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Add a dollop of XTC to your network infrastructure

- May 10, 2017 - 2 Comments

Google XTC and you find out it was an English rock band formed in 1972 and active till 2006 … It probably does not ring a bell to most of you – at least for me, I can’t recall any of their songs. XTC had another connotation in the 1980’s, but that’s not the point here either.

So, what does XTC mean in the context of networking?

XTC is the acronym for XR Traffic Controller and can be considered as a Path Computation Element (PCE). PCE has been around for quite some time now (e.g. RFC4655 has been published back in 2006), so what’s really noteworthy about XTC?

The uptake of SDN and the increasing level of network automation shed new light on the major role a PCE can play to deliver a new and broad range of advanced network services.

As an example, Service Providers have been exploring solutions to run their networks hotter, e.g. to make the most optimal use of their infrastructure assets. Traditionally, providers run their networks at about 45% utilization but have the objective to run it at around 70% percent of capacity. This can be accomplished only if you have a feedback loop that can extract real-time information from the network, compute and analyze this data and then dynamically reprogram the network.

Telemetry combined with Segment Routing and XTC can deliver such a feedback loop.

So, what’s the role of XTC here?

You can make an analogy with Waze, the traffic and navigation app you’re likely have on your smartphone. Waze is collecting live traffic information from drivers’ smartphones to get the most accurate view of the traffic, then processes these data to compute the most optimal route to user’s destinations of choice.

XTC does to networking what Waze does to traffic jams.

XTC has 3 main elements – SouthBound interfaces, NorthBound interfaces and a core component that does algorithmic computation.


As Segment Routing was designed from the ground up to seek the right balance between distributed intelligence and centralized optimization, we quickly realized that the algorithms we had for RSVP-TE could not be reused as such. We had to come up with brand-new algorithms that fully leverage the new paradigm Segment Routing was setting. That’s exactly what we did and that’s what sits at the very heart of XTC.

SouthBound interface

XTC is collecting network topology information through multiple routing protocols: OSPF, IS-IS, BGP Link-State (BGP LS). The topology database is by design multi-domain to overcome the limitations of former Traffic Engineering solutions. This end-to-end topologic data view can be supplemented by a bunch of other information extracted from the network by model-driven telemetry.

XTC is making use of PCEP (Path Computation Element Communication Protocol) to push updates to the network.

NorthBound interface

This is a very important interface for integration with other applications/products. You don’t want to be overly innovative here but you want to make sure you deliver the right set of protocols that are widely used in the industry – you name them NETCONF/YANG, REST/JSON and gRPC.

Let me now give you 3 examples of Use Cases that XTC enables.


XTC can compute two distinct paths (not sharing the same fiber, not sharing the same duct and so on …). That way, you increase network resiliency and can offer advanced SLAs to your end-customers.

Low Latency

XTC can compute a path where latency is guaranteed and is delivered below a certain threshold. With looming 5G and its latency-sensitive applications such as self-driving cars, this will be an increasingly important service the network will have to deliver.

On-demand Next Hop

Provisioning multi-domain services (L2VPN & L3VPN) comes with complexity and scalability issues notably when routing information needs to be redistributed across domains … With the On-Demand Next Hop (ODN) feature, there is no need to do any redistribution. ODN does trigger delegation of computation of an end-to-end LSP to XTC, including constraints and policies.

XTC addresses Traffic Engineering limitations in large, multi-domain networks where path computation is complex due to limited visibility into neighboring domains, such as another Autonomous System or neighboring IGP areas.

You may ask yourself whether this product is shipping or under development. The good news is XTC is already shipping but the even greater news is that it has already been implemented in live networks!

Stephane Litkowski, Network Architect at Orange Business Services, not only tested the product but also rolled it out in live networks. Discover what he has to say about XTC:

“In the framework of SDN and network automation, the Path Computation Element (PCE) is a critical piece for steering the traffic in the IP/MPLS network. The distributed traffic engineering model that has been used for years has unfortunately some limitations like non- optimal LSP placement and the inability to provide disjoint paths starting from multiple head ends. The introduction of a central computation (the PCE) in a network allows to solve those limitations.

In the market of PCEs, where the product architecture may be complex to deploy and operate, Cisco XTC feature (provided in IOS XR) provides a very simple way to implement a PCE in the network as it is managed as a regular IOS XR network node. XTC has been intensively tested in our labs, and we demonstrated that it can provide disjoint paths (for both RSVP-TE and Segment Routing LSPs) with an optimal LSP placement whatever the disjoint flavor requested: link disjointness, SRLG disjointness, node disjointness…

XTC has been successfully deployed in our network to provide a path disjointness service and it runs as a virtual machine (thanks to virtual IOS XR).

We are also working on some global network optimization scenarios leveraging on the northbound API available on XTC to program the network.

XTC is definitely a simple and powerful PCE solution for both RSVP-TE and Segment Routing: easy to deploy, easy to operate, with powerful algorithms and programmable interfaces.“

I hope this blog triggers your ideas for interesting new use cases. If that is the case, please reach out to us to discuss them. We value your ideas and we are always ready to partner.

If you want to see XTC in action, go and watch the recording of this SDx Central Demo Friday webinar on Multi-Domain Network Optimization and Simplification – Why and How…


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    Network improvement and performance achievement. Excellent article and insights.

    Sweet ! and informative !