North American Network Operators Group

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Re: Optical Crossconnects and IP

  • From: Danny McPherson
  • Date: Sun May 14 18:34:51 2000

> I don't care about transient loop induction while in the process of
> converging. That problem is much harder to solve.  What I do care about is
> a table like the following handed to the NOC/operational folks. 

If it were actually implemented it wouldn't be something you'd 
hand to the NOC .. unless I'm missing something.  You don't hand 
them your SPF algorithm, or your BGP decision algorithm .. it's 
all "magic".  You'd much more likely be handing them something 
stating "We've enabled this feature, here's the knob that did it, 
here's how it works...".

My concern with these packet-based pre-calculated restoration 
mechanisms is that they near deterministically introduce transient 
forwarding loops, loops that result in the same amounts of 
non-forwarding (network unavailability) time that normal 
path recalculation/IGP convergence would result in.  

The benefit of a circuit-based restoration mechanism (i.e. MPLS 
fast reroute with a pre-defined backup LSP) is that when you switch 
to a backup connection you know (with some level of confidence) that 
packets forwarded on the connection will not be tossed around like
hot potatos until the entire IGP converges, SPF calculation throttles
are reset, etc.., introducing instability in the network.