On 10/13/2010 11:04 AM, Adam Gomes wrote:
Are there really any affordable consumer grade wireless adapters that have the capability of four spatial streams? I ask because if there aren't then paying
Doubtful, on both the AP and client end. Even the high grade commercial stuff that we're deploying on campus doesn't come higher than 3x3. A quick google search shows that 4x4 chipsets are just now being bragged about by Marvell, which means that they're not going to be widespread in on the shelf products for probably another year or so.
the premium for "600N" maybe be a waste. I know that Intel started selling
600N is nothing more than a marketing label these days. For example, on the 3700, the "600" number was from adding up 300 on 2.4 plus 300 on 5. Not technically wrong, but... well, marketing. 99% of what you're buying out there is going to be 2x2, which maxes out at an on-paper speed of 300Mbit, or about 160Mbit of real work useful throughput.
relatively affordable 3x3:3 cards, but that's still going to cap-out at 450MB for MAC/PHY layer speeds. To me, what's more important is having simultaneous access to both bands (2.4Ghz, and 5.1Ghz) so I can avoid interference when possible. Anything over a single 150MB spatial stream at that point is just gravy. Especially since most of my network at home is still 10/100, and most of my larger data transfers are over the Internet ... so well, no ISP around me offers speed in excess of 100MB sustained. :)
You should also be aware that there are other variables that factor into the speed, including inter frame spacing and channel width (20MHz vs 40MHz), and the RF environment. Traditional wireless with a single spatial stream (11a/b/g) requires a good, strong single signal between the endpoints. 11n, on the other hand, supports MIMO. Basically it sends out multiple streams on the same channel (up to four in the specs) and then depends on having the different streams bounce around slightly differently. For example, stream A may be strongest on the direct path, while stream B may be a little stronger bouncing off a nearby fridge. MIMO then performs dark magic to use these different properties to split the streams back out, allowing them to carry different data. If you don't have a good diverse RF environment, it's quite possible that your 4x4 degrades down to an effect 2x2. With 11n, sitting 10 feet away from the AP in a big empty nothing is not going be near best case performance.
Well, there's that, and since a number of devices in my house are still 802.11b/g only devices (e.g. my Wii), and there are just so many of these wifi enabled devices, I don't expect to get close to the top end throughput rates on these newer 'n' capable APs anyway. That is to say, while operating in the 2.4Ghz space, I'm still going to have to wait for my 54MB devices to send their frames before I get the chance to transmit my frames at 150 - 600MB. Just having that second 5Ghz band and singel spatial stream is good enough, I think. Make sense?
Just having legacy clients associated at all will absolutely drag your throughput down. You're best off trying to keep the legacy clients on 2.4, and focus on putting new 11n stuff on 5, to keep it operating in pure 11n mode. At that point, a typical 2x2 device should give you plenty of performance. -- Frank Sweetser fs at wpi.edu | For every problem, there is a solution that WPI Senior Network Engineer | is simple, elegant, and wrong. - HL Mencken GPG fingerprint = 6174 1257 129E 0D21 D8D4 E8A3 8E39 29E3 E2E8 8CEC