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

Michael Loftis mloftis at wgops.com
Wed Aug 31 19:42:51 UTC 2005




--On August 31, 2005 2:03:01 PM +0100 Michael.Dillon at 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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