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I've read that Iperf basically tries to send as much information down a connection as quickly as possible reporting on the throughput achieved. This tool is especially useful in determining the volume of data that links between two machines can supply.

Is it possible to gather the same results by sending regular data, as in not testing data?

What I'm trying to do is sending data in the foreground while gathering statistics in the background (throughput and jitter).

How iperf calculates these two values?

Błażej Michalik
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Varda Elentári
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3 Answers3

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This is the closest thing I've found

http://openmaniak.com/iperf.php

Varda Elentári
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I have the similar question about how iperf works. Please refer to the following post where I did some research and gave an overview.

How iperf calculates network statistics

Generally, in iperf, it embedded timestamps and sequence number in the payload in the sender side. When receiver receives the packet, it extracts these content and calculates the statistics. You can find more detail in the post.

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Jack Chan
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Throughput is simple: assuming the client is saturating the network, the server only needs to count the received bytes, and divide that by some duration.

This post explains this topic in a greater detail.

Iperf 2 calculates Jitter for UDP only. It is based on what is prescribed within by RTP implementation, as stated by the code.

RTP is used in implementations of audio streaming, where jitter plays a major role, so it's a good place to take the algorithm from - what Iperf reports is what many applications where you would be interested in jitter would see.

See RFC 1889, section 6.3.1, "interarrival jitter" field:

The interarrival jitter J is defined to be the mean deviation (smoothed absolute value) of the difference D in packet spacing at the receiver compared to the sender for a pair of packets. As shown in the equation below, this is equivalent to the difference in the "relative transit time" for the two packets; the relative transit time is the difference between a packet's RTP timestamp and the receiver's clock at the time of arrival, measured in the same units.

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 is 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=J+(|D(i-1,i)|-J)/16
Błażej Michalik
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