External antenna and coverage problems

[Clemens Gruber]

Hi,

we use a WLC 2504 in an old museum with thick stone walls, with 4 intersecting tunnel-like corridors/hallways and several rooms and little halls connected to the corridor.

Besides two CAP2602i internal access points which work fine, we use a CAP2602e with the 4 default dipole antenna and one CAP2602e with an omnidirectional AIR-ANT2544V4M-R

Question 1: Which of the 4 antenna cables from the omnidirectional antenna go into which antenna connector on the CAP2602e (A, B, C or D?), is there a special mapping? I just plugged them in "in order" but had to pick a antenna cable randomly to start with and then go clockwise from A to D.

Question 2: We have several coverage holes. We expected more from the Omni-directional antenna, so I'd like to know if I did something wrong: I set the antenna gain in the antenna parameters to 8x 0.5 dBi = 4dBi for g/n and a/n

(For the CAP2602e with the dipole antennas I used 4x 0.5dBi = 2dBi for g/n and 8x 0.5dbI = 4dBi for a/n)

What can I do besides increasing the Power threshold in the RF settings to the maximum value (-50) ?

For g/n I set 12Mbps as Mandatory and everything else as supported, I use TPCv1 (coverage-optimal-mode) with automatic channel assignment and default mobility settings from the WLC 2504.

Do you have some tips for the AIR-ANT2544V4M-R ? I already read the specs and the mounting guides. At the moment it is mounted at a wall in about 2m height with elevation of 10° down and I did not adjust the azimuth. Could/should this help?

Our location is a museum, here a picture of one corridor: http://www.kaindl.breitenbach.at/images/ausflug/augustinermuseum_001.jpg

You can see the arcs/notches, our omni-directional antenna is mounted at the left wall (so the antenna is a little bit occluded by the surrounding arcs of the wall). Should I add more space between antenna and wall (to get free-sight to the door at the end of the corridor, visible in the picture) or would an azimuth-adjustement be more effective?

Please help me, I am glad about every hint and tip I can get. Thank you.

Best regards, Clemens

[Clemens Gruber]

Ok, just to let others know who stumble upon this thread via Google, etc.

I got help by Cisco TAC support (the TAC engineer did a great job!)

I just want to share what I learnt in the process, maybe it is helpful for someone else:

Question 1:

• It does not matter, the four cables from the AIR-ANT2544V4M-R lead to 4 separate antennas on the inside. It only looks as if it is one big antenna, in reality there are four inside the enclosure.

Question 2:

• The biggest improvement was to change the lowest mandatory 802.11g data rate from 6 Mbit/s to 1 Mbit/s, because the lowest mandatory data rate is the rate used for re-association / etc.  Before, when one of our clients lost the connection he had to go back into an area of good coverage to reassociate. Now it is much better.
• I also disabled Multicast VLAN on my WLANs (because I do not have Wireless clients using multicast and this would pollute the air for no reason).
• To disable 802.11b, instead of disabling data rates, I set the "radio policy" on the WLANs to 802.11a/g.
• Oh and I disabled a few data rates, because the clients down-switch rate by rate, so if there are fewer, it adapts faster to lower rates. But you have to be careful to not disable too many.

Have a nice day :)

[vinod rathore]

Thanks Clemens,

It helped me too .. i'm too having client roaming and client disconnection issue.

After making changes to data rates 1Mbps as mandatory and rest other higher rates to supported.

apart from i did change in client roaming parameters from default to -

Mode                    Custom

Minimum RSSI   -65dBm

Hysteresis              3dB

Scan Threshold -60dBm

Transition Time 3 Seconds

[Clemens Gruber]

You're welcome!

According to an engineer, I should not touch the client roaming parameters, defaults should be fine in most cases.

Did those custom settings improve your situation? Are your clients roaming faster now? Maybe I'll do some testing myself with the client roaming settings.

Your Minimum RSSI is rather high, if I understand your settings correctly, the clients have to be at least at -65dBM to connect at all and between -65 and -60 you let them be in active scanning mode.

I am not sure how the transition time plays into this. Are there any negative side-effects when setting it lower than 5 secs? This is just the minimum waiting time, right? If the client does not find anything in 3 secs, the search goes on. But if a AP with a RSSI > Minimum RSSI is visible the client can only connect after those 3 secs. Why don't we set it to 1 sec then? To avoid hopping too early between neighboring APs?

But overall, the minimum mandatory rate, the power threshold in TPC settings and the access point specific RF settings (antenna gain according to my antenna's parameters) were the most significant parts. Oh and of course disabling 802.11b, it looks like 802.11b traffic even has a negative impact on other clients using 802.11g.

[vinod rathore]

I can say YES, because being on default client parameters most of the clients were not switching to new AP even they are underneath the AP but after change, same clients are switching quite faster ...

Although still few of clients are left which are not switching even after spending 20 min down to new AP. hence i applied your way too.. might help else that can be the issue from client it self may be driver causing some issue...not sure.

Yes, between -60 to -65 client will be in active scanning mode because i don't want to let them be on poor RSSI (less than -60dbm) so that they may get good b/w though i have to put more APs.

Transition time we shouldn't set just to minimum because quite faster client roaming also may cause unnecessary movement/switching between APs. 

"Oh and of course disabling 802.11b, it looks like 802.11b traffic even has a negative impact on other clients using 802.11g."

Don't you have clients which connects 2.4Ghz ?. i didn't get purpose to disable 802.11b/g/n radio.

[Clemens Gruber]

I did not disable 802.11b/g/n, just 802.11b. In the WLAN settings, you can decide between 802.11b/g/n and 802.11g/n, if I remember correctly.

802.11b is very old. As far as I observed, all my clients support 802.11g

But it's not just the age, 802.11b traffic has a negative impact on all other 802.11g/n clients in the vicinity. So it's a bad idea to leave it enabled, if you don't have a special use case for it.

Some guides suggested disabling some 802.11b-only rates to forbid 802.11b traffic, but the engineer I talked to, suggested leaving the rates at supported and set it per WLAN ("Radio policy" setting)

[vinod rathore · Accepted solution]

Ok, You had mentioned that you did that through radio policy .. i missed that...then its fine.

Nice idea, i should also disable 802.11b by selecting "802.11a/g only" under wlan > radio policy.

I see my most of clients are connected to 802.11bn, hopefully they should be able to connect to 802.11n over 2.4Ghz after disabling 802.11b.

[Leo Laohoo]

Nice idea, i should also disable 802.11b by selecting "802.11a/g only" unde
r wlan > radio policy.

That's NOT a smart way of disabling 802.11b.  The most effective way of disabling 802.11b is to disable 802.11b data rates.  

Go to Wireless > 802.11b/g/n > Networks.  Disable anything and everthing between 1 Mbps and 11 Mbps.  Make 18 Mbps as "Mandatory" and the rest, from 12 Mbps and up, as "Supported". 

[Clemens Gruber]

Why is this "NOT a smart way"?

Those data rates overlap and I for example need the lower rates. We also needed to set 1Mbps as Mandatory in our use cases, to let clients with low RSSI reconnect immediately in areas of poor coverage.

I have a low-throughput application in an area with parts of poor coverage. I need the lower data rates for the clients to stay connected, As 802.11g also supports 1Mbps, 2Mbps, etc. (and does this in an improved way, in comparison to 802.11b, right?) I can't just disable the data rates, that would be counterproductive.

Instead a TAC engineer suggested selecting 802.11a/g and leaving the data rates as is (except skipping some in between for faster down-switching). Please tell me, what's wrong with that?

Thank you.

[Leo Laohoo]

Because, if I'm not mistaken, your method of going to disable 802.11b (via the Radio Policy) also means you disable 802.11g.  

With the method I've mentioned, this is a well-known method (to all vendors), of disabling 802.11b and ONLY 802.11b but leaving 802.11g operational.  

[Clemens Gruber]

I think you are mistaken, 802.11g still works just fine here. The radio policy is set to "802.11a/g only", so it means no 802.11b but still 802.11g and 802.11a.

Your method is only viable in scenarios with enough access points to not depend upon data rates below 12Mbit/s. If you do depend on them, because you have poor-coverage-areas and it is not possible to add additional access points, I guess you have to keep the lower data rates enabled, right?

802.11g uses the lower data rates too, just a little more efficient than 802.11b. And in the process it does not disturb other 802.11a/g/n traffic.

[dinaa12902]

She choose the world-renowned Palm Springs Modern Art Museum to host her first Dinah. Mariah knew an event inside this spectacular museum, surrounded by priceless artwork, was just the kind of statement she was trying to make – that our community is worth the very best and she was going to offer it.