[c-nsp] L2 Switchover

[Tim Franklin]

> If it's *SDH* "active, backup", your router will not even notice that
> SDH switched to the backup path - that's what it is for, almost-instant
> cutover ("as soon as the first SDH frame is corrupted").  No way to
> see this from the router (that I know of), this is all happening inside
> SDH, so the SDH monitoring needs to pick this up.

APS all the way to the router.  Have the SDH provider present the active and backup paths to you on different fibres from the ADM, POS line cards with the appropriate magic.  ISTR you can even put the line cards in different chassis and have full hardware resilience.  It's been more than a decade since I did it in anger though...

Regards,
Tim.