Applicability of Abstraction and Control of Traffic Engineered Networks (ACTN) to Packet Optical Integration (POI)

Applicability of Abstraction and Control of Traffic Engineered Networks (ACTN) to Packet Optical Integration (POI) TIM

fabio.peruzzini@telecomitalia.it

Vodafone

jeff.bouquier@vodafone.com

Huawei

italo.busi@huawei.com

Old Dog Consulting

daniel@olddog.co.uk

Cisco

daniele.ietf@gmail.com

Routing Traffic Engineering Architecture and Signaling next generation unicorn sparkling distributed ledger This document considers the applicability of Abstraction and Control of TE Networks (ACTN) architecture to Packet Optical Integration (POI) in the context of IP/MPLS and optical internetworking. It identifies the YANG data models defined by the IETF to support this deployment architecture and specific scenarios relevant to Service Providers. Existing IETF protocols and data models are identified for each multi-technology (packet over optical) scenario with a specific focus on the MPI (Multi-Domain Service Coordinator to Provisioning Network Controllers Interface)in the ACTN architecture. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Traffic Engineering Architecture and Signaling Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction The complete automation of the management and control of Service Providers transport networks (IP/MPLS, optical, and microwave transport networks) is vital for meeting emerging demand for high-bandwidth use cases, including 5G and fiber connectivity services. The Abstraction and Control of TE Networks (ACTN) architecture and interfaces facilitate the automation and operation of complex optical and IP/MPLS networks through standard interfaces and data models. This allows a wide range of network services that can be requested by the upper layers fulfilling almost any kind of service level requirements from a network perspective (e.g. physical diversity, latency, bandwidth, topology, etc.) Packet Optical Integration (POI) is an advanced use case of traffic engineering. In wide-area networks, a packet network based on the Internet Protocol (IP), and often Multiprotocol Label Switching (MPLS) or Segment Routing (SR), is typically realized on top of an optical transport network that uses Dense Wavelength Division Multiplexing (DWDM)(and optionally an Optical Transport Network (OTN)layer). In many existing network deployments, the packet and the optical networks are engineered and operated independently. As a result, there are technical differences between the technologies (e.g., routers compared to optical switches) and the corresponding network engineering and planning methods (e.g., inter-domain peering optimization in IP, versus dealing with physical impairments in DWDM, or very different time scales). In addition, customers needs can be different between a packet and an optical network, and it is not uncommon to use other vendors in both domains. The operation of these complex packet and optical networks is often siloed, as these technology domains require specific skill sets. The packet/optical network deployment and operation separation are inefficient for many reasons. First, both capital expenditure (CAPEX) and operational expenditure (OPEX) could be significantly reduced by integrating the packet and the optical networks. Second, multi-technology online topology insight can speed up troubleshooting (e.g., alarm correlation) and network operation (e.g., coordination of maintenance events), and multi-technology offline topology inventory can improve service quality (e.g., detection of diversity constraint violations). Third, multi-technology traffic engineering can use the available network capacity more efficiently (e.g., coordination of restoration). In addition, provisioning workflows can be simplified or automated across layers (e.g., to achieve bandwidth-on-demand or to perform activities during maintenance windows). This document uses packet-based Traffic Engineered (TE) service examples. These are described as "TE-path" in this document. Unless otherwise stated, these TE services may be instantiated using RSVP-TE-based or SR-TE-based, forwarding plane mechanisms. The ACTN framework enables the complete multi-technology and multi-vendor integration of packet and optical networks through a Multi-Domain Service Coordinator (MDSC), and packet and optical Provisioning Network Controllers (PNCs). This document describes critical scenarios for POI from the packet service layer perspective and identifies the required coordination between packet and optical layers to improve POI deployment and operation. These scenarios focus on multi-domain packet networks operated as a client of optical networks. This document analyses the case where the packet networks support multi-domain TE paths. The optical networks could be either a DWDM network, an OTN network (without DWDM layer), or a multi-layer OTN/DWDM network. Furthermore, DWDM networks could be either fixed-grid or flexible-grid. Multi-technology and multi-domain scenarios, based on the reference network described in and very relevant for Service Providers, are described in and . For each scenario, existing IETF protocols and data models, identified in and , are analyzed with a particular focus on the MPI in the ACTN architecture. For each multi-technology scenario, the document analyzes how to use the interfaces and data models of the ACTN architecture. A summary of the gaps identified in this analysis is provided in . Understanding the level of standardization and the possible gaps will help assess the feasibility of integration between packet and optical DWDM domains (and optionally OTN layer) in an end-to-end multi-vendor service provisioning perspective.

Terminology This document uses the ACTN terminology defined in . In addition, this document uses the following terminology.

Customer service:: The end-to-end service from CE to CE.
Network service:: The PE to PE configuration, including both the network service layer (VRFs, RT import/export policies configuration) and the network transport layer (e.g. RSVP-TE LSPs). This includes the configuration (on the PE side) of the interface towards the CE (e.g. VLAN, IP address, routing protocol etc.).
Technology domain:: short for "switching technology domain", defined as "region" in , where the term "region" is applied to (GMPLS) control domains.
PNC Domain:: part of the network under control of a single PNC instance. It is subject to the capabilities of the PNC which technology is controlled.
Port:: The physical entity that transmits and receives physical signals.
Interface:: A physical or logical entity that transmits and receives traffic.
Link:: An association between two interfaces that can exchange traffic directly.
Intra-domain link:: a link between two adjacent nodes that belong to the same PNC domain.
Inter-domain link:: a link between two adjacent nodes that belong to different PNC domains.
Ethernet link:: A link between two Ethernet interfaces.
Single-technology Ethernet link:: An Ethernet link between two Ethernet interfaces on physically adjacent IP routers.
Multi-technology Ethernet link:: An Ethernet link between between two Ethernet interfaces on logically adjacent IP routers, which is supported by an underlay tunnel in a different technology domain.
Cross-technology Ethernet link:: An Ethernet link between an Ethernet interface on an IP router and an Ethernet interface on a physically adjacent optical node.
Inter-domain Ethernet link:: An Ethernet link between between two Ethernet interfaces on physically adjacent IP routers that belong to different P-PNC domains.
Single-technology intra-domain Ethernet link:: An Ethernet link between between two Ethernet interfaces on physically adjacent IP routers that belong to the same P-PNC domain.
Multi-technology intra-domain Ethernet link:: An Ethernet link between between two Ethernet interfaces on logically adjacent IP routers that belong to the same P-PNC domain, which is supported by supported by two cross-technology Ethernet links and an optical tunnel in between.
IP link:: A link between two IP interfaces.
Single-technology intra-domain IP link:: An IP link supported by a single-technology intra-domain Ethernet link.
Inter-domain IP link:: An IP link supported by an inter-domain Ethernet link.
Multi-technology intra-domain IP link:: An IP link supported by a multi-technology intra-domain Ethernet link.

Reference Network Architecture This document analyses several deployment scenarios for Packet and Optical Integration (POI) in which ACTN hierarchy is deployed to control a multi-technology and multi-domain network with two optical domains and two packet domains, as shown in :

Reference Network The ACTN architecture, defined in , is used to control this multi-technology and multi-domain network where each Packet PNC (P-PNC) is responsible for controlling its packet domain and where each Optical PNC (O-PNC) in the above topology is responsible for controlling its optical domain. The packet domains controlled by the P-PNCs can be Autonomous Systems (ASes), defined in , or IGP areas, within the same operator network. The IP routers between the packet domains can be either AS Boundary Routers (ASBR) or Area Border Router (ABR): in this document, the generic term Border Router (BR) is used to represent either an ASBR or an ABR. The MDSC is responsible for coordinating the whole multi-domain multi-technology (packet and optical) network. A specific standard interface (MPI) permits MDSC to interact with the different Provisioning Network Controller (O/P-PNCs). The MPI interface presents an abstracted topology to MDSC, hiding technology-specific aspects of the network and hiding topology details depending on the policy chosen regarding the level of abstraction supported. The level of abstraction can be obtained based on P-PNC and O-PNC configuration parameters (e.g., provide the potential connectivity between any PE and any BR in a packet network). In the reference network of , it is assumed that:

The domain boundaries between the packet and optical domains are congruent. In other words, one optical domain supports connectivity between IP routers in one and only one packet domain;
There are no inter-domain physical links between optical domains. Inter-domain physical links exist only:
- between packet domains (i.e., between BRs belonging to different packet domains): these links are called inter-domain Ethernet or IP links within this document;
- between packet and optical domains (i.e., between routers and optical nodes): these links are called cross-technology Ethernet links within this document;
- between customer sites and the packet network (i.e., between CE devices and PE routers): these links are called access links within this document.
All the physical interfaces at inter-domain links are Ethernet physical interfaces.

Although the new optical technologies (e.g., QSFP-DD ZR 400G) allow the operators to provide DWDM pluggable interfaces on the IP routers, the deployment of those pluggable optics is not yet widely adopted. The reason is that most operators are not yet ready to manage packet and optical networks in a single unified domain. Therefore, a unified use case analysis is outside the scope of this document. This document analyses scenarios where all the multi-technology IP links, supported by the optical network, are intra-domain (intra-AS/intra-area), such as PE-BR, PE-P, BR-P, P-P IP links. Therefore the inter-domain IP links are always single-technology links supported by Ethernet physical links. The analysis of scenarios with multi-technology inter-domain IP links is outside the scope of this document. Therefore, if inter-domain links between the optical domains exist, they would be used to support multi-domain optical services, which are outside the scope of this document. The optical nodes within the optical domains can be either:

WDM nodes, as defined in , with an integrated ROADM functions and with or without integrated optical transponders;
OTN nodes, with integrated an OTN cross-connect function and with or without integrated ROADM functions or optical transponders.

Multi-domain Service Coordinator (MDSC) functions The MDSC in is responsible for multi-domain and multi-technology coordination across multiple packet and optical domains and provides multi-layer/multi-domain L2/L3 VPN network services requested by an OSS/Orchestration layer. From an implementation perspective, the functions associated with MDSC described in may be grouped differently.

The service- and network-related functions are collapsed into a single, monolithic implementation, dealing with the end customer service requests received from the CMI (Customer MDSC Interface) and adapting the relevant network models. An example is represented in Figure 2 of .
An implementation can choose to split the service-related and the network-related functions into different functional entities, as described in and in section 4.2 of . In this case, MDSC is decomposed into a top-level Service Orchestrator, interfacing the customer via the CMI, and into a Network Orchestrator interfacing at the southbound with the PNCs. The interface between the Service Orchestrator and the Network Orchestrator is not specified in .
Another implementation can choose to split the MDSC functions between an "higher-level MDSC" (MDSC-H) responsible for packet and optical multi-technology coordination, interfacing with one Optical "lower-level MDSC" (MDSC-L), providing multi-domain coordination between the O-PNCs and one Packet MDSC-L, providing multi-domain coordination between the P-PNCs (see for example Figure 9 of ).
Another implementation can also choose to combine the MDSC and the P-PNC functions.

In the current service provider's network deployments, at the North Bound of the MDSC, instead of a CNC, typically, there is an OSS/Orchestration layer. In this case, the MDSC would implement only the Network Orchestration functions, as in described in point 2 above. Therefore, the MDSC deals with the network services requests received from the OSS/Orchestration layer. The functionality of the OSS/Orchestration layer and the interface toward the MDSC are usually operator-specific and outside the scope of this draft. Therefore, this document assumes that the OSS/Orchestrator requests the MDSC to set up L2/L3 VPN network services through mechanisms outside this document's scope. There are two prominent workflow cases when the MDSC multi-technology coordination is initiated:

Initiated by request from the OSS/Orchestration layer to setup L2/L3 VPN network services that require multi-layer/multi-domain coordination;
The MDSC initiates them to perform multi-layer/multi-domain optimizations and/or maintenance activities (e.g. rerouting LSPs with their associated services when putting a resource, like a fibre, in maintenance mode during a maintenance window). Unlike service fulfillment, these workflows are not related to a network service provisioning request received from the OSS/Orchestration layer.

The latter workflow cases are outside the scope of this document. This document analyses the use cases where multi-layer coordination is triggered by a network service request received from the OSS/Orchestration layer.

Multi-domain L2/L3 VPN Network Services and provide an example of a hub & spoke multi-domain L2/L3 VPN with three PEs where the hub PE (PE13) and one spoke PE (PE14) are within the same packet domain, and the other spoke PE (PE23) is within a different packet domain.

Multi-domain VPN topology example

Multi-domain VPN TE paths example There are many options to implement multi-domain L2/L3 VPNs, including:

BGP-LU ()
Inter-domain RSVP-TE
Inter-domain SR-TE

This document analyses the inter-domain TE options for which the TE tunnel model, defined in , could be used at the MPI for intra-domain or inter-domain TE configuration. The analysis of other options is outside the scope of this draft. It is also assumed that:

the bandwidth of each intra-domain TE path is managed by its respective P-PNC;
technology-specific mechanisms (in the case of inter-domain SR-TE, the binding SID) are used for the inter-domain TE path stitching;
each packet domain in uses technology-specific local protection mechanisms (such as Fast Reroute (FRR) in case of MPLS-TE or Topology Independent Loop-free Alternate Fast Reroute (TI-LFA) in case of SR-TE), with the awareness of multi-technology TE path properties (e.g., SRLG).

In the case of inter-domain TE-paths, it is also assumed that each packet domain in and implements the same TE technology, and the stitching between two domains is done using inter-domain TE. In this scenario, one of the key MDSC functions is to identify the multi-domain/multi-layer TE paths to be used to carry the L2/L3 VPN traffic between PEs belonging to different packet domains and to relay this information to the P-PNCs, to ensure that the PEs' forwarding tables (e.g., VRF) are properly configured to steer the L2/L3 VPN traffic over the intended multi-domain/multi-layer TE paths. The selection of the TE path should take into account the TE requirements and the binding requirements for the L2/L3 VPN network service. In general, the binding requirements for a network service (e.g., L2/L3 VPN) can be summarized within three cases:

The customer is asking for VPN isolation to dynamically create and bind tunnels to the service so that they are not shared by other services (e.g. VPN). The level of isolation can be different:
1. Hard isolation with deterministic latency means L2/L3 VPN requires a set of dedicated TE Tunnels (neither sharing with other services nor competing for bandwidth with other tunnels), providing deterministic latency performances
2. hard isolation but without deterministic characteristics
3. Soft isolation means the tunnels associated with L2/L3 VPN are dedicated to that but can compete for bandwidth with other tunnels.
The customer does not ask for isolation and could request a VPN service where associated tunnels can be shared across multiple VPNs.

For each TE path required to support the L2/L3 VPN network service, it is possible that:

A TE path that meets the TE and binding requirements already exists in the network.
An existing TE path could be modified (e.g., through bandwidth increase) to meet the TE and binding requirements:
1. The TE path characteristics can be modified only in the packet layer.
2. One or more new underlay optical tunnels need to be setup to support the requested changes of the overlay TE paths (multi-layer coordination is required).
A new TE path needs to be setup to meet the TE and binding requirements:
1. The new TE path reuses existing underlay optical tunnels;
2. One or more new underlay optical tunnels need to be setup to support the setup of the new TE path (multi-layer coordination is required).

This document analyses scenarios where only one TE path is used to carry the VPN traffic between PEs. Scenarios, where multiple parallel TE paths are used in load-balancing to carry the VPN traffic between PEs, are possible but their analysis is outside the scope of this document.

Multi-domain and Multi-layer Path Computation When a new TE path needs to be setup, the MDSC is also responsible for coordinating the multi-layer/multi-domain path computation. Depending on the knowledge that MDSC has of the topology and configuration of the underlying network domains, three approaches for performing multi-layer/multi-domain path computation are possible:

Full Summarization: In this approach, the MDSC has an abstracted TE topology view of all of its packet and optical, underlying domains. In this case, the MDSC does not have enough TE topology information to perform multi-layer/multi-domain path computation. Therefore the MDSC delegates the P-PNCs and O-PNCs to perform local path computation within their respective controlled domains. Then, it uses the information returned by the P-PNCs and O-PNCs to compute the optimal multi-domain/multi-layer path. This approach presents an issue to P-PNC, which does not have the capability of performing a single-domain/multi-layer path computation, since it can not retrieve the topology information from the O-PNCs nor delegate the O-PNC to perform optical path computation. A possible solution could include a CNC function within the P-PNC to request the MDSC multi-domain optical path computation, as shown in Figure 10 of . Another solution could be to rely on the MDSC recursive hierarchy, as defined in section 4.1 of , where, for each IP and optical domain pair, a "lower-level MDSC" (MDSC-L) provides the essential multi-layer correlation and the "higher-level MDSC" (MDSC-H) provides the multi-domain coordination. In this case, the MDSC-H can get an abstract view of the underlying multi-layer domain topologies from its underlying MDSC-L. Each MDSC-L gets the full view of the IP domain topology from P-PNC and can get an abstracted view of the optical domain topology from its underlying O-PNC. In other words, topology abstraction is possible at the MPIs between MDSC-L and O-PNC and between MDSC-L and MDSC-H.
Partial summarization: In this approach, the MDSC has complete visibility of the TE topology of the packet network domains and an abstracted view of the TE topology of the optical network domains. The MDSC then has only the capability of performing multi-domain/single-layer path computation for the packet layer (the path can be computed optimally for the two packet domains). Therefore, the MDSC still needs to delegate the O-PNCs to perform local path computation within their respective domains. It uses the information received by the O-PNCs and its TE topology view of the multi-domain packet layer to perform multi-layer/multi-domain path computation.
Full knowledge: In this approach, the MDSC has a complete and enough detailed view of the TE topology of all the network domains (both optical and packet). In such case MDSC has all the information needed to perform multi-domain/multi-layer path computation, without relying on PNCs. This approach may present, as a potential drawback, scalability issues and, as discussed in section 2.2. of , performing path computation for optical networks in the MDSC is quite challenging because the optimal paths depend also on vendor-specific optical attributes (which may be different in the two domains if different vendors provide them).

This document analyses scenarios where the MDSC uses the partial summarization approach to coordinate multi-domain/multi-layer path computation. Typically, the O-PNCs are responsible for the optical path computation of services across their respective single domains. Therefore, when setting up the network service, they must consider the connection requirements such as bandwidth, amplification, wavelength continuity, and non-linear impairments that may affect the network service path. The methods and types of path requirements and impairments, such as those detailed in , used by the O-PNC for optical path computation are not exposed at the MPI and therefore out of scope for this document.

IP/MPLS Domain Controller and IP router Functions Each packet domain in , corresponding to either an IGP area or an Autonomous System (AS) within the same operator network, is controlled by a packet domain controller (P-PNC). P-PNCs are responsible for setting up the TE paths between any two PEs or BRs in their respective controlled domains, as requested by MDSC, and providing topology information to the MDSC. For example, for inter-domain SR-TE, the setup bidirectional SR-TE path from PE13 in domain 1 to PE23 in domain 2, as shown in , requires the MDSC to coordinate the actions of:

P-PNC1 to push a SID list to PE13 including the Binding SID associated to the SR-TE path in Domain 2 with PE23 as the target destination (forward direction);
P-PNC2 to push a SID list to PE23, including the Binding SID associated with the SR-TE path in Domain 1 with PE13 as the target destination (reverse direction).

With reference to , P-PNCs are then responsible:

To expose to MDSC their respective detailed TE topology
To perform single-layer single-domain local TE path computation, when requested by MDSC between two PEs (for single-domain end-to-end TE path) or between PEs and BRs for an inter-domain TE path selected by MDSC;
To configure the routers in their respective domain to setup a TE path;
To configure the VRF and PE-CE interfaces (Service access points) of the intra-domain and inter-domain network services requested by the MDSC.

Domain Controller & node Functions ]]> When requesting the setup of a new TE path, the MDSC provides the P-PNCs with the explicit path to be created or modified. In other words, the MDSC can communicate to the P-PNCs the complete list of nodes involved in the path (strict mode). In this case, the P-PNC is just responsible to set up that explicit TE path. For example:

with SR-TE, the P-PNC pushes to headend PE or BR the list of SIDs to create the explicit SR-TE path, provided by the MDSC;
with RSVP-TE, the P-PNC requests the headend PE or BR to start signaling the explicit RSVP-TE path, provided by the MDSC.

To scale in large SR-TE packet domains, the MDSC can provide P-PNC a loose path, together with per-domain TE constraints. The P-PNC can then select the complete path within its domain. In such a case, it is mandatory that P-PNC signals back to the MDSC which path it has chosen so that the MDSC keeps track of the relevant resources utilization. From the example, the TE path requested by the MDSC touches PE13 - P16 - BR12 - BR21 - PE23. P-PNC2 is aware of two paths with the same topology metric, e.g. BR21 - P24 - PE23 and BR21 - BR22 - PE23, but with different loads. It may prefer to steer the traffic on the latter because it is less loaded. For the purposes of this document it is assumed that the MDSC always provides the explicit list of all the hops to the P-PNCs to setup or modify the TE path.

Optical Domain Controller and NE Functions The optical network provides underlay connectivity services to IP/MPLS networks. The packet and optical multi-layer coordination is done by the MDSC, as shown in . The O-PNC is responsible to:

provide to the MDSC an abstract TE topology view of its underlying optical network resources;
perform single-domain local path computation, when requested by the MDSC;
perform optical tunnel setup, when requested by the MDSC.

The mechanisms used by O-PNC to perform intra-domain topology discovery and path setup are usually vendor-specific and outside the scope of this document. Depending on the type of optical network, TE topology abstraction, path computation and path setup can be single-layer (either OTN or WDM) or multi-layer OTN/WDM. In the latter case, the multi-layer coordination between the OTN and WDM layers is performed by the O-PNC.

Interface Protocols and YANG Data Models for the MPIs This section describes general assumptions applicable to all the MPI interfaces, between each PNC (Optical or Packet) and the MDSC, to support the scenarios discussed in this document.

RESTCONF Protocol at the MPIs The RESTCONF protocol, as defined in , using the JSON representation defined in , is assumed to be used at these interfaces. In addition, extensions to RESTCONF, as defined in , to be compliant with Network Management Datastore Architecture (NMDA) defined in , are assumed to be used as well at these MPI interfaces and also at MDSC NBI interfaces.

YANG Data Models at the MPIs The data models used on these interfaces are assumed to use the YANG 1.1 Data Modeling Language, as defined in . This section describes the YANG data models that are applicable to the Packet and Optical MPIs. Some of these YANG data models can be optional depending on the specific network configuration detailed in and .

Common YANG Data Models at the MPIs As required in , the "ietf-yang-library" YANG module defined in is used to allow the MDSC to discover the set of YANG modules supported by each PNC at its MPI. Both Optical and Packet PNCs can use the following common topology YANG data models at the MPI:

The Base Network Model, defined in the "ietf-network" YANG module of ;
The Base Network Topology Model, defined in the "ietf-network-topology" YANG module of , which augments the Base Network Model;
The TE Topology Model, defined in the "ietf-te-topology" YANG module of , which augments the Base Network Topology Model.

Optical and Packet PNCs can use the common TE Tunnel Model, defined in the "ietf-te" YANG module of , at the MPI. All the common YANG data models are generic and augmented by technology-specific YANG modules, as described in the following sections. Both Optical and Packet PNCs can also use the Ethernet Topology Model, defined in the "ietf-eth-te-topology" YANG module of , which augments the TE Topology Model with Ethernet technology-specific information. Both Optical and Packet PNCs can use the following common notifications YANG data models at the MPI:

Dynamic Subscription to YANG Events and Datastores over RESTCONF as defined in ;
Subscription to YANG Notifications for Datastores updates as defined in .

PNCs and MDSCs comply with subscription requirements as stated in .

YANG models at the Optical MPIs The Optical PNC can use the following technology-specific topology YANG data models, which augment the generic TE Topology Model:

The WSON Topology Model, defined in the "ietf-wson-topology" YANG module of ;
the Flexi-grid Topology Model, defined in the "ietf-flexi-grid-topology" YANG module of ;
the OTN Topology Model, as defined in the "ietf-otn-topology" YANG module of .

The optical PNC can use the following technology-specific tunnel YANG data models, which augments the generic TE Tunnel Model:

The WDM Tunnel Model, defined in the "ietf-wdm-tunnel" YANG module of ;
the OTN Tunnel Model, defined in the "ietf-otn-tunnel" YANG module of .

The optical PNC can use the generic Path Computation YANG RPC, defined in the "ietf-te-path-computation" YANG module of . Note that technology-specific augmentations of the generic path computation RPC for WSON, Flexi-grid and OTN path computation RPCs have been identified as a gap. The optical PNC uses can use the following client signal YANG data models:

the CBR Client Signal Model, defined in the "ietf-trans-client-service" YANG module of ;
the Ethernet Client Signal Model, defined in the "ietf-eth-tran-service" YANG module of .

YANG data models at the Packet MPIs The Packet PNC can use the following technology-specific topology YANG data models:

The L3 Topology Model, defined in the "ietf-l3-unicast-topology" YANG module of , which augments the Base Network Topology Model;
the Packet TE Topology Mode, defined in the "ietf-te-topology-packet" YANG module of , which augments the generic TE Topology Model;
The MPLS-TE Topology Model, defined in the "ietf-te-mpls-topology" YANG module of , which augments the TE Packet Topology Model with or without the L3 TE Topology Model, defined in "ietf-l3-te-topology" YANG module of ;
the SR Topology Model, defined in the "ietf-sr-mpls-topology" YANG module of .

The Packet PNC can use the following technology-specific tunnel YANG data models, which augments the generic TE Tunnel Model:

The MPLS-TE Tunnel Model, defined in the "ietf-te-mpls" YANG modules of ;
the SR-TE Tunnel Model which is to be defined as described in .

The packet PNC can use the following network service YANG data models:

L3VPN Network Model (L3NM), defined in the "ietf-l3vpn-ntw" YANG module of ;
L3NM TE Service Mapping, defined in the "ietf-l3nm-te-service-mapping" YANG module of ;
L2VPN Network Model (L2NM), defined in the "ietf-l2vpn-ntw" YANG module of ;
L2NM TE Service Mapping, defined in the "ietf-l2nm-te-service-mapping" YANG module of .

Path Computation Element Protocol (PCEP) examines the applicability of a Path Computation Element (PCE) and PCE Communication Protocol (PCEP) to the ACTN framework. It further describes how the PCE architecture applies to ACTN and lists the PCEP extensions needed to use PCEP as an ACTN interface. The stateful PCE , PCE-Initiation , stateful Hierarchical PCE (H-PCE) , and PCE as a central controller (PCECC) are some of the key extensions that enable the use of PCE/PCEP for ACTN. Since the PCEP supports path computation in the packet and optical networks, PCEP is well suited for inter-layer path computation. describes a framework for applying the PCE-based architecture to interlayer (G)MPLS traffic engineering. Furthermore, section 6.1 of states the H-PCE applicability for inter-layer or POI. lists various PCEP extensions that apply to ACTN. It also lists the PCEP extension for the optical network and POI. Note that the PCEP can be used in conjunction with the YANG data models described in the rest of this document. Depending on whether ACTN is deployed in a greenfield or brownfield, two options are possible:

The MDSC uses a single RESTCONF/YANG interface towards each PNC to discover all the TE information and request TE tunnels. It may perform full multi-layer path computation or delegate path computation to the underneath PNCs. This approach is desirable for operators from a multi-vendor integration perspective as it is simple. We need only one type of interface (RESTCONF) and use the relevant YANG data models depending on the operator use case considered. The benefits of having only one protocol for the MPI between MDSC and PNC have already been highlighted in .
The MDSC uses the RESTCONF/YANG interface towards each PNC to discover all the TE information and requests the creation of TE tunnels. However, it uses PCEP for hierarchical path computation. As mentioned in Option 1, from an operator perspective, this option can add integration complexity to have two protocols instead of one unless the RESTCONF/YANG interface is added to an existing PCEP deployment (brownfield scenario).

and of this draft analyze the case where a single RESTCONF/YANG interface is deployed at the MPI (i.e., option 1 above).

Inventory, Service and Network Topology Discovery In this scenario, the MSDC needs to discover through the underlying PNCs:

the network topology, at both optical and IP layers, in terms of nodes and links, including the access links, inter-domain IP links as well as cross-technology Ethernet links;
the optical tunnels supporting multi-technology intra-domain IP links;
both intra-domain and inter-domain L2/L3 VPN network services deployed within the network;
the TE paths supporting those L2/L3 VPN network services;
the hardware inventory information of IP and optical equipment.

The O-PNC and P-PNC could discover and report the hardware network inventory information of their equipment used by the different management layers. In the context of POI, the inventory information of IP and optical equipment can complement the topology views and facilitate the packet/optical multi-layer view, e.g., by providing a mapping between the lowest level LTPs in the topology view and corresponding ports in the network inventory view. The MDSC could also discover the entire network inventory information of both IP and optical equipment and correlate this information with the links reported in the network topology. Reporting the entire inventory and detailed topology information of packet and optical networks to the MDSC may present scalability issues as a potential drawback. The analysis of the scalability of this approach and mechanisms to address potential issues is outside the scope of this document. Each PNC provides the MDSC the topology view of the domain it controls, as described in and . The MDSC uses this information to discover the complete topology view of the multi-layer multi-domain networks it controls. The MDSC should also maintain up-to-date inventory, service and network topology databases of IP and optical layers through IETF notifications through MPI with the PNCs when any network inventory/topology/service change occurs. It should also be possible to correlate information from IP and optical layers (e.g., which port, lambda/OTSi, and direction are used by a specific IP service on the WDM equipment). In particular, for the cross-technology Ethernet links, it is key for MDSC to automatically correlate the information from the PNC network databases about the physical ports from the routers (single link or bundle links for LAG) to client ports in the ROADM. The analysis of multi-layer fault management is outside the scope of this document. However, the discovered information should be sufficient for the MDSC to correlate optical and IP layers alarms to speed-up troubleshooting easily. Alarms and event notifications are required between MDSC and PNCs so that any network changes are reported almost in real-time to the MDSC (e.g., node or link failure). As specified in , MDSC must subscribe to specific objects from PNC YANG datastores for notifications.

Optical Topology Discovery The WSON Topology Model and the Flexi-grid Topology model can be used to report the DWDM network topology (e.g., WDM nodes and OMS links), depending on whether the DWDM optical network is based on fixed-grid or flexible-grid or a mix of fixed-grid and flexible-grid. It is worth noting that, as described in Appendix I of , a fixed-grid can also be described as a flexible grid with constraints: for example a 50GHz fixed-grid can be described as a flexible-grid which supports only m=4 and values of n which are only multiplier of 8. As a consequence:

A flexible-grid DWDM network topology can only be reported using the Flexi-grid Topology model;
A fixed-grid DWDM network topology, can be reported using either the WSON Topology model or the Flexi-grid Topology model;
A mixed fixed and flexible grid DWDM network topology can be reported using either the Flexi-grid Topology model or both WSON and Flexi-grid topology models.

Clarifying how both WSON and Flexi-grid topology models could be used together (e.g., through multi-inheritance as described in ) has been identified as a gap. The OTN Topology Model is used to report the OTN network topology (e.g., OTN switching nodes and links), when the OTN switching layer is deployed within the optical domain. To allow the MDSC to discover the complete multi-layer and multi-domain network topology and to correlate it with the hardware inventory information, the O-PNCs report an abstract optical network topology where:

one TE node is reported for each optical node deployed within the optical network domain; and
one TE link is reported for each OMS link and, optionally, for each OTN link.

Since the MDSC delegates optical path computation to its underlay O-PNCs, the following information can be abstracted and not reported at the MPI:

the optical parameters required for optical path computation, such as those detailed in ;
the underlay OTS links and ILAs of OMS links;
the physical connectivity between the optical transponders and the ROADMs.

The OTN Topology Model also reports the CBR client LTPs that terminates the cross-technology Ethernet links: once CBR client LTP is reported for each CBR or multi-function client interface on the optical nodes (see sections 4.4 and 5.1 of for the description of multi-function client interfaces). The Ethernet Topology Model reports the Ethernet client LTPs that terminate the cross-technology Ethernet links: one Ethernet client LTP is reported for each Ethernet or multi-function client interface on the optical nodes. The optical transponders and, optionally, the OTN access cards, are abstracted at MPI by the O-PNC as Trail Termination Points (TTPs), defined in , within the optical network topology. This abstraction is valid independently of the fact that optical transponders are physically integrated within the same WDM node or are physically located on a device external to the WDM node since it both cases the optical transponders and the WDM node are under the control of the same O-PNC and abstracted as a single WDM TE Node at the O-MPI. The association between the Ethernet or CBR client LTPs terminating the Ethernet cross-technology Ethernet links and the optical TTPs is reported using the Inter Layer Lock-id (ILL) identifiers, defined in . For example, with a reference to , the ILL values X and Y are used to associated the client LTPs (7-0) in NE11 and (8-0) in NE12 with the corresponding optical TTPs (7) in NE11 and (8) in NE12, respectively.

Multi-layer optical topology discovery / / +------O------+ +------O------+ / / | (7-0) | | (8-0) | / / | | | | / / | NE11 | | NE12 | / / +-------------+ +-------------+ / / Ethernet or OTN Topology (O-PNC 1) / +-----------------------------------------------------------+ +----------------------------------------------------------+ / (7) (8) / / --- --- / / +-----\ /-----+ +-----\ /-----+ / / | V | | V | / / | | | | / / | NE11 | | NE12 | / / +-------------+ +-------------+ / / Optical Topology (O-PNC 1) / +----------------------------------------------------------+ Legenda: ======== O LTP --- \ / TTP V < > Inter-Layer Lock-id reported by the PNC ]]> The intra-domain optical links are discovered by O-PNCs, using mechanisms which are outside the scope of this document, and reported at the MPIs within the optical network topology. In case of a multi-layer DWDM/OTN network domain, multi-layer intra-domain OTN links are supported by underlay WDM tunnels: this relationship is reported by the mechanisms described in .

Optical Path Discovery The WDM Tunnel Model is used to report all the WDM tunnels established within the optical network. When the OTN switching layer is deployed within the optical domain, the OTN Tunnel Model is used to report all the OTN tunnels established within the optical network. The Ethernet client signal model and the Transparent CBR client signal model are used to report all the connectivity services provided by the underlay optical tunnels between Ethernet or CBR client LTPs, depending on whether the connectivity service is frame-based or transparent. The underlay optical tunnels can be either WDM tunnels or, when the optional OTN switching layer is deployed, OTN tunnels. The WDM tunnels can be used to support either Ethernet or CBR client signals or multi-layer intra-domain OTN links. In the latter case, the hierarchical-link container, defined in , associates the underlay WDM tunnel with the supported multi-layer intra-domain OTN link and it allows discovery of the multi-layer path supporting all the connectivity services provided by the optical network. The O-PNCs report in their operational datastores all the Ethernet and CBR client connectivities and all the optical tunnels deployed within their optical domain regardless of the mechanisms being used to set them up, such as the mechanisms described in , as well as other mechanism (e.g., static configuration), which are outside the scope of this document.

Packet Topology Discovery The L3 Topology Model is used report the IP network topology. The L3 Topology Model, SR Topology Model, TE Topology Model and the TE Packet Topology Model are used together to report the SR-TE network topology, as described in Figure 2 of . The TE Topology Model, TE Packet Topology Model and MPLS-TE Topology Model are used together to report the MPLS-TE network topology, as described in . As described in , the relationship between the IP network topology and the MPLS-TE network topology depends on whether the two network topologies are congruent or not: in the latter case, the L3 TE Topology Model is used, together with the L3 Topology Model to provide the association between the two network topologies. To allow the MDSC to discover the complete multi-layer and multi-domain network topology and to correlate it with the hardware inventory information as well as to perform multi-domain TE path computation, the P-PNCs report the full packet network, including all the information that the MDSC requires to perform TE path computation. In particular, one TE node is reported for each IP router and one TE link is reported for each intra-domain IP link. The packet topology also reports the IP LTPs terminating the inter-domain IP links. The Ethernet Topology Model is used to report the intra-domain Ethernet links supporting the intra-domain IP links as well as the Ethernet LTPs that might terminate cross-technology Ethernet links, inter-domain Ethernet links or access links, as described in detail in and in . All the intra-domain Ethernet and IP links are discovered by the P-PNCs, using mechanisms, such as LLDP , which are outside the scope of this document, and reported at the MPIs within the Ethernet or the packet network topology.

TE Path Discovery We assume that the discovery of existing TE paths, including their bandwidth, at the MPI is done using the generic TE tunnel YANG data model, defined in , with packet technology-specific (e.g., MPLS-TE or SR-TE) augmentations. Note that technology-specific augmentations of the generic path TE tunnel model for SR-TE path setup and discovery is outlined in section 1 of but are currently identified as a gap in . To enable MDSC to discover the full end-to-end TE path configuration, the technology-specific augmentation of the should allow the P-PNC to report the TE path within its domain (e.g., the SID list assigned to an SR-TE path). For example, considering the L3VPN in , the TE path 1 in one direction (PE13-P16-PE14) and the TE path in the reverse direction (between PE14 and PE13) should be reported by the P-PNC1 to the MDSC as TE primary and primary-reverse paths of the same TE tunnel instance. The bandwidth of these TE paths represents the bandwidth allocated by P-PNC1 to the two TE paths, which can be symmetric or asymmetric in the two directions. The P-PNCs use the TE tunnel model to report, at the MPI, all the TE paths established within their packet domain regardless of the mechanism being used to set them up; i.e., independently on whether the mechanisms described in or other means, such as static configuration, which are outside the scope of this document, are used.

Inter-domain Link Discovery In the reference network of , there are three types of inter-domain links:

Inter-domain Ethernet links supporting inter-domain IP links between two adjacent IP domains;
Cross-technology Ethernet links between an an IP domain and an adjacent optical domain;
Access links between a CE device and a PE router.

All the three types of links are Ethernet links. It is worth noting that the P-PNC may not be aware whether an Ethernet interface terminates a cross-technology Ethernet link, an inter-domain Ethernet link or an access link. The TE Topology Model supports the discovery for all these types of links with no need for the P-PNC to know the type of inter-domain link. There are two possible models to report the access links between CEs and PEs: the TE Topology Model, defined in , or the Service Attachment Points (SAP) Model, defined in . Although the discovery of access links is outside the scope of this document, clarifying the relationship between these two models has been identified as a gap. The inter-domain Ethernet links and cross-technology Ethernet links are discovered by the MDSC using the plug-id attribute, as described in section 4.3 of . More detailed description of how the plug-id can be used to discover inter-domain links is also provided in section 5.1.4 of . The plug-id attribute can also be used to discover the access-links, but the analysis of the access-link discovery is outside the scope of this document. This document considers the following two options for discovering inter-domain links:

Static configuration
LLDP automatic discovery

Other options are possible but not described in this document. As outlined in , the encoding of the plug-id namespace and the specific LLDP information reported within the plug-id value, such as the Chassis ID and Port ID mandatory TLVs, is implementation specific and needs to be consistent across all the PNCs within the network. The static configuration requires an administrative burden to configure network-wide unique identifiers: it is therefore more viable for inter-domain Ethernet links. For the cross-technology Ethernet links, the automatic discovery solution based on LLDP snooping is preferable when possible. The routers exchange standard LLDP packets as defined in and the optical nodes snoop the LLDP packets received from the local Ethernet interface and report to the O-PNCs the extracted information, such as the Chassis ID, the Port ID, System Name TLVs. Note that the optical nodes do not actively participate in the LLDP packet exchange and does not send any LLDP packets.

Cross-technology Ethernet link Discovery The MDSC can discover a cross-technology Ethernet link by matching the plug-id values of the two LTPs reported by two adjacent O-PNC and P-PNC: in case LLDP snooping is used, the P-PNC reports the LLDP information sent by the corresponding Ethernet interface on the IP router while the O-PNC reports the LLDP information received by the corresponding Ethernet interface on the optical node, e.g., between LTP 5-0 on PE13 and LTP 7-0 on NE11, as shown in .

Cross-technology Ethernet link discovery Link discovered by the MDSC { } LTP Plug-id reported by the PNC ]]> As described in , the LTP terminating a cross-technology Ethernet link is reported by an O-PNC in the Ethernet topology or in the OTN topology model or in both models, depending on the type of corresponding physical port on the optical node. It is worth noting that the discovery of cross-technology Ethernet links is based only on the LLDP information sent by the Ethernet interfaces of the routers and snooped by the Ethernet interfaces of the optical nodes. Therefore the MDSC can discover these links also before optical paths, supporting overlay multi-technology IP links, are setup.

Inter-domain IP Link Discovery The MDSC can discover an inter-domain Ethernet link which supports an inter-domain IP link, by matching the plug-id values of the two Ethernet LTPs reported by the two adjacent P-PNCs: the two P-PNCs report the LLDP information being sent and being received from the corresponding Ethernet interfaces, e.g., between the Ethernet LTP 3-1 on BR11 and the Ethernet LTP 4-1 on BR21 shown in .

Inter-domain Ethernet and IP link discovery O(4-2) | / / | |\ / / /| | / / +-------------+| / / |+-------------+ / / | / / | / +------------------------|-+ +-------------------------+ | | Supporting LTP | | Supporting LTP | | | | +--------------|----------+ +|------------------------+ / V / / V / / +-------------+/ / / \+-------------+ / / | {1}(3-1)O<................>O(4-1){1} | / / | |\ / / /| | / / | BR11 |V(*) / / (*)V| BR21 | / / | |/ / / \| | / / | {2}(3-0)O<~~~~~~~~~~~~~~~~>O(4-0){3} | / / +-------------+ / / +-------------+ / / Eth. Topology (P-PNC 1) / / Eth. Topology (P-PNC 2) / +-------------------------+ +-------------------------+ Notes: ===== (*) Supporting LTP {1} {BR11,3,BR21,4} {2} {BR11,3} {3} {BR21,4} Legenda: ======== O LTP ----> Supporting LTP <...> Link discovered by the MDSC <~~~> Link inferred by the MDSC { } LTP Plug-id reported by the PNC ]]> Different information is required to be encoded by the P-PNC within the plug-id attribute of the Ethernet LTPs to discover cross-technology Ethernet links and inter-domain Ethernet links. If the P-PNC does not know a priori whether an Ethernet interface on an IP router terminates a cross-technology Ethernet link or an inter-domain Ethernet link, it has to report at the MPI two Ethernet LTPs representing the same Ethernet interface, e.g., both the Ethernet LTP 3-0 and the Ethernet LTP 3-1, supported by LTP 3-0, shown in :

The physical Ethernet LTP (e.g., LTP 3-0 in BR11, as shown in ) is used to represent the physical adjacency between the Ethernet interface on an IP router and the Ethernet interface on its physically adjacent node, which can be either an IP router (in case of a single-technology Ethernet link) or an optical node (in case of a multi-technology Ethernet link). Therefore, as described in , the P-PNC reports, within the plug-id attribute of this LTP, the LLDP information sent by the corresponding Ethernet interface on the IP router; such as the {BR11,3} and {BR21,4} plug-id values reported, respectively, by the Ethernet LTP 3-0 on BR11 and by the Ethernet LTP 4-0 on BR21, as shown in ;
The logical Ethernet LTP (e.g., LTP 3-1 in BR11, as shown in ), supported by a physical Ethernet LTP (e.g., LTP 3-0 in BR11, as shown in ), is used to discover the logical adjacency between the Ethernet interfaces on IP routers, which can be either single-technology or multi-technology. Therefore, the P-PNC reports, within the plug-id attribute of this LTP, the LLDP information sent and received by the corresponding Ethernet interface on the IP router; such as the {BR11,3,BR21,4} plug-id values reported by the Ethernet LTP 3-1 on BR11 and by the Ethernet LTP 4-1 on BR21, as shown in .

It is worth noting that in case of an inter-domain Ethernet links, the MDSC cannot discover, using the LLDP information reported in the plug-id attributes, the physical adjacency between the two Ethernet interfaces on physically adjacent IP routers, because these two plug-id values do not match, such as the plug-id values {BR11,3} and {BR21,4} shown in . However, the MDSC may infer the physical intra-domain Ethernet links if it knows a priori, using mechanisms which are outside the scope of this document, that the Ethernet interfaces on the IP routers either terminates a cross-technology link or a single-technology (intra-domain or inter-domain) Ethernet link, e.g., as shown in . The P-PNC can omit reporting the physical Ethernet LTPs when it knows, by mechanisms which are outside the scope of this document, that the corresponding Ethernet interfaces terminate inter-domain Ethernet links. The MDSC can then discover an inter-domain IP link between the two IP LTPs that are supported by the two Ethernet LTPs terminating an inter-domain Ethernet link, discovered as described in , e.g., between the IP LTP 3-2 on BR21 and the IP LTP 4-2 on BR22, supported respectively by the Ethernet LTP 3-1 on BR11 and by the Ethernet LTP 4-1 on BR21, as shown in .

Multi-technology IP Link Discovery A multi-technology intra-domain IP link and its supporting multi-technology intra-domain Ethernet link are discovered by the P-PNC like any other intra-domain IP and Ethernet links, as described in , and reported at the MPI within the packet and the Ethernet network topologies, e.g., as shown in .

Multi-technology intra-domain Ethernet and IP link discovery O(6-2) | / / | | | | | / / +---------+ | +---------+ / / | / +-----------------------------------|-----------------------+ | | Supporting Link | +---------------------------|-------------------------------+ / Ethernet Topology (P-PNC 1)| / / +-------------+ | +-------------+ / / | PE13 | V | BR11 | / / | (5-1)O<==============>O(6-1) | / / | (5-0) |\ /| (6-0) | / / +------O------+|(*) (*)|+------O------+ / / ^ \<----+ +----->/^ / +-----------------:------------------------------:----------+ : : : : : : +---------:------------------------------:------------------+ / : Ethernet or OTN Topology : / / V (O-PNC 1) V / / +------O------+ ETH/CBR +------O------+ / / | (7-0) | client sig. | (8-0) | / / | X----------+-------------------X | / / | NE11 | | | NE12 | / / +-------------+ | +-------------+ / +----------------------------|------------------------------+ | Underlay | tunnel | +----------------------------------------------------------+ / (7) | (8) / / --- | --- / / +-----\ /-----+ v +-----\ /-----+ / / | V | | V | / / | X======|================|======X | / / | NE11 | Opt. Tunnel | NE12 | / / +-------------+ +-------------+ / / Optical Topology (O-PNC 1) / +----------------------------------------------------------+ Notes: ===== (*) Supporting LTP Legenda: ======== O LTP --- \ / TTP V ----> Supporting LTP or Supporting Link or Underlay tunnel <===> Link discovered by the PNC and reported at the MPI <...> Link discovered by the MDSC x---x Ethernet/CBR client signal X===X Optical tunnel ]]> The P-PNC does not report any plug-id information on the logical Ethernet LTPs terminating intra-domain Ethernet links, such as the LTP 5-1 on PE13 and LTP 6-1 in BR11 shown in , since these links are discovered by the PNC. In addition, the P-PNC also reports the physical Ethernet LTPs that terminate the cross-technology Ethernet links supporting the multi-technology intra-domain Ethernet links, e.g., the Ethernet LTP 5-0 on PE13 and the Ethernet LTP 6-0 on BR11, shown in . The MDSC discovers, using the mechanisms described in , which cross-technology Ethernet links support the multi-technology intra-domain Ethernet links, e.g., the link between LTP 5-0 on PE13 and LTP 7-0 on NE11, shown in . The MDSC also discovers, from the information provided by the O-PNC and described in , which optical tunnels support the multi-technology intra-domain IP links and therefore the path within the optical network that supports a multi-technology intra-domain IP link, e.g., as shown in .

Intra-domain single-technology IP Links It is worth noting that the P-PNC may not be aware of whether an Ethernet interface on the IP router terminates a multi-technology or a single-technology intra-domain Ethernet link. In this case, the P-PNC, always reports two Ethernet LTPs for each Ethernet interface on the IP router, e.g., the Ethernet LTP 1-0 and 1-1 on PE13, shown in .

Single-technology intra-domain Ethernet and IP link discovery O(2-2) | / / | | | | | / / +---------+ | +---------+ / / | / +---------------------------------|-------------------------+ | | Supporting Link | | +-----------------------|---------------------------------+ / | / / +---------+ v +---------+ / / | (1-1)O<======================>O(2-1) | / / | |\ /| | / / | PE13 |V(*) (*)V| P16 | / / | |/ \| | / / | {1}(1-0)O<~~~~~~~~~~~~~~~~~~~~~~>O(2-0){2} | / / +---------+ +---------+ / / Ethernet Topology (P-PNC 1) / +---------------------------------------------------------+ Notes: ===== (*) Supporting LTP {1} {PE13,1} {2} {P16,2} Legenda: ======== O LTP ----> Supporting LTP <===> Link discovered by the PNC and reported at the MPI <~~~> Link inferred by the MDSC { } LTP Plug-id reported by the PNC ]]> It is worth noting that in case of an intra-domain single-technology Ethernet links, the MDSC cannot discover, using the LLDP information reported in the plug-id attributes, the physical adjacency between the two Ethernet interfaces on physically adjacent IP routers, because the two plug-id values do not match, such as the plug-id values {PE13,1} and {P16,2} shown in . However, the MDSC may infer the physical intra-domain Ethernet links, e.g., between LTP 1-0 on PE13 and LTP 2-0 on P16, as shown in , if it knows a priori, using mechanisms which are outside the scope of this document, that all the Ethernet interfaces on the IP routers either terminates a cross-technology or a single-technology (intra-domain or inter-domain) Ethernet link, e.g., as shown in . The P-PNC can omit reporting the physical Ethernet LTP if it knows, by mechanisms which are outside the scope of this document, that the intra-domain Ethernet link is single-technology.

LAG Discovery The P-PNCs can discover the configuration of the LAG groups within its domain and report each intra-domain LAG as an Ethernet bundle link, within the Ethernet topology exposed at the MPI. This is done bundling multiple single-domain Ethernet links, as shown in . For example, the Ethernet bundled link between the Ethernet LTP 5-1 on BR21 and the Ethernet LTP 6-1 on P24, is built from the Ethernet links setup respectively:

between the Ethernet LTP 1-1 on BR21 and the Ethernet LTP 2-1 on P24; and
between the Ethernet LTP 3-1 on BR21 and the Ethernet LTP 4-1 on P24.

LAG O(6-2) | / / | | | | | / / +---------+ | +---------+ / / | / +---------------------------------|-------------------------+ | | Supporting Link | | +-----------------------|---------------------------------+ / | / / +---------+ v +---------+ / / | (5-1)O<======================>O(6-1) | / / | BR21 | Bundled Link | P24 | / / | | | | / / | (3-1)O<======================>O(4-1) | / / | (1-1)O<======================>O(2-1) | / / +---------+ +---------+ / / Ethernet Topology (P-PNC 2) / +---------------------------------------------------------+ Legenda: ======== O LTP <===> Link discovered by the PNC and reported at the MPI ]]> The mechanisms used by the MDSC to discover single-technology and multi-technology intra-domain LAG link is the same (the only difference being whether the bundled links are single-technology or multi-technology). Instead, the mechanisms used by the MDSC to discover single-technology inter-domain LAG links between two BRs are different and outside the scope of this document since they do not imply any cross-technology coordination between packet and optical domains. As described in , the mechanisms used by the P-PNC to discover the configuration of the LAG groups within its domain, such as LLDP , are outside the scope of this document. However, it is worth noting that according to , LLDP can be configured on a LAG group (Aggregated Port) and/or on any number of its LAG members (Aggregation Ports). If LLDP is enabled on both LAG members and groups, two types of LLDP packets are transmitted by the routers and received by the optical nodes on some cross-technology Ethernet links: one sent for the LLDP session configured at LAG member (Aggregation Port)level and another one for the LLDP session configured at LAG group (Aggregated Port)level. This could cause some issues when LLDP snooping is used to discover the cross-technology Ethernet links, as defined in . The cross-technology Ethernet link discovery is based only on the LLDP session configured on the LAG members (Aggregation Ports) to allow discovery of these links independently from the configuration of the underlay optical tunnel or from the LAG group. To avoid any ambiguity on how the optical nodes can identify which LLDP packets belong to which LLDP session, the P-PNC can disable the LLDP sessions on the LAG groups configured by the MDSC (e.g., the multi-technology single-domain LAG groups configured using the mechanisms described in ), keeping the LLDP sessions on the LAG members enabled. Another option is to rely on other mechanisms (e.g., the Port type field in the Link Aggregation TLV defined in Annex F of ) that allow the optical node to identify which LLDP packets belong to which LLDP session: the O-PNC can then use only the LLDP information from the LLDP sessions configured on the LAG members to support the cross-technology Ethernet link discovery mechanisms defined in .

L2/L3 VPN Network Services Discovery The P-PNC reports the L2/L3 VPN services configured within its domain, using the L2NM and L3NM network service models, and which packet TE tunnels (e.g., MPLS-TE or SR-TE) are used by each L2/L3 VPN service, using the L2NM and L3NM TE service mapping models. The MDSC can use the information mentioned above together with the packet TE path, packet topology, multi-technology IP links, optical topology and optical path information discovered as described in the previous sections, to discover the multi-technology path used to carry the traffic for each L2/L3 VPN service.

Inventory Discovery The are no YANG data models in IETF that could be used to report at the MPI the whole inventory information discovered by a PNC. had foreseen some work for inventory as an augmentation of the network model, but no YANG data model has been developed so far. There are also no YANG data models in IETF that could be used to correlate topology information, e.g., a link termination point (LTP), with inventory information, e.g., the physical port supporting an LTP, if any. Inventory information through MPI and correlation with topology information is identified as a gap requiring further work and outside of the scope of this draft.

Establishment of L2/L3 VPN Services with TE Requirements In this scenario the MDSC needs to setup a multi-domain L2VPN or a multi-domain L3VPN with some SLA requirements. The MDSC receives the request to setup a L2/L3 VPN network service from the OSS/Orchestration layer (see ). The MDSC translates the L2/L3 VPN SLA requirements into TE requirements (e.g., bandwidth, TE metric bounds, SRLG disjointness, nodes/links/domains inclusion/exclusion) and find the TE paths that meet these TE requirements (see ). For example, considering the L3VPN in and , the MDSC finds that:

PE13-P16-PE14 TE path already exists but have not enough bandwidth to support the new L3VPN, as described in ;, and that:
- the IP link(s) between PE13 and P16 has not enough bandwidth to support increasing the bandwidth of that TE path, as described in ;
- a new underlay optical tunnel could be setup to increase the bandwidth of the IP link(s) between PE13 and P16 to support increasing the bandwidth of that overlay TE path, as described in . The dimensioning of the underlay optical tunnel is decided by the MDSC based on the TE requirements (e.g., the bandwidth) requested by the TE path and on its multi-layer optimization policy, which is an internal MDSC implementation issue;
- a new multi-domain TE path needs to be setup between PE13 and PE23, e.g., either because existing TE paths between PE13 and PE23 are not able to meet the TE and binding requirements of the L2/L3 VPN service or because there is no TE path between PE13 and PE23.

As described in , with partial summarization, the MDSC will use the TE topology information provided by the P-PNCs and the results of the path computation requests sent to the O-PNCs, as described in , to compute the multi-layer/multi-domain path between PE13 and PE23. For example, the multi-layer/multi-domain performed by the MDSC could require the setup of:

a new underlay optical tunnel between PE13 and BR11, supporting a new IP link, as described in ;
a new underlay optical tunnel between BR21 and P24 to increase the bandwidth of the IP link(s) between BR21 and P24, as described in .

When the setup of the L2/L3 VPN network service requires multi-domain and multi-layer coordination, the MDSC is also responsible for coordinating the network configuration required to realize the request network service across the appropriate optical and packet domains. The MDSC would therefore request:

the O-PNC1 to setup a new optical tunnel between the ROADMs connected to PE13 and P16, as described in ;
the P-PNC1 to update the configuration of the existing IP link, in case of LAG, or configure a new IP link, in case of Equal Cost Multi-Path (ECMP), between PE13 and P16, as described in ;
the P-PNC1 to update the bandwidth of the selected TE path between PE13 and PE14, as described in .

After that, the MDSC requests P-PNC2 to setup a TE path between BR21 and PE23, with an explicit path (BR21, P24, PE23) to constrain this new TE path to use the new underlay optical tunnel setup between BR21 and P24, as described in . The P-PNC2 properly configures the routers within its domain to setup the requested path and returns to the MDSC the information which is needed for multi-domain TE path stitching. For example, in case of inter-domain SR-TE, the P-PNC2, knowing the node and the adjacency SIDs assigned within its domain, can install the proper SR policy, or hierarchical policies, within BR21 and returns to the MDSC the binding SID it has assigned to this policy in BR21. Then the MDSC requests P-PNC1 to setup a TE path between PE13 and BR11, with an explicit path (PE13, BR11) to constrain this new TE path to use the new underlay optical tunnel setup between PE13 and BR11, specifying also which inter-domain link should be used to send traffic to BR21 and the information to be used for the multi-domain TE path stitching, as described in (e.g., in case of inter-domain SR-TE, the binding SID that has been assigned by P-PNC2 to the corresponding SR policy in BR21). The P-PNC1 properly configures the routers within its domain to setup the requested path and the multi-domain TE path stitching. For example, in case of inter-domain SR-TE, the P-PNC1, knowing also the node and the adjacency SIDs assigned within its domain and the EPE SID assigned by P-PNC1 to the inter-domain link between BR11 and BR21, and the binding SID assigned by P-PNC2, installs the proper policy, or policies, within PE13. Once the TE paths have been selected and, if needed, setup/modified, the MDSC can request to both P-PNCs to configure the L3VPN and its binding with the selected TE paths, as described in .

Optical Path Computation As described in , the optical path computation is usually performed by the O-PNCs. When performing multi-layer/multi-domain path computation, the MDSC can delegate the O-PNC for single-domain optical path computation. As described in , and , there is a one-to-one relationship between a multi-layer intra-domain IP link and its underlay optical tunnel. Therefore, the properties of an optical path between two optical TTPs, as computed by the O-PNC, can be used by the MDSC to infer the properties of the associated multi-layer single-domain IP link. As discussed in , there are two options to request an O-PNC to perform optical path computation: either via a "compute-only" TE tunnel path, using the generic TE tunnel YANG data model defined in or via the path computation RPC defined in . This draft assumes that the path computation RPC is used. There are no YANG data models in IETF that could be used to augment the generic path computation RPC with technology-specific attributes. Optical technology-specific augmentation for the path computation RPC is identified as a gap requiring further work outside of this draft's scope.

Multi-technology IP Link Setup As described in , there is a one-to-one relationship between a multi-technology intra-domain IP link and its underlay optical tunnel. Therefore, to setup a new multi-technology intra-domain IP link, the MDSC requires the O-PNC to setup the optical tunnel (using either the WDM Tunnel model or the OTN Tunnel model, if the optional OTN switching is supported) within the optical network and to steer the client traffic between the two cross-technology Ethernet links over that optical tunnel, using either the Ethernet Client Signal Model (for frame-based transport) or the Transparent CBR Client Signal Model (for transparent transport). For example, with a reference to , the MDSC can request the O-PNC1 to setup an optical tunnel between the optical TTPs (7) on NE11 and (8) on NE12 and to steer over this tunnel the client traffic between LTP (7-0) on NE11 and LTP (8-0) on NE12.

Multi-technology IP link setup O(6-2) | / / | | | | | / / +---------+ | +---------+ / / | / +-----------------------------------|-----------------------+ | | Supporting Link | +---------------------------|-------------------------------+ / Ethernet Topology (P-PNC 1)| / / +-------------+ | +-------------+ / / | PE13 | V | BR11 | / / | (5-1)O<==============>O(6-1) | / / | (5-0) |\ /| (6-0) | / / +------O------+|(*) (*)|+------O------+ / / ^ \<----+ +----->/^ / +-----------------:------------------------------:----------+ : : : : : : +---------:------------------------------:------------------+ / : Ethernet or OTN Topology : / / V (O-PNC 1) V / / +------O------+ ETH/CBR +------O------+ / / | (7-0) | client sig. | (8-0) | / / | X----------+-------------------X | / / | NE11 | | | NE12 | / / +-------------+ | +-------------+ / +----------------------------|------------------------------+ | Underlay | tunnel | +----------------------------------------------------------+ / (7) | (8) / / --- | --- / / +-----\ /-----+ v +-----\ /-----+ / / | V | | V | / / | X======|================|======X | / / | NE11 | Opt. Tunnel | NE12 | / / +-------------+ +-------------+ / / Optical Topology (O-PNC 1) / +----------------------------------------------------------+ Notes: ===== (*) Supporting LTP Legenda: ======== O LTP --- \ / TTP V ----> Supporting LTP or Supporting Link or Underlay tunnel <===> Link discovered by the PNC and reported at the MPI <...> Link discovered by the MDSC x---x Ethernet/CBR client signal X===X Optical tunnel ]]> Note: is an exact copy of . After the optical tunnel has been setup and the client traffic steering configured, the two IP routers can exchange Ethernet frames between themselves, including LLDP messages. If LLDP or any other discovery mechanisms, which are outside the scope of this document, is used between the adjacency between the two IP routers' ports, the P-PNC can automatically discover the underlay multi-technology single-domain Ethernet link being set up by the MDSC and report it to the P-PNC, as described in . Otherwise, if there are no automatic discovery mechanisms, the MDSC can configure this multi-technology single-domain Ethernet link at the MPI of the P-PNC. The two Ethernet LTPs terminating this multi-technology single-domain Ethernet link are supported by the two underlay Ethernet LTPs terminating the two cross-technology Ethernet links, e.g., the LTP 5-1 on PE13 and 6-1 on BR11 shown in . After the multi-technology single-domain Ethernet link has been configured by the MDSC or discovered by the P-PNC, the corresponding multi-technology single-domain IP link can also be configured either by the MDSC or by the P-PNC. This document assumes that this IP link is configured by the P-PNC. It is worth noting that if LAG is not supported within the domain controlled by the P-PNC, the P-PNC can configure the multi-technology single-domain IP link as soon as the underlay multi-technology single-domain Ethernet link is either discovered by the P-PNC or configured by the MDSC at the MPI. However, if LAG is supported the P-PNC has not enough information to know whether the discovered/configured multi-technology single-domain Ethernet link would be:

Used to support a multi-technology single-domain IP link;
Used to create a new LAG group;
Added to an existing LAG group.

Therefore the P-PNC does not take any further action after a multi-technology single-domain Ethernet link is discovered or configured by the MDSC at the MPI. The MDSC can request the P-PNC to configure a new multi-technology single-domain IP link, supported by the the just discovered or configured multi-technology single-domain Ethernet link, by creating an IP link within the running datastore of the P-PNC MPI. Only the IP link, IP LTPs and the reference to the supporting multi-technology single-domain Ethernet link are configured by the MDSC. All the other configuration is provided by the P-PNC. For example, with a reference to , the MDSC can request the P-PNC1 to setup a multi-technology single-domain IP Link between IP LTP 5-2 on PE13 and IP LTP 6-2 on BR11 supported by the multi-technology single-domain Ethernet link between ETH LTP 5-1 on PE13 and ETH LTP 6-1 on BR11. The P-PNC configures the requested multi-technology single-domain IP link and, once finished, reports it to the MDSC within the IP topology exposed at its MPI.

Multi-technology LAG Setup The P-PNC configures a new LAG group between two routers when the MDSC creates at the MPI a new Ethernet bundled link (using the bundled-link container defined in ) bundling the multi-technology single-domain Ethernet link(s) being created, as described above. When a new LAG link is created, it is also recommended to configure the minimum number of active member links required to consider the LAG link as being up. For example, a LAG link with three members can be considered up when only one member link fails and down when at least two member links fail. The attribute required to configure the minimum number of active member links is missing in and this is identified as a gap in . It is worth noting that a new LAG group can be created to bundle one or more multi-technology single-domain Ethernet link(s). For example, with a reference to , the MDSC can request the P-PNC2 to setup an Ethernet bundled link between the Ethernet LTP 5-1 on BR21 and the Ethernet LTP 6-1 on P24, bundling the multi-technology single-domain Ethernet link between the Ethernet LTP 1-1 on BR21 and the Ethernet LTP 2-1 on P24. It is worth noting that the MDSC needs to create also the Ethernet LTPs terminating the Ethernet bundled link. The MDSC can request the P-PNC to configure a new multi-technology single-domain IP link, supported by the the just configured Ethernet bundled link, following the same procedure described in above. For example, with a reference to , the MDSC can request the P-PNC2 to setup a multi-technology single-domain IP Link between IP LTP 5-2 on BR21 and IP LTP 6-2 on P24 supported by the Ethernet bundle link between ETH LTP 5-1 on BR21 and the Ethernet LTP 6-1 on P24.

Multi-technology LAG Update The P-PNC adds new member(s) to an existing LAG group when the MDSC updates at the MPI the configuration of an existing Ethernet bundled link adding the multi-technology single-domain Ethernet link(s) being created, as described above. When member links are added or removed from a LAG link, the minimum number of active member links required to consider the LAG link as being up may also need to be updated. For example, with a reference to , the MDSC can request the P-PNC2 to add the multi-technology single-domain Ethernet link setup between the Ethernet LTP 3-1 on BR21 and the Ethernet LTP 4-1 on P24 to the existing Ethernet bundle link setup between the Ethernet LTP 5-1 on node BR21 and the Ethernet LTP 6-1 on node P24. After the LAG configuration has been updated, the P-PNC can also update the bandwidth information of the multi-technology single-domain IP link supported by the updated Ethernet bundled link.

Multi-technology TE path properties Configuration The MDSC can discover the TE path properties (e.g., the list of SRLGs, the delay) of a multi-technology IP link from the TE properties of:

the IP LTPs terminating the multi-technology IP link (e.g., the list of SRLGs reported by the P-PNC using the packet TE topology model);
the optical path (e.g., the list of SRLGs reported by the O-PNC using the WDM or OTN tunnel model); and
the cross-domain links (e.g., the list of SRLGs reported by the O-PNC and P-PNC respectively, using the WSON and/or flexi-grid, the OTN and the packet TE topology models).

The MDSC can also report this information to the P-PNC by properly configuring the multi-technology IP link properties using the packet TE topology model at the packet PNC MPI. This information is used by the P-PNC at least when computing the local protection path, as described in , e.g., to ensure that the local protection path is SRLG disjoint with the primary path. It is worth noting that the list of SRLGs for a multi-technology IP link can be quite long. Implementation-specific mechanisms can be implemented by the MDSC or by the O-PNC to summarize the SRLGs of an optical tunnel. These mechanisms are implementation-specific and have no impact on the YANG models nor on the interoperability at the MPI, but cares have to be taken to avoid missing information.

TE Path Setup and Update This version of the draft assumes that TE path setup and update at the MPI could be done using the generic TE tunnel YANG data model, defined in , with packet technology-specific augmentations, described in . When a new TE path needs to be setup, the MDSC can use the model to request the P-PNC to set it up, properly specifying the path constraints, such as the explicit path, to force the P-PNC to setup an TE path that meets the end-to-end TE and binding constraints and uses the optical tunnels setup by the MDSC for the purpose of supporting this new TE path. The model supports requesting the setup of both end-to-end as well as segment TE tunnels (within one domain). In the latter case, the technology-specific augmentations should allow the configuration of the information needed for multi-domain TE path stitching. For example, the SR-TE specific augmentations of the model should be defined to allow the MDSC to configure the binding SIDs to be used for the multi-domain SR-TE path stitching and to allow the P-PNC to report the binding SID assigned to the segment TE paths. Note that the assigned binding SID should be persistent in case IP router or P-PNC rebooting. The MDSC can also use the model to request the P-PNC to increase the bandwidth allocated to an existing TE path, and, if needed, also on its reverse TE path. The model supports both symmetric and asymmetric bandwidth configuration in the two directions. [Editor's Note:] Add some text about the protection options (to further discuss whether to put this text here or in ). The MDSC also request the P-PNC to configure local protection mechanisms. For example, the FRR local protection, as defined in in case of MPLS-TE domain or the TI-LFA local protection, as defined in in case of SR-TE domain. The mechanisms to request the configuration TI-LFA local protection for SR-TE paths using the are a gap in the current YANG models. The requested local protection mechanisms within the P-PNC domain are configured by the P-PNC through implementation specific mechanisms which are outside the scope of this document. The P-PNC takes into account the multi-layer TE path properties (e.g., SRLG information), configured by the MDSC as described in , when computing the protection configuration (e.g., in case of SR-TE domains, the TI-LFA post-convergence path or, in case of MPLS-TE domain, the FRR backup tunnel) for multi-technology single-domain IP links. SR-TE path setup and update (e.g., bandwidth increase) through MPI is identified as a gap requiring further work, which is outside of the scope of this draft.

L2/L3 VPN Network Service Setup The MDSC can use the L2NM and L3NM network service models to request the P-PNCs to setup L2/L3 VPN services and the L2NM and L3NM TE service mapping models to request the P-PNCs to configure the PE routers to steer the L2/L3 VPN traffic to the selected TE tunnels (e.g., MPLS-TE or SR-TE). It is worth noting that the L2NM and L3NM TE service mapping models, defined in , provide a list of TE tunnel(s) that should be used to forward L2/L3 VPN traffic between the two PEs terminating the listed TE tunnel(s). If the list contains more than one TE tunnel for the same pair of PEs, these TE tunnels are used for load balancing the associated L2/L3 VPN traffic between the same set of two PEs. The possibility to request splitting the traffic, between multiple TE tunnels for the same PEs pair, in a different way than load balancing is identified as a gap requiring further work and outside of the scope of this draft.

Conclusions The analysis provided in this document has shown that the IETF YANG models described in 3.2 provides useful support for Packet Optical Integration (POI) scenarios for resource discovery (network topology, service, tunnels and network inventory discovery) as well as for supporting multi-layer/multi-domain L2/L3 VPN network services. Few gaps have been identified to be addressed by the relevant IETF Working Groups:

how both WSON and Flexi-grid topology models could be used together (through multi-inheritance): this gap has been identified in ;.
network inventory model: this gap has been identified in and the solution in has been proposed to resolve it;
technology-specific augmentations of the path computation RPC, defined in for optical networks: this gap has been identified in and the solution in has been proposed to resolve it;
relationship between a common discovery mechanisms applicable to access links, inter-domain IP links and cross-technology Ethernet links and the UNI topology discover mechanism defined in : this gap has been identified in ;
a mechanism applicable to the P-PNC NBI to configure the SR-TE paths. Technology-specific augmentations of TE Tunnel model, defined in , are foreseen in section 1 of but not yet defined: this gap has been identified in ;
an attribute, which is used to configure the minimum number of active member links required to consider the LAG link as being up, is missing from the topology model defined in : this gap has been identified in ;
a mechanism to configure splitting the L2/L3 VPN traffic, between multiple TE tunnels for the same PEs pair, in a different way than load balancing: this gap has been identified in ;
a mechanism to report client connectivity constraints imposed by some muxponder design: this gap has been identified in .

Although not applicable to this document, it has been noted that being able to use WSON and Flexi-grid topology models together (through multi-inheritance) is not only useful in cases of mixed fixed-grid and flexible-grid DWDM network topology but also the only viable option in case of a mixed CWDM and DWDM network topology. Although not applicable to this document, it has been noted that the WDM tunnel model would support also optical tunnel setup in case of a mixed CWDM and DWDM network topology. Although not analysed in this document, it has been noted that the TE Tunnel model, defined in , needs also to be enhanced to support scenarios where multiple parallel TE paths are used in load-balancing to carry the traffic between two end-points (e.g., VPN traffic between two PEs).

Security Considerations This document highlights how the ACTN architecture can deploy packet over optical infrastructure services. It highlights how existing IETF protocols and data models may be used for multi-layer services. It reuses several existing IETF protocols and data models for the MPI interfaces between each PNC (Optical or Packet) and the MDSC, including:

RESTCONF
NETCONF
PCEP
YANG

Several existing authentication and encryption practices and techniques may be used to help secure these MPI interfaces. These mechanisms include using Transport Layer Security (TLS) to provide secure transport for RESTCONF, NETCONF and PCEP. Furthermore, access control techniques can also provide additional security. NETCONF supports an Access Control Model (NACM), and RESCONF supports Role Based Access Control (RBAC), which should also ensure that MDSC to PNC communication is based on authorised use and granular control of connectivity and resource requests.

LLDP Snooping Security Considerations Earlier in the document, LLDP is discussed as a mechanism for the PNCs to discover the intra-domain Ethernet and IP links. While LLDP provides valuable information for network management and troubleshooting, it also presents several security issues:

Eavesdropping: LLDP transmissions are not encrypted. Potentially, LLDP packets could be captured using a packet sniffer. An attacker can leverage this information to gain insights into the network topology, device types, and configurations, which could be used for further attacks;
Unauthorized Access: Information disclosed by LLDP can include device types, software versions, and network configuration details. This might help an attacker identify vulnerable devices or configurations that can be exploited to gain unauthorized access or escalate privileges within the network;
Data Manipulation: If an attacker gains access to a network device, they could manipulate LLDP information to advertise false device information, leading to potential misconfigurations or trust relationships being exploited. This can disrupt network operations or redirect traffic to malicious devices;
Denial of Service (DoS): By flooding the network with fake LLDP packets, an attacker could overwhelm network devices or management systems, potentially leading to a denial of service where legitimate network traffic is disrupted;
Spoofing: An attacker could spoof LLDP packets to impersonate other network devices. Potentially, this might lead to incorrect network mappings or trust relationships being established with malicious devices;
Lack of Authentication: LLDP does not include mechanisms for authenticating the source of LLDP messages, which means that devices accept LLDP information from any source as legitimate.

To mitigate these security issues, network administrators might implement several security measures, including:

Disabling LLDP on ports where it is not needed, especially those facing untrusted networks;
Using network segmentation and Access Control Lists (ACLs) to limit who can send and receive LLDP packets;
Employing network monitoring and anomaly detection systems to identify unusual LLDP traffic patterns that may indicate an attack;
Regularly updating and patching network devices to address known vulnerabilities that could be exploited through information gathered via LLDP.

Operational Considerations This document has identified the need and enabling components for automating the management and control of multi-layer Service Providers' transport networks, combining the optical and microwave transport layer with the packet (IP/MPLS) layer to create a more efficient and scalable network infrastructure. This approach is particularly beneficial for Service Providers and large enterprises dealing with high bandwidth demands and looking for cost-effective ways to expand their networks. However, integrating these two traditionally separate network layers involves several operational considerations:

Network Design and Capacity Planning: Deciding the degree of integration between the packet and optical layers is critical. Furthermore, this includes determining whether to pursue a loose integration (keeping layers distinct but coordinated) or a tight integration (combining layers more closely, potentially at the hardware level) coordinated via the MDSC. Accurate forecasting and planning will also be essential to ensure that the integrated ACTN infrastructure can handle future capacity demand without excessive over-provisioning;
System Interoperability: Networks often comprise equipment from various vendors. Ensuring that packet and optical devices can interoperate seamlessly and the PNCs can manage them is crucial for a successful integration. The Service Provider must also check with the vendors to ensure they support the IETF-based technologies outlined in this document;
Performance Monitoring: The integrated POI network will require comprehensive monitoring solutions that can provide visibility to the PNCs across both packet and optical layers. Identifying and diagnosing issues may become more complex with integrated layers. Telemetry data may also be required to collect lower-layer networking health and consider network and service performance. This topic is further discussed in [ACTN Assurance];
Fault Management and Recovery: The POI networks should be resilient, including considerations for automatic protection switching and fast reroute mechanisms that span both layers. Fault isolation and recovery may become more challenging, as issues in one layer can have cascading effects on the other. Effective fault management strategies must be in place to quickly identify and rectify such issues. This topic is further discussed in [ACTN Assurance];

Specific Security Considerations are discussed in .

IANA Considerations This document requires no IANA actions.

References Normative References Spectral grids for WDM applications: DWDM frequency grid International Telecommunication Union IEEE Standard for Local and metropolitan area networks - Station and Media Access Control Connectivity Discovery Institute of Electrical and Electronics Engineers IEEE Standard for Local and metropolitan area networks - Link Aggregation Institute of Electrical and Electronics Engineers Framework for Abstraction and Control of TE Networks (ACTN) Traffic Engineered (TE) networks have a variety of mechanisms to facilitate the separation of the data plane and control plane. They also have a range of management and provisioning protocols to configure and activate network resources. These mechanisms represent key technologies for enabling flexible and dynamic networking. The term "Traffic Engineered network" refers to a network that uses any connection-oriented technology under the control of a distributed or centralized control plane to support dynamic provisioning of end-to- end connectivity. Abstraction of network resources is a technique that can be applied to a single network domain or across multiple domains to create a single virtualized network that is under the control of a network operator or the customer of the operator that actually owns the network resources. This document provides a framework for Abstraction and Control of TE Networks (ACTN) to support virtual network services and connectivity services. Requirements for GMPLS-Based Multi-Region and Multi-Layer Networks (MRN/MLN) Most of the initial efforts to utilize Generalized MPLS (GMPLS) have been related to environments hosting devices with a single switching capability. The complexity raised by the control of such data planes is similar to that seen in classical IP/MPLS networks. By extending MPLS to support multiple switching technologies, GMPLS provides a comprehensive framework for the control of a multi-layered network of either a single switching technology or multiple switching technologies. In GMPLS, a switching technology domain defines a region, and a network of multiple switching types is referred to in this document as a multi-region network (MRN). When referring in general to a layered network, which may consist of either single or multiple regions, this document uses the term multi-layer network (MLN). This document defines a framework for GMPLS based multi-region / multi-layer networks and lists a set of functional requirements. This memo provides information for the Internet community. A YANG Data Model for Traffic Engineering Tunnels, Label Switched Paths and Interfaces Cisco Systems Inc Cisco Systems Inc Alef Edge Juniper Networks Individual This document defines a YANG data model for the provisioning and management of Traffic Engineering (TE) tunnels, Label Switched Paths (LSPs), and interfaces. The model covers data that is independent of any technology or dataplane encapsulation and is divided into two YANG modules that cover device-specific, and device independent data. This model covers data for configuration, operational state, remote procedural calls, and event notifications. A YANG Data Model for requesting path computation Huawei Technologies Nokia Telefonica Google China Unicom There are scenarios, typically in a hierarchical Software-Defined Networking (SDN) context, where the topology information provided by a Traffic Engineering (TE) network provider may be insufficient for its client to perform multi-domain path computation. In these cases the client would need to request the TE network provider to compute some intra-domain paths to be used by the client to choose the optimal multi-domain paths. This document provides a mechanism to request path computation by augmenting the Remote Procedure Calls (RPCs) defined in RFC YYYY. [RFC EDITOR NOTE: Please replace RFC YYYY with the RFC number of draft-ietf-teas-yang-te once it has been published. Moreover, this document describes some use cases where the path computation request, via YANG-based protocols (e.g., NETCONF or RESTCONF), can be needed. RESTCONF Protocol This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF). JSON Encoding of Data Modeled with YANG This document defines encoding rules for representing configuration data, state data, parameters of Remote Procedure Call (RPC) operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text. RESTCONF Extensions to Support the Network Management Datastore Architecture This document extends the RESTCONF protocol defined in RFC 8040 in order to support the Network Management Datastore Architecture (NMDA) defined in RFC 8342. This document updates RFC 8040 by introducing new datastore resources, adding a new query parameter, and requiring the usage of the YANG library (described in RFC 8525) by RESTCONF servers implementing the NMDA. Network Management Datastore Architecture (NMDA) Datastores are a fundamental concept binding the data models written in the YANG data modeling language to network management protocols such as the Network Configuration Protocol (NETCONF) and RESTCONF. This document defines an architectural framework for datastores based on the experience gained with the initial simpler model, addressing requirements that were not well supported in the initial model. This document updates RFC 7950. The YANG 1.1 Data Modeling Language YANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols. This document describes the syntax and semantics of version 1.1 of the YANG language. YANG version 1.1 is a maintenance release of the YANG language, addressing ambiguities and defects in the original specification. There are a small number of backward incompatibilities from YANG version 1. This document also specifies the YANG mappings to the Network Configuration Protocol (NETCONF). YANG Library This document describes a YANG library that provides information about the YANG modules, datastores, and datastore schemas used by a network management server. Simple caching mechanisms are provided to allow clients to minimize retrieval of this information. This version of the YANG library supports the Network Management Datastore Architecture (NMDA) by listing all datastores supported by a network management server and the schema that is used by each of these datastores. A YANG Data Model for Network Topologies This document defines an abstract (generic, or base) YANG data model for network/service topologies and inventories. The data model serves as a base model that is augmented with technology-specific details in other, more specific topology and inventory data models. YANG Data Model for Traffic Engineering (TE) Topologies This document defines a YANG data model for representing, retrieving, and manipulating Traffic Engineering (TE) Topologies. The model serves as a base model that other technology-specific TE topology models can augment. A YANG Data Model for Ethernet TE Topology Huawei Technologies Huawei Technologies Futurewei Huawei Technologies CAICT China Mobile Alef Edge This document describes a YANG data model for Ethernet networks when used either as a client-layer network of an underlay transport network (e.g., an Optical Transport Network (OTN)) or as a transport network itself. Dynamic Subscription to YANG Events and Datastores over RESTCONF This document provides a RESTCONF binding to the dynamic subscription capability of both subscribed notifications and YANG-Push. Subscription to YANG Notifications for Datastore Updates This document describes a mechanism that allows subscriber applications to request a continuous and customized stream of updates from a YANG datastore. Providing such visibility into updates enables new capabilities based on the remote mirroring and monitoring of configuration and operational state. Requirements for Subscription to YANG Datastores This document provides requirements for a service that allows client applications to subscribe to updates of a YANG datastore. Based on criteria negotiated as part of a subscription, updates will be pushed to targeted recipients. Such a capability eliminates the need for periodic polling of YANG datastores by applications and fills a functional gap in existing YANG transports (i.e., Network Configuration Protocol (NETCONF) and RESTCONF). Such a service can be summarized as a "pub/sub" service for YANG datastore updates. Beyond a set of basic requirements for the service, various refinements are addressed. These refinements include: periodicity of object updates, filtering out of objects underneath a requested a subtree, and delivery QoS guarantees. A YANG Data Model for Wavelength Switched Optical Networks (WSONs) This document provides a YANG data model for the routing and wavelength assignment (RWA) TE topology in Wavelength Switched Optical Networks (WSONs). The YANG data model defined in this document conforms to the Network Management Datastore Architecture (NMDA). A YANG Data Model for Flexi-Grid Optical Networks Naudit HPCN Universidad Autonoma de Madrid Old Dog Consulting Samsung Huawei Technologies This document defines a YANG module for managing flexi-grid optical networks. The model defined in this document specifies a flexi-grid traffic engineering database that is used to describe the topology of a flexi-grid network. It is based on and augments existing YANG models that describe network and traffic engineering topologies. A YANG Data Model for Optical Transport Network Topology Huawei Technologies Huawei Technologies IBM Corporation Nokia Telefonica This document defines a YANG data model for representing, retrieving, and manipulating Optical Transport Network (OTN) topologies. It is independent of control plane protocols and captures topological and resource-related information pertaining to OTN. A YANG Data Model for WDM Tunnels Futurewei Technologies Nokia Individual Naudit HPCN Universidad Autonoma de Madrid This document defines a YANG data model for the provisioning and management of Traffic Engineering (TE) tunnels and Label Switched Paths (LSPs) in Optical Networks (Wavelength Switched Optical Networks (WSON) and Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks). The YANG data model defined in this document conforms to the Network Management Datastore Architecture (NMDA). OTN Tunnel YANG Model Huawei Technologies Huawei Technologies Nokia Nokia CAICT This document describes the YANG data model for tunnels in OTN TE networks. The model can be used to do the configuration in order to establish the tunnel in OTN network. This work is independent with the control plane protocols. A YANG Data Model for Transport Network Client Signals Huawei Technologies Futurewei Huawei Technologies Cisco Huawei Technologies A transport network is a server-layer network to provide connectivity services to its client. The topology and tunnel information in the transport layer has already been defined by generic Traffic- engineered models and technology-specific models (e.g., OTN, WSON). However, how the client signals are accessing to the network has not been described. These information is necessary to both client and provider. This draft describes how the client signals are carried over transport network and defines YANG data models which are required during configuration procedure. More specifically, several client signal (of transport network) models including ETH, STM-n, FC and so on, are defined in this draft. A YANG Data Model for Layer 3 Topologies This document defines a YANG data model for Layer 3 network topologies. YANG Data Model for Layer 3 TE Topologies Alef Edge Individual Juniper Networks Cisco Systems Inc Ciena Telefonica This document defines a YANG data model for layer 3 traffic engineering topologies. A YANG Data Model for MPLS-TE Topology Huawei Technologies Futurewei Inc. Alef Edge Cisco Systems, Inc. Cisco Systems, Inc. This document defines a YANG data model for representing, retrieving, and manipulating MPLS-TE network topologies. It is based on and augments existing YANG models that describe network and traffic engineering packet network topologies. This document also defines a collection of common YANG data types and groupings specific to MPLS-TE. These common types and groupings are intended to be imported by modules that model MPLS-TE technology- specific configuration and state capabilities. The YANG models defined in this document can also be used for MPLS Transport Profile (MPLS-TP) network topologies. YANG Data Model for SR and SR TE Topologies on MPLS Data Plane Alef Edge Individual Juniper Networks Juniper Networks Ciena Cisco This document defines a YANG data model for Segment Routing (SR) topology and Segment Routing (SR) traffic engineering (TE) topology, using MPLS data plane. A YANG Data Model for MPLS Traffic Engineering Tunnels Cisco Systems Inc Cisco Systems Inc IBM Corporation Juniper Networks Individual This document defines a YANG data model for the configuration and management of Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) tunnels, Label Switched Paths (LSPs) and interfaces. The model augments the TE generic YANG model for MPLS packet dataplane technology. This model covers data for configuration, operational state, remote procedural calls, and event notifications. Informative References Guidelines for creation, selection, and registration of an Autonomous System (AS) This memo discusses when it is appropriate to register and utilize an Autonomous System (AS), and lists criteria for such. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. A YANG Data Model for Optical Impairment-aware Topology Nokia Orange Nokia Individual Huawei Technologies In order to provision an optical connection through optical networks, a combination of path continuity, resource availability, and impairment constraints must be met to determine viable and optimal paths through the network. The determination of appropriate paths is known as Impairment-Aware Routing and Wavelength Assignment (IA-RWA) for WSON, while it is known as Impairment-Aware Routing and Spectrum Assignment (IA-RSA) for SSON. This document provides a YANG data model for the impairment-aware TE topology in optical networks. Service Models Explained The IETF has produced many modules in the YANG modeling language. The majority of these modules are used to construct data models to model devices or monolithic functions. A small number of YANG modules have been defined to model services (for example, the Layer 3 Virtual Private Network Service Model (L3SM) produced by the L3SM working group and documented in RFC 8049). This document describes service models as used within the IETF and also shows where a service model might fit into a software-defined networking architecture. Note that service models do not make any assumption of how a service is actually engineered and delivered for a customer; details of how network protocols and devices are engineered to deliver a service are captured in other modules that are not exposed through the interface between the customer and the provider. Using BGP to Bind MPLS Labels to Address Prefixes This document specifies a set of procedures for using BGP to advertise that a specified router has bound a specified MPLS label (or a specified sequence of MPLS labels organized as a contiguous part of a label stack) to a specified address prefix. This can be done by sending a BGP UPDATE message whose Network Layer Reachability Information field contains both the prefix and the MPLS label(s) and whose Next Hop field identifies the node at which said prefix is bound to said label(s). This document obsoletes RFC 3107. A YANG Network Data Model for Layer 3 VPNs As a complement to the Layer 3 Virtual Private Network Service Model (L3SM), which is used for communication between customers and service providers, this document defines an L3VPN Network Model (L3NM) that can be used for the provisioning of Layer 3 Virtual Private Network (L3VPN) services within a service provider network. The model provides a network-centric view of L3VPN services. The L3NM is meant to be used by a network controller to derive the configuration information that will be sent to relevant network devices. The model can also facilitate communication between a service orchestrator and a network controller/orchestrator. Traffic Engineering (TE) and Service Mapping YANG Data Model Samsung Electronics Huawei Huawei Huawei Cisco Nvidia This document provides a YANG data model to map customer service models (e.g., L3VPN Service Delivery model) to Traffic Engineering (TE) models (e.g., the TE Tunnel or the Virtual Network (VN) model). These models are referred to as TE Service Mapping Model and are applicable generically to the operator's need for seamless control and management of their VPN services with underlying TE support. The models are principally used for monitoring and diagnostics of the management systems to show how the service requests are mapped onto underlying network resource and TE models. A YANG Network Data Model for Layer 2 VPNs This document defines an L2VPN Network Model (L2NM) that can be used to manage the provisioning of Layer 2 Virtual Private Network (L2VPN) services within a network (e.g., a service provider network). The L2NM complements the L2VPN Service Model (L2SM) by providing a network-centric view of the service that is internal to a service provider. The L2NM is particularly meant to be used by a network controller to derive the configuration information that will be sent to relevant network devices. Also, this document defines a YANG module to manage Ethernet segments and the initial versions of two IANA-maintained modules that include a set of identities of BGP Layer 2 encapsulation types and pseudowire types. Applicability of the Path Computation Element (PCE) to the Abstraction and Control of TE Networks (ACTN) Abstraction and Control of TE Networks (ACTN) refers to the set of virtual network (VN) operations needed to orchestrate, control, and manage large-scale multidomain TE networks so as to facilitate network programmability, automation, efficient resource sharing, and end-to-end virtual service-aware connectivity and network function virtualization services. The Path Computation Element (PCE) is a component, application, or network node that is capable of computing a network path or route based on a network graph and applying computational constraints. The PCE serves requests from Path Computation Clients (PCCs) that communicate with it over a local API or using the Path Computation Element Communication Protocol (PCEP). This document examines the applicability of PCE to the ACTN framework. Path Computation Element (PCE) Communication Protocol (PCEP) This document specifies the Path Computation Element (PCE) Communication Protocol (PCEP) for communications between a Path Computation Client (PCC) and a PCE, or between two PCEs. Such interactions include path computation requests and path computation replies as well as notifications of specific states related to the use of a PCE in the context of Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering. PCEP is designed to be flexible and extensible so as to easily allow for the addition of further messages and objects, should further requirements be expressed in the future. [STANDARDS-TRACK] Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Client (PCC) requests. Although PCEP explicitly makes no assumptions regarding the information available to the PCE, it also makes no provisions for PCE control of timing and sequence of path computations within and across PCEP sessions. This document describes a set of extensions to PCEP to enable stateful control of MPLS-TE and GMPLS Label Switched Paths (LSPs) via PCEP. Path Computation Element Communication Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a Stateful PCE Model The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Client (PCC) requests. The extensions for stateful PCE provide active control of Multiprotocol Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE LSPs) via PCEP, for a model where the PCC delegates control over one or more locally configured LSPs to the PCE. This document describes the creation and deletion of PCE-initiated LSPs under the stateful PCE model. Hierarchical Stateful Path Computation Element (PCE) A stateful Path Computation Element (PCE) maintains information on the current network state received from the Path Computation Clients (PCCs), including computed Label Switched Paths (LSPs), reserved resources within the network, and pending path computation requests. This information may then be considered when computing the path for a new traffic-engineered LSP or for any associated/dependent LSPs. The path-computation response from a PCE helps the PCC to gracefully establish the computed LSP. The Hierarchical Path Computation Element (H-PCE) architecture allows the optimum sequence of interconnected domains to be selected and network policy to be applied if applicable, via the use of a hierarchical relationship between PCEs. Combining the capabilities of stateful PCE and the hierarchical PCE would be advantageous. This document describes general considerations and use cases for the deployment of stateful, but not stateless, PCEs using the hierarchical PCE architecture. An Architecture for Use of PCE and the PCE Communication Protocol (PCEP) in a Network with Central Control The Path Computation Element (PCE) is a core component of Software- Defined Networking (SDN) systems. It can compute optimal paths for traffic across a network and can also update the paths to reflect changes in the network or traffic demands. PCE was developed to derive paths for MPLS Label Switched Paths (LSPs), which are supplied to the head end of the LSP using the Path Computation Element Communication Protocol (PCEP). SDN has a broader applicability than signaled MPLS traffic-engineered (TE) networks, and the PCE may be used to determine paths in a range of use cases including static LSPs, segment routing, Service Function Chaining (SFC), and most forms of a routed or switched network. It is, therefore, reasonable to consider PCEP as a control protocol for use in these environments to allow the PCE to be fully enabled as a central controller. This document briefly introduces the architecture for PCE as a central controller, examines the motivations and applicability for PCEP as a control protocol in this environment, and introduces the implications for the protocol. A PCE-based central controller can simplify the processing of a distributed control plane by blending it with elements of SDN and without necessarily completely replacing it. This document does not describe use cases in detail and does not define protocol extensions: that work is left for other documents. Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic Engineering A network may comprise multiple layers. It is important to globally optimize network resource utilization, taking into account all layers rather than optimizing resource utilization at each layer independently. This allows better network efficiency to be achieved through a process that we call inter-layer traffic engineering. The Path Computation Element (PCE) can be a powerful tool to achieve inter-layer traffic engineering. This document describes a framework for applying the PCE-based architecture to inter-layer Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) traffic engineering. It provides suggestions for the deployment of PCE in support of multi-layer networks. This document also describes network models where PCE performs inter-layer traffic engineering, and the relationship between PCE and a functional component called the Virtual Network Topology Manager (VNTM). This memo provides information for the Internet community. Profiles for Traffic Engineering (TE) Topology Data Model and Applicability to non-TE Use Cases Huawei Alef Edge Individual Cisco Systems Inc Telefonica This document describes how profiles of the Traffic Engineering (TE) Topology Model, defined in RFC8795, can be used to address applications beyond "Traffic Engineering". Transport Northbound Interface Applicability Statement Huawei Old Dog Consulting Huawei CAICT This document provides an analysis of the applicability of the YANG models defined by the IETF (in particular in the Traffic Engineering Architecture and Signaling (TEAS) and Common Control and Measurement Plane (CCAMP) working groups) to support ODU transit services, transparent client services, and Ethernet Private Line/Ethernet Virtual Private Line (EPL/EVPL) services over Optical Transport Network (OTN) in single and multi-domain network scenarios. This document also describes how existing YANG models can be used through several worked examples and JSON fragments. A YANG Network Data Model for Service Attachment Points (SAPs) This document defines a YANG data model for representing an abstract view of the provider network topology that contains the points from which its services can be attached (e.g., basic connectivity, VPN, network slices). Also, the model can be used to retrieve the points where the services are actually being delivered to customers (including peer networks). This document augments the 'ietf-network' data model defined in RFC 8345 by adding the concept of Service Attachment Points (SAPs). The SAPs are the network reference points to which network services, such as Layer 3 Virtual Private Network (L3VPN) or Layer 2 Virtual Private Network (L2VPN), can be attached. One or multiple services can be bound to the same SAP. Both User-to-Network Interface (UNI) and Network-to-Network Interface (NNI) are supported in the SAP data model. Fast Reroute Extensions to RSVP-TE for LSP Tunnels This document defines RSVP-TE extensions to establish backup label-switched path (LSP) tunnels for local repair of LSP tunnels. These mechanisms enable the re-direction of traffic onto backup LSP tunnels in 10s of milliseconds, in the event of a failure. Two methods are defined here. The one-to-one backup method creates detour LSPs for each protected LSP at each potential point of local repair. The facility backup method creates a bypass tunnel to protect a potential failure point; by taking advantage of MPLS label stacking, this bypass tunnel can protect a set of LSPs that have similar backup constraints. Both methods can be used to protect links and nodes during network failure. The described behavior and extensions to RSVP allow nodes to implement either method or both and to interoperate in a mixed network. [STANDARDS-TRACK] Topology Independent Fast Reroute using Segment Routing Cisco Systems Cisco Systems Cisco Systems INSA Lyon Orange Bell Canada This document presents Topology Independent Loop-free Alternate Fast Reroute (TI-LFA), aimed at providing protection of node and adjacency segments within the Segment Routing (SR) framework. This Fast Reroute (FRR) behavior builds on proven IP-FRR concepts being LFAs, remote LFAs (RLFA), and remote LFAs with directed forwarding (DLFA). It extends these concepts to provide guaranteed coverage in any two- connected networks using a link-state IGP. A key aspect of TI-LFA is the FRR path selection approach establishing protection over the expected post-convergence paths from the point of local repair, reducing the operational need to control the tie-breaks among various FRR options. A YANG Data Model for Network Inventory Huawei Technologies Nokia Vodafone TIM Cisco This document defines a base YANG data model for network inventory that is application- and technology-agnostic. This data model can be augmented with application-specific and technology-specific details in other, more specific network inventory data models. YANG Data Models for requesting Path Computation in WDM Optical Networks Huawei Technologies Futurewei Technologies Nokia This document provides a mechanism to request path computation in Wavelength-Division Multiplexing (WDM) optical networks composed of Wavelength Switched Optical Networks (WSON) and Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) switched technologies. This model augments the Remote Procedure Calls (RPCs) defined in RFC YYYY. [RFC EDITOR NOTE: Please replace RFC YYYY with the RFC number of draft-ietf-teas-yang-path-computation once it has been published. A YANG Data Model for Virtual Network (VN) Operations Samsung Electronics Huawei Cisco Individual ETRI A Virtual Network (VN) is a network provided by a service provider to a customer for the customer to use in any way it wants as though it was a physical network. This document provides a YANG data model generally applicable to any mode of VN operations. This includes VN operations as per the Abstraction and Control of TE Networks (ACTN) framework.

Additional Scenarios

OSS/Orchestration Layer The OSS/Orchestration layer is a vital part of the architecture framework for a service provider:

to abstract (through MDSC and PNCs) the underlying transport network complexity to the Business Systems Support layer;
to coordinate NFV, Transport (e.g. IP, optical and microwave networks), Fixed Acess, Core and Radio domains enabling full automation of end-to-end services to the end customers;
to enable catalogue-driven service provisioning from external applications (e.g. Customer Portal for Enterprise Business services), orchestrating the design and lifecycle management of these end-to-end transport connectivity services, consuming IP and/or optical transport connectivity services upon request.

As discussed in , in this document, the MDSC interfaces with the OSS/Orchestration layer and, therefore, it performs the functions of the Network Orchestrator, defined in . The OSS/Orchestration layer requests the creation of a network service to the MDSC specifying its end-points (PEs and the interfaces towards the CEs) as well as the network service SLA and then proceeds to configuring accordingly the end-to-end customer service between the CEs in the case of an operator managed service.

MDSC NBI As explained in , the OSS/Orchestration layer can request the MDSC to setup L2/L3VPN network services (with or without TE requirements). Although the OSS/Orchestration layer interface is usually operator-specific, typically it would be using a RESTCONF/YANG interface with a more abstracted version of the MPI YANG data models used for network configuration (e.g. L3NM, L2NM). shows an example of possible control flow between the OSS/Orchestration layer and the MDSC to instantiate L2/L3 VPN network services, using the YANG data models under the definition in , , and .

Service Request Process

The VN YANG data model, defined in , whose primary focus is the CMI, can also provide VN Service configuration from an orchestrated network service point of view when the L2/L3 VPN network service has TE requirements. However, this model is not used to setup L2/L3 VPN service with no TE requirements.
- It provides the profile of VN in terms of VN members, each of which corresponds to an edge-to-edge link between customer end-points (VNAPs). It also provides the mappings between the VNAPs with the LTPs and the connectivity matrix with the VN member. The associated traffic matrix (e.g., bandwidth, latency, protection level, etc.) of VN member is expressed (i.e., via the TE-topology's connectivity matrix).
- The model also provides VN-level preference information (e.g., VN member diversity) and VN-level admin-status and operational-status.
The L2NM and L3NM YANG data models, defined in and , whose primary focus is the MPI, can also be used to provide L2VPN and L3VPN network service configuration from a orchestrated connectivity service point of view.
The TE & Service Mapping YANG data model provides TE-service mapping.
TE-service mapping provides the mapping between a L2/L3 VPN instance and the corresponding VN instances.
The TE-service mapping also provides the binding requirements as to how each L2/L3 VPN/VN instance is created concerning the underlay TE tunnels (e.g., whether they require a new and isolated set of TE underlay tunnels or not).
Site mapping provides the site reference information across L2/L3 VPN Site ID, VN Access Point ID, and the LTP of the access link.

Multi-layer and Multi-domain Resiliency

Maintenance Window Before planned maintenance operation on DWDM network takes place, IP traffic should be moved hitless to another link. MDSC must reroute IP traffic before the events takes place. It should be possible to lock IP traffic to the protection route until the maintenance event is finished, unless a fault occurs on such path.

Router Port Failure The focus is on client-side protection scheme between IP router and reconfigurable ROADM. Scenario here is to define only one port in the routers and in the ROADM muxponder board at both ends as back-up ports to recover any other port failure on client-side of the ROADM (either on the IP router port side or on the muxponder side or on the link between them). When client-side port failure occurs, alarms are raised to MDSC by IP-PNC and O-PNC (port status down, LOS etc.). MDSC checks with OP-PNC(s) that there is no optical failure in the optical layer. There can be two cases here:

LAG was defined between the IP routers at the two ends. MDSC, after checking that optical layer is fine between the two edge WDM nodes, triggers the WDM edge node re-configuration so that the IP router's back-up port with its associated muxponder port can reuse the WDM tunnel that was already in use previously by the failed IP router port and adds the new link to the LAG on the failure side. While the ROADM reconfiguration takes place, IP/MPLS traffic is using the reduced bandwidth of the IP link bundle, discarding lower priority traffic if required. Once back-up port has been reconfigured to reuse the existing WDM tunnel and the new link has been added to the LAG then original Bandwidth is recovered between the end routers. Note: in this LAG scenario let assume that BFD is running at LAG level so that there is nothing triggered at MPLS level when one of the link member of the LAG fails.
If there is no LAG then the scenario is not clear since a IP router port failure would automatically trigger (through BFD failure) first a sub-50ms protection at MPLS level :FRR (MPLS RSVP-TE case) or TI-LFA (MPLS based SR-TE case) through a protection port. At the same time MDSC, after checking that optical network connection is still fine, would trigger the reconfiguration of the back-up port of the IP router and of the muxponder to re-use the same WDM tunnel as the one used originally for the failed IP router port. Once everything has been correctly configured, MDSC Global PCE could suggest to the operator to trigger a possible re-optimization of the back-up MPLS path to go back to the MPLS primary path through the back-up port of the IP router and the original WDM tunnel if overall cost, latency etc. is improved. However, in this scenario, there is a need for protection port PLUS back-up port in the IP router which does not lead to clear port savings.

Muxponders The setup of a client connectivity service between two transponders is relatively clear and its implementation simple. There is a one to one relationship between the tranponder's client and trunk (or DWDM) port. The client port bitrate determines the trunk port bit rate which will also determine the Baud-rate, the modulation format, the FEC etc. The controller, when asked to set up a client connectivity service, needs to find a WDM tunnel suitable to comply the DWDM port parameters. The setup of a client connectivity service between two muxponders is different since there is a one to many relationship between the muxponder's trunk (or DWDM) port and client ports. For example, there might be a 100Gb/s trunk port shared by ten 10GE client ports. The controller, when asked to set a 10GE client connectivity service between two muxponder's client ports, needs first to check whether there is already an existing WDM tunnel between the two muxponders and then take different actions:

if the WDM tunnel already exists, the controller needs only to enable the 10GE client ports to establish the 10GE client connectivity service;
if the WDM tunnel does not exist, the controller has to first establish the WDM tunnel, finding a proper optical path matching the optical parameters of the two muxponders' trunk ports (e.g., an OTSi carrying an OTU4), and then enable the 10GE client ports to establish the 10GE client connectivity service.

Since multiple client connectivity services are sharing the same WDM tunnel, a multiplexing label shall be assigned to each client connectivity service. The multiplexing label can either be a standard label (e.g., an OTN timeslot) or a vendor-specific label. The multiplexing label can be either configurable (flexible configuration) or assigned by design to each muxponder's client port (fixed configuration). In the former case, any muxponder client port can be connected with any other client port of the peer muxponder (for example client port 1 on one muxponder can be connected with client port 5 on the peer muxponder) while in the latter case only client ports with the same port number can be connected (for example client port 2 on one muxponder can be connected only with client port 2 on the peer muxponder and not with any other client port). In case of flexible configuration, since the two muxponders are under the control of the same O-PNC, the configuration of the multiplexing label, regardless of whether it is a standard or vendor-specific label, can be done by the O-PNC using mechanisms which are vendor-specific and outside the scope of this document. The MDSC can just request the O-PNC to setup a client connectivity service over a WDM tunnel. In case of fixed configuration, the multiplexing label is assigned by the muxponder but the O-PNC and MDSC needs to be aware of the connectivity constraints to avoid try and fail. It is worth noting that the current WSON and Flexi-grid topology models in and do not provide sufficient information to the MDSC about this connectivity constraint and this is identified as a gap.

Acknowledgments Some of this analysis work was supported in part by the European Commission funded H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727). Previous versions of document were prepared using 2-Word-v2.0.template.dot. This document was prepared using kramdown.

Contributors Nokia

sergio.belotti@nokia.com

ggalimbe56@gmail.com

Cisco

asnizar@cisco.com

TIM Brasil

wcorreia@timbrasil.com.br

Hochschule Esslingen - University of Applied Sciences

michael.scharf@hs-esslingen.de

Sung Kyun Kwan University

younglee.tx@gmail.com

Apstra

jefftant.ietf@gmail.com

Huawei

paolo.volpato@huawei.com

Cisco

brfoster@cisco.com

Telefonica

oscar.gonzalezdedios@telefonica.com