Hi Ivan,

On Wed, Nov 11, 2020 at 01:26:01AM +0300, Ivan Babanov wrote:
> After it we tried to use default config from master branch initially
> created for RBS-2308.
> It worked pretty fine except RF Power which was configured as 41dBm and 41
> - 12 = 29 dBm. Value 29 was not acceptable for our RBS.
> I checked with Ericsson BSC Doc and found that our RBS2206 has max RF
> output 47dBm for DCS1800. (btw, RBS2308 has only 34dBm max output according
> to the same document, maybe config needs to be corrected)

feel free to send a patch.

> Looks like internal oscillator is not ready. So, the question is how to
> make internal oscillator synchronized? Could it be an E1 Sync stability
> issue caused by Digium cards?

The question is not "could".  Any BTS always needs a proper, stable
reference clock.  So unless your BTS has a built-in GPS clock refrence (and that
reference is configured/enabled), your E1 will have to provide a stable clock
reference.

"stable" means (likely) fulfilling a clock stability that is _at the very least_ the
stability of what commercial TDM/ISDN networks used to have.  It doesn't hurt to have
better stability.

Any crystal oscillator on any E1/T1 peripheral card (digium or not) is by far not stable
enough, possibly up to 1000 times worse than required.

> 1. Set Digium card to get Sync from RBS. Now Digium is configured for
> Internal clocking and acts as master. Maybe in case when both sides will be
> configured to get sync from E1 it will decrease difference between internal
> clock of RBS and E1 and RBS will get Synced state.

And what would that get you to?  In the end, a BTS that transmits at a frequency that
will likely be so far off that you have serious problems connecting phones to it.

> 2. Theoretically I can try to use Nokia DX200 BSC as a clock master for
> Digium and deliver sync to RBS from Digium. I'm not sure if timing accuracy
> is the same for Nokia and Ericsson HW.

Sure, that should work.  You can use any proper clock reference.  One option I'm using
here is to use a SIU-02.  It has a 1PPS input for GPS, and it clocks up to 16 E1/T1
interfaces with that clock.  You can then feed that clock signal to one port of your
multi-port Digium card, and configure that as clock source, and the other ports will
use that clock when talking to your BTSs.

> One more question is where can I find some info about timing accuracy for
> BTS and any possible way to check it on the existing E1 line?

You would have to use some kind of test equipment that has a much more accurate/stable
clock itself, like a rubidium oscillator or a GPS-DO.  And then you can
try to measure the Allan deviation/variance.  But why do that?  It's
obvious that a normal crystal oscillator is way insufficient, no need to
measure it.

--
- Harald Welte <laforge@osmocom.org>            http://laforge.gnumonks.org/
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