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I just got a 802.11n wireless AP and hooked it up. After some testings with my MacBook Pro just beside the AP(~30cm, 100% signal), I noticed LAN FTP transfer speeds were between 3 to 5 MB per second, which means not even reaching 100Mbit.

Is this normal? It says the connection is 144Mbit in the wireless details.

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There are too many potential sources of interference from wireless that it's performance will vary using the same hardware in a different location. The connection speed of 144Mbit is the theoretical maximum that your connection can achieve you'll never reach that level. But the 5MB per second is actually 40Mbits per second which isn't all that bad. Is that what you mean or do you mean 3-5Mbits per second? –  chunkyb2002 Sep 11 '10 at 19:38
    
Yes I mean 5MB per second(40Mbit). Since this is the first time setting up a wireless network I really have no idea how fast the average speeds are. I expected to see 70 ~ 80Mbit/s when positioned beside the AP. Btw the transfers are as follow : Laptop (Wireless) => AP (Wired) => Router (Wired) => Second PC (Wired). –  user49081 Sep 11 '10 at 20:23
    
Can you log in to your AP and check the precise value of the signal in dB? Also, there should be an option to do a site survey. Check if there is anything else on the channel you're using. –  phil Jan 8 '12 at 18:01
    
possible duplicate of Slower than expected 802.11n wireless network speeds –  techie007 Jan 8 '12 at 19:25
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1 Answer

What you're seeing sounds a little on the slow side, but pretty close to normal.

  1. Wi-Fi has lots of overhead. The rule of thumb is that your TCP throughput should be a little over 50% of your Wi-Fi signaling rate. So since your signaling rate is 144 megabits/sec, I'd expect to see 72 megabits/sec of TCP throughput. Divide that by about 8.4 to convert to MebiBytes/sec, and I'd expect to see about 8.6 MebiBytes/sec of TCP throughput.

  2. That 50% number I quoted above is for an app that knows how to use TCP efficiently, such as IPerf. I don't know how efficient the FTP client and server implementations you're using are, so I'm not terribly surprised that you're seeing less than 8.6 MebiBytes/sec. It would be interesting to use a tool like IPerf, and make sure to give it proper-sized TCP receive windows with -w 256K.

  3. You could get an even better signaling rate by having your MacBook Pro join your 802.11n network in 5GHz instead of 2.4GHz. It would more than double the signaling rate to 300 megabits/sec. This is because Apple products impose a "good neighbor" policy when using 802.11n in 2.4GHz, and limit themselves to traditional 20MHz-wide channels, instead of the 40MHz-wide channels that 802.11n introduced. This cuts the speed Apple products get for 802.11n in 2.4GHz, but it allows other uses of the band to coexist better, such as Bluetooth.

  4. Where on the network was the other FTP machine? If it was wireless too, that would explain why you were seeing only half the throughput you should have been seeing. When one wireless client sends a frame to another, it actually goes to the AP first, and then from the AP to the other client. This is called "IntraBSS Relay", and the 802.11 standard requires that all APs do it, to avoid the "hidden node problem" where two clients are each in range of the AP, but not in range of each other.

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