Re: SONET ring questions

["Dave Cooper" <dave_cooper () eli net>]

At 10:36 PM 10/16/98 +0100, Manar Hussain wrote:
> > How many significant digits do you consider acceptable?  Even in an ideal
> > APS environment, link failure detection and protection switching does take
> > finite time.  You might get 99.999% uptime, but probably not 99.9999999%.
>
> The thing that always got me was that there never seems to be a mention of
> the sampling period for the stat.
>
> > Methinks that you've been subjected to Marketing.  ;-)
>
> Well ... I'll give you 99.9999999% on any system you like - with a sampling
> period of say every billion years. I think that allows me to stay down for
> the first 100 years, long enough to extend beyong the life of any stressed
> sysadmin :)
>
> More seriously - SLA's that specify a sampling period then also give an
> indication what is considered too long an outage. If you get just under the
> .1% downtime allowed per year all in one go you may well be pretty pissed
> at being told the 8 hour outage was within the SLA.

The quasi Engineering guidelines for many CLECs when calculating average
downtime over a year's span is 52 minutes (meaning .0001% downtime over
the year).  Anything above and beyond this estimate would be suspect.
Obviously, these Engineering baselines vary from carrier to carrier. 
Also, this 52 minute guideline relates to the SONET ring and the muxes
and not the tributaries (OC-3 or OC-12) or the optical/electrical hand-offs
that might fail due to bad terminations/bad wiring/or misconfigured nodes.
A common failure for OC-3c or OC-12c is the 2-fiber optical handoff to the
customer which has nothing to do with the SONET ring itself or the associated
SONET gear.

Dave Cooper
Electric Lightwave, Inc.
Disclaimer: Comments above reflect my experience with numerous CLECs and
not specifically ELI. 


> Manar