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Jacob Erlbeck jerlbeck at sysmocom.deDear Andreas, On 02.02.2014 13:09, Andreas Eversberg wrote: > > holger mentioned that you also had a problem with speech frames in > conjunction with ipaccess BTS. was it a similar problem? how did you > solve this? that BTS silently drops frames that do not have a RTP timestamp of T0 + 160 * k, where T0 is the first timestamp (I ignore the modulo here). In addition it ceases to transmit audio from RTP if there is a pause (e.g. no RTP for >1s) but the timestamps are not incremented accordingly (probably because they've been considered to be too late). In short: that BTS expects proper timestamps. I've solved this by optionally allowing the MGCP daemon to enforce the 160*k requirement by rounding the timestamp towards the next valid one. In addition, when SSRCs are patched, the new timestamp offset is calculated based on (monotonic) system time that has passed between the last packet of the old SSRC and the first of the new. Since the RTP timestamp problems only happened when the network side switched streams (and thus luckily SSRCs), this was sufficient. In theory, the BTS should be able to detect SSRC changes and reset its timing accordingly. But since this is not the case with that BTS, those workarounds are neccessary :-( Cheers Jacob