Ahoy, SLA boffins!

Leo Bicknell bicknell at ufp.org
Wed Jul 29 14:33:14 UTC 2009

I think the desired goal here is to separate the access SLA from
the backbone SLA.  That is, consider a simple picture:

Network Cloud------Provider Edge Router-----Local Loop-----Customer Router

Network availability is the % of the time the customer router and
provider edge router can communicate, and is designed to measure
if the local loop is up.  For instance, let's say the provider edge
router looses all its uplinks to the Network Cloud, your local loop
is up and functioing but you have 100% packet loss to all destinations.

The "packet loss" SLA kicks in on a per-destination basis.  Everything
is up and working, but the provider has a full circuit and is
dropping 20% of the packets on that link.  You catch it, you get a

I think the technical reason why these are separate has to do with
the expectations.  If my local loop is dropping 0.5% of the packets
due to errors, it is broken and must be fixed.  If some random
destination on the Internet is dropping 0.5% of the packets well,
that's a normal day in the life of the network.  Plus, if your local
loop takes errors then you get a credit.  However, if there's a
full link in the backbone but none of your packets take it, and
thus you are unaffected, you don't.

Now, having said all that, and having been one of the people who've
attempted to communicate sane, rational, technical ideas to marketing
and legal the chance that anything sane made it in the actual contract
is, well, nil.

       Leo Bicknell - bicknell at ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
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