6 Dec
2011
6 Dec
'11
7:02 p.m.
And in the general case (beyond the specific OpenBSC implementation) it's even more
complicated than that, depending on the assignment type (early, late, very early) and
whether or not the network uses early media for in-patterns. (In other words, the sound
of the phone ringing at the other end might come over the speech channel before the call
is actually connected.) For most purposes, the receipt of Connect Acknowledge is
considered to be the start of the call, but as Harald points out, that does not happen in
the BTS, which is mostly a layer-2 device. (Unless you are using OpenBTS, which is a
different matter altogether.)
On Dec 6, 2011, at 1:43 AM, Harald Welte wrote:
On Tue, Dec 06, 2011 at 08:57:58AM +0100, Tobias Engel
wrote:
Hi,
does anybody know when the exact moment in a call is, when the NanoBTS
starts forwarding audio from a MS to OpenBSC?
I guess as soon as
1) a RTP stream is configured, and
2) there are actual audio speech frames received from the phone
Each frame on the TCH can be either audio or FACCH, this is
differentiated in L1 by the use of the stealing flags. So as long as
the phone is sending FACCH frames, they go to the LAPDm implementation
in the BTS. Once it sends voice frames, they go to the RTP socket.
The RSL CHANNEL MODE (speech) might also have an influence on it.
Or could it be that the BTS waits for the
"Connect" message from the MS?
The BTS doesn't have anythin to do with call control.
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
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