I've wondered about this myself. Consider the Catalyst 4006 as an example.
It has a 60 Gbps backplane. Yes, you read that correctly...SIXTY gigabits
per second...in a chassis that can hold five modules plus a supervisor
module. Do we really *need* that much?
My guess is no, we do not need quite that much. however, nowadays I would
pick the switch with the higher backplane if I had the bucks to get it.
It's nice to know that what's under the hood can handle anything we throw at
it.
Another example: we are going to be purchasing a 6509 with 256 Gbps
backplane. Why? Because we can. No other reason. Never in a million
years will we need that much capacity on this particular switch, especially
since we'll initially only have five modules in it. But we'll have plenty
of room for growth and it's one less thing to worry about.
Besides, I'm a speed demon and as long as it's someone else's money (my
employer's) then I want the biggest, fastest, coolest stuff around. <g>
Now, if it were MY money, that's another story. I'd be a little more
realistic about my needs. No one is going to be running every port, full
duplex, at max capacity. It will never happen, and if it does then you have
much greater problems on your hands than just the backplane capacity of your
switch.
John Neiberger
> Got another discussion question before I start work this morning ( no 4
day
> holiday for me :-< ) sort of a continuation of the Brad Ellis
discussion
> about the SE over-engineering solutions for customers.
>
> Cisco of late is starting to talk about backplane capacity, and in
> particular expandable backplane capacity in some of their switches.
>
> So the question I have revolves around backplane capacity and
> "oversubscription" of the backplane on a switch.
>
> For example, if I have a Cat 3524 in the closet, and pop in cards to
permit
> me 24 ports of 100 mbs full duplex, under what circumstances might I be
> concerned about "oversubscription". If I indeed had 24 devices plugged
in,
> theoretically I could be pumping 4.8 gigs of data simultaneously ( less a
> little for interframe gaps, and other overhead kinds of things ) that
puts
> me a theoretical 5 times oversubscription of this guy's backplane
capacity.
> On the other hand, seems to me that if I were popping that much data
> simultaneously from my 24 devices I would have other problems. Even that
> proverbial high speed database / transaction / e-commerce server is not
> going to be running full tilt in and out all the time. Let alone user
> stations, no matter how much radio they listen to, or how many avi's or
CBT
> videos they are watching. Those stream one way, recall.
>
> So... what kinds of things do you consider when provisioning or
> recommending? How would you approach this as a design issue?
>
> ( and no I do NOT have a customer for whom I am asking ;-> )
>
> Chuck
>
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>
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> http://www.certificationzone.com
> An excellent study focal point for all levels of certification, as well
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>
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