Question on Loosely Synchronized Router Clocks

Robert E. Seastrom rs at seastrom.com
Tue Sep 18 00:48:04 UTC 2007


"Xin Liu" <smilerliu at gmail.com> writes:

> Sorry for the confusion. Let me clarify.
>
> We are interested in a number of questions:
> 1. Can we assume loosely synchronized router clocks in the Internet,
> or we have to make absolutely no assumption about router clocks at
> all?

Make no assumption.

> 2. If the router clocks are indeed loosely synchronized, what is the
> granularity we can assume? Particularly, we are interested in whether
> we can assume router clocks are synchronized within 10 minutes.

It's not even a fair assumption that all routers have clocks (as in
wall time / time of day or year clocks, not CPU clocks).

> 3. It's always possible that a router's clock goes wrong. In practice,
> how often does this happen?

Let's suppose you were writing software for a router and you wanted it
to behave in a certain fashion if its clock were out of sync with some
time standard, say for the sake of argument, TAI.  How would the
software in this router go about determining that it was out of sync
with standard time?

                                        ---Rob

> Thank you for all the replies.
>
> Best
> Regards,
>
> Xin Liu
>
> On 9/17/07, Randy Bush <randy at psg.com> wrote:
>>
>> i conversed offline with the OP.  he was reading a sigcomm research
>> paper and confusing it with the internet.
>>
>> randy



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