Poor 802.11n Performance Compared to Ethernet

[owensdj]

I changed some Windows XP client machines in an office Active Directory domain network from 100Mbit ethernet to 802.11n wireless by adding a PCI wireless card. The users of the wireless clients are now having performance problems with the network applications, even though they're getting a good signal from the access point and are connecting at 270Mbit.

Is there anything I can do to increase the performance or decrease the latency of the wireless clients? I was expecting their performance to be about the same as it was using 100Base-T.

 

[Goosemaster]

try to test the connection quality (ping at the very least) to see if you are getting packet loss, and also test for possible radio interference.
Also, define what you mean by "good signal." in dB

 

[spidey07]

Wireless is like a hub, half duplex, everybody shares the same capacity. Switched ethernet everybody gets 100 megabit full duplex all to themselves. Plus with wireless you have noise and other factors outside your control. Basically it's slow and it gets slower and slower the more people on the access point.

Wireless will never be nor is it intended to replace wired. It's only application is mobility and convience, not performance.

 

[JackMDS]

Originally posted by: spidey07

Wireless will never be nor is it intended to replace wired. It's only application is mobility and convience, not performance.

LOL, we are trying to "hammer" this for almost two years. :shocked:

But I guess that Wishful thinking overcomes "hammering" of reality.

 

[spidey07]

Originally posted by: JackMDS

Originally posted by: spidey07

Wireless will never be nor is it intended to replace wired. It's only application is mobility and convience, not performance.

LOL, we are trying to "hammer" this for almost two years. :shocked:

But I guess that Wishful thinking overcomes "hammering" of reality.

You'd be surprised how many times I've been called in to "fix" somebody's wireless network. It normally goes they build a new office and somebody has the great idea to do it all wireless "look at how much money I'm saving! those dumb consultants told me to not use wireless".

Well now you have 100 people on 4 access points and wanting to "fix" it? It's not broke, it's working just as designed - dog slow.

 

[kevnich2]

In an office environment, wireless is a bad idea for stationary computers. As spidey said, it's good for mobility and convenience but for business computer that need reliability, wired always.

 

[spidey07]

Also, what kind of connection does the AP have? If it's 100 base-T then it doesn't matter if the clients connect at 40 gigabit or whatever. that's another bottleneck. If I sound like a broken record I'm sorry. But to expect wireless to have the same kind of performance as wired is just not going to happen.

 

[owensdj]

spidey07, yes the AP is connected to the same 100Mbit switch as the wired clients. I knew that would be a bottleneck, but I thought the wired clients would get close to 100Mbit speed since there are only a few using the AP.

 

[owensdj]

Here are the signal levels from a machine close to the AP:
Link Quality 100%
Signal Strength 1 -51 dBm
Signal Strength 2 -49 dBm
Signal Strength 3 -47 dBm
Noise Strength 26% -92 dBm

Here are the signal levels from the machine furthest away from the AP:
Link Quality Good 71%
SS1 Normal -70dBm
SS2 Weak -74 dBm
SS3 Weak -74dBm
Noise Level -92 dBm

Any observations anyone have on the signal levels? The problem seems to be that there are many, many retransmissions and CRC errors, even from the machine that's a few feet from the AP. Here is what I was getting:
Frames Transmitted Successfully 9671
Frames Retransmitted Successfully 2880

Frames Received 15103
Frames Received with CRC Rrror 1575

Isn't the number of frames being retransmitted and CRC errors on frames received way too high? I rescanned and there doesn't appear to be any wireless networks using the same channel.

 

[spidey07]

That's normal with wireless, hence why it's slow.

Have your forced pre-n mode only? What's your channel width? Another thing is make sure there isn't a duplex mismatch.

Also try to use the 5 Ghz spectrum instead of 2.4. 2.4 is pretty noisy from other non wifi devices.

 

[owensdj]

spidey07, the AP's Wireless Mode is set for 802.11n-only and the Operating Mode is Green Field. Channel Bandwidth is set to 20/40. How do I check for a duplex mismatch? Both the AP and the wireless clients only support 2.4GHz.

 

[Goosemaster]

1. consumer wireless sucks for serious work

2. more troubleshooting:

By duplex Spidey means check the speed settings from wire to wireless to make sure they coordinate.
Also, use netstumbler etc to see what the dB readings are other APs in the area. Strong signals mean you'll have to change channels, and if all channels are saturated, you'll have to move to 5.4ghz or you a SOL

 

[owensdj]

Goosemaster, thanks for the reply. By duplex do you mean the setting for the ethernet port on the access point? I'm not sure how to check that because the AP's configuration doesn't have a way to check to see if it's using 10Mbit or 100Mbit or if it's using half or full duplex.

 

[Goosemaster]

Originally posted by: owensdj
Goosemaster, thanks for the reply. By duplex do you mean the setting for the ethernet port on the access point? I'm not sure how to check that because the AP's configuration doesn't have a way to check to see if it's using 10Mbit or 100Mbit or if it's using half or full duplex.

I meant that in addition to the configuration of your clients as well. Try to one only one of them at a time on a set channel (one that isn't in heavy use) and hard set the transmission speed.

Either way, as was pointed out, consumer "wireless" means shared medium which turns to mush when you pile on the clients.

As a last resort, I would try to create ideal conditions for the setup to minimize the amount of variables. Just place a laptop/workstation right next to it (<10 or 20ft) and set it up as the only client on a good channel. See if you get something acceptable. Unfortunately this will only result in proving that your device or environment is at fault. This will either necessitate the purchase/replacement of new equipment, proliferation of more APs, a change in freq,, or a move back to wired.

 

[drebo]

Wireless is always half duplex. The only place a duplex mismatch could occur is the access point's connection to the wired network.

 

[owensdj]

drebo, thanks. I don't understand how a "duplex mismatch" would cause any performance problems. If the access point is connecting to the switch at full duplex, it'll just either send or receive, just not at the same time as the full duplex connection would allow.

 

[spidey07]

A duplex mismatch between the AP and the switch will severely hamper performance.

 

[owensdj]

spidey07, ohh ok. I understand now. The mismatch is with the wired ethernet, not the wireless in the AP. I'm not sure how I can detect a duplex mismatch with this AP because it doesn't appear to have anything in the setup that lets the user determine if it's using half or full duplex on the ethernet port. Any ideas?