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Updated Draft Liaiosn to Q6/15
Had some comments off-list.
New version with minor changes...
CCAMP experts are looking forward to our joint meeting with Q6/5 on March
20th to discuss optical impairments and the control plane operation of
wavelength switched optical networks (WSONs).
This liaison is to summarise the activity within CCAMP on this subject so
far and to set out our objectives for this work.
As you will be aware, the GMPLS control plane is designed to provide a
dynamic control plane for a variety of switching technologies. Amongst these
is the "lambda switch capable" data plane where devices are OEOs, ROADMs,
and photonic cross-connects (PXCs). In fact, lambda switching was the
technology that led to the development of MPLS from the packet switching
MPLS control plane.
The IETF's CCAMP working group is the design authority for all extensions to
the GMPLS family of protocols.
The original work on lambda switching networks within CCAMP recognised that
there is a subset of optical networks in which it is possible to disregard
optical impairments and where the number of regeneration points is high. In
these environments, path computation can be performed on a reachability
graph, and lambda conversion can be performed as necessary within the
As PXCs were introduced into WSONs, it remained the case that optical
impairments could be disregarded by the control plane. Where necessary,
optimal impairment-aware paths could be computed off-line and supplied to
the control plane, leaving the control plane to handle establishment of
connections and recovery after failure. Failure recovery scenarios might
lead to contention for wavelengths or suboptimal optical paths, but these
could be handled by crankback within the signaling protocol.
More recent work on WSONs indicates that the proportion of pure optical
devices (ROADMs and PXCs) is increasing. This means that it is necessary to
compute paths that offer end-to-end lambda continuity. This problem (called
the routing and wavelength assignment (RWA) problem) must be solved, and may
be compounded by devices with limited cross-connect capabilities (for
example, with glass-through, a limited OEO matrix, or restricted
port-to-port capabilities). In approaching this problem it is convenient if
there is a common identification scheme for wavelengths across the whole
network (previously, wavelength identification was a local matter between
the nodes at the ends of each link). To aid with this, the CCAMP working
group has developed
that provides a protocol-independent encoding for wavelengths in a way that
is compliant with G.694. Further work on this problem space can be seen in
the following CCAMP documents:
"Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks
"Routing and Wavelength Assignment Information Model for Wavelength Switched
"Routing and Wavelength Assignment Information Encoding for Wavelength
Switched Optical Networks"
CCAMP participants have further identified cases where they believe it would
be helpful to consider optical impairments during the control plane
operation of a WSON. This gives rise to four distinct deployment scenarios:
1. No concern for impairments or lambda continuity.
2. No concern for impairments, but lambda continuity is
important. (The RWA problem)
3. Concern for "basic" impairments
4. Concern for "advanced" impairments
In focusing on the third of these categories, CCAMP intends to base its work
on G.680 and related recommendations with the following understanding:
- G.680 (et al.) provides a complete list of simple constraints
- Where G.680 refers to "single vendor" domains, it does not
mean single manufacturer, but rather "single system integrator".
That is, the equipment is not "plug and play", but has been
tested to interoperate and the network has been planned.
- There is no requirement to measure impairments.
- Many networks are engineered such that configured
impairment values are enough information
- Measuring can often produce ambiguous values
- Equipment to perform measurement may be expensive
However, if an implementer chooses to measure impairments
on their device, this should not be prohibited, and should be
With this in mind, CCAMP is looking to Q6/15 to work as a partner in
- the complete list of impairments suitable for this type of network
- and the complete list of Recommendations to use as references
- the rules by which such impairments are accumulated along a path
- generic encodings and ranges of values for the impairments
For reference, some early work on impairment-aware GMPLS is listed below.
This work is not yet adopted as CCAMP work, but is likely to form the basis
of such work once we have discussed the way forward with Q6/15.
"A Framework for the Control of Wavelength Switched Optical Networks (WSON)
"Information Model for Impaired Optical Path Validation"
Looking forward to a profitable meeting,
Deborah Brungard and Adrian Farrel
CCAMP Working Group Co-Chairs