An Inconvenient Truth

Updated 10/10/2007 - Postscript added with 100 Mbps test results

Despite a certain networking publication's enthusiasm for the still not-fully-baked draft 802.11n wireless LAN technology, you can safely continue to install CAT 5e cabling without fear of wasting your hard-earned money. Wired Ethernet is not going to be replaced by 802.11n or any other wireless technology on the horizon anytime soon, if ever.

How do I make such a bold statement? Well, the facts really speak for themselves. Figures 1 and 2 are taken from our Wireless Performance Charts and show downlink and uplink throughput vs. path loss curves for three draft 11n products, representing the three major draft 11n chipsets.

The Netgear WNR854T uses Marvell's TopDog, the D-Link DIR-655 represents Atheros' XSPAN while the Netgear WNR834Bv2 has Broadcom's Intensi-fi inside. Note that the WNR834B has only 100 Mbps WAN and LAN Ethernet ports, while the other products have gigabit Ethernet.

Figure 1: Downlink Throughput - 20 MHz bandwidth mode

It's clear to see that none of the products even approaches 100 Mbps of TCP/IP throughput in either up or downlink directions. Note that these plots have the devices configured in their "out of the box" condition, which is with no encryption and using the 20 MHz bandwidth mode which ensures peaceful coexistence with existing 802.11b and g networks.

Figure 2: Uplink Throughput - 20 MHz bandwidth mode

But say that you don't give a damn about messing up existing WLANs and change the devices to use the 40 MHz bandwidth mode. Figure 3 shows that only one product—the Netgear WNR854T— provides throughput equivalent to 100 Mbps Ethernet.

Figure 3: Downlink Throughput - 40 MHz bandwidth mode

Unfortunately, that high throughput doesn't last very long. According to my correlation study with real-world performance, the ~80 dB of path loss where performance starts to sharply drop corresponds to about 50 feet through a few sheetrock walls or about 25 feet through a residential wood-frame floor.

Figure 4: Uplink Throughput - 40 MHz bandwidth mode

Figure 4 shows that the two products with Marvell and Atheros chipsets provide around 80 Mbps of TCP/IP throughput in the uplink direction. But the Netgear WNR834Bv2 using the Broadcom chipset actually loses around 20 Mbps of throughput when running uplink.

Tags: 802.11n, WiFi,

Related Articles: