Hi Nate, When an SM is really close in distance to a tower, the RSSI of course is very strong. However, the SM when too close falls below the azimuth antenna pattern because it is below the elevation antenna pattern. Therefore, the gain is greatly reduced. The backside AP as a result now has an antenna gain similar to the front side antenna. Therefore, the front to back ratio is very small and the SM will see both APs at a similar high RSSI.
On AP -> Configuration -> Radio -> Access Point Configuration -> Frequency Reuse there is a setting of Off, Front Sector, and Back Sector. You want to make sure that the settings of the two APs is different with one being Front Sector and the other being Back Sector. This causes an offset of the start of each frame between the sectors. If this is not set such as both are Off or both are the same setting, then the frames will transmit at the same time. This could cause the back side AP GPF (GPFs are the first packet in each 5 msec and 2.5 msec frame) to be heard right before or at the same time as the intended AP GPF and thus the GPF is lost because you are listening to the wrong GPF first or at the same time causing too much interference and loss of the GPF. If the settings are correct, then one AP will always transmit in front of the other (I cannot remember which is first). If in your case the back side AP transmits first, then the SM could lock onto this GPF first and then miss the correct GPF. In release 2.4.3 we made an improvement to ignore packets that are a certain dB less than previous packets have been received at so the back side GPF is ignored in a case like you described. But, if the RSSI level between the two APs is too close, then this will not help. If you are on a release older than 2.4.3, then you should upgrade to at least 2.4.3. So the answer to your question is it too close and too strong is you are probably correct, but perhaps the SM in question can be helped with these suggestions of correct settings and software version. Daniel Sullivan ePMP Software Manager -----Original Message----- From: Af [mailto:[email protected]] On Behalf Of Nate Burke Sent: Wednesday, December 16, 2015 12:28 PM To: Animal Farm <[email protected]> Subject: [AFMUG] EPMP De-registering from being too strong? I have an EPMP SM that is close to the tower, it see's the AP Facing it at -36, it keeps jumping off of that AP, and linking into one of the other sectors at -60. The SM reports "SM deregistered - No GPFs from AP. Check signal level and interference on channel." Other SM's stay associated to the AP. Is it just because it's too close and too strong?
