High ping time?


#1

Latency is around 10-12ms on a 8KM hop with B5c 2x20MHz . Had old Cisco AP1250 running 11a 5GHz with 2ms latency over the same hop with same antennas. Tried to set TDMA window to 2ms, but it got horrible.
Channels and signal seems to be clean and strong. What is the lowest ping times achievable?


#2

When you are using GPS on an non-duplex PTP system you are going to average around double the timing window. Here is an general explanation.

http://backhaul.help.mimosa.co/backhaul-faq-link-latency

If you would like some help diagnosing the connection please post screen shots of your config and the spectrum. Do you have other 5 GHz equipment at the site? if so what is it and what is it set to?


#3

Hi @IT1,

If you switch your timing mode to Auto, you should see considerably lower ping times.

Keep in mind though that if you use Auto, you won’t be able to GPS sync other Mimosa radios on the same tower. Those will all need to be set to the same timing.


#4

Have colocation with a WISP running Mikrotik gear at both ends. At the second/remote tower we have totally 4 Mimosa B5C so we rely on GPS sync and channel reuse. Try to use the U-NII-3 band if possible.
What seems to be strange is that the B5C dont care what dBi i set on antenna settings. They adjusted themself to lower dBi !?.. We use 2x MTI 26dBi flat panels at both ends on this link.
Here are some screenshots.



#5

I would recommend using the correct antenna gain settings in the config, 5680 is DFS and all. It looks like your SNR is less then optimal on Chains 1-3, you might want to see about adjusting the link to see if you can get a more equal spread. The radio is probably spending some time re-transmitting the packets which will increase your latency intermittently.

I don’t know MTI pannels very well but you might double check the spec sheet to make sure you are not loosing signal by playing in a part of the band that the antenna does not perform well on.

I am not a fan of flat panels, they have lots of side/back lobes and noise rejection is almost non-existent. Especially in Co-Location situations it can be beneficial to use antennas that have good isolation, Ubiquiti’s Air Fiber dishes are pretty good for the price, RF Elements dishes are good, especially their ultra-horn if price isn’t a problem.


#6

Thanks for great advices. The flat panels was that we had at the moment and its a hassle to allign two separate antennas, so will replace them when soon. Have now Jirous 24dBi and Ubiqiti 31dBi dual polarity dishes delivered.
We are in the arctic with extreme weather and wind sometimes so dont want too big antennas if not needed. Looks like there is very few dishes between 24 and 29dBi to choose from atleast in our market. A 26-27dBi model i think would be optimal for us with most distances around 10-12km.