Tackle Unprecedented Growth in Bandwidth Demand with Segment Routing and Cisco Metro Fabric Architecture

Exponential bandwidth growth brought on by more digitally savvy people and businesses is placing unprecedented pressure on service providers' network architecture. Such bandwidth demand is only going to grow, and fast.

Today's 4G networks can support roughly 4,000 devices per square mile. Networks providing 5G connectivity will dramatically increase that figure to roughly 3 million devices per square mile. To put that into perspective, New York City covers more than 300 square miles, which translates into nearly 1 billion devices needing connectivity in the Big Apple alone.

Service providers and other large enterprises, whose legacy network architectures simply weren't built for such high workloads, need to be refreshed. If they aren't, those networks risk failing completely.

Cisco's Compass Metro Fabric Architecture can help revive such legacy networks.

The primary goal of Metro Fabric Architecture is to provide a flexible and scalable model that can be customized to meet the needs of any organization. It targets customers that need a lean, simple and scalable design that supports future growth, is 5G and IoT ready, employs software-defined networking (SDN), and offers industry-leading and future-proof architecture.

World Wide Technology engineers working in our Advanced Technology Center (ATC) over the last two years have worked intricately with proof of concepts and tested Compass Metro Fabric Architecture and have found the solution to be extremely flexible and robust, and simpler than previous deployment models. The ease at which the solution can be deployed and implemented is demonstrated by its adoption rate, which is unprecedented.

Organizations big and small can utilize our ATC lab environment to replicate their own network architectures — no matter the size and complexity — to assess and validate how Metro Fabric Architecture would work within their own system to make sure the solution works as intended when deployed.

Whether you're building large-scale service provider networks or doing business across organizations (such as in a business merger), Metro Fabric Architecture can provide an end-to-end path selection and source-based routing across different Autonomous System that mitigates the need for inter-autonomous system reachability as well as tedious and costly network migrations.

Translation: It can help service providers modernize and make more efficient their network architecture while enabling faster service delivery to generate revenue.

Accelerate service delivery

Cisco's Metro Fabric Architecture is designed for service providers' metro network (access, aggregation) and mobile backhauling, and is built on top of Cisco's Evolved Programmable Network (EPN 5.0) architecture.

The design is an evolution of the existing Unified MPLS architecture and simplifies the transport by employing network programmability using Segment Routing (SR) and a centralized SR-PCE Controller.

It simplifies service deployment with end-to-end automated service provisioning using Cisco's Network Service Orchestrator (NSO). The design uses a unified Border Gateway Protocol (BGP)-based control plane for layer 2 (EVPN) and layer 3 services (BGP L3VPN) and is based on IOS-XR.

Simplify network deployments

Metro Fabric Architecture also targets organizations that have deployed Cisco's Unified MPLS design and are interested in eliminating some of the deployment and operational complexity of that design by using Segment Routing and centralized a SR-Path Computation Element (SR-PCE) controller.

Segment Routing, which is based on the source-routing paradigm, makes the network more scalable and intelligent while improving capacity utilization, leading to lower cost and greater user satisfaction. It leverages source routing by providing a simple, stateless mechanism to program the path a packet takes through the network.

Segment Routing was designed to simplify the deployment for service providers by:

• Making things simple by utilizing Segment Routing as unified forwarding plane.
• Being programmable through the use of an SR-PCE controller.
• Automating service provisioning through the use of NSO.

Segment Routing dramatically reduces the number of protocols needed in service provider and enterprise networks alike by using the MPLS data plane and advertising the prefix labels with standard extensions to the ISIS and OSPF routing protocols.

ISIS or OSPF routing protocols provide Intra-Domain Routing and Forwarding information over a label switched path through the addition of simple TLV extensions to the protocols. High Availability (HA) is achieved through Fast Re-Route (FRR) capabilities in the form of TI-LFA (Topology Independent LFA).

Both prefix segment identifiers and adjacency segment identifiers are building blocks of Segment Routing:

• Prefix SID – A node identifier that must be unique for each node in the IGP domain. This is defined along with the loopback address and is statically provisioned. This dramatically simplifies troubleshooting by assuring that every node in the network is referenced by the same Prefix SID or label.
• Adjacency SID – Each link in the network is assigned a SID or label identifier that must be unique for each link belonging to the same node. Adjacency-SID are assigned dynamically and are locally significant only but may be assigned statically if needed.

Segment Routing with a MPLS data plane or SR-MPLS uses MPLS labels for both prefix and adjacency SIDs. These values are advertised by the IGP protocol, either ISIS or OSPF, which eliminates the need to for LDP or RSVP protocols to exchange MPLS labels, hence simplifying implementation and operations.

TI-LFA is a technology solely implemented using Segment Routing that is simple to deploy and provides sub-50 millisecond convergence for link and node protection. TI-LFA is handled completely by the IGP, ISIS or OSPF, and is locally managed and independent of any other node in the network, which allows for incremental deployment of one node at a time.

Unlike MPLS-TE FRR, which is extremely complex and requires diligent capacity planning for backup paths, TI-LFA always uses the post convergence path as the backup path.

Enable flexibility and agility

As stated, the goal of Metro Fabric Architecture is to provide a flexible and scalable model that can be customized to meet the needs of the organization. This approach divides the network into separate IGP domains for the core, aggregation and access networks as shown in Figure 1 below.

Figure 1 - Each color is a totally separate IGP domain.

Each IGP domain is a separate IGP routing process with no IP reachability between the domains, which allows for increased scale and relies on segment routing in combination with an external SR-PCE controller to program the end-to-end path across the network.  The controller learns the entire topology through the use of BGP-LS feeds from the individual domains.

Below is a diagram of the Cisco Metro Fabric with MPLS Segment Routing Lab available in the ATC. The lab includes three separate ISIS IGP domains with no IP reachability, and demonstrates end-to-end L3VPN connectivity. The path is programmed dynamically at first and then explicitly.  The configurations are deployed using a Cisco NSO server that has been preconfigured for the lab.

Figure 2 - Compass Metro Fabric Lab Architecture

Business models are rapidly changing as organizations adopt more digitally savvy strategies, spurring the need to deploy multi-vendor solutions that enable agility and scalability.

Cisco's Metro Fabric architecture design can help transform service provider networks by simplifying the architecture and automating processes to achieve scale, thus enabling telcos to better handle the unprecedented bandwidth demand expected to be brought on by 5G.

WWT's ATC and lab services can help customers evaluate, design and validate MPLS and segment routing networks by replicating large network architectures to make sure solutions work as intended when deployed to the field.

Once validated, our integration and supply chain capabilities can help stage, configure and ship fully-built solutions, thus avoiding on-site assembly, which demands time and financial resources.