Subject: [CCAMP] upstream label and label symmetry

From: Ramon Casellas <[email-masked]>
Date: Fri, 08 Nov 2013 03:32:42 +0100

All,

If I may, just my 2 cents, and trying to summarize the main raised 
points. For people working on GMPLS for optical networks it is a common 
requirement.

* Use case: for example, transparent WSON, it is required to fulfil the 
wavelength continuity constraint (WCC); likewise, although the optical 
receiver/photodetector may be broadband it is a common requirement that 
both labels (that are contiguous due to the WCC) are the same 
(symmetry). Someone put it better than me [2] including our soon to be 
ex-secretary:

 > Title   : Extensions to GMPLS RSVP-TE for Bidirectional Lightpath with
 >           the Same Wavelength
 > Authors : S. Xu, H. Harai, and D. King
 > Filename: draft-xu-rsvpte-bidir-wave-00.txt
 >
 > Abstract: For bidirectional lightpaths provisioning, in the case of
 > optical nodes that do not support wavelength conversion, it would be
 > necessary to use the same wavelength along the route on each
 > direction. In certain optical network scenarios, the use of the same
 > wavelength on both directions would be advantageous.  For instance,
 > some type of ROADMs may add/drop the same wavelength
 > simultaneously. In another case, the users' optical end nodes are
 > equipped with fixed-wavelength transponders.
 >
 > This document describes extensions to RSVP-TE signaling for
 > bidirectional wavelength lightpaths that require the same wavelength on
 > both directions. By using an LSP_ATTRIBUTES object defined in [RFC4420],
 > the extensions enable the new type lightpaths to support the low cost
 > configuration at users' optical end nodes.

* IMHO it is true that a node needs to cross-connect before forwarding 
the PATH message downtream: RFC3473
"3.1. Procedures

    support bidirectional LSPs an Upstream_Label object is added to the
    Path message.  The Upstream_Label object MUST indicate a label that
    is valid for forwarding at the time the Path message is sent.

    When a Path message containing an Upstream_Label object is received,
    the receiver first verifies that the upstream label is acceptable.
    If the label is not acceptable,(...)

    An intermediate node must also allocate a label on the outgoing
    interface and establish internal data paths before filling in an
    outgoing upstream label and propagating the Path message

* The fact that the label is set to some value 0xFFF...FF and that the 
node must cross-connect justifies the need for a two step process as 
Dieter mentioned.

In short, IMHO there is a requirement to request symmetrical labels.  
This problem has been mentioned in the past, you may want to check

[1] http://tools.ietf.org/html/draft-oki-ccamp-upstream-labelset-00

[2] draft-xu-rsvpte-bidir-wave-00.txt
      see http://permalink.gmane.org/gmane.ietf.ccamp/6023

Thanks

Ramon