Acceptable signal strength?

[sjones@techsgi.com]

Hi everyone--i find myself having to venture out into the realm of wireless (I'm more of a UC/DC engineer...) and i've got a problem i'm trying to track down.  Installed two WLC 5508s, WCS, 3502i APs (123 of them...) in a 4-floor high school.  What i'm finding is lousy throughput from a lab of PCs with little USB b/g/n adapters.  I took my Macbook in and ran iStumbler to get an idea of the SNR but honestly, i'm not sure what i'm looking for.

For the particular room/SSID/band that i was looking at, i found that in the 2.4 range, i was getting 53% signal strength and about 16% noise.  Is that a good level?  In WCS, i can see close to a dozen APs in relation to the AP in question, so i'm wondering if the SNR is too high...not sure what to tune/tweak/do to make it perform better...

Any ideas would gladly be welcome.

Thanks all

SJ

[Leo Laohoo]

What i'm finding is lousy throughput from a lab of PCs with little USB b/g/n adapters.

How many WAPs and how many of these PC's?

What kind of traffic are you dealing with?  Browsing the web?  Video download? 

[sjones@techsgi.com]

1 ap in the room. 16 pcs. Just logging into the machines takes between 7-10 minutes per box. In other areas, it's much speedier by comparison.

Scott A. Jones, CCVP

IPLogic, Inc.

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[Leo Laohoo]

Hmmmm ... Somethings not right.

This particular WAP is connected on a FULL duplex link with the switch, right?

If you console into the WAP and do a "sh log", what output do you see?

[sjones@techsgi.com]

I see the IDS engine detecting a replay attack about once a day, then it clears and the dot11radio0 resets. It’s full-duplex, 1Gb speed. One thing interesting yesterday—it reported the replay attack, but I was the only one in the building, trying to login to one of the PCs in question (the rest were logged off).

[Scott Fella]

Check to see if the users are connecting to that ap or an ap nearby.  Is this the only dense area that you have issues with?

[sjones@techsgi.com]

Great point—I did notice they all connect to that AP. There is one other area that had issues…a lab with about 2 dozen iMacs. Moved them to WPA2 security so that N would work, and they picked up a little bit. Eventually they hard-wired the lab, so that one went away. Tried that with the lab in question, issue still persists…

One thing I noticed though—on the show interface, there’s a really high number of unknown protocol drops on the gi 0 interface of the AP. Not sure if that could be related…

[Scott Fella]

Can you post the show wlan

[sjones@techsgi.com]

Just had a chance to jump in to the AP.  It doesn't recognize that command...i guess i should specify they're LWWAPs, so should i be running that command on the controller?

[Scott Fella]

That command needs to be ran from the wlc CLI. The WLAN id is the SSID that is having the issues.

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[sjones@techsgi.com]

Sorry about that! The joy of learning as you go…output is below

WLAN Identifier.................................. 2

Profile Name..................................... old HS wireless

Network Name (SSID).............................. HS-Wireless

Status........................................... Enabled

MAC Filtering.................................... Disabled

Broadcast SSID................................... Enabled

AAA Policy Override.............................. Disabled

Network Admission Control

Radius-NAC State............................... Disabled

SNMP-NAC State................................. Disabled

Quarantine VLAN................................ 0

Maximum number of Associated Clients............. 0

Number of Active Clients......................... 290

Exclusionlist Timeout............................ 60 seconds

Session Timeout.................................. 1800 seconds

CHD per WLAN..................................... Enabled

Webauth DHCP exclusion........................... Disabled

Interface........................................ old-hs-wireless

Multicast Interface.............................. Not Configured

More or (q)uit

WLAN ACL......................................... unconfigured

DHCP Server...................................... Default

DHCP Address Assignment Required................. Disabled

Static IP client tunneling....................... Disabled

Quality of Service............................... Silver (best effort)

Scan Defer Priority.............................. 4,5,6

Scan Defer Time.................................. 100 milliseconds

WMM.............................................. Allowed

WMM UAPSD Compliant Client Support............... Disabled

Media Stream Multicast-direct.................... Disabled

CCX - AironetIe Support.......................... Enabled

CCX - Gratuitous ProbeResponse (GPR)............. Disabled

CCX - Diagnostics Channel Capability............. Disabled

Dot11-Phone Mode (7920).......................... Disabled

Wired Protocol................................... None

IPv6 Support..................................... Disabled

Passive Client Feature........................... Disabled

Peer-to-Peer Blocking Action..................... Disabled

Radio Policy..................................... All

DTIM period for 802.11a radio.................... 1

DTIM period for 802.11b radio.................... 1

Radius Servers

Authentication................................ Global Servers

More or (q)uit

Accounting.................................... Global Servers

Dynamic Interface............................. Disabled

Local EAP Authentication......................... Disabled

Security

802.11 Authentication:........................ Open System

Static WEP Keys............................... Enabled

Key Index:...................................... 1

Encryption:..................................... 104-bit WEP

802.1X........................................ Disabled

Wi-Fi Protected Access (WPA/WPA2)............. Disabled

CKIP ......................................... Disabled

Web Based Authentication...................... Disabled

Web-Passthrough............................... Disabled

Conditional Web Redirect...................... Disabled

Splash-Page Web Redirect...................... Disabled

Auto Anchor................................... Disabled

H-REAP Local Switching........................ Disabled

H-REAP Local Authentication................... Disabled

H-REAP Learn IP Address....................... Enabled

Client MFP.................................... Optional but inactive (WPA2 not configured)

Tkip MIC Countermeasure Hold-down Timer....... 60

Call Snooping.................................... Disabled

More or (q)uit

Roamed Call Re-Anchor Policy..................... Disabled

SIP CAC Fail Send-486-Busy Policy................ Enabled

SIP CAC Fail Send Dis-Association Policy......... Disabled

Band Select...................................... Enabled

Load Balancing................................... Disabled

[Scott Fella]

That looks okay. So the issue is only with iMacs, nothing else. These the newer iMacs or older ones? You mentioned you tried using WPA2 so why did you go back using WEP. If the iMac support WPA2/AES, then I would use that. Along with WMM being required for 802.11N. All you really need to do is set the 802.11an channel to 40mhz.

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[sjones@techsgi.com]

That’s a great tip for the a/n spectrum. I’ll do that. In the lab I’m having issues with though, it’s a bunch of PCs running b/g/n only adapters. The iMacs were a separate thing and have since been hard-wired, so they’re not so much of a problem anymore. Any thoughts on things I can tweak for the 2.4 GHz?

As far as the switch between WPA2 and WEP, the WEP is there to support machines that were moved in (they’ve only been in this building for around 3 weeks…). They won’t be able to switch things around until summer. I did try moving a couple of the PCs to the WPA2 test network, but with the same results…I wish I could test a/n but the cheap adapters prevent that.

Appreciate the help

SJ

[Scott Fella]

That is okay.... You can still achieve up to 144mbps on the 2.4ghz. All you need is WPA2/AES and WMM enabled. The thing with WEP is that sometimes you can't use key #1. Maybe moving the WEP key to key #2 might help but you would need to change that on the devices also. If you have to make changes, its probably better to jut move those machines to WPA2.

Thanks,

Scott Fella

Sent from my iPhone

[sjones@techsgi.com]

Ok. I’ll give it a shot and let you all know what happens. Thanks for the info.

SJ