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

[Keegan Holley]

2011/10/20 Pavel Lunin <plunin at senetsy.ru>

> Folks, let me make a tiny semi-philosophical summarization on this :)
>
> Any layer of hierarchy in packet networks gives you another chance to
> benefit from statistical multiplexing (trick, because of which packet
> switching rules). The more flows from individual users/subscribers you
> aggregate in a single link/box, the less dispersion of their insensitivity
> and the denser you pack the packets on a line (the more it's like TDM),
> thus
> the bigger the benefits.


You could do the same by just adding more links in the same layer.  If you
have a core layer but only two links to it that is still your bottle neck.
Also MPLS doesn't do statistical multiplexing or load-balancing the same way
TDM would.  Most flows will follow the same path from point A to point B so
even though it's packet switched it has some of the constraints of circuit
switched topologies.  Statistical multiplexing within a box or within the
queues in a box is a different discussion.


> In addition if your core serves users from
> different time-zones, its efficiency will be even higher because of the
> 'natural TDM' human biology creates.
>

lol I'm pretty sure people still use their lines at night.  Backup traffic
has to go somewhere.

>
> However you won't earn anything if the streams are already well packed
> (someone has already skimmed the cream off). As Mark has mentioned, there
> is
> no point in selling switched vll/vpn/anything to customers who fully fill
> their last-miles of capacity close to that of your core-links. Well, at
> least if the number of such customers is statistically significant. This is
> what L1 multiplexing is invented for.
>

This depends on your pricing.  Hopefully those customers that are allowed to
saturate the PE links are paying enough to finance bandwidth/box upgrades.
Hopefully, the financials work out so that profit is made if 100 customers
fill the pipes or 10 or 2 for that matter.