Synchronizing a network

I'm putting together an order for a small network that will include several access points at several locations. One site will have the uplink, three Force 110 PTPs, and two ePMP 2000s to serve sites that can see it directly. It seems fairly straightforward to set them all to use the same fixed ratio (e.g., 50:50) and timing (e.g., 2.5 ms.).

But then at the other end of the Force links, I'll have local access ponts, and I'll want to make sure everything is sync'd cleanly. And one of the links goes back-to-back to another, to relay around a hill. Here's the backhaul map:

X - Y -HUB - Z



Now on a Mimosa radio, there's a Gender setting A:B. You would just say that Hub is A (all three PTP links plus ePMP 2000 APs), and then everything one hop from Hub is B, and whatever's one hop past that is A again. So X (one PTP and its own ePMP 2000s) and Hub are A, while sites W, Y and Z are all B. And ALL of the APs at a site are the same gender.

What is the setting in the ePMP to allow me to do the same thing? WIthout it, sync won't do nearly as much good, except at the Hub. Thanks...

The answers to this will depend heavily on geometry and channel availability...

The most stable approach is to use distinct channels for the PtP links (we use DFS channels usually) as compared to the APs, then work out frequency reuse for the APs based on geometry.  (if timing is the same and sync is stable then two APs facing each other on the same channel, or two back-to-back on the same channel, would both be stable arrangements)

On our network, I would use DFS channels for the backhauls, (clear line-of-sight far easier to ensure when both ends are towers) reusing channels as necessary.  (I.E. in your diagram I'd look at using the same freq on Hub<->W as on X<->Y, a second and third channel for the other two directions out from Hub)  Even with sync, geometry and geography (and ground cover and other factors) will largely determine what channels are reusable for the APs.

Cambium has some useful documentation at covering ABAB frequency reuse (applicable more generally than ABAB cases) and on the necessary settings.

If it's at all possible, I'd suggest keeping PtP links in an isolated chunk of spectrum unused for your APs.  If you reuse a frequency back-to-back for PtP (say Hub<->Y then Y<->X) it will probably only work right if the synchronized master radios are both at Y, set exactly the same.  If you don't need to reuse PtP frequencies then everything becomes far more flexible running the backhauls unsynced.

Also, I have no idea what your network load will look like, but for our network we keep all the sectors set to 75/25, and backhauls that are not full-duplex we set to either 75/25 or flexible.



I've got a tentative frequency plan, but that' s not the issue. I have a two-hop link X-Y-Hub. For simplicity I'll keep it all 50:50 to start. Now, I want to make sure that X and Hub transmit at the same time, and both Y radios transmit at the same time. Hub is the AP to Y, and Y is the AP to X, and X will have sectors sync'd to Hub.

So what seems to be missing is a gender switch. It looks like all APs want to transmit at the same time. But that fails when there is a multi-hop link with back to back radios, and I don't really want to "near" end to be Station to the far end AP. When you transmit ("gender" in Miimosa terms) should be independent of whether you're AP or Station.

In other places I've just designed in Mimosa backhaul and Cambium access, using frequency spacing. (Mimosa uses 2/4/8 timing options, vs. 2.5/5 for ePMP; note LTE TDD is 5/10.)  But Force 110 PTP is a very attractive sync'd backhaul option. And I suspect (but haven't tried it) that Mimosa A5 APs can be either gender too.