Understanding the IETF's Control Plane Roadmap

Automated control of optical has been an industry topic for decades. Yet the increasing focus on multi-vendor interoperability in the transport network signifies that this trend is set to move from labs and single-vendor deployments into the mainstream in the coming years -- with 5G as a driver.

Achieving multi-vendor and multi-domain control plane interoperability using IETF technologies was the focus of a workshop hosted by the European Commission's Metro-Haul Project, which took place at NGON 2019 in Nice. Halfway through its three-year charter, Metro-Haul is broadly tasked with defining future metro networks -- the infrastructure that sits between coming 5G access networks and evolving long haul/core networks. The workshop itself focused specifically on one important aspect of metro network evolution: optical control plane development using IETF protocols, architectures and data models.

IETF TEAS Working Group Technical Advisor Adrian Farrel of Old Dog Consulting gave a historical perspective on the origins of generalized MPLS (GMPLS) as a means to extend an MPLS-based control plane to circuit-based optical networks (including Sonet/SDH and OTN), as well as layer 2 networks. Distributed GMPLS control planes were used in optical networks for years, but the advent of SDN turned the focus to centralized control and automation. Orange's Julien Meuric explained that SDN "is a second life" for the IETF's Path Computation Element (PCE) which has been adapted to act as a centralized controller in SDN networks (RFC 8283).

Both Meuric and Huawei presenter Italo Busi detailed ongoing work to develop a hierarchical SDN reference architecture, called Abstraction and Control of Traffic Engineered Networks (ACTN), in which PCE can act as one of the important components of the SDN controller. Based on IETF technologies, this hierarchical architecture is necessary to achieve multi-domain interoperability, through which different vendors' domains can communicate with each other at the control plane layer. Significantly, interoperability under ACTN encompasses domains both within OSI layers (i.e., optical-optical) and across OSI layers (i.e., optical-IP). ACTN framework and info models are published in RFCs 8453 and 8454.

Key to ACTN interoperability is the development of standardized YANG models to address TE topology, virtual network operations, and layer 1, 2 and 3 service models. Huawei's Busi provided an update on the relevant YANG models that are being adapted and developed within the IETF to meet these needs. The CMI is the interface that governs communication “northbound” from the multi-domain controller to customer controllers, while MPI is the interface that governs communication “southbound” from the multi-domain controller to the domain controllers. According to Busi, common/standardized YANG models are in various IETF Working Group stages (pre-RFC) across customer/service functions and network functions.

Next, Jorge López de Vergara from the Universidad Autónoma de Madrid described some of his own experience in developing YANG models for the IETF and particularly his work with Vodafone as well as with Huawei. He addressed the fundamental question of why the IETF would need standardized data models at all. The answer is that standardized models provide the multi-vendor interoperability that is required by operators that have complex multi-vendor networks -- including Vodafone, which is why the operator has been so committed to non-proprietary technology for network control and automation. He also highlighted that, beyond the IETF, there are other standards being developed for optical SDN, including OpenROADM, OpenConfig and ONF T-API. These are competing standards approaches to address similar problems.

Vodafone's Jean-François Bouquier, who concluded the workshop presentations, said that commonalities between the Vodafone's transport architecture vision and the IETF's ACTN Reference Architecture led the operator to place its backing behind the IETF. Vodafone required multi-domain and multi-vendor control interoperability from day one, and the IETF's ACTN is, according to Bouquier, the best industry means to meet this requirement.

Vodafone has selected a hierarchical controller vendor that is IETF-aligned and successfully conducted more than 50 tests covering network discovery, layer 1 OTN, layer 2 Ethernet, and UNI/NNI/IDL notification -- with recommendations for improvements. Bouquier mentioned several next steps. The operator is planning to use IETF layer 1 and layer 2 service YANG models for orchestrated transport connectivity services and considers IETF as the target standard implementation for its overall SDN transport architecture, across all transport technologies. Here, further testing will be required to demonstrate interoperability across multiple hardware vendors, according to Bouquier.

By focusing exclusively on IETF technologies, the Metro-Haul workshop provided a rare opportunity to understand the IETF's overall multi-domain control architecture and plans. Through this workshop, we learned that ACTN and the related YANG models were designed through the time-tested IETF standards process, have strong support among major hardware suppliers and third-party controller vendors, and have been extensively tested by tier one network operators. These are rapidly maturing technologies that are ready for commercial deployment. As a final note, given its IP heritage, the IETF may be in a unique position to fully bring together the worlds of IP and optical at the control and management layers.

— Sterling Perrin, Principal Analyst, Heavy Reading

This blog is sponsored by Metro-Haul.