Virtual layer 1 - Questions

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Sebastian Stumpf sebastian.stumpf87 at
Fri Mar 3 16:56:13 UTC 2017

Hi Harald,

> This is likely a result of the MS somehow not receiving/processing the
> downlink signalling messages. [on TCH]

I found the reason for that. I thought I need to forward incoming messages
on TCH/H TCH/F as L1CTL_TRAFFIC_IND if the ACCH flag is not set in the
GSMTAP header channel type. But in case of a msg on FACCH this is wrong
and needs to be L1CTL_DATA_IND. As the CM Service Accept is sent on
FACCH it was not forwarded correctly to l23 and thus not processed.

Unfortunately I do not know, how to distinguish FACCH from TCH based on
the information available in the GSMTAP messages.
The stealing flag indicating a FACCH is set before and after the training
sequence in the burst I think, but this info is no longer available in the msg
as it is sent over the virtual um.

Or do I miss something here?

Do you have an idea how to check if the msg is TCH or FACCH?

> Also, what's noteworthy (but likely unrelated) is that the BTS is
> sending empty idle/padding frames on the TS7 all the time (those
> containing 0x2b2b2b2b) but the MS is not doing that in uplink.

That's because I just implemented some kind of one time scheduler.
If I do not get frames/data to schedule from the upper layer for a tdma slot,
I currently do not have any logic that fills these up with empty/idle frames.
Seems as if I need this, though.

Thanks a lot for your support, I am glad you are taking the time to help me
out :).

With kind regards,
Sebastian Stumpf

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