Segment Routing Part II: Traffic Engineering

As more and more Service Providers and Enterprises operate a single network infrastructure to support an ever-increasing number of services, the ability to custom fit transport to application needs is of paramount importance.

In that respect, network operators have been exploring Traffic Engineering techniques for some years now but have obviously run into many scaling issues preventing them from having an end-to-end, fine-grained control over the myriad services they offer.

Segment Routing Traffic Engineering (SR-TE) has changed that game and has become the undisputed solution to deliver Traffic Engineering capabilities at scale.

Segment Routing enables the deployment of end-to-end policies across independent Metro, WAN and Data Center domains. This avoids complex protocol conversion between network domains while maintaining scalability – simplification at its best.

A broad range of advanced network services can be delivered by leveraging efficient SR-native algorithms, such as low-delay paths based on dynamically measured link-delays. SR-TE can also compute and maintain disjoint paths (not sharing the same fiber, not sharing the same duct and so on …). This improves network resiliency and end-user satisfaction.

The IOS XR built-in SR Path Computation Element (SR PCE) extends the SR-TE capabilities by offering path computation and path maintenance services to headend routers. The horizontally scalable SR PCE solution enables reaching very high scalability.

The Automated Steering functionality uses existing BGP communities to automatically steer service traffic in the desired SR Policy.

While in the past provisioning multi-domain services (L2VPN & L3VPN) came with complexity and scalability issues, the SR-TE On-Demand Next Hop (ODN) innovation has drastically scaled and automated the establishment of inter-domain policies. Routes no longer need to be redistributed, policies no longer need to be pre-configured. ODN automatically triggers generation of an end-to-end SR Policy upon signaling of a service route. This tremendously simplifies the network operation.

IGP SR Flexible Algorithm (Flex-Algo) enriches the SR-TE solution by adding additional segments having different properties than the IGP Prefix segments. The network operator defines the properties of these Flex-Algo segments, hereby providing the ultimate flexibility.

Flex-Algo makes multiple optimizations of the same physical network infrastructure along various dimensions possible – one can be optimized for low-latency vs. another one for bandwidth, one can offer disjoint paths via two distinct planes. IGP SR Flex-Algo readily provides a simple support for 5G slices.

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