DS-3 Error Stats

Sean Donelan SEAN at SDG.DRA.COM
Mon Jun 14 22:37:33 UTC 1999

jhawk at bbnplanet.COM (John Hawkinson) writes:
>Most carries have "performance objectives" which they adhere to,
>and they specify some number of errored seconds per day per circuit,
>and those numbers may vary based on route-milage.
>Unfortunately I think most of those numbers are covered under NDAs,
>but I can safely say that 1 errored second/day would be well
>under the criteria and 1,000 would be well over, and anything in
>between depends on your carrier and route miles, etc., etc.

In most cases, DS3's are sold by carriers as a tariffed service.  The
carrier may not like disclosing the numbers, but buried in the public
tariff's "incorporated by reference" list of documents are the performance
objective for that carrier's DS3 service.  Most carriers' tariffs refer
back to either Bellcore(telcordia), ANSI/T1 or ITU specifications (generally
in that order).

However, I'm not sure knowing them will do you much good.  I tracked
down the numbers for DS1 once upon a time.  Like any good-one-sided
telco tariff, the circuit could be very bad and still meet the "acceptable"
performance objectives for the service.  If I recall correctly, a DS1 could
have several thousand error seconds a day, and be considered "acceptable"
according to the tariff.  I've never looked up the DS3 numbers, so I don't
know the official tariff numbers.  As always, the tariff overrides anything
the sales person told you, or anything written in your contract.

However after saying that, digital lines usually only have 'noise' for a
reason.  The question is how bad does it have to be before you can get the
telco to track it down.  Here are my rules of thumb for most digital circuits:
    Error seconds/15 minutes               Classification
          0                                Perfect
          1-5                              Look at the circuit during the next
                                           maintenance window if it doesn't
                                           clear up
          6-29                             Open a ticket
          30+                              Immediate action required (its
                                           likely the circuit is bouncing
                                           or 'down' at this point)

Other people prefer to use a long-term bit error-rate, or packet/cell errors.
But then you have to explain to the telco what a packet or bit is.  For those
ISPs which own their facility provider, they may be able to get the facility
folks to monitor the circuits.  But for the rest of us, you have to monitor
your own circuits.  The facility provider is never going to tell you about
a potential problem.
Sean Donelan, Data Research Associates, Inc, St. Louis, MO
  Affiliation given for identification not representation

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