Bandwidth Upgrade

Thu Nov 17 20:34:52 UTC 2011

On Thu, 17 Nov 2011, Bielawa, Daniel Walter wrote:

>                My team is in the process of putting some documentation 
> together to justify a bandwidth upgrade. I am asking if you would be 
> willing to reply back to me, with how you decide that it is time to 
> upgrade your bandwidth. On-line or off-line reply's will be acceptable.

Capacity planning is one of those things that (can) fall into the 
technical, business, and political aspects of network engineering.

Addressing the technical aspects is pretty straightforward.  The first 
thing is having data to show how much of your bandwidth you're using now. 
Even something as basic as a set of MRTG (not knocking MRTG at all) graphs.
If you have that, or data from some other package, then that's a good 
start.  If they show things like saturation of your existing pipe, then 
that's an important data point to share with your management, because 
flat-topping has a tendency to turn into sluggish performance and unhappy 
customers pretty quickly.  I would agree with other posters that we start 
looking at capacity upgrades when we get to about 65% usage, and have the 
upgrades completed before we get to 80-85%.  Depending on what size 
pipes you have now, you can also possibly significantly reduce your cost 
per Mb/s, though this depends a lot on your location and what sort of 
comms facilities are in your area.  Don't be afraid to call some carriers 
and get quotes.

Having historical data that shows the growth of your bandwidth needs is 
even more useful, to a point.  The reason I said to a point, is because a 
straight graph of inbound and outbound traffic doesn't answer questions 
about what is going on that is driving traffic growth.  At that point, you 
start getting into the realm of traffic analysis.

Addressing the business aspects starts to get into areas that we (people 
on NANOG) can only offer generic advice, because you would know how to 
present the business case for an upgrade to your management better than we 
would.  For example, if keeping customer complaints about network 
performance as low as possible is a business priority, then showing 
reports of related trouble tickets your helpdesk has received from your 
user base might be another important data point as well.

Also keep in mind that what might start out as "we need more bandwidth" 
could turn into other costs as well.  A larger pipe might mean you need a 
new interface card for your router, or other upgrades to the internal 
network to make use of that larger external pipe.  Most managers I've 
worked with would rather get the bad news (requests for money) all at 
once, so they only have to 'go to the well' one time, rather than making 
requests for money to upgrade the pipe, then another request for the new 
interface card, etc.  That also starts to get you into the possibly 
political aspects of working through your business environment.

Hope this helps.

jms