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Wireshark-users: Re: [Wireshark-users] end-to-end delay calculation using tcp

From: "Ji Zhang" <Ji.Zhang@xxxxxxx>
Date: Thu, 10 Apr 2008 18:30:46 +0100

With TCP you don’t really get any packets lost eventually, however if your streaming client somehow decides not to wait for a retransmitted packet, the retransmitted packet could be dropped by the client itself.

 

Given TCP is reliable, however, by looking at the number of retransmissions, you may have some idea about how good/bad the network is.

 

If you’d like to have a quick look at the round-trip time, you may wish to use Statistics->TCP Stream Graph->Round Trip Time Graph, which gives you some idea about the end-to-end delay (roughly half the round-trip time).

 

For better analyzing, it may be good to grasp some more TCP basics.

 

Cheers,

Ji  

 


From: wireshark-users-bounces@xxxxxxxxxxxxx [mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Fabiana moreno
Sent: 10 April 2008 17:31
To: Community support list for Wireshark
Subject: Re: [Wireshark-users] end-to-end delay calculation using tcp

 

So every retransmission is a packet lost?

On 10/04/2008, Hansang Bae <hbae@xxxxxxxxxx> wrote:

Fabiana moreno wrote:
> Hello guys,
>
> I am streaming a video using tcp and i was wondering how could i
> calculate certain parameters such as end-to-end delay or frame loss?? is
> it hard to acomplish?
>


You are streaming or downloading the video?  if you're streaming, I
guess you use a buffer of some sort?

end to end delay can be somewhat tricky but there are some rules of
thumb you can use to calculate it.

1)  Look at SYN and SYN+ACK.  The time it takes for syn_ack to come back
is your round trip delay
2)  Look at ACKs coming back after two successive full sized packets.
This too can be used to calculate the round trip time.  The reason is
that the receivers tcp stack will immediately ACK after receiving two
full size packets (w/o app intervention).

You can also look for packet loss by using the filter
"tcp.analysis.flags" display filter and looking for retransmissions.


--

Thanks,
Hansang
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