Measuring RTT of RTCP using RR packet

asked 2022-11-20 18:01:10 +0000

nifty gravatar image

updated 2022-11-23 09:42:36 +0000

I have a capture packet of RTCP received report. I attached the screenshot. My question is how to measure the RTT using the Last Sending report (LSR), Delay since last sending report (DLSR) and Arrival time. I know the formula and way to calculate which is, RTT= A(arrival time) - LSR - DLSR

  • LSR= 1257767217 sec
  • DLSR = 1416160922 (21608900 milliseconds)

But now my confusion is what is the arrival time in conversion which is related to the LSR and DLSR time. Because LSR is the time of the last Sending report which is the middle 32 bits of the NTP timestamps. But now I have Arrival Time: Nov 18, 2022 15:55:13.464735796 CET, what should be do to measure the RTT. please guide.


Arrival Time: Nov 18, 2022 15:55:13.464735796 CET
Frame 733: 88 bytes on wire (704 bits), 88 bytes captured (704 bits) on interface ens18, id 0
Interface id: 0 (ens18)
Encapsulation type: Ethernet (1)
Arrival Time: Nov 18, 2022 15:55:13.464735796 CET
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1668783313.464735796 seconds
[Time delta from previous captured frame: 0.008838038 seconds]
[Time delta from previous displayed frame: 0.116259430 seconds]
[Time since reference or first frame: 31.638257256 seconds]
Frame Number: 733
Ethernet II, Src: Cisco_ac:bc:00 (00:1c:b1:ac:bc:00), Dst: 9a:21:30:09:d7:85 (9a:21:30:09:d7:85)
Internet Protocol Version 4, Src:, Dst: 
User Datagram Protocol, Src Port: 41867, Dst Port: 44976 
Real-time Transport Control Protocol (Receiver Report)
10.. .... = Version: RFC 1889 Version (2)
..0. .... = Padding: False
...0 0001 = Reception report count: 1
Packet type: Receiver Report (201)
Length: 7 (32 bytes)
Sender SSRC: 0x0f187a4b (253262411)
Source 1
    Identifier: 0x9e3f641b (2654954523)
    SSRC contents
    Extended highest sequence number received: 2357644957
    Interarrival jitter: 1302420865
    Last SR timestamp: 1257767217 (0x4af80131)
    Delay since last SR timestamp: 1416160922 (21608900 milliseconds)
[RTCP frame length check: OK - 32 bytes]
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Could you make available a PCAP with the relevant RTCP frames?

MartinM gravatar imageMartinM ( 2022-11-22 21:14:29 +0000 )edit

I am not able to add the file.?

nifty gravatar imagenifty ( 2022-11-23 13:38:28 +0000 )edit

Place the file on a public share and then add a link to the file by editing your question.

grahamb gravatar imagegrahamb ( 2022-11-23 13:54:48 +0000 )edit