Link to home
Start Free TrialLog in
Avatar of BradyAU
BradyAUFlag for Australia

asked on

Wireless channels and roaming

Hi all,

I currently have 3 Linksys E4200 routers that run a roaming wireless network. Authentication is WPA2 Enterprise and of late, there have been some authentication issues with EAP timeouts etc...

From what I can see, all was working fine up until about a week ago when I decided to change the wireless channels on all 3 devices to auto (on both 2.4 and 5.8 bands). Now some devices (ranging from mobile phones to laptops) will see the single SSID, attempt to connect and will fail. Laptops will give the certificate prompt, then say it was unable to connect.

2 of the 3 devices are relatively close together and will sometimes 'argue' with each other while the 3rd device is far enough away not to cause interference.

What I'm thinking is I should change the channels on all 3 devices back to manual.

There is a person in the vicinity who uses 2.4 channel 1. What channels would I best be using?

So far:

Device 1: 2.4 channel 6, 5.8 channel 44
Device 2: 2.4 channel 11, 5.8 channel 36 (this device is the closest to the other persons device that uses channel 2.4 channel 1)
Device 3: 2.4 channel 1, 4.8 channel 48 (this device is the furtherest away from all devices including the other persons device that uses 2.4 channel 1)
Avatar of BradyAU
BradyAU
Flag of Australia image

ASKER

Attached is a site survey which shows device 1 and device 2.
sc.jpg
ASKER CERTIFIED SOLUTION
Avatar of Darr247
Darr247
Flag of United States of America image

Link to home
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
Start Free Trial
Avatar of BradyAU

ASKER

Hi Darr,

The E4200 only lists 4 options for the 5.8GHZ channels:

Auto (DFS)
36 - 5.180GHz
40 - 5.200GHz
44 - 5.220GHz
48 - 5.240GHz
SOLUTION
Link to home
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
Start Free Trial
SOLUTION
Link to home
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
Start Free Trial
Avatar of BradyAU

ASKER

I'm in Australia :)
Profile will be updated shortly.

Our version the FCC is ACMA - Australian Communications and Media Authority (www.acma.gov.au)
Avatar of BradyAU

ASKER

It won't cause the problem you're seeing with authentication though.

Since I've switched to different channels manually, there have been no connection/authentication problems. The main problem was the connecting device would timeout (I think) maybe due to some sort of interference.
It was already locked before I could edit out the extra "different" in the last sentence... and I was going to add:

I'm not exactly sure what the name of Japan's broadcast regulating agency is. The only expansion of the acronym MKK I can find related to Japan is Mitsubishi Kakoki Kaisha.
Darr, I hate to argue, but RF in WiFi doesn't behave like that.  If you have two devices on the same channel they will not wait for the other radio with the same SSID to finish transmitting.  They use CSMA/CA which works on a random timeout.  No conversation between APs takes place to tell each when the other has finished sending so at some point you WILL interfere with the other AP.

You may be talking about a SCA solution such as Meru's offering, but that uses an airtime-fairness algorithm which is proprietary to Meru.
Yes they will, it's part of the 802.11 specification - carrier sense multiple access with collision avoidance (CSMA/CA).
They listen first to see if the channel is in use... usually they can just calculate by the duration field from the last frame heard... if it's the same SSID. But if they're not on the same SSID, they don't recognize it's in use and will just start sending, which causes interference. The only time that doesn't work is you're not broadcasting the SSID (just another reason not to bother with trying to hide the SSID).

Normally, for maximum throughput you would put them on channels 1, 6 and 11. However, in this case the site survey shows another nearby radio using channel 1, and the default used by most manufacturers is channel 6 so I prefer not to even use it... any new AP installed nearby will likely start up on channel 6, causing instant interference. That's why I recommended putting them all on channel 11.

It does look like Oz requires a license for those upper 5GHz channels, too, by the way...
#19a on http://www.comlaw.gov.au/Details/F2011C00543
You're wrong Darr!  I'm a Cisco Advanced WLAN Specialist, and I've NEVER heard of this behaviour.
I can't help that you've never heard of it, but I'm surprised Cisco doesn't teach it before certifying someone on WLANs...  Still, I'll wager if you search their site for CSMA/CA you'll find it's as I described. As I said, it's part of the IEEE 802.11 specification, just as CSMA/CD is part of their 802 wired specs.
e.g.
http://www.cisco.com/en/US/docs/wireless/technology/mesh/7.0/design/guide/MeshAP_70.html#QoS_and_DSCP_Marking

http://www.cisco.com/en/US/products/ps10315/products_tech_note09186a0080b4bdc1.shtml#ca3

http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/vowlan/41dg/vowlan_ch3.html#wp1057675

et al, et cetera.

Note that if they were Cisco APs run by a WLC, the WLC would automatically set them to all use the same channel if that provided the least amount of interference.
Thanks for clarifying the fact that the WLC would set the APs to the same channel if that provided the 'least' amount of interference.

Next time I install a wireless LAN I'll make sure I set everything to the same channel, and also tell the vendor that they only need one channel on their kit ;-)