Change:
draft-ietf-ccamp-optical-impairment-topology-URL for IETF 115 submission --> draft-ietf-ccamp-optical-impairment-topology-yang-URL Related to pull request URL Addressing and resolving .

Discussion:
A YANG Data Model for Optical Impairment-aware Topology <del> draft-ietf-ccamp-optical-impairment-topology-yang-10 </del> <ins> draft-ietf-ccamp-optical-impairment-topology-yang-11 </ins> Abstract

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.

2.10. The YANG model defined in this document supports the following <del> protection architectures: </del> <ins> optical protection architectures: </ins> Individual OTSi protection OMS MCG protection = TE-link protection between adjacent WDM-TE-

2.10.1. Individual OTSi protection is a protection architecture where an <del> individual OTSi signal is protected as defined in Appendix III of </del> <ins> individual OTSi signal is protected as described in Appendix III of </ins> ITU-T Recommendation G.873.1 G.873.1.  This protection architecture <del> 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). </del> <ins> 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. </ins> In case of individual OTSi protection, there are two network media channel paths associated with the OTSi signal.  In the YANG model,

for the two network media channel paths associated with the individually protected otsi. <del> [Editor's note: this section is still work in progress] </del> <ins> Individual OTSi protection use cases: 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. 2.10.1.1. This use case is based on the architecture illustrated in Figure-6 and the following entities are all integral parts of the WDM-TE-node: 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. 2.10.1.2. This use case is based on the architecture illustrated in Figure-7 where the optical transponder is not part of the WDM-TE-node containing the ROADM function (WDM-TE-Node-2) but is part of a separate WDM-TE-node (WDM-TE-Node-1) containing one or more optical transponders (remote OTs).  WDM-TE-Node-2 contains: 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. 2.10.1.3. The use case illustrated in Figure-15 is similar to the use case in Protection UC (i).  The difference compared to use case (i) is that WDM-TE-Node-1 does not contain the ROADM function but contains: 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. </ins> 2.10.2.