[time-nuts] SLIP vs Ethernet for NTP

Magnus Danielson magnus at rubidium.dyndns.org
Mon Oct 24 00:26:49 EDT 2011

On 10/24/2011 05:14 AM, Doug Calvert wrote:
> On 10/23/2011 08:37 AM, Tijd Dingen wrote:
>> I seriously doubt that piping it through slip is going to help. You
>> still get to deal with slip + tcp protocol stack. I would expect gbit
>> ethernet with possibly some fifo/buffering setting adjusted gets you
>> better performance that RS232 (with or without slip). Just assemble
>> some raw frames on the source side and go.
>> regards
>> Fred
> I think gig ethernet has a higher delay for smaller packets (ntp's udp
> datagram is tiny) than 100mbit ethernet.

There is very little to support this claim. The line-encoding could 
possibly cause a small difference, but other than that I suspect 
implementation issues rather than protocol by itself.

Even if you said that gigabit ethernet cards tend to have a higher delay 
for smaller packets I would react, but then not on the technical aspect 
but rather that I would like to see some statistics supporting the claim.

Only real technical issue is that datagram size needs to be 64 bytes and 
that the header, trailer and inter-packet gap has the same size, but 
behaves like larger relative parts than for larger packets. However, 
this effect would be valid for fast ethernet too.


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