hi. would like to know the advantages of back haul over the ap-sm in terms of rf signalling. i had an experience where i set up an 5.7 ap-sm link but it did not work. it was just up to registering only. i changed every configuration but still it didnt work but when i set up a pair of back haul in that same locations, it worked. can anybody explain to me what are the possible reasons for this.
your response will be much appreciated.
thanks 
What was the link distance? Did you use reflectors? Were the AP-SM and BHs using the same frequency band? Does AP Eval data on the SM show other APs that you might have been attempting to register to?
AFAIK, a BH and AP-SM combo are the same in terms of RF signalling. Where an AP-SM combo will work, a BH combo will work and vice versa.
besides the distance, the BH is just 2ms on latency, while AP - SM can be 22-44 depending on signal quality.
we run a 5.7 omni to connect our towers together - there are no backhauls here.
Uplink dish:
Reply from 192.168.1.198: bytes=32 time=66ms TTL=254
Reply from 192.168.1.198: bytes=32 time=65ms TTL=254
Reply from 192.168.1.198: bytes=32 time=66ms TTL=254
Reply from 192.168.1.198: bytes=32 time=75ms TTL=254
Actual omni - 5.36 miles away
Reply from 192.168.1.197: bytes=32 time=73ms TTL=254
Reply from 192.168.1.197: bytes=32 time=73ms TTL=254
Reply from 192.168.1.197: bytes=32 time=71ms TTL=254
Reply from 192.168.1.197: bytes=32 time=70ms TTL=254
That’s 4-6 ms difference…not bad for a non-backhaul. 
Oh, i pinged across our vpn too - i’m pretty sure if you were on the network it’d be a lot less.
put hundreds of customers over that link, you’ll see.
AP’s have a downlink maximum limitation to one SM of 1800 pps
(packets per second)
Backhauls, however, have a maxmimum of 3000.
our sites are all connected via backhauls, but another ISP that purchases bandwidth from us used to be connected via 5.7SM - until their customers needed more packets per second. we found that out pretty quickly that the limitation is actually that - a limitation.
switched to their own dedicated backhaul on one of our sites, and away it went! check the release 7 and 8 user’s manuals, they spell that out pretty well.
i thought the SM was 300pps? Is there a difference between hardware and software scheduling? Also on firmware 8+ vs 7-?
We have some remote sites that are running by SM’s as the backhauls. This connection usually works for up to ~30-50 customers if you are only offering 256-384k speeds. Bittorrents can really take up pps. we had one customer on a repeater site (fed by an SM) and he caused the latency to go up to near 500ms. on a backhauled site this will not happen (or at least with just one customer doing it)
vince wrote: i thought the SM was 300pps? Is there a difference between hardware and software scheduling? Also on firmware 8+ vs 7-?
i was stating the SM's *downlink* limitation, not uplink. 300pps is the uplink limitation from SM to AP.