The MPLS WG Archive

[Kireeti Kompella <kireeti@juniper.net>]

> I don't see why TE and protection require the routers to specify explicit
> routes.
> The routers can simply specify to the optical layer what type of optical
> layer protection
> it requires.

Suppose router A wants to get to router B, and wants to take two
different ingress and egress points in the optical domain, X->Y
for the primary LSP, and W->Z for the backup.  A does not require
optical protection for the X->Y path, nor for the W->Z path.  A
*does* require that the X->Y path and the W->Z path do not share
common links.  How is this to be done?

If A did the full path computation, this is simplicity itself.

> Based on its traffic flow a router only needs to know between
> which
> two routers it needs to establish a new lightpath.  How the lightpath is
> routed in the
> optical layer seems to me irrelevant to TE.

It's not up to you or me to say "irrelevant to TE"; the judge of
relevancy is the user (SP), and it depends very much on how
integrated the TE is between the optical domain and the routing
domain.  I know several SPs that would like *in the long term* to
have a tightly integrated TE between the two domains; of course
the majority today prefer loose or no coupling, as that fits their
current mode of operation.

>From an analytical point of view, though, if you define TE as the
mapping of flows to physical links, then it seems to me that how
the lightpath is routed in the optical domain is very relevant.

Kireeti.