I was testing the new 5.6.0 firmware on an ePMP 400c backhaul and I was wondering why the bandwidth was cut in half when I switch to TDD? First screen shot is before the upgrade the second is after the upgrade in TDD mode. This is 6.4 mile link -59/-58 dBm MCS DS11/DS11 no other settings have been changed other than switching from ePTP mode to TDD mode.
Which TDD mode or ratio are you using? Flexible, or a fixed ratio, and if so, what ratio?
I have it set to TDD PTP fixed ratio at 50/50.
Well, that’s your answer right there. ePTP is a half duplex flexible frames mode, so you’ll see the best possible throughput with 100% of the frames in either direction.
With TDD fixed 50/50 you’ll see the best possible throughput with 50% of the frames in either direction.
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Is TDD full duplex then?
So for max throughput am I better to run it in ePTP Master/Slave or will I give up overall performance?
TDD using a 50/50 ratio could be considered a pseudo form of full duplex (I’m sure some others in the forum will disagree and chime in on this from a technical standpoint). Most operators would only use a fixed TDD ratio if they needed to sync with other adjacent radios.
If you don’t need to sync, then using ePTP mode is the optimal mode to use for PtP’s.
One last benefit to using TDD mode for PtP is if you have an extremely long link distance. ePTP’s limit is around 20 miles or 32 Km… so if you have a link distance greater then that, you’ll need to use TDD mode.
So since the 400c radios are not GPS synced I think it would be better to run them with new firmware and set them to ePMP Master/Slave to gain the extra throughput and fix any bugs from the older firmware. Would you agree?
Yes, running 5.6.0 and using ePTP mode for your application is recommended.
Thanks Eric for all your help!
TDD is not full duplex, it is a frame usage for duplex traffic. like a one lane bridge traffic takes turns crossing, using a 5ms frame: 2.5ms (not exactly correct but simplified) is used for AP to SM traffic and the next 2.5ms is used for SM to AP traffic. All ePMP hardware is TDD but some radios like the PTP550 and PTP8xx radios can be frequency isolated full duplex.
Full duplex is where data traffic flows in both directions at the same time and there is no frame ratio to account for. Two methods of full duplex operation is frequency isolated and polarization isolated,
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I was waiting for you to chime in on why TDD isn’t actually full duplex 
Because the name Time Division Duplex doesnt seem to make much sense?
I like to think of it as Time division for duplex operation
That would give a false understanding of what TDD really is. With TDD there is only one direction flow of data at a time, there can be many separate data streams but only in one direction at a time.
TDD is realy best described as a one lane bridge and traffic crosses both directions.
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I like the description here:
TDD would be half-duplex and FDD would be full-duplex.