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Re: [perfsonar-user] I have retransmissions without packet loss


Chronological Thread 
  • From: Chris Welti <>
  • To: Tom Yard <>, <>
  • Subject: Re: [perfsonar-user] I have retransmissions without packet loss
  • Date: Mon, 24 Sep 2018 15:27:10 +0200
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Hi Tom,

There could be local loss on the packet buffers of the card used for
throughput tests, so on the network you will not have loss but internally in
the system.
What's more likely though is that you just don't see the loss in the one way
and RTT graphs, as those test packets are sent at a much much lower
frequency, so the probability
that those packets are dropped even if there is congestion is lower than that
TCP packets of the throughput test are hit.

Best regards,
Chris

On 24.09.18 12:57, Tom Yard wrote:
> Dear people, we have tested two perfSONAR servers in the same network
> segment: one as a client and the other as a server. 
>
> In the perfSONAR client box we have two interfaces in the same network
> segment,  using policy routing to make internal IP stack route the packets
> out on the designated interface: one interface for throughput tests with
> iperf3 at both machines and the other interface for latency and packet loss
> tests.
>
> As a result, we have a graphic with 0% packet loss (one way and RTT), but
> we have some retransmissions in the throughput graphic.
>
> Why do we have retransmissions if I have no packet loss at all ? I can't
> understand this situation...
>
> Thanking in advance !!!
>
> Tom

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