RE: Comparison of restoration requirements between transport and packet networks

[neil.2.harrison@bt.com]

Vishal, some remarks in-line.  regards, Neil

Vishal Sharma wrote 18 September 2003 06:31

<snipped>
> So would you agree that if one looks at the "classical" client/server
> layer relationships, the notion of notification time bounds 
> makes sense?
NH=> Yes in principle.....the basic rule is 'as fast as sensible, as close
to the duct as possible;  as slow as reasonable, as close to the application
as possible'.
> 
> For (ii), when a carrier has no visibility into the
> server layer,
NH=> very common

> it seems to me that it is perhaps _even more 
> important_ that
> the server layer guarantee notification timing bounds (and, 
> by extension,
> some
> reasonable protection switching timing bounds), so that these 
> can be built
> into the SLAs that the client-layer provider and server-layer provider
> sign with each other.
NH=> Nice idea in principle...and if there are only 2 parties involved where
the 'server' party owns all layers to the duct it might work.  However, it
does, as you noted previously, require some notional agreement on the
'allowed' X/Y client server relationships.
> 
> This would allow the carrier operating the client layer to make some
> definite assumptions about the reaction time of its server layer, and
> build its service based on that.
> 
> The notification work, in fact, makes no assumption that the 
> same carrier
> has to have control of the complete layered network.
> 
> Hope this helps to clarify a bit the thinking behind the notification
> work.
NH=> Yes.....but your call (with Richard) today explained a piece of the
puzzle I had not properly appreciated until then.....and that is you are
postulating a case where the *protection route* between 2 nodes, A and B
say, carries 'extra' traffic that is from >=2 disjoint trails, eg extra
traffic trail 1 say A->N->O, and extra traffic trail 2 say O->P->B......and
this is why you need to inform (at least) node O of the failure on the
working path (to co-ordinate removal of the 2 extra traffic trails).
Clearly FDI/BDI would tell A and B from the failed working path.

I guess providing the extra traffic once 'dumped' stays dumped the system
ought to be stable.  I am not in favour of multiple class
pre-emption/bumping schemes.  

regards, Neil