B24 MTU sizes - modes and modulation levels


#1

The Traffic Handling FAQ mentions: Mimosa backhaul radios support “baby jumbo” frames up to 3200 bytes without fragmentation in certain modes and modulation levels.

Does anyone know what the “certain modes and modulation levels” actually are?


#2

Dunno about modulations, but I am pretty certain that the Jumbo frame stuff is only available in SRS.


#3

I just got around to looking at the manual for the backhauls and going through my own B11s and they do not have an explicit “Jumbo Frame” switch, unlike the A5/A5c which have it under “Management >> Miscellaneous”

My recommendation would be to go to Mimosa Support, they should be able to clarify. If you are willing, I would greatly appreciate it if you would report back here and let the community know what the answer is.


#4

Still no response at all from Mimosa Support but I’ll try prodding them again.


#5

Have you tried going to the “Chat with us”? They have answered my questions right off the bat the last couple times I have chatted with them.


#6

Got a reply after going through chat as per William5’s advice.

"I got the answer for the MTU size.

If you’re running on tdma window 2ms you’ll need MCS 7+ for passing up to 3200 bytes. When running on 4 ms window it’s mcs 4+ and for 8 ms window it is mcs 3+."

The only option I can see that mentions TDMA is set to Auto and unchangeable so I’ve asked for some clarification.


#7

Hi @Andy3,

If you’re set to Auto, you cannot change your Window Size. You will need to click on the Auto dropdown on the AP and select 50/50, 75/25, or 25/75 before you can change the window size.


#8

Ah gotcha, that helps. The one I was looking at had the Traffic Split set to Auto and wouldn’t allow TDMA to be changed.

Are you able to advise how to check or change the MCS? There doesn’t appear to be any options relating to it.


#9

MCS is the negotiated bandwidth between the AP and the Station. This is done automatically (or Automagically if you prefer) between the Station and AP and is a product of basically Signal Strength Minus Noise (SNR) and Error Vector Magnitude (EVM), with a few other things mixed in for special cases.

I don’t think this table applies exactly to the B24, but it was on top of my browser history and I didn’t see a comparable one for the B24 in my quick search, so here:
http://backhaul.help.mimosa.co/backhaul-faq-snr-mcs

This might also be appropriate:
http://backhaul.help.mimosa.co/backhaul-faq-sensitivity-for-each-mcs-index