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Delta time with previous frame

asked 2020-05-14 08:44:47 +0000

Hilman gravatar image

Hallo, I want to ask about delta time with previous frame. In VoIP communication using the RTP protocol, is the sender's time process included in the delta time count with the previous frame?


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answered 2020-05-14 10:21:24 +0000

Anders gravatar image

Delta time is the time difference between the time stamps made by the capturing mechanism on the computer doing the capturing. To measure RTP delays you probably have to make capture at the sending side and the receiving side and that may not be the full story of the delays.

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@Anders Thanks for your answer. I have another question. Suppose I install Wireshark on the receiver, when there are two RTP data with a delta value of 25 ms. The value of delta with previous frame states the difference in timestamp time with the previous frame. When the first frame enters, it states that the packet has passed through the sender and arrived at the receiver. Then when the second data is entered, it also states that the packet has passed through the sender and arrived at the receiver. Is it true my assumption if the value of delta with previous frame states the delay time for the sender process as well as the packet transmission time?

Please correct if I'm wrong

Hilman gravatar imageHilman ( 2020-05-14 12:34:27 +0000 )edit

Sorry I don't get that. RTP packets are sent with a fixed delta time, packatesation time. Witch depends on codec and sampling time. Variation in this time is called jitter. The time it takes a sender to assemble the speech entering trough the microphone and assemble an RTP packet is not possible to measure with Wireshark. To measure the time it takes to send a RTP packet through the network and any nodes inbetween you need to time the packet at the sender and then at the receiver and calculate the difference.

Anders gravatar imageAnders ( 2020-05-14 13:09:57 +0000 )edit

Okey @Anders, thank for your answer again

Hilman gravatar imageHilman ( 2020-05-15 06:03:30 +0000 )edit

Hello @Anders, there another problem in my mind. To measure time to send RTP packet through network, you suggest using wireshark on the sender and receiver. From the captured data, what value can be used to calculate the delay ? I mean what value can be used as parameter to identify the delivery time of packet of sender ?

Hilman gravatar imageHilman ( 2020-05-26 04:39:07 +0000 )edit

It is not easy to set up and get good relable values but the theory is, take a trace near the sender with a accurate and precise timestamp NTP syncronised. Do the same at receiver side idetify sent and recived packet and do (recived_time - sent_time) = delay or transport time. My estmate is that the accurasy would be in the range of +-10ms.

Anders gravatar imageAnders ( 2020-05-26 08:50:01 +0000 )edit

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Asked: 2020-05-14 08:44:47 +0000

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Last updated: May 14 '20