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

[Jared Mauch]

On Oct 19, 2011, at 12:35 AM, Mark Tinka wrote:

> On Wednesday, October 19, 2011 11:46:53 AM Keegan Holley 
> wrote:
> 
>> If you can
>> connect all your PE's without adding aggregation and
>> core layers you'd obviously time, money and avoid
>> complexity.
> 
> Correct on time and money, but curious about complexity. 
> 
> I find having a core layer in an IP/MPLS network increases 
> simplicity due to the abstraction and demarcation it 
> provides, but YMMV.


The real question:

Are you selling customer links that are near to or equal to the size of your core links(s).

Anyone doing 10GE edge or looking at 100GE for customer-facing handoffs can save significant amounts of money by doing P/PE.  While there are tradeoffs, not having the cumulative cost of a packet being A+B+C and perhaps can be localized to a single device has value.  I'm surprised that Rolland doesn't see this as an optimization as it would be something the Arbor equipment could help you optimize.

While some may see these cost savings as inelegant, the idea of a core will continue to come under these pressures.  Keep in mind the fraction of a chassis you must allocate for these edge <-> core links and core <-> core links.  These have real world costs.  There's a reason everyone didn't go out there and load-up on OC768 hardware and just stuck with N*10G.  The finances don't work out.

The core has mostly gone ethernet for the major carriers that have high traffic loads.  The extra cost of the ethernet frame header, preambles, etc.. are worth the cost savings when compared to the lower SDH/SONET overhead at a higher per port cost.

Take a traceroute tour across major networks.  You likely will see many signs of ethernet interfaces vs SONET.  I think one of the last remaining carriers that is using SONET for their core is AT&T.  There may be others, and the international circuit market is different, but most in-country links have been migrating to 10G.  This is evidenced in the volume and low cost and near commodity nature of this hardware, at least in the core networking space.

- Jared