[c-nsp] Downsides of combining P and PE functions into a single box

[Mark Tinka]

On Thursday, October 20, 2011 12:58:41 AM Keegan Holley 
wrote:

> Cards are cheaper than entire routers in most cases
> especially at N*10 and 40G speeds.  Assuming you want
> chassis based, with redundant control planes and
> whatever the vendor uses for fabirc blades.  I'm not
> saying everyone should throw their core P routers into a
> dumpster, but I don't see how having them saves money. 
> You also have to add the cost of service contacts,
> power, fingers and eyes to keep them running, etc..  I
> think people who need separate cores should have them. 
> However, I don't see how P routers save money or reduce
> complexity.

Example - I have a PE router which is aggregating GPON and 
Metro-E Access devices. I have more Access devices that need 
aggregating than I have ports, partly because the device 
also has P functionality. So half the slots are running P, 
the other half, PE.

If I keep my design philosophy, I'll just buy another box or 
bigger one and continue the same approach. At some point, it 
stops making sense because on the one hand, you need lots of 
ports but can take a little oversubscription (PE side), 
while on the other, you need lots of ports but want large 
bandwidth + line rate performance (P side). The math works 
against you here as you scale up.

Moreover, $$ isn't the only factor to consider when deciding 
how layered you want your network to be. Ongoing operations 
is a huge concern, at least for us.

Mark.
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