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Updated 7/29/2011: Added WNDR4000 routing throughput info

Three 3 stream routers

Long time readers know that I've held off investing in the ability to properly test three stream 802.11n routers. I recently relented, however, due to shame or the realization that manufacturers are bound and determined to foist yet another technology-in-development upon gullible consumers and someone has to test these things properly.

Either way, I recently cowboyed up and purchased a Lenovo x220i notebook with Intel Centrino Ultimate-N 6300 card and three antenna option. Actually, I purchased two x220i's. The first came with the 6300 card, but not the three antenna option. Unfortunately, I didn't check this until after the 21 day return period passed. So I had to order and pay for a second one and am waiting for the full refund on the first RMA'd one. (Yes, I verified that the replacement x220i has the 6300 card and three antennas connected.)

So now I no longer have an excuse for not testing three stream operation on routers that support it. I recently revised the wireless test process to reflect the longer test times that these products require.

Before I get to the results, a word about the settings available on three stream routers, for those of you who haven't yet put hands on one. Three stream routers don't really have a way to put them into two-stream mode. Some have the ability to set the MCS (Modulation and Coding Scheme) rate. But I'm not going to rely on that until I get an understanding from manufacturers exactly how it operates.

Just like dual-stream routers, three streamers only let you set the mode to some mix of 802.11 a,b,g and n (you get 802.11a only with dual-band products) and set 20 MHz, Auto 20/40 or 40 MHz channel bandwidth modes. Of course, you can set the channel, too.

The maximum link rate you see reported by your 802.11n client depends on the number of streams it supports and any bandwidth mode limitations that the client driver allows. In other words, a two-stream client associated with a three-stream N router can only operate at two-stream rates.

Table 1, borrowed from our Wireless FAQ, has a quick rundown of maximum link rates. A full list of 802.11 rates is here.

Product Technology Maximum Link Rate (Mbps)
20 MHz B/W 40 MHz B/W
802.11b 11 N/A
802.11g 54 N/A
Enhanced 802.11g
54 108
802.11n - 1 stream 65 150
802.11n - 2 stream 130 300
802.11n - 3 stream 217 450
Table 1: Maximum 802.11 link rates

Now without further ado, let's get to the testing. We're going to look at three routers I've previously tested with a two-stream client: Belkin's N750 DB, NETGEAR's WNDR4000 and TRENDnet's TEW-691GR.

Belkin N750 DB

I wasn't very impressed with the two-stream performance of the Ralink RT3883F 3X3 N radio in Belkin's latest top-of-line router. So I didn't have very high hopes for its three-stream performance and testing proved this out. The Wireless Performance table in Figure 1 shows results for both the Belkin and NETGEAR WNDR4000, which I'll get to next.

N routers usually can't reach to my low signal test locations E and F in two stream mode and their performance is no better with three stream clients. In fact, the same fallback mechanism applies in three stream as in two. So at low signal levels, your fancy three stream router has transmogrified itself back into operating like your old 802.11g or even 11b router!

The summary table in Figure 1 shows maximum throughput in 20 MHz bandwidth mode in the 35 - 45 Mbps range—even lower than many two-stream routers! I think the reason is the constant link rate switching that I observed during testing, with link rates even in Location A rarely reaching above 300 Mbps.

Three stream performance - 5 GHz band

Figure 1: Three stream performance - 5 GHz band

Switching to Auto 20/40 bandwidth mode was a bit better, goosing thoughput to around 60 Mbps. But this is more typical of what I see in dual-stream products.

The IxChariot plot in Figure 2 shows some attempt by the router and client to move to higher throughput. But such efforts were generally short lived.

Belkin N750 DB IxChariot plot summary - 5 GHz, 20 MHz mode, downlink

Figure 2: Belkin N750 DB IxChariot plot summary - 5 GHz, 20 MHz mode, downlink, three stream client

I was able to measure 101 Mbps of total throughput running simultaneous up and downlink tests in location A in Auto 20/40 mode.

Here are links to the other 5 GHz plots if you'd like to check them out.

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