Re: Hardware Timestamping Problem

[Christian Rupp <christian.rupp.stuttgart () freenet de>]

Yes, one tcpdump entity per server, after Both are started I start a 
Package Generator which sends a 900kbs Trace.

There shouldn't be a big buffering effect, if I'm not using the hardware 
timestamp options the one way delay is at a few 100 µs, or am I 
misunderstanding something?
The 36 seconds are only showing up, when I'm using the -j 
adapter_unsynced option.
The goal is to measure the one way delay, so I simply take the timestamp 
of the Receiver and subtract the timestamp of the sender.

I'm using  ptp4l for the synchronisation.(I have run ptp oder the same 
link as the measurement, and on a different link, synchronising the 
clocks with phc2sys. Both implementations had the 36s error)

Am 08.06.2016 um 16:24 schrieb Michael Richardson:
> {please keep it on the list for archival purposes}
>
> Christian <christian.rupp.stuttgart () freenet de> wrote:
>      > between sender and receiver
>      > so from the point when tcpdump grabs the time off of the Sender and to the
>      > point where tcpdump grabs the time off of the receiver.
>
> So you are running a tcpdump on sender, using the timestamping service from
> the hardware, and the same on receiver, and then you send traffic?
>
> How much traffic? Is it being buffered?
> How do you correlate traffic?
>
> How are the *hardware* clocks being synchronzied?
>
> AFAIK, no NICs timestamp traffic on outgoing, tcpdump captures before the
> hardware queue.  A big hardware send buffer would result in significant skew.
>
> --
> ]               Never tell me the odds!                 | ipv6 mesh networks [
> ]   Michael Richardson, Sandelman Software Works        | network architect  [
> ]     mcr () sandelman ca  http://www.sandelman.ca/        |   ruby on rails    [

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