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

Commentary: draft - ietf - ccamp - optical - impairment - topology- for IETF 113 submission --draft - ietf - ccamp - optical - impairment - topology - yang- Related to pull request . Addressing and resolving several open issues . 
 +1 the TE - node does n’t include BA / PA , a physical node however could . 
 In TIP , carrier use cases exist for copropagating  . It has been verified that gnpy can model those by indicating the direction ( see snippet below ) . So the provisional limit to consider only counterpropagating raman in can be lifted . example : " ramanpumps " : [ { " power " : 224.403e-3 , " frequency " : , " propagationdirection " : " coprop " } , { " power " : 231.135e-3 , " frequency " : , " propagation_direction " : " coprop " } 
 There is agreement to introduce also co - propagating option . The model as it is can support the feature using type - variety . Only one point has to be verified : if in the case of co - propagation we can report the gain . he pump power is in the type - variety . The text in the draft has to updated without the limitation of counter - propagating . 
 During the meeting on February 15th , we agree to add two attributes pump - power and frequency . Also direction has to be in alignment with the GNPy . Need to clearly say in the text that these attributes are needed for RAMN only . 
 Meeting 02/15/22 : The agreement was to add " pump - power " , " frequency " and " direction " attributes as described in  's comment Meeting 02/22/22 : Esther sent a proposed description of attributes to TIP experts for revision . 
 From  : Compared to GNPy data model , the pumps are listed in an ‘ amplifier element ’ , not in a fiber . I have assumed that a given amplifier element can not hold the two co and contra propagation roles . Final result : “ Raman - direction ” : " counter - propagating " " Raman - pumps " : [ { " power " : 224.403e-3 , " frequency " : , } , { " power " : 231.135e-3 , " frequency " : , } ] Descriptions : Raman - pumps container : list of pumps for the  amplifier Power : Total pump power in W considering a depolarized pump at frequency “ frequency ” Frequency : Pump central frequency in THz Raman - direction : direction of injection of the pump in the OMS . Contra - propagating means that optical pumps are injected in opposite direction to the optical signal that is amplified ( backward pump ) . Co - propagating means that the optical pumps are injected in the same direction to the optical signal that is amplified ( forward pump ) . enumerate type “ co - propagating ” or “ contra - propagating ” This porposal has been sent also to TIP experts for comments . 
 ITU - T G.872 ( 12/2019 ) The draft text needs to be aligned with the latest revisions of the referenced ITU - T Recommendations G.807 and G.872 . 
 I have a mixed feeling about this ... On one side , I can understand that using the terms OTS / OMS MCG would align the terminology used in the draft with the ITU - T G.807 terminology On the other side , the OTS / OMS MCG from a topological perspective are modelled as links ( at least the OMS MCG ) so I am not sure whether the term MCG to represent a link would cause some confusion 
 Here is the text update I prepared with the objective to align with ITU - T G.807 and describe how the new terms map to the IETF TE - topology terminology : OMS Media Channel Group According to [ G.807 ] and [ G.872 ] , an OMS Media Channel Group ( MCG ) represents a topological construct between two WDM - TE - nodes . In TE- topolgy terms , an OMS MCG corresponds to a WDM TE - link interconnecting two WDM - TE - nodes . Specifically , it originates at the ROADM in the source WDM - TE - node and terminates at the ROADM in the destination ROADM including the Booster Amplifier ( BA ) and the Pre- Amplifier in the WDM - TE - nodes as well as In - Line Amplifiers ( ILAs ) . OTS Media Channel Group represents a link : ( i ) between a WDM - TE - node 's BA and the adjacent ILA , ( ii ) between a pair of ILAs , ( iii ) between an ILA and the adjacent WDM - TE - node 's PA . An OMS MCG can be decomposed into a sequence of OTS MCGs of type ( i ) , ( ii ) , and ( iii ) as listed above . An OMS MCG ( TE - link ) provides the optical impairment data for its elements defined in the layer-0 topology YANG model and can be retrieved by a network controller . For the sake of optical impairment modeling , an OMS MCG can also be decomposed into a sequence of elements such as BA , fiber section , ILA , concentrated loss , and PA . An OMS MCG is terminated on both ends by a link termination point ( LTP ) as defined in [ RFC8345 ] . Links in optical transport networks are typically bidirectional but have to be modeled as a pair of two unidirectional links following the [ RFC8345 ] modeling approach . Unlike TE - links , which are unidirectional , the LTPs on either end of the TE - link pair forming the bidirectional link , are bidirectional as described in [ I - D.ietf - teas - te - topo - and - tunnel - modeling ] and the pair of unidirectional links are connected to the same bidirectional LTP on either end of the link pair . 
 few nits : The OMS - MCG starts from the ROADM element in the WDM - TE - node , but the description of OTS - MCG does n't cover the link between ROADM element and  / PA . To cover this , a case iv should be . ( see G.807 Fig 11 - 1 ) last paragraph : [ RFC8345 ] does not specifically define LTPs . It defines Termination Points ( TPs ) in a generic manner . So " LTP " would better be replaced by " TP " 
 : thanks  to pointed out , we need to substitute RFC8345 with RFC8795 , since LTP it is a a te - topology defined entity . 
 Fixed by PR 
 Elements as they are defined may be enough to handle Raman amplification , but I would like to have the feedback from the group about the possible missing attributes or change to the model . For example , it is not said in the model if the loss of the fiber should be its loss with or without  gain if any . 
 As per action point , here is a proposal for the text : " Hybrid backward Raman +  amplification can be modelled for example by using an amplifier element in front of the EDFA amplifier element to represent the amplifier pump place and the resulting gain . In this case tilt target is not mandatory " ( Ithink that nominal power should not be mandatory either , this is not something configurable ) " In case of  amplification on a fiber section , the total - loss of the corresponding fiber element should contain only the fiber loss and not the resulting loss including  gain " . 
 Here is a revised text proposal for section " 2.4 . Amplifiers " : some editorial as well as format changes have been made to the a new paragraph on Raman amplifiers has been ( paragraph at the bottom below ) addressing the modeling approach for  amplifiers the remaining text in this section is unchanged 
 Thanks , that 's clear for me ! shall we also amend the model and put nominal - power as optional ? 
 : sorry , which nominal - power are you referring to ? 
 I was refering to nominal - carrier - power and nominal - power - spectral - density , but I just realized that they are already optional ! 
 I would propose some text update to the last part of Dieter 's text proposal : The remaining text proposal from  is fine for me 
 I like proposal including amendments : however I 'm wondering if it 's worth mentioning the amplifier element shall model  gain tilt and bandwidth as well . something like an amplifier element at the pump location which reports all the optical properties ( gain , tilt , etc ) of the  amplification . 
 What about : " an amplifier element whose location ( provided by both the position in the OMS - link list of elements and geolocation ) reports the pump place and whose parameters reports all the optical properties ( gain , tilt , etc ) of the  amplification . 
 I ’m OK with the text with only one comment : there are co - propagating and counter - propagating raman pumps , do We want to limit the solution to counter - propagating pumps ? 
 Here the text we agree during the December 14th meeting : Optical amplifiers are used in WDM networks for amplifying the optical signal in the optical domain without any optical to electrical and electrical to optical conversion . There are three main optical amplifier technologies : o Erbium Doped Fiber Amplifiers ( EDFAs ) o Raman Amplifiers o Semiconductor Optical Amplifiers ( SOAs ) In today 's WDM networks EDFAs and  amplifiers are widely used . Raman amplifiers have become attractive due to their large spectral gain bandwidth , which can be quite flat , with similar or even lower noise figures compared to EDFAs . On the other hand , Raman amplifiers consume more power and are usually more expensive than EDFAs . Raman amplifiers are distributed amplifiers where an optical pump signal is injected in opposite direction to the optical signal that is amplified ( backward pump ) . Due to the distributed nature of the  amplifier it is difficult to clearly separate the amplifier from the fiber span into which the pump signal is injected . From a topology modeling perspective , the  amplifier is modeled as two OMS link elements : a passive fiber element whose loss accounts only the fiber loss and not the resulting loss including  gain an amplifier element whose location ( provided by both the position in the OMS - link list of elements and geolocation ) reports the pump place and whose parameters reports all the optical properties ( gain , tilt , etc ) of the  amplification 
 During December 14th meeting it was decided that is acceptable , for the moment , to limit the solution to counter - propagating pumps only . An explicit sentence regarding this point will be , together with the text suggested by  . 
 Updated section 2.4 text addressing the previous comment , text proposal from Dec 14 , 2021 , slightly modified - pure editorial changes only - see numbered list items at the bottom : Amplifiers Optical amplifiers are used in WDM networks for amplifying the optical signal in the optical domain without any optical to electrical and electrical to optical conversion . There are three main optical amplifier technologies : o Erbium Doped Fiber Amplifiers ( EDFAs ) o Raman Amplifiers o Semiconductor Optical Amplifiers ( SOAs ) In today 's WDM networks EDFAs and  amplifiers are widely used . Raman amplifiers have become attractive due to their large spectral gain bandwidth , which can be quite flat , with similar or even lower noise figures compared to EDFAs . On the other hand , Raman amplifiers consume more power and are usually more expensive than EDFAs . Raman amplifiers are distributed amplifiers where an optical pump signal is injected in opposite direction to the optical signal that is amplified ( backward pump ) . Injecting the pump signal in the same directions as the optical signal that is amplified ( forward pump ) is currently not considered . Due to the distributed nature of the  amplifier it is difficult to clearly separate the amplifier from the fiber span into which the pump signal is injected . From a topology modeling perspective , the  amplifier is modeled as two OMS line elements : a passive fiber element accounting for the fiber loss only and not the resulting loss including the Raman gain an amplifier element providing all optical amplifier properties ( gain , tilt , etc . ) . On the OMS - link , the amplifier element is placed where the pump is located and the geolocation information also indicates the location of the pump . 
 I like the editorial modifications and new structure of the text , with the numbered list bullets at the bottom . 
 Thanks , Ok for me ! 
 The new formulation is fine for me ( and it will address comment too ) . 
 Fixed by PR 
 We would like to use the model to describe a topology where the ROADMs have one / multiple external shelves with OTs . For management reason we want to represent the external shelf as a te - node ( in the ietf model ) , to represent all names and adresses ( we do not want to represent the shelf+ROADM as a single abstract ROADM ) . The links between the OTs hosted in this shelf can be described using te - link with optical impairment augmentation to describe possible loss or noise ( the tooling provided by the model is enough to handle this case ) . However the external shelf does not contain any mux , so that the link between the remote transceiver and the ROADM is not an OMS . However all the impairments we have defined in our model have this ' OMS ' attribute . This mismatch between the name of the attributes ( containing OMS ) and its usage for non OMS links might be confusing for implementers . We thus would like to say explicitely in the draft that the links between ROADMs and external shelves can also be described with our model . Currently , this sentence is in the draft : for example in the client device with a single channel link between the OT and the add / drop port of the ROADM requires further investigations and will be addressed in a future revision of this document . ] Would it be possible instead to say : The impairments related to the link between remote optical transponders located in a different shelf from the ROADM itself , can also be modelled using the same optical impairments as those defined for a link between ROADMs ( OMS ) . 
 in the scenario the external shelf can be considered as TE - node with termination capability only ( not switching ) the external shelf is under the control of the same controller as the ROADM 
 the external shelf is under the control of the same controller as the ROADM : the text is no more used . -AP : to add specific issue to clarify how the link between external shelf and ROADM is discovered . No impact on this issue that we can consider as closed . 
 This is the " agreed " text , to be in the draft in the next version upload ( by IETF-113 ): " The impairments related to the link between remote optical transponders located in a different shelf from the ROADM itself , can also be modelled using the same optical impairments as those defined for a link between ROADMs ( OMS ) . In the scenario the external shelf can be considered as TE - node with termination capability only ( not switching ) " 
 Let me suggest a couple of tweaks : " The impairments related to the link between remote optical transponders , located in a different node from the ROADM itself , can also be modeled using the same optical impairments as those defined for a link between ROADMs ( OMS ) . In this scenario , the transponder - carrying node can be considered as TE - node with termination capability only ( i.e. no switching ) . " 
 :   for the suggested modifications , why at this point do not use the terminology proposed in issue ? " The impairments related to the link between remote optical transponders , located in a different WDM - TE - node from the ROADM itself , can also be modeled using the same optical impairments as those defined for a link between ROADMs ( OMS ) . In this scenario , the transponder - carrying node can be considered as WDM - TE - node with termination capability only ( i.e. no switching ) . " 
 If we agree on the terms in , I concur : we MUST use them here . 
 Fixed by PR
This document augments the generic TE topology draft RFC8795 where
possible.
This document augments the generic TE topology YANG model defined in
RFC8795 where possible.
The term ROADM in this document refers to the term "multi-degree
reconfigurable optical add/drop multiplexer (MD-ROADM)" as defined in
G.672.  It does not include local optical transponders, which can be
co-located in the same physical device (managed entity).
The term WDM-node refers to a physical device, which is managed as a
single network element.
The term WDM-TE-node refers to those parts of a WDM-node (physical
device) that are modeled as a TE-node as defined in RFC8795, which
may include a ROADM and/or multiple local optical transponders(OTs).
Hence, a WDM-TE-node may only contain OTs.
The term "WDM-TE-network" refers to a set of WDM-TE-nodes as defined
above that are interconnected via TE-links carrying WDM signals.
These TE-links may include optical amplifiers.
The models developed in this document is an abstracted YANG model
that may be used in the interfaces between the MDSC and the Optical
Domain Controller (aka MPI) and between the Optical Domain Controller
and the Optical Device (aka SBI) in Figure-1.  It is not intended to
support a detailed low-level DWDM interface model.  DWDM interface
model is supported by the models presented in I-D.ietf-ccamp-dwdm-if-
param-yang.
This section provides the description of the reference optical
network architecture and its relevant components to support optical
impairment-aware path computation.
BA (on the left side ROADM) is the ingress Amplifier and PA (on the
right side ROADM is the egress amplifier for the OMS link shown in
Figure-2.
According to G.872, OMS Media Link represents a media link between
two ROADMs.  Specifically, it originates at the ROADM's Filter in the
source ROADM and terminates at the ROADM's Filter in the destination
ROADM.
OMS Media link can be decomposed in a sequence of OTS links type (i),
(ii), and (iii) as discussed above.  OMS Media link would give an
abstracted view of impairment data (e.g., power, OSNR, etc.) to the
network controller.
For the sake of optical impairment evaluation OMS Media link can be
also decomposed in a sequence of elements such as BA, fiber section,
ILA, concentrated loss and PA.
An OMS Media link is terminated on both ends by a link termination
point (LTP) as defined in RFC8345.  Links in optical transport
networks are typically bidirectional but have to be modeled as a pair
of two unidirectional links following the RFC8345 modeling approach.
Unlike TE links, which are unidirectional, the LTPs on either end of
the TE link pair forming the bidirectional link, are bidirectional as
described in I-D.ietf-teas-te-topo-and-tunnel-modeling and the pair
of unidirectional links are connected to the same bidirectional LTP
on either end of the link pair.
The topology model developed in this document is an abstracted
topology YANG model that can be used at the interfaces between the
MDSC and the Optical Domain Controller (aka MPI) and between the
Optical Domain Controller and the Optical Device (aka SBI) in Figure-
1.  It is not intended to support a detailed low-level DWDM interface
model.  DWDM interface model is supported by the models presented in
I-D.ietf-ccamp-dwdm-if-param-yang.
This section provides the description of the optical transport
network reference architecture and its relevant components to support
optical impairment-aware path computation.
BA (on the left side WDM-TE-node) is the engress Amplifier and PA (on
the right side WDM-TE-node is the ingress amplifier for the OMS Media
Channel Group (MCG) Figure-2.
According to G.807 and G.872, an OMS Media Channel Group (MCG)
represents a topological construct between two WDM-TE-nodes.
Specifically, it originates at the ROADM in the source WDM-TE-node
and terminates at the ROADM in the destination WDM-TE-node including
the Booster Amplifier (BA) and the Pre-Amplifier (PA) in the WDM-TE-
nodes as well as the In-Line Amplifiers (ILAs) between the two WDM-
TE-nodes.
An OMS MCG can be decomposed into a sequence of OTS MCGs and
amplifiers.
An OMS MCG can be described as a sequence of elements such as BA,
fiber section, ILA, PA, and concentrated loss wherever there is an
insertion loss caused for example by a fiber connector.
In TE-topology terms, the OMS MCG is modeled as a WDM TE-link
interconnecting two WDM-TE-nodes.  A network controller can retrieve
the optical impairment data for all the WDM TE-link elements defined
in the layer-0 topology YANG model.
The optical impairments related to the link between remote optical
transponders, located in a different WDM-TE-node (an IP router with
integrated optical transponders for example), can also be modeled as
a WDM TE-link using the same optical impairments as those defined for
a WDM TE-link between WDM-TE-nodes (OMS MCG).  In this scenario, the
node containing the remote optical transponders can be considered as
WDM-TE-node with termination capability only and no no switching
capabilities.
An OMS MCG is terminated on both ends by a link termination point
(LTP) as defined in RFC8345.  Links in optical transport networks are
typically bidirectional but have to be modeled as a pair of two
unidirectional links following the RFC8345 modeling approach.  Unlike
TE-links, which are unidirectional, the LTPs on either end of the TE-
link pair forming the bidirectional link, are bidirectional as
described in I-D.ietf-teas-te-topo-and-tunnel-modeling and the pair
of unidirectional links are connected to the same bidirectional LTP
on either end of the link pair.
Additionally, it is necessary for each ROADM node in the network to
know the OTSi signals that are added to or dropped from an OMS link
as well as the optical power of these OTSi signals to check whether
the ROADM's optical power constraints are met.
Additionally, it is necessary for each WDM-TE-node in the network to
know the OTSi signals that are added to or dropped from an WDM TE-
link (OMS MCG)link as well as the optical power of these OTSi signals
to check whether the WDM-TE-node's optical power constraints are met.
G.807 defines a "media channel" as "A media association that
represents both the topology (i.e., the path through the media) and
the resource (i.e., frequency slot or effective frequency slot) that
it occupies."  In this document, the term "channel" is occasionally
used to indicate the resource of an MC (i.e., frequency slot or
effective frequency slot), without representing topology.
Optical amplifiers are in charge of amplifying the optical signal in
the optical itself without any electrical conversion.  There are
three main technologies to build amplifiers: Erbium Doped Fiber
Amplifier (EDFA), Raman Fiber Amplifier (RFA), and Semiconductor
Optical Amplifier (SOA).  Nowadays, most of optical networks uses
EDFAs.  However, RFA has an attractive feature that it works in any
wavelength band with a similar or lower noise figures compared to
EDFA.  On the other hand, RFAs consumes more power and are more
expensive than EDFAs.
Amplifiers can be classified according to their location in the
communication link.  There are three basic types of amplifiers: ILA,
Pre-Amplifier and Booster.  ILA is In-Line Amplifier which is a
separate node type while Pre-Amplifier and Booster Amplifier are
integral elements of ROADM node.  From a data modeling perspective,
Pre-Amplifier and Booster Amplifier are internal functions of a ROADM
node and as such these elements are hidden within ROADM node.  In
this document, we would avoid internal node details, but attempt to
abstract as much as possible.
ILAs are placed at locations where the optical amplification of the
WDM signal is required on the OMS link between two ROADM nodes.
Geolocation information is already defined for TE nodes in RFC8795
and is also beneficial for ILAs.  Therefore, the same geolocation
container has been added to the amplifier element on an OMS link
containing altitude, latitude, and longitude as optional attributes.
In today's WDM networks EDFAs and Raman amplifiers are widely used.
Raman amplifiers have become attractive due to their large spectral
gain bandwidth, which can be quite flat, with similar or even lower
noise figures compared to EDFAs.  On the other hand, Raman amplifiers
consume more power and are usually more expensive than EDFAs.
a passive fiber element accounting for the fiber loss only and not
the resulting loss including the Raman gain
an amplifier element providing all optical amplifier properties
(gain, tilt, etc.).  On the OMS-link, the amplifier element is
placed where the pump is located and the geolocation information
also indicates the location of the pump.
Amplifiers can be classified according to their location along the
TE-link (OMS MCG).  There are three basic amplifier types: In-Line
Amplifiers, Pre-Amplifiers and Booster Amplifiers.  ILAs are separate
physical devices while Pre-Amplifiers and Booster Amplifiers are
integral elements of a WDM-node.  From a data modeling perspective,
node-internal details should not be modeled and should be abstracted
as much as possible.  For Pre-Amplifiers and Booster Amplifiers,
however, a different approach has been taken and they are modeled as
TE-link elements as they have the same optical impairments as ILAs.
ILAs are placed at locations where the optical amplification of the
WDM signal is required on the TE-link (OMS MCG) between two WDM-TE-
nodes nodes.  Geolocation information is already defined for TE nodes
in RFC8795 and is also beneficial for ILAs.  Therefore, the same
geolocation container has been added to the amplifier element on an
OMS link containing altitude, latitude, and longitude as optional
attributes.
The TE topology YANG model augmentations including optical
impairments for DWDM networks defined below intend to cover all the 3
categories of ROADM architectures listed above.  In the case of a
disaggregated ROADM architecture, it is assumed that optical domain
controller already performs some form of abstraction and presents the
TE-node representing the disaggregated ROADM in the same way as an
integrated ROADM with integrated optical transponders if the optical
transponder subsystems and the add/drop subsystems are collocated
(short fiber links not imposing significant optical impairments).
The different ROADM architectures are briefly described and
illustrated in the following subsections.
Figure-2 and Figure-6 below show the typical architecture of an
integrated ROADM node, which contains the optical transponders as an
integral part of the ROADM node.  Such an integrated ROADM node
provides DWDM interfaces as external interfaces for interconnecting
the device with its neighboring ROADMs (see OTS link above).  The
number of these interfaces denote also the degree of the ROADM.  A
degree 3 ROADM for example has 3 DWDM links that interconnect the
ROADM node with 3 neighboring ROADMs.  Additionally, the ROADM
provides client interfaces for interconnecting the ROADM with client
devices such as IP routers or Ethernet switches.  These client
interfaces are the client interfaces of the integrated optical
transponders.
The TE topology YANG model augmentations including optical
impairments for DWDM networks defined below intend to cover all the 3
categories of WDM-node architectures listed above.  In the case of a
disaggregated WDM-node architecture, it is assumed that the optical
domain controller already performs some form of abstraction and
presents the WDM-TE-node representing the disaggregated WDM-node in
the same way as an integrated WDM-TE-node with local optical
transponders if the optical transponder subsystems and the add/drop
subsystems are collocated (short fiber links not imposing any
significant optical impairments).
The different WDM-node architectures are briefly described and
illustrated in the following subsections.
Figure-2 and Figure-6 below show the typical architecture of an
integrated WDM-node, which contains the optical transponders as an
integral part of the WDM-node.  Such an integrated WDM-node provides
DWDM interfaces as external interfaces for interconnecting the device
with its neighboring WDM-node (see OMS MCG above).  The number of
these interfaces denote also the degree of the WDM-node.  A degree 3
WDM-node for example has 3 DWDM links that interconnect the WDM-node
with 3 neighboring WDM-nodes.  Additionally, the WDM-node provides
client interfaces for interconnecting the WDM-node with client
devices such as IP routers or Ethernet switches.  These client
interfaces are the client interfaces of the integrated optical
transponders.
Recently, some DWDM network operators started demanding ROADM
subsystems from their vendors.  An example is the OpenROADM project
where multiple operators and vendors are developing related YANG
models.  The subsystems of a disaggregated ROADM are: single degree
subsystems, add/drop subsystems and optical transponder subsystems.
These subsystems separate network elements and each network element
provides a separate management and control interface.  The subsystems
are typically interconnected using short fiber patch cables and form
together a disaggregated ROADM node.  This disaggregated ROADM
architecture is depicted in Figure-8 below.
As this document defines TE topology YANG model augmentations RFC8795
for the TE topology YANG model provided at the north-bound interface
of the optical domain controller, it is a valid assumption that the
optical domain controller abstracts the subsystems of a disaggregated
ROADM and presents the disaggregated ROADM in the same way as an
integrated ROADM hiding all the interconnects that are not relevant
from an external TE topology view.
These subsystems are separate network elements and each network
element provides a separate management and control interface.  The
subsystems are typically interconnected using short fiber patch
cables and form together a disaggregated WDM-TE-node.  This
disaggregated WDM-TE-node architecture is depicted in Figure-8 below.
As this document defines TE topology YANG model augmentations RFC8795
for the TE topology YANG model provided at the north-bound interface
of the optical domain controller, it is a valid assumption that the
optical domain controller abstracts the subsystems of a disaggregated
WDM-TE-node and presents the disaggregated WDM-TE-node in the same
way as an integrated WDM-node hiding all the interconnects that are
not relevant from an external TE topology view.