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

Commentary: draft - ietf - ccamp - optical - impairment - topology- for IETF 114 submission --draft - ietf - ccamp - optical - impairment - topology - yang- Related to pull request . Addressing and resolving several open issues . 
 May need to rebase this branch with the master branch to make sure all the validation checks pass
The definition of the OTSiG is currently being moved from ITU-T
Recommendation G.709 G.709 to the new draft Recommendation G.807
(still work in progress) [G.807].  The OTSiG is an electrical signal
that is carried by one or more OTSi's.  The relationship between the
OTSiG and the the OTSi's is described in ITU-T draft Recommendation
G.807, section 10.2 [G.807].  The YANG model below supports both
cases: the single OTSi case where the OTSiG contains a single OTSi
(see ITU-T draft Recommendation G.807, Figure 10-2) and the multiple
OTSi case where the OTSiG consists of more than one OTSi (see ITU-T
draft Recommendation G.807, Figure 10-3).  From a layer 0 topology
YANG model perspective, the OTSiG is a logical construct that
associates the OTSi's, which belong to the same OTSiG.  The typical
application of an OTSiG consisting of more than one OTSi is inverse
multiplexing.  Constraints exist for the OTSi's belonging to the same
OTSiG such as: (i) all OTSi's must be co-routed over the same optical
fibers and nodes and (ii) the differential delay between the
different OTSi's may not exceed a certain limit.  Example: a 400Gbps
client signal may be carried by 4 OTSi's where each OTSi carries
100Gbps of client traffic.
The OTSi signals in the YANG model are described by augmenting the
network and each OTSi signal is uniquely identified by its otsi-
carrier-id, which is unique within the scope the OTSiG [see OTSiG
below] the OTSi belongs to.
The OTSiG is defined in ITU-T Recommendation G.807 G.807 as a "set of
optical tributary signals (OTSi) that supports a single digital
client".  Hence, the OTSiG is an electrical signal that is carried by
one or more OTSi's.  The relationship between the OTSiG and the the
OTSi's is described in G.807, section 10.2.  The YANG model below
supports both cases: the single OTSi case where the OTSiG contains a
single OTSi (see G.807, Figure 10-2) and the multiple OTSi case where
the OTSiG consists of more than one OTSi (see G.807, Figure 10-3).
From a layer 0 topology YANG model perspective, the OTSiG is a
logical construct that associates the OTSi's, which belong to the
same OTSiG.  The typical application of an OTSiG consisting of more
than one OTSi is inverse multiplexing.  Constraints exist for the
OTSi's belonging to the same OTSiG such as: (i) all OTSi's must be
co-routed over the same optical fibers and nodes and (ii) the
differential delay between the different OTSi's may not exceed a
certain limit.  Example: a 400Gbps client signal may be carried by 4
OTSi's where each OTSi carries 100Gbps of client traffic.
All OTSiGs are described in the YANG model by augmenting the network
and each OTSiG is uniquely identified by its otsi-group-id, which is
unique within the network.  Each OTSiG also contains a list of the
OTSi signals belonging to the OTSiG.
The frequency slot of the MC is defined by the n value defining the
central frequency of the MC and the m value that defines the width of
the MC following the flexible grid definition in ITU-T Recommendation
G.694.1 G.694.1.  In this model, the effective frequency slot as
defined in ITU-T draft Recommendation G.807 is equal to the frequency
slot of this end-to-end MC.  It is also assumed that ROADM devices
can switch MCs.  For various reasons (e.g.  differential delay), it
is preferred to use a single MC for all OTSi's of the same OTSiG.  It
may however not always be possible to find a single MC for carrying
all OTSi's of an OTSiG due to spectrum occupation along the OTSiG
path.
The frequency slot of the MC is defined by the n value defining the
central frequency of the MC and the m value that defines the width of
the MC following the flexible grid definition in G.694.1.  In this
model, the effective frequency slot as defined in G.807 is equal to
the frequency slot of this end-to-end MC.  It is also assumed that
ROADM devices can switch MCs.  For various reasons (e.g. differential
delay), it is preferred to use a single MC for all OTSi's of the same
OTSiG.  It may however not always be possible to find a single MC for
carrying all OTSi's of an OTSiG due to spectrum occupation along the
OTSiG path.
The termination of an OTSi signal by a transceiver is modeled as a
function of the tunnel termination point (TTP) as defined in RFC8795.
Due to the fact that optical transport services (TE tunnels) are
typically bidirectional, a TTP is also modeled as a bidirectional
entity like the LTP described above.  Moreover, a TTP can terminate
one or several OTSiG signals (tunnels) as described in I-D.ietf-teas-
te-topo-and-tunnel-modeling and each OTSiG consists of one or
multiple OTSi signals as described in sect-2.3.2.  Therefore, a TTP
may be associated with multiple transceiver modules.
The termination of an OTSi signal by a transceiver is modeled as a
function of the tunnel termination point (TTP) as defined in RFC8795.
Due to the fact that optical transport services (TE tunnels) are
typically bidirectional, a TTP is also modeled as a bidirectional
entity like the LTP described above.  Moreover, a TTP can terminate
one or several OTSiG signals (tunnels) as described in I-D.ietf-teas-
te-topo-and-tunnel-modeling and each OTSiG consists of one or
multiple OTSi signals as described in OTSiG.  Therefore, a TTP may be
associated with multiple transceiver modules.
Implemantations may support the change of the carrier frequency
where the receiver may operate at a different optical frequency as
the transmitter.  The transceiver mode is a property of the
transceiver and is applied to the transmitter and the receiver.
Therefore, the transceiver mode is the same for the two segments
on the two sides of the 3R regenaretor realised by two
transceivers operated in the uni-directional mode.
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).
In case of individual OTSi protection, there are two network media
channel paths associated with the OTSi signal.  In the YANG model,
this is modeled as a leaf list of the otsi providing the nmc-path-id
for the two network media channel paths associated with the
individually protected otsi.
OMS MCG protection is a protection architecture where a TE-link
between two adjacent WDM-TE-nodes is protected.  This is a local
protection scheme, which can be modeled as a TE-link property.