Making the 5G connection — with Network Functions Interconnect
The introduction of 5G technology enables innovative services that can deliver massive capacity and support ultra-reliable, low-latency communication. This evolution is accompanied by agile and open digital infrastructures that dramatically improve service velocity by disaggregating and virtualizing network functions in the cloud, where they can scale in and scale out depending on application demands.
The challenge is that these virtualized network functions (VNFs) can be highly dispersed over hundreds of locations in the edge cloud servers and core data centers and must interwork seamlessly with the physical network functions (PNFs) in the network to build end-to-end services.
Network Functions Interconnect (NF-IX) is an innovative architecture for interworking PNFs and VNFs in a unified and scalable manner and is based on proven protocols and standards. Nokia is currently preparing an informational IETF draft submission to document the NF-IX architecture.
Digital services on demand
To address the needs of the digital era, Communications service providers are architecting digital infrastructures that combine the openness, programmability and economics of web-scale IT technologies with the performance and reliability of carrier-grade IP networking technologies.
Digital services are offered in network slices of a common physical transport network that must be created on demand to meet specific SLAs. Network slices must also be assured and optimized to ensure SLAs are maintained and not impacted by other slices and services as they evolve.
To orchestrate digital services requires a perfect union of webscale IT and carrier-grade IP network technology, but there are several operational and administrative boundaries that may prevent interworking, impede service velocity and obstruct process automation.
Interconnecting PNFs and VNFs with deterministic SLAs
When network functions are virtualized and moved into the edge or core cloud, the user network interface (UNI) shifts. For example, when disaggregating a Broadband Network Gateway and moving its control plane (CP) functions on a server in the cloud, it is necessary to interwork the physical user plane functions in the Multi-Service Edge (MSE) router with the virtualized control plane functions in the data center.
However, disjoint service policies and mismatching interworking protocols can make it complex and costly to interwork network functions for this simple use case — and virtually impossible for 5G service-based architectures containing an order of magnitude more functions.
The key to overcome these barriers is an intelligent Network Functions Interconnect (NF-IX) fabric that dynamically and seamlessly delivers the necessary IP transport services across the WAN. An NF-IX fabric enables dynamically placing network functions anywhere in the 5G service cloud to optimize cost and performance. The NF-IX fabric also automatically provisions and assures the necessary transport services in the appropriate network slices to meet deterministic latency and throughput objectives.
NF-IX is a functional architecture that leverages proven standards and technologies to address the interworking of physical and virtualized network functions in digital service networks.
Multiprotocol Border Gateway Protocol (MP-BGP) has been adopted as the unified routing control plane to acquire topology information from the virtualized service overlay (e.g., IP/Ethernet VPNs) as well as the IP/MPLS transport underlay. BGP offers tremendous scalability and versatility and is the principal routing protocol used on the internet.
Overlay service characteristics are captured in policy abstractions that allow mapping overlay SLA policies on appropriately engineered network slices in the underlying WAN. For example, the SLA requirements for a network functions interconnection might be expressed as abstract policy colors such as low latency, high availability and guaranteed throughput. The process of mapping network functions interconnections is done by a path computation element (PCE), which is effectively a centralized software-defined network (SDN) controller that engineers optimal inter-domain segment routes across the WAN using segment routing (SR). Predefined SR templates match the abstract SLA policy colors to specify the various delivery constraints.
SR has been adopted as the unified forwarding control plane. SR is an extremely scalable source-based routing technology for engineering dynamic service tunnels with fast restoration options that meet deterministic bandwidth, latency and path diversity constraints. SR implicitly supports load-balancing of traffic over all available links that meet the route policy.
SR also supports various data path implementations, including MPLS and Unreliable Datagram Protocol (UDP), for seamless, end-to-end connectivity between distributed edge and core data centers across the WAN.
Figure 2 NF-IX architecture
Due to node or link failures, maintenance activities or network congestion, certain traffic engineering characteristics of the underlying IP transport network may potentially impact the SLA conformance of an overlay service. For SLA assurance, the SDN controller therefore collects real-time traffic engineering metrics, conducts periodical latency measurements of SR service tunnels, and dynamically resizes or re-optimizes SR paths as required. If network service functions or workloads are moved between data centers in the cloud, the SDN controller automatically receives MP-BGP updates and adjusts underlay transport connectivity as needed.
Over the past few years, Nokia has dedicated a significant amount of time to validate the NF-IX architecture and its proofs of concept with industry partners. Nokia is committed to open standards and solutions and is currently preparing an informational IETF draft submission on NF-IX. In late 2019, Nokia presented the NF-IX architecture at the 106th IETF meeting in Singapore in the session “5G Impact on Networks – Edge cloud and slicing”.
The NF-IX approach establishes a dynamic, seamless and automated connectivity model that makes carrier-grade networks highly consumable for cloud-based services. It helps communications service providers on their journey of transforming their networks into agile, scalable and highly efficient digital service infrastructures by overcoming the operational barriers and interworking issues between data centers and the WAN.
To learn more about NF-IX:
- View the IETF “5G impact on networks – edge cloud and slicing” video and host session slides
- Read the NF-IX architecture white paper
- Consult the following three documents:
Reza Rokui (Nokia), “IETF Draft for Transport Slice Definition”, November 2019
Reza Rokui (Nokia), “IETF Draft for 5G Transport Slice Connectivity Interface”, July 2019
S. Homma (NTT), “IETF Draft for Network Slice Provisioning Models”, November 2019
- Read the NF-IX IETF draft submission.
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