Re: SE style in optical neyworks

[Sudheer Dharanikota <sudheer@nayna.com>]

Hi John:

John Ellson wrote:

> Sudheer Dharanikota wrote:
> > Hi Gentelmen:
> >
> > I changed this list to camp, as it is more appropriate
> > for this discussion.
> >
> > I would like to understand the following..
> >
> > Assumptions:
> >
> > - Segments of network are inherantly made protected.
> >   For example, as suresh said, span/UPSR/BLSR etc protected.
> >
> > - PAth request contains requirements to set up a path
> >   of *certain* protection guarantees without knowing the
> >  topoogy and its capability
> >
> > Now ...
> >
> > If i want to set up an end-to-end *backup* path, it is the network
> > (intermediate nodes) which has to decide if a *backup*
> > link or a segment need to be overloaded. Don't you think in this
> > case SE may make sense.
>
> I the circuit world, if you obtain a second circuit for use as backup
> you don't need to tell the network about it.  Its just going to
> give you a dedicated circuit, with whatever reliability guarantees
> you have in your service contract, and with an expectation of being
> paid for the circuit wether or not the end-system chooses to
> put bits on it.

Not necessarily. Establishment of a secondary circuit could be a
policy decision based on the customer SLA.

Shared mesh restoration is one case where you can see the need
for SE based reservation for backup path.

BLSR etc where both the primary and secondary take the same
span protected ring can be another case.


>
>
> In the packet world its different.  I suppose you could obtain
> a second circuit with a service contract that allowed the network
> to stat-mux the bandwidth with other traffic.   I still don't
> know why you would tell the network what you wanted it for.

Agreed on this explanation.

>
>
> BTW. If you used such a circuit for protection it would have to be
> 1:1, not 1+1, because the sharing on the standby channel clearly
> means that you can't duplicate the working channel data.

Agreed. May be UPSR is a bad example.


- sudheer

>
>
> John
>
> > Thanks for your input.
> >
> > sudheer
> >
> > John Ellson wrote:
> >
> >
> >>Suresh Katukam wrote:
> >>
> >>>Zhi,
> >>>
> >>>You are correct about 1+1 path protected...
> >>>
> >>>But if you have a LSP that is protected by some 1+1 links and some
> >>>UPSRs, BLSRs etc.. then this LSP contains mixed protection schemes
> >>>(I am not sure what you call this LSP - 1+1 protected, just Protected
> >>>circuit).
> >>>In this case, SE style can be used..
> >>
> >>If you're talking about nodes other than the nodes that are
> >>at the the ends of the protection span, then I suggest that you just refer
> >>to it as a "reliable segment".  It shouldn't matter
> >>to the end-systems how that segment reliability is achieved.
> >>
> >>Protection is only interesting to nodes that have to take part in it,
> >>otherwise its just a segment of a connection with a greater or
> >>lesser propensity to failure.
> >>
> >>John Ellson
> >