Wireless Access

Hello,

 

Running into an issue with a customer reporting 'bad connectivity' in a certain area.

These issues seem to be related only to a specific area of the installation so I'm guessing interference or something being the culprit.

 

When running "show ap debug client-table ap-name <ap-name>"  I can see all clients with good SNR (>35). However the Tx_Retries for these clients is extremely high (~30% of the Tx_Pkts for all the clients connected to this AP).

 

When I do a "show ap arm neighbors" for this AP I can see quite a few AP's with SNR-0 up to SNR-6 with everything inbetween. On the same channel (CH-6) I can see 2 AP's with SNR-2.

I'm guessing these SNR values aren't absolute dB values? So how do I interprete these SNR-0 to SNR-6? Is 2 AP's with SNR-2 on the same channel an issue and possible the cause to my issues?

 

Looking at the arm rf-summary doesn't realy explain why there are so many retransmits for this AP on its channel (6) either. The channel seems to be relativly free of interference. Although the list mentions 19 retries. Again, how do I interprete these?

 

(Aruba_ctrl1) #show ap arm rf-summary ap-name ap-name 

Channel Summary
---------------
channel  retry  phy-err  mac-err  noise  cov-idx  intf_idx
-------  -----  -------  -------  -----  -------  --------
1        0      0        0        86     7/3      35/2//16/0
116      0      0        0        89     6/0      33/7//2/0
140      0      0        0        89     0/0      0/0//0/0
48       0      0        0        91     0/0      0/2//0/1
5        0      0        0        83     0/0      0/16//0/8
120      0      0        0        89     0/0      0/11//0/0
6        19     0        0        86     7/0      9/13//2/3
52       0      0        0        88     0/0      5/0//0/0
7        0      0        0        83     0/0      0/19//0/5
100      0      0        0        90     0/0      0/0//1/0
124      0      0        0        88     0/0      0/0//0/0
56       0      0        0        90     0/0      0/3//0/1
11       0      0        23       81     7/0      37/2//2/0
104      0      0        0        90     0/0      0/2//0/0
128      0      0        0        90     0/0      0/4//0/0
36       0      0        0        90     4/0      24/0//3/0
60       0      0        0        89     8/1      0/0//5/0
108      0      0        0        90     0/0      6/7//0/0
132      0      0        0        89     0/0      9/0//0/0
40       0      0        0        90     0/0      0/8//1/2
64       0      0        0        89     0/0      0/0//0/2
112      0      0        0        90     4/0      22/13//0/1
136      0      0        0        88     0/0      0/4//0/0
44       0      0        0        89     0/0      0/0//2/0
HT Channel Summary
------------------
channel_pair  Pairwise_intf_index
------------  -------------------
1-5           77
116-120       53
52-56         9
7-11          65
100-104       3
124-128       4
36-40         38
60-64         7
108-112       49
132-136       13
44-48         5

Interface Name           :wifi0
Current ARM Assignment   :60+/24
Covered channels a/g     :3/0                     
Free channels a/g        :16/0
ARM Edge State           :disable
Last check channel/pwr   :5m:37s/2m:13s
Last change channel/pwr  :53d:9h:45m:42s/53d:13h:44m:54s
Next Check channel/pwr   :1m:52s/5m:13s

Interface Name           :wifi1
Current ARM Assignment   :6/21
Covered channels a/g     :0/3
Free channels a/g        :0/0
ARM Edge State           :enable
Last check channel/pwr   :3h:57m:59s/3m:4s
Last change channel/pwr  :3d:17h:17m:31s/3d:17h:17m:31s
Next Check channel/pwr   :0s/1m:21s

 

 

Any ideas on how to troubleshoot this further? Why are we seeing so many retransmits for all clients on this AP?

 

 

 

 

#AP124

The noise on the 2.4ghz band looks a little low especially on channel 11 (86, 86, 81 for channels 1,6, 11).   To see all the access points that an AP can see to get an idea please type:

 

show ap monitor ap-list  ap-name <name of ap>

 It could either be congestion/interference from neighboring non-Aruba APs, non-802.11 interference or both.

Ok, now it gets confusing.

 

"show ap arm neighbors" gives 2 bssid's in channel 6 with SNR-2 for both.

"show ap monitor ap-list" gives only 1 AP in channel 6 (with 4 bssid's): the AP I ran the command for itself. Other channels only have valid ap-types aswell.

 

Any chance you can explain the above? :)

 

Congestions is highly unlikely since the only clients active are barcode scanners. I guess I'll set up a spectrum-monitor and see if that adds anything usefull.

 

 

Don't be too alarmed with some of those rf-summary counters. They are percentages, so a 19% could refer to only 1 frame of 5 frames being retried. I feel this can give a falsely inflated perspective at times. The best course of action if a spectrum analysis like Colin suggested, or even better, an in-air packet capture.

 

Remember you can also isolate RF problems by having an AP in a known clean environment aggregate to the same controller to see if it has issues. You can do the reverse, too, terminating one of the production APs to a different controller so see if the problems follows or not.

Arm neighbors only shows Aruba access points. Since you see very little foreign access points , it is probably non 802.11 interference and a spectrum analysis is best.