Draft: draft-ietf-ccamp-optical-impairment-topology-yang

Commentary: draft - ietf - ccamp - optical - impairment - topology- for IETF 115 submission --draft - ietf - ccamp - optical - impairment - topology - yang- Related to pull request Addressing and resolving .
It is worth noting that optical data plane interoperability is a
complex topic especially in a multi vendor environment and usually
requires joint engineering, which is independent from control plane
and management plane capabilities.  The YANG data model defined in
this draft is providing sufficient information to enable optical
impairment aware path computation.
Optical data plane interoperability is outside the scope of this
draft.
It is worth noting that optical data plane interoperability is a
complex topic especially in a multi vendor environment and usually
requires joint engineering, which is independent from control plane
and management plane capabilities.  The YANG data model defined in
this draft is providing sufficient information to enable optical
impairment aware path computation.
Optical data plane interoperability is outside the scope of this
draft.
Individual OTSi protection is a protection architecture where an
individual OTSi signal is protected as defined in Appendix III of
ITU-T Recommendation G.873.1 G.873.1.  This protection architecture
requires dedicated photonic protection functions that are typically
provided by dedicated protection hardware.  These photonic protection
functions are a photonic splitter function splitting the OTSi signal
in transmit direction and a photonic selector function selecting the
OTSi signal in receive direction from one of the two protection legs
between the protection functions terminating the individual OTSi
protection.  This individual OTSi protection scheme can be considered
as a photonic 1+1 protection scheme (1+1 sub-network connection
protection (SNCP) in ITU-T terminology).
Individual OTSi protection is a protection architecture where an
individual OTSi signal is protected as described in Appendix III of
ITU-T Recommendation G.873.1 G.873.1.  This protection architecture
requires dedicated photonic protection functions in the optical
domain that are typically provided by dedicated protection hardware.
These photonic protection functions are a photonic splitter function
splitting the OTSi signal in transmit direction and a photonic
selector function selecting the OTSi signal in receive direction from
one of the two protection legs between the two protection functions
terminating the individual OTSi protection.  This individual OTSi
protection scheme can be considered as a photonic 1+1 protection
scheme (1+1 sub-network connection protection (SNCP) in ITU-T
terminology).
In order to achieve short protection switching times, it is necessary
that the OTSi signals of the two legs are identical in terms of
wavelength, modulation format, FEC, etc., which means no receiver
configuration changes when a protection switch at the selector occurs
selecting the other leg.  This is important when 3R regenerators are
needed between the two end-points terminating the protected segment,
which typically is end-to-end.
The different use cases are described in following sub-sections and
examples are provided how these uses cases can be modeled properly
using the optical impairment aware TE-topology YANG data model.
Figure-11 illustrates such a WDM-TE-node configuration in transmit/
forward direction where the protection function is an optical
splitter and Figure-12 illustrates the same WDM-TE-node configuration
in receive/reverse direction where the protection function is an
optical selector selecting one of the two incoming OTSi signals and
switching to the other incoming OTSi signal when the optical power of
the selected OTSi signal drops below a pre-defined threshold.
The TE-topology YANG model has been augmented to describe this
protection architecture.  The already existing optional protection-
type leaf of the TTP associated with the optical transceiver is used
to indicate whether the TTP is protected, i.e., whether it is
connected to a protection function or whether it is unprotected,
i.e., whether it is directly connected to an add-drop port of the
ROADM function in the WDM-TE-node.
For unprotected TTPs associated with an optical transceiver, the
local-link-connectivity list describes the potential connectivity
between the TTP and the LTPs of the WDM-TE-node that are the local
end-points of the TE-links (OMS MCGs) interconnecting the WDM-TE-node
with its neighbors, also often called degrees of the WDM-TE-node as
opposed to its add-drop ports.
For protected TTPs, the local-link-connectivity list has been
augmented such that is is capable of describing the potential
connectivity not only between the TTP and a single LTP a (unprotected
case) but is now capable to describe the potential connectivity to
additional LTPs including the related optical impairments.  If the
optical impairments are the same for all local-link-connectivity list
entries for a particular TTP, which is usually the case, the optical
impairments shall be omitted for the additional LTPs leading to a
more compact topology description.  If the optical impairments are
different, however, they can be described for each additional LTP
entry separately.
A local-link-connectivity list example for a protected TTP in JSON
format is provided in JSON Examples.
Figure-13 illustrates such a network configuration in transmit/
forward direction showing the two WDM-TE-nodes where the protection
function is the optical splitter in WDM-TE-Node-2 and Figure-14
illustrates the same network configuration in receive/reverse
direction where the protection function is the optical selector in
WDM-TE-Node-2 selecting one of the two incoming OTSi signals and
switching to the other incoming OTSi signal when the optical power of
the selected OTSi signal drops below a pre-defined threshold.
In the network configuration shown in Figure-13 and Figure-14,
respectively, the two WDM-TE-nodes are interconnected via a TE-link
only carrying a single OTSi signal.  This TE-link interconnects the
remote OT with an add-drop port of WDM-TE-Node-2 and in the following
the qualifier "add-drop" is used to refer to that LTP as opposed to
the line LTPs representing degrees of WDM-TE-Node-2.  Similar to the
protected TTP in Protection UC (i), the optional protection-type leaf
is used to indicate whether the add-drop LTP is connected to a
protection function and then to two line LTPs via the ROADM function
inside WDM-TE-Node-2 or whether it is connected to a single line LTP
via the ROADM function inside WDM-TE-Node-2 (unprotected add-drop
LTP).  While the protection-type attribute was already defined for
the TTP, the YANG model has been augmented to also support this
optional attribute for the LTP.
For protected LTPs, the connectivity-matrix has been augmented such
that it is capable of describing the potential connectivity not only
from an add-drop LTP to a single line LTP (unprotected case) but is
now capable to describe the potential connectivity to additional line
LTPs (protected case) including the related optical impairments.  If
the optical impairments are the same from the protected ad-drop LTP
to all line LTPs, which is usually the case, the optical impairments
shall be omitted for the additional LTPs leading to a more compact
connectivity matrix description.  If the optical impairments are
different, however, they can be described for each additional LTP
separately.
WDM-TE-Node-1 can be a data center device or a router router device
that supporting 1+1 OTSi protection for its OTs while WDM-TE-Node-2
is a WDM-TE-node providing add-drop ports for remote OTs as depicted
in Figure-7.  WDM-TE-Node-1 and WDM-TE-Node-2 are interconnected via
two separate TE-links, each carrying a single OTSi signal.  The
protection configuration for the protected TTP in WDM-TE-Node-1 can
be described in the same way as for use case (i) using the local-
link-connectivity list.