Hi all,
I am having some problems calculating the round-trip-delay of an
RTCP Sender Report packet.
I have a method to calculate the round trip delay for a Sender Report,
but sometimes it gives me the round trip delay to be a negative number.
Could someone please help me out if the method I use to calculate
round-trip-delay is correct or not?
And if it is correct, why do I get the round-trip as negative?
A packet has the following specifications:
*Timestamp, MSW: 8509 (0x0000213d)
Timestamp, LSW: 1317011456 (0x4e800000)
Last SR timestamp: 556982720 (0x2132e1c0)
Delay since last SR timestamp: 308288
*
What I do:
Round trip delay = Arrival time- LSR - DLSR
= (NTP MSW + NTP LSW) - (LSR MSW + LSR LSW) - DLSR
= (NTP MSW - LSR MSW) + (NTP LSW - LSR LSW) - DLSR
From the data given :
(NTP MSW - LSR MSW) = 0x0000213d - 0x002132 = B = 11 D (in seconds)
(NTP LSW - LSR LSW) = 0x4e800000 - 0xe1c0000 = -2470445056 D
I assume that the unit of NTP LSW is in nanoseconds (or is it 232
picoseconds??).
So (NTP LSW - LSR LSW) = -2.4 seconds
DLSR = 308288/65535 seconds = 4.7 seconds
Therefore, RTD = 11 - 2.4 - 4.7 = 3.896 seconds
Please correct me if I am wrong in the above procedure to calculate RTD.
Now there is a packet which has the following specifications:
*
Timestamp, MSW: 8505 (0x00002139)
Timestamp, LSW: 1065353216 (0x3f800000)
Last SR timestamp: 557665920 (0x213d4e80)
Delay since last SR timestamp: 108992*
So here:
(NTP MSW - LSR MSW) = 0x00002139 - 0x0000213d
= -4
So what is the cause of a negative RTD??
I am really sorry if I appear to be dumb but I would also like to know
how the inter arrival jitter is calculated?
I know how to calculate jitter in seconds but the unit of jitter as
specified in the RTCP packet appears to be something else.
Thanks in advance
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