North American Network Operators Group

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Re: MCI WorldCom fiber cut in White Plains, NY

  • From: Jesper Skriver
  • Date: Mon Oct 11 04:57:56 1999

On Mon, Oct 11, 1999 at 01:33:23AM -0700, Paul A Vixie wrote:
> > > why pay the complexity and cost overhead of SONET if you're not
> > > building rings?
> > 
> > In a IP backbone, we prefer to have 2 diverse path's to IP use, than one
> > with protection, this gives a better overall utilisation, and more
> > control of what happends.
> i don't entirely agree.  two reasons.  one: you have to build headroom into
> your network (whether sonet or IP) to handle at least 2X nominal load -- and
> this is harder, not easier, in the case of IP level diversity (since it is
> easier to squeeze past the 2X requirement when the beancounters aren't giving
> you everything you say you need, and they'll learn this.)  two: i prefer to
> have redundancy at the physical level AND at the IP level -- because back
> when all my network was carrying was spam and netnews, i actually welcomed
> the peace and quiet of an outage, but now that there are customers involved,
> i want peace of mind instead.

We're so lucky to get what we ask for ;-)

It's all down to having enough spare capacity, and when you have half of
your capacity stuck in SONET/SDH protection, you cannot use that for
short peaks of traffic, and you dont have the option of saying, in case
of a outage, we will suffer 20% performance drop, which on expensive
circuits (like trans atlantic ones) could be what one wanted.

One of our trans atlantic STM1/OC3's are with protection (the only way we
could get it, as the protection is on STM16/OC48 level), meaning we have
310 Mbps of capacity but can only use 155 Mbps both in the normal and
outage senario, where if we had 2 STM1/OC3's with diverse routing, we
could choose to use 200 Mbps in the normal senario, and live with 155
Mbps in the backup senario.

> i take it that it's mostly the bypass carriers and the long haul carriers who
> cheese out on ringing their sonet on diverse paths?  i know pac bell rings
> just about everything.  how are the other regionals?

Here the most normal is to get circuits without protection, but with the
option of manual rerouting in case of a longer outage.


Jesper Skriver (JS4261-RIPE), Network manager      
Tele Danmark DataNet, IP section (AS3292)

One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.