North American Network Operators Group

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Re: Statistical Games Providers Play (RE: availability and resiliency)

  • From: Alex Bligh
  • Date: Sat Sep 30 05:41:14 2000

Sean et al.,

Excluding force-majeure from availability is not totally unuseful
(provided you can still compare apples with apples), on the basis
that (historically at least) many other things are likely to
cause more worry than failure of your internet/telecoms service
in the event of war/asteroid strike etc.

However, I've seen force-majeure clauses which exclude for instance
weather (drizzle?), actions by telecoms providers (mmm.. didn't
even exclude the contracting party and its suppliers) etc. etc. -
these are about as useful as excluding actions by backhoe operators
and train derailments. Part of the problem is noone ever reads
these clauses, often titled (at least in the UK) 'Acts of God'.
Many of us do not consider backhoe operators to be God.

Also it's reasonable common to exclude
actions by the customer or failures of their equipment - given
many /system/ faults are still down to customer power etc., this
may give telecoms elements with higher availability than the
system as a whole, which is what you were refering to with FEDWIRE.
(i.e. when users look at their systems they need to combine
availability data and carefully consider whether the probabilities
of failures of particular elements are or are not independent).
Some ISPs exclude the tail circuit from their availability figures
in its entirity.

Finally, the availability number is meaningless unless there is
a clear way of measuring what period it applies to. Five nines
availabilty over a day is completely different to five nines
availability over a year, if there is a fixed MTTR (think about

IE availability numbers are *not* useless - but they generally
aren't comparible without looking at the contract, and system
in depth.

Alex Bligh
VP Core Network, XO Communications -
(formerly Nextlink Inc, Concentric Network Corporation
GX Networks, Xara Networks)