Sorry to dig up an old thread but rather than explainin what "Front sector" / "Back sector" actualy does can someone explain hwo to choose which sector should be front and which sector should be back in an ABAB setup please?
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AFAIK, you just arbitrarily pick that in a pair of your sectors.
So, for us, we use ‘North, South, East, West’ for ordering in our minds… so we consider North to be “Front” and South to be “Back” in that pair… and then do the same for East/West as Front/Back in their pair.
That way, all North sectors in our Network are all set to “front,” and any South sectors on our Network are all set to “back”, and therefore we figure that all “fronts” should isolated from each other by either channel separation, or filtering, or shielding, or distance.
the front to back doesn't have to match other towers unless you reuse the channel.
any "front" ap on channel 5835 can hear any number of back APs on the same 5835, but it cannot hear another "front" louder than -90 otherwise, you will take interference... I don't know what is happening under the hood that causes this, but you will need to watch for that.
@Chris_Bay wrote:the front to back doesn't have to match other towers unless you reuse the channel.
any "front" ap on channel 5835 can hear any number of back APs on the same 5835, but it cannot hear another "front" louder than -90 otherwise, you will take interference... I don't know what is happening under the hood that causes this, but you will need to watch for that.
Is it other AP's that matter or the subscriber radios from other APs that matter ? Maybe I'm not understanding the question/answer here but if the AP's all TX/RX at the same time regardless of front/back secret sauce then you should be able to set every single AP on every tower to the exact same frequency and they would never see each other. Of course this would render your network unusable because the Subscriber Radios that can see more than one AP or be seen by more than one AP would not work at all because they can't see their own AP due to Interference from all the other APs or because their AP is being over powered from interference from the SM's on other AP's interfering with it.
If AP's are hearing other APs' then they are not in Sync. The entire point of GPS is to keep AP's from interfering with each other leaving only the SM's connected to different APs as a source / recipient of interference.
This whole Front/Back secret sauce thing concerns me because I don't understand why I need it on ePMP when I don't need it on the old Canopy or the 450 gear. It's my understanding that all on the old canopy and 450 stuff all the GPS does is make the APs TX and RX at the same time and that's all I need them to do and that makes them work. So here we have ePMP and they say GPS makes them TX and RX at the same time and that's all you nee... wait, no, you need this front back setting on ePMP but we can't tell you what it does cause it's a secret.
The fact that what the documentation says and what the guys here say are often not in agreement makes it even more concerning. I just want want the AP's to RX/TX in sync and all the mumbo jumbo over the "secret" front/back setting makes wonder if that is really happening.
@brubble1 wrote:
@Chris_Bay wrote:the front to back doesn't have to match other towers unless you reuse the channel.
any "front" ap on channel 5835 can hear any number of back APs on the same 5835, but it cannot hear another "front" louder than -90 otherwise, you will take interference... I don't know what is happening under the hood that causes this, but you will need to watch for that.
Is it other AP's that matter or the subscriber radios from other APs that matter ? Maybe I'm not understanding the question/answer here but if the AP's all TX/RX at the same time regardless of front/back secret sauce then you should be able to set every single AP on every tower to the exact same frequency and they would never see each other. Of course this would render your network unusable because the Subscriber Radios that can see more than one AP or be seen by more than one AP would not work at all because they can't see their own AP due to Interference from all the other APs or because their AP is being over powered from interference from the SM's on other AP's interfering with it.
If AP's are hearing other APs' then they are not in Sync. The entire point of GPS is to keep AP's from interfering with each other leaving only the SM's connected to different APs as a source / recipient of interference.
This whole Front/Back secret sauce thing concerns me because I don't understand why I need it on ePMP when I don't need it on the old Canopy or the 450 gear. It's my understanding that all on the old canopy and 450 stuff all the GPS does is make the APs TX and RX at the same time and that's all I need them to do and that makes them work. So here we have ePMP and they say GPS makes them TX and RX at the same time and that's all you nee... wait, no, you need this front back setting on ePMP but we can't tell you what it does cause it's a secret.
The fact that what the documentation says and what the guys here say are often not in agreement makes it even more concerning. I just want want the AP's to RX/TX in sync and all the mumbo jumbo over the "secret" front/back setting makes wonder if that is really happening.
its AP to AP. the GPS front to back is to handle timing from AP to AP. if an SM hears the same channel from 2 different APs no matter the front to back mark with less than 28 db (i go by 30 for good measure) then you will begin to lose modulation steps. that is the reason the front to back stats on sector antennas are important.
for example, if you have 5 towers all 1 mile apart, in a straight line, and you neglect to tilt the sectors, all north and south sectors are on 5835, and your north sectors are all front, and all south sectors are all back, and your sectors are tilted as needed, you'll never run into the 2 fronts or 2 backs hearing each other within the 28db mark of the CPEs uplink power.
what does front and back do? cambiums secret.
what happens when 2 front APs hear each other louder than say 80 db? your uplink modulations suffer and you'll get random disconnects on weaker CPEs etc. etc. since the epmp is a modified wifi chipset under the hood, I'm going to guess the contention time portion may be the reason for the front and back mark. that's an item we cannot define in the EPMP, yet essentially exists in all other radios i've played with in one manner or another, even if it's not user controllable in the gui. I'll take a guess and say the contention slots are fixed, and not many of them. so cambium sliced them in half, half for front, half for back. being how wifi handles keepalives, and a few other wifi related necessities, the AP probably speaks during those times so a CPE could be overspoken easily in that time slot. though everything else is GPS synced, some activities under the hood may simply have to be left to contention and that's just the way it is. I'd love for the front and back marks to go away, I'd squeeze a few more APs up in the same spectrum.
as far as it is a problem, for us it's not. we stack APs really deep, and usually 4 to a pole. some of the areas we work, we will have 10 or 12 2.4 APs in just a few square miles up on 100' wooden poles using just 3 10mhz channels.
the front to back has rarely being a series problem, just something to watch for. its much less of a worry with 5ghz given the spectrum and antenna characteristics.
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The front to back setting has to do with AP to SM management frame communications. Let's say AP1 and AP2 are pointed north and south respective. And let's say SM1 is connected to AP1. Now let's say SM1 can see AP1 at -40 and AP2 at -70. As Chris pointed out, this is enough SNR for MCS15 and all should run fine. And all will run fine as long as AP1 is set to "Front" and AP2 is set to "Back" (or vise versa). If AP1 and AP2 are both set to the same F/B setting SM1 will randomly disconnect from the AP, along with other erratic behavior, for example reporting its RSSI from AP1 as -70.
To put it another way, if a SM sees (can demodulate the management frames of) another AP on the same channel and with the same F/B setting as the AP it is connected to, it will have issues, regardless of the signal.
The reason why you don't have to do this on PMP gear is becaue of limitations in the wifi chipset ePMP is using.
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