Personally i think its the tcp overhead.
Wich a download app won't show.
And if the TCP throughput graph just look at the data en not the
overhead wich can be up to 14% on the internet.
Greetings,
Yorian Wiltjer
2010/11/22 Michal Kepien <wireshark@xxxxxxxxxx>:
> Greetings,
>
> I cannot understand how the TCP throughput graph is created by Wireshark. I
> have done the following:
>
> 1. Start packet capture.
> 2. Start a single web download on a 2 Mbit/s link.
> (The transfer was stable at 230 kB/s.)
> 3. Stop packet capture.
> 4. Filter the packets so that I only get the receiving side's packets from a
> one second long fragment of the transmission.
> 5. Save the filtered packets to a separate PCAP file.
>
> When I open that file in Wireshark, the summary shows that the file contains
> 170 frames, each 1514 bytes long, which translates to 170 * 1460 = 248200
> bytes of raw TCP payload. That means the effective transfer rate was around
> 242 kB/s. (That's inconsistent with what the download application was
> showing, but read on.)
>
> When I view the TCP throughput graph, most of the graph oscillates around
> 235000 bytes per second, which is around 230 kB/s - exactly what the
> download application was showing. But how can this be? Why does the graphed
> transfer rate differ by over 10 kB/s from a simple calculation? I've read a
> thread from a while back
> (http://www.wireshark.org/lists/wireshark-users/200701/msg00024.html) and
> when I calculate the throughput manually using the method described there,
> it's still inconsistent with what the graph is showing. What am I missing
> here?
>
> I attach the PCAP file in question. Thanks in advance for any tips,
>
> --
> Best regards,
> Michal Kepien
>
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