Hi, Oh my, it's been a long time since I have written that code and i didn't check the diffs that have been contributed since, but i'll give it a try...
(Code uses real time units instead of RTP timestamp units but that doesn't matter for the argument) Saved values from previous packet: statinfo->time == R(i-1) statinfo->lastnominaltime == S(i-1) statinfo->jitter == J(i-1) Value from current packet: current_time == Ri nominaltime == Si Thus... expected_time == R(i-1) + (Si - S(i-1)) current_diff == |Ri - expected_time| == |Ri - (R(i-1) + (Si - S(i-1)))| == |D(i-1,i)| current_jitter == (15 * J(i-1) + |D(i-1,i)|) / 16 == J(i-1) - J(i-1)/16 + |D(i-1,i)|/16 == J(i) Bingo! Regards, Lars -----Original Message----- From: wireshark-dev-boun...@wireshark.org [mailto:wireshark-dev-boun...@wireshark.org] On Behalf Of Chaswi Przellczyk Sent: mercredi 6 avril 2011 17:12 To: Wireshark Dev Subject: [Wireshark-dev] RTP Jitter calculation (Telephony->RTP Stream Analysis) Dear all, I'm trying to match --------------------------- http://wiki.wireshark.org/RTP_statistics --------------------------- How jitter is calculated Wireshark calculates jitter according to RFC3550 (RTP): If Si is the RTP timestamp from packet i, and Ri is the time of arrival in RTP timestamp units for packet i, then for two packets i and j, D may be expressed as * D(i,j) = (Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si) The interarrival jitter SHOULD be calculated continuously as each data packet i is received from source SSRC_n, using this difference D for that packet and the previous packet i-1 in order of arrival (not necessarily in sequence), according to the formula * J(i) = J(i-1) + (|D(i-1,i)| - J(i-1))/16 --------------------------- to the following code from tap-rtp-common.c (rtp_packet_analyse): --------------------------- if( !statinfo->first_packet ) { /* Calculate the current jitter(in ms) */ expected_time = statinfo->time + (nominaltime - statinfo->lastnominaltime); current_diff = fabs(current_time - expected_time); current_jitter = (15 * statinfo->jitter + current_diff) / 16; statinfo->delta = current_time - (statinfo->time); statinfo->jitter = current_jitter; statinfo->diff = current_diff; } statinfo->lastnominaltime = nominaltime; --------------------------- And I can't find (m)any similarities between the two. Can anyone lend a hand? Thanks! CP. -- Empfehlen Sie GMX DSL Ihren Freunden und Bekannten und wir belohnen Sie mit bis zu 50,- Euro! https://freundschaftswerbung.gmx.de ___________________________________________________________________________ Sent via: Wireshark-dev mailing list <wireshark-dev@wireshark.org> Archives: http://www.wireshark.org/lists/wireshark-dev Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev mailto:wireshark-dev-requ...@wireshark.org?subject=unsubscribe ___________________________________________________________________________ Sent via: Wireshark-dev mailing list <wireshark-dev@wireshark.org> Archives: http://www.wireshark.org/lists/wireshark-dev Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev mailto:wireshark-dev-requ...@wireshark.org?subject=unsubscribe
