Hello, We are in the process of debugging a voice quality issue for a client of ours that is a VoIP services provider. The client uses a softphone that runs on a pjsip stack.
When placing a call using the softphone, it negotiates the use of G729 codec with the remote endpoint (ptime = 20ms). The endpoint transmits RTP packets with encoded G729 payload. VAD/DTX is enabled. We see that the last frame transmitted by the carrier side endpoint, before the beginning of a period of discontinuous transmission has 20 bytes of payload. We have verified that VAD/DTX is used by the carrier side endpoint by noting that there exist successive RTP packets that differ by 1 in their sequence number but have a timestamp difference > 160 and MARK bits are set in the RTP header. Our understanding is that for G729B, the SID frame that is transmitted before a period of discontinuous transmission has a size of 2 bytes. However we see that ALL RTP packets sent by the carrier side end point has a length of 20 bytes. Has anybody else seen this behavior from a carrier side endpoint ? Is there an RFC or document that specifies -- Thanks and Regards, Vikram Ragukumar. -- _____________________________________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- New to Asterisk? Join us for a live introductory webinar every Thurs: http://www.asterisk.org/hello asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
