controller graphical user interface (GUI) or at Cisco

Wireless Control System reports and using this historic mix of information for planning purposes. Unless the

WLAN is very unique, most environments will likely be dealing with a diverse mix of clients and protocols for the

near future. Consider that other factors, such as the number of connections, can also be expected to vary over

time and for these reasons it is often a best practice to build in some buffer to smooth the long term results. The

raw speed advantage of 802.11n high throughput (HT) rates is impressive and boosts the overall efficiency and

capacity of the design by permitting more users or higher speeds to be realized on the same channel. Figure 4

shows mixed client protocol capacities for a given cell.

Figure 4. Mixed Wireless Client Protocol Performance in a Cell (802.11a/g/n Data Rates)

The graph above shows throughput rates under varying mixes of HT20 modulation coding scheme-15 (MCS15)

2SS data rates and legacy 802.11a/g (for the purpose of this discussion 802.11a and 802.11g are the same

protocol - different bands and are considered equal) data rates within a single isolated cell.

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With either all MCS15 or all 802.11a/g clients, the difference in throughput is 480 percent.

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With a 50/50 mix, there is a 400 percent increase over legacy throughput.

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With a drop to just 25 percent of MCS15 clients, the increase is 300 percent.