The MPLS WG Archive

[suchauhan@hss.hns.com]

hi Marline!
     In the case of using MPLS for IP, the consumable resource is a label that
is assigned to the FEC/flow of IP packets.
     In that respect once an LSP is setup the label is assigned for all traffic
belonging to that FEC/flow to be switched on
     this LSP. If these is no traffic to be forwarded on that LSP then the label
remains in use but the bandwidth of the
     outgoing link is free to be used/shared by other LSP. Again the assumption
here is that the TE policies in use
     allow/necessitate such a sharing/use by other LSPs.

     In case of GMPLS (more so in case of Optical domain) the label itself
generally maps to a frequency/wavelength for
     the optical stream. Once a label(frequency) is being assigned to a
FEC/(optical)flow, then the OXC all along the LSP
     reserve this frequency for this flow. Hence it cannot be shared between
other LSPs.

     In this regard the restoration capacity allocation for failure conditions
in Optical domain have to be dome more
     prudently as the reserved paths (backup paths) are actually equivalent to
allocating bandwidth even though they are
     not carrying data in case there is no failure/restoration.

     I hope this is of some help to you!

regards
sumit




Mareline Sheldon <marelines@yahoo.com> on 09/17/2002 02:03:05 PM

To:   mpls@UU.NET
cc:   jyates@research.att.com (bcc: Sumit Chauhan/HSS)

Subject:  GMPLS Doubt




Hi,
I am aware that this is a MPLS mailing list but since i could not get this doubt
clarified
from any other place ..

This is in reference to "Challenges for MPLS in Optical Network Restoration" by
Robert
Doverspike and Jennifer Yates which appeared in IEEE Communications Magazine
(Feb 2001)

The authors say that an "Optical transport system (OTS) multiplexes multiple
optical signals
onto a common fiber, necessitating the concept of a channel. An optical network
connection is
provisioned by cross connecting channels within individual OTSs along its path.
This fact
implies that zero-bandwidth paths cannot be established for later use. In
contrast, in IP
networks MPLS LSPs may be established such that if no packets  are switched into
the links
along the path, no bandwidth is consumed. Switching packets onto these
predefined paths at
their endpoints is simple and rapid. This important difference between IP and
optical networks
becomes crucial in allocating restoration capacity"

Can somebody help me understand the above?

regards,
mareline s.


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