Re: Sonet protection usage

[Danny McPherson <danny () tcb net>]

> Think about it -- are they really provisioning two circuits, leaving 
> one available as a backup?  Of course not!

I think you missed on of my points, which was APS on the trib side of the ADM, 
only a small mention of APS on the network side.  If you can't figure out 
whether you've two circuits sitting there you've got bigger problems...

> This may be a useful feature for voice circuits, where most of the 
> capacity sits idle most of the time.  It's worse than useless for data. 

Again, I think you're missing the application wrt it residing on the trib side 
of the ADM -- to protect against router failures -- continuing to use the same 
network portion (i.e. the expensive portion) of the connection.

> APS was designed to protect against the failure of the electronics 
> for a single fiber in a cable.  Often, a dozen other circuits are 
> "protected" by a single APS.  It's a ripoff.

Perhaps in your experience, though I can argue quite the contrary, especially 
when your company owns the the transmission facilities.  Though again, I was 
referring primarily to local protection against router failure on the trib 
side of the ADM.

> Of course, the usual failure mode is backhoe fade, not electronics.  
> In which case, that APS circuit was cut along with the rest.

Of course, backhoes don't normally work inside PoPs, which is the application 
of APS I was referring to.  Routers do fail though (often more than links), 
and APS has been demonstrated to work relatively well for protecting against 
such failures.
 
> For transoceanic links, diverse APS is even more unlikely, and unless 
> you are paying serious money, you won't be a priority over the other 
> hundred customers that are sharing that APS circuit.

Not on the trib side, when protecting against router failures.

> Diverse links _are_ the only _real_ protection.  You might even get 
> what you pay for....  And in the short term, you at least get twice 
> the bandwidth

Again, APS w/two local links to an ADM sufficiently protect against a local 
router failure.

-danny