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David A. Burgess dburgess at jcis.netAnd 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 at gnumonks.org> http://laforge.gnumonks.org/ > ============================================================================ > "Privacy in residential applications is a desirable marketing option." > (ETSI EN 300 175-7 Ch. A6)