[asterisk-dev] definition of RTP jitter - potential bug in Asterisk

[Klaus Darilion]

looks like the some scaling is done in trunk too (res/res_rtp_asterisk.c)


Klaus Darilion schrieb:
> Hi!
> 
> In Asterisk 1.6.2.0-beta4, the jitter is internally calculated in 
> seconds (see calc_rxstamp() in main/rtp.c).
> 
> When the jitter is sent in RTCP reports, the jitter value is multiplied 
> with 65536 (e.g. ast_rtcp_write_sr()).
> 
> This value of 65536 is all over rtp.c. Also the received RTCP jitter 
> reports are scaled by 65536.
> 
> I wonder where this 65536 comes from? RFC 3350 describes the jitter in 
> "timestamp units". The RTP timestamps are the sample times, and thus the 
>   usual timestamp unit is 1s/8000.
> 
> Thus, I think if jitter is computed locally in seconds, the scaling 
> should use 8000 instead of 65536.
> 
> I also observed that the sent jittervalue differs much from the incoming 
> jitter value (e.g. tested with eyebeam and pjsip).
> 
> Thus, I think the scaling with 65536 is wrong. If there is a reason why 
> 65536 is used, please describe.
> 
> thanks
> Klaus
> 
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