[30284] in North American Network Operators' Group
Re: Sonet protection usage
daemon@ATHENA.MIT.EDU (Danny McPherson)
Tue Jul 25 23:30:42 2000
Message-Id: <200007260329.VAA15085@tcb.net>
To: Steve Feldman <feldman@twincreeks.net>
Cc: nanog@merit.edu
From: Danny McPherson <danny@tcb.net>
Reply-To: danny@tcb.net
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Date: Tue, 25 Jul 2000 21:29:20 -0600
Errors-To: owner-nanog-outgoing@merit.edu
> Are many ISPs taking advantage of SONET APS protection
> to provide port or router redundancy on short (metro-area)
> circuits? Or is it more typical to get two circuits and
> load-share? Or just not bother?
I know of a few providers that use inter-router APS to protect against router
and ADM trib port (mainly router) failures in the core. The optical network
side is protected by BLSR or the like. The optical protection options still
seem to be much more cost-effective then simply provisioning parallel (but
presumably diverse) links between two locations, not to mention that if some
load-balancing schema is employed one needs to consider accommodating
additional propagation delay incurred on the less optimal path (an ideal
application for CoS & TE, perhaps).
Inter-router APS proves itself especially useful on trans-oceanic circuits
where simply acquiring additional capacity often isn't a viable option, nor is
allowing some really expensive circuit to sit idle for 5 or 10 minutes while a
router boots and becomes synchronized.
As you can imagine, there are lots of interesting issues with inter-router APS
and IGP interaction, most of which seem to cast a considerable shadow on its
value when considering network availability and convergence in the event of
failures. Intra-router APS is much more appealing, assuming stateful port
mirroring is implemented, though it doesn't address the main concern of
protecting against router failures.
Of course, it's definitely better than simply selecting an alternative,
presumably less optimal network path simply because a local router becomes
unavailable.
-danny
