[time-nuts] Low-long-term-drift clock for board levelintegration?

Jim Lux jimlux at earthlink.net
Tue Feb 21 20:02:12 UTC 2012


On 2/21/12 10:47 AM, Attila Kinali wrote:
> On Tue, 21 Feb 2012 10:05:04 -0800
> Chris Albertson<albertson.chris at gmail.com>  wrote:
>
>> Perhaps he has now given up on that approach and has
>> gone to using relative time and round trip timing which would work
>> even using a $2   TTL "can oscillator"
>
> If you read carefully what the OP wrote, you'll see that he
> wants to measure one way trips.
>
> RTT is easy and well understood. You can use a standard PC and
> get to ~100us resolution with no special components. If you take
> a NIC with time stamping, you get well below that.
>
> But the problem is, in order to understand how networks behave
> exactly and how this behaviour is changing over time, you need
> to know the one way delays (mostly due to asymetric routing
> which leads to asymetric load etc pp). And to do this, you need
> a global time scale for time stamping. There is no way around it.
>

What if one sends a message one way that triggers say, 10 response 
messages 1 second apart.   Then you get distribution statistics on the 
return path.  You still don't know what the absolute forward or reverse 
path time was, of course.




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