Chan_pjsip packetization time

We experienced choppy lines in our SIP Trunks. The resolution was to apply a packetization time of 20 ms (default) across all peers. Previous configuration has one peer with packetization time set to 30 ms : allow=ulaw:30.

We find this weird because, when we reverted the packetization time to 30 ms on one of the peers, we can no longer reproduce the choppy lines. And this peer was not even used for the call leg with choppy lines.

RTP Packetization - Asterisk Project - Asterisk Project Wiki says that packetization can be set either by peers or globally. Although, chan_pjsip was not mentioned in the article.

Should the packetization time be the same for all peers in an ASTERISK Server? Does this apply in both chan_sip and chan_pjsip? If we use autoframing=yes, can we add this in pjsip.conf file in the same way that it appears in sip.conf?

Autoframing is always enabled in PJSIP. Packetization in PJSIP is set per-endpoint on the codec. It doesn’t have to be the same, depending on what is negotiated the RTP layer will repacketize as needed, though not in the most tolerable fashion due to being done before Asterisk had any concept of timing. For example receiving 20ms on one side and sending 10ms on the other side would result in two 10ms packets being sent at once generally.

Thanks jcolp

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