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ACK_RTT for packet send from server

Hello everyone,

I want to ask how is it possible to get a ACK_RTT time for a packet that is send from my computer, and received by some server.

I have this lines in wireshark:

No    Time       ACK_RTT  protocol    SRC IP ADDR        DST IP ADDR
543 0.000000               TCP      192.168.0.105    www.dropbox-dns.com    SYN
550 0.060792    0.060792   TCP     www.dropbox-dns.com  192.168.0.105      SYN,ACK
552 0.000207    0.000207   TCP      192.168.0.105   www.dropbox-dns.com     ACK

I can't understand how is it possible to have ACK_RTT Time for the Line 3 (No. 552), its just ACK to the server.

Thank you in advance!

ille's avatar
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ille
asked 2017-11-09 21:05:49 +0000, updated 2017-11-09 21:27:19 +0000
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You need take into consideration where the packets get captured. This typically happens at layer 2 or layer 3 within an operating system. The ACKs which is the basis of wireshark's RTT calculations is sent by layer 4 of the OSI model .
The 0.00207 seconds is the time between the trace tool saw the SYN_ACK and the time the ACK completing the 3-way-handshake was seen.
Assuming the trace was taken at the client, the 209 µs is the internal RTT within the operating system,
the 60.792 is the round-trip-time through the network (+ the remote internal RTT) . Regards Matthias

mrEEde's avatar
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mrEEde
answered 2017-11-09 22:13:08 +0000
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But, also in the 'TCP Stream Graph' for 'Round Trip Time' Graph we can make a Switch Directions and then we see the Graph for RTT from the Server to us. How is then this possible?

ille's avatar ille (2017-11-13 12:41:30 +0000) edit
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