[c-nsp] availability

Tassos Chatzithomaoglou achatz at forthnet.gr
Sun Feb 21 14:24:01 EST 2010

Some presentations at 
include the basic calculations that you can use in order to simulate 
serial or parallel scenarios.

Besides Vincent's excellent book, there is "*High Availability Network 
Fundamentals*" by Chris Oggerino, which is also a very good read if 
you're interested in maths. It also includes its own availability 
calculator: SHARC.

btw, there is a reference of some internal cisco tools (i.e. NARC) in 
the the above cisco link, but i was never able to get them from my 
account manager :(


Vincent C Jones wrote on 21/02/2010 20:42:
> On Sat, 2010-02-20 at 17:16 +0200, Saku Ytti wrote:
>> On (2010-02-19 11:44 -0500), My Name wrote:
>>> Does anyone have information concerning calculating
>>> network availability based on a network design?
>>> For example, is redundant P and PE routers more available statistically
>>> than single P and PEs with redundant route processors, etc .....?
>>> I am looking to input network design parameters and produce an
>>> availability/probability number?
>>> is there such an animal?
>> If not anything else, this might point to some directions or help with more
>> precise questions: http://iplu.vtt.fi/
>> Unfortunately some of the material is finncryp() and it is also very high
>> level, done by professional academics on goverment grands, some co-workers
>> of mine have met these people to give them some real life data to work with
>> and they reported that it was really hard to follow what they were doing,
>> so expect formulae etc.
>> I think in real life engineers know this stuff intuitively.
>> I sometimes wonder if high network quality even pays off, at least our
>> claimed SLA compensations are very low so it would be hard to justify any
>> CAPEX increase to increase quality. Rather it would seem that network
>> quality can be decreased if it means we can be more competitive or have
>> higher margins.
>> Spending money on brand, creating high perceived quality might be wiser
>> than actually trying to increase quality, since actual quality is quite
>> hard to measure.
>> But of course it is much more fun and satisfying to create the best network
>> you can. Too bad majority of customers claim they want quality, but seen to
>> choose cheapest option from market, perhaps even the worst product is good
>> enough.
> There is an overview of the math involved in calculating the
> availability of a network design in the first chapter of my book "High
> Availability Networking with Cisco." While quite simple in theory, it
> can be notoriously inaccurate in the real world due to GIGO (if the
> component availabilities you start with are garbage, so will the
> calculated overall availability). The book is out of print, but is
> frequently available on Amazon at bargain prices. Feel free to contact
> me off-list if you have trouble finding a copy.
> Do keep in mind Saku's warnings. Over the years I've seen a number of
> networks where the added redundancy decreased availability. If not
> implemented properly, the only thing which will be improved are the
> vendor's profit.
> Good luck and have fun!


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