[ntp:questions] ntp server specs

unruh unruh at wormhole.physics.ubc.ca
Thu Jun 16 20:41:38 UTC 2011

On 2011-06-16, Rick Jones <rick.jones2 at hp.com> wrote:
> unruh <unruh at wormhole.physics.ubc.ca> wrote:
>> On 2011-06-15, Chris Albertson <albertson.chris at gmail.com> wrote:
>> > One hundred??
>> >
>> > Best to use a decentralized design.  Buy 100 rs442 to rs232 receiver
>> > chips.  You can place then in a box on the back of each of the 100
>> > computers.
>> >
>> > The specs say one 442 driver can connect to ten receivers.  So you'd
>> > need a ten port distribution system to drive 10 buses.
>> >
>> > Please remind us why you can't use NTP.  It would be less work to buy
>> > a 100 port Eithernet hub.  You can get very good timing with NTP on a
>> > short run of 100BaseT
>> But terrible on 1000BaseT.
> I know it is a convenient shorthand to use the link-technology name,
> but is it really that 1000BaseT as specified by the IEEE is terrible,
> or the *implementation* specifics of various, perhaps many network
> interface cards supporting 1000BaseT?  I'm thinking, specifically of
> interrupt coalescing.

No idea. All I know is that on my network before I put some 1000BT cards
onto the network, the round trip time was very very stable at 130us. Now
it flops around- sometimes 140 us, sometimes 280, sometimes 10ms. It
(whatever it is) has destroyed a good timekeeping system.

> rick jones

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