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Re: Replacing PSTN with VoIP wise? Was Re: Phone networks strugglein Hurricane Katrina's wake

  • From: Michael Loftis
  • Date: Wed Aug 31 15:44:16 2005



--On August 31, 2005 2:03:01 PM +0100 Michael.Dillon@btradianz.com wrote:

<...>
On the other hand, in a circuit switched
network you can do all kinds of interesting stuff (such as restarting
all your control software) without breaking your sessions. We're only
now seeing this in IP, and I think it's not really possible to reach
the same levels with IP routing even in the long run.
MPLS may have the edge here because you can have backup paths
and fast reroute to keep traffic flowing if you have an
orderly plan for rebooting routers.
Which does us no good in the case that we're "close" to the edge device and need to reboot the control plane of a nearby router. To me it seems Juniper and Cisco are both making huge steps in understanding this is necessary technology they can 'borrow' from telco's. You've a highly intelligent, but fairly decoupled control plane, with a fairly dumb, but largely automatic 'forwarding' or 'circuit fabric' plane being directed by the control plane. If the control plane takes a nap, the bottom end continues what it was doing until something (control plane coming back online, backup control plane doing takeover) tells it otherwise. No this isn't easily possible in most instances, even with just bare IP and with NAT it becomes really difficult because of the large amount of intelligence (relatively speaking) required to handle NAT. I should clarify that when I say NAT I mean PNAT and application/protocol specific NAT that requires more than just simple packet mangling.


I think though, that eventually this will be commonplace, certainly in the core, and even really close to the edges. the M10i's approach this sort of resiliency. the T series and the larger M series also work like this....I think that the ONS' also are pushing on this (though admittedly aren't exactly IP...)

Anyway, point is, that if you're right up close to the edge, MPLS may not matter, towards the core sure, where you're away from actual end connections and there's redundancy around you when you need to do a control plane restart.

There will always be upgrades. Further there will always be other issues, however, in my mind atleast, today's networks are far more resilient and faster to heal than they've been in the past, atleast in IP.... PSTN...well...They're reliability king, until something unexpected happens. There were reports on here I believe it was even about call routing issues during this outage, not capacity type issues, simple lack of the systems ability to reconfigure and cope with loss of connectivity.

There are places for both PSTN and IP though.






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