Evolution of Path Computation Towards Generalized Resource Computation Adrian Farrel Old Dog Consulting

History of PCE We know where PCE comes from – Simple CSPF computation of paths for MPLS-TE But RFC 4655 was not quite so limited in its definition an entity that is capable of computing a network path or route based on a network graph, and of applying computational constraints during the computation

Evolution In keeping with that definition PCE has evolved The complexity of path computation that PCE was asked to perform extended rapidly – Multiple paths (global concurrent optimization, SVEC list) – Point to multipoint – More complex constraints and objectives DiffServ, exclude route, vendor constraints Images probably copyright Nintendo or someone, but no charge is made for advertising

Taking Other Things into Account Paths and networks have all sorts of attributes and characteristics A PCE can specialise – Optical networks Wavelength continuity Limited switching capabilities Optical impairments – Multi-layer networks

Beyond a Passive Server Original implementations were passive servers – They respond to queries, but do nothing else Two additional functions wanted by operators – Tell us changes we could make to existing paths Stateful – Tell us about new LSPs we could set up “Advisory” Quickly evolves to active control of the network Still with primary function of computing paths

Paths for Different Purposes A path is a path is a path – It is just a route through a network But what travels on the path? – Packets and frames MPLS, Ethernet, Segment Routing – Optical signals TDM, ASON, WSON – Utilities Cars, trains, electricity, water, sewerage

PCE in SDN We all love shiny things – Today’s sparkle is called SDN – So we need to see where PCE fits Recall that the essence of SDN is programmatic control of the network – Centralised decision-making – Decouple control and data planes – Application-aware network usage – Smart software is in charge That sounds a lot like PCE – And see the Application-Based Network Operation (ABNO) architecture [RFC 7491]…

Active PCE with a Control Plane PCE TED Orchestrator / ABNO Controller Compute how to provide a connection – Instruct the head end to signal the connection

PCE as the SDN Controller Compute how to provide a connection – Instruct the network PCE TED Orchestrator / ABNO Controller

PCE as the SDN Orchestrator Determine what connections are needed Compute how to provide the connections – Instruct the network ABNO Controller PCE TED Applications

Placing / Enabling Resources A PCE can see what connections cannot be set up – Hence, what services cannot be delivered This is a pre-emptive path computation function So a PCE can help the operator – Enable out-of-service resources to be turned on “just in time” – Work out where to add links and nodes to support future traffic demands This makes PCE a network planning tool It can also be used to coordinate resources to build virtual networks – Network slicing – Setting up paths through server networks See Abstraction and Control of Transport Networks (ACTN) draft-ceccarelli-actn-framework – TE abstraction draft-ietf-teas-interconnected-te-info-exchange

What is a Resource? Are we clear what a network resource is? – Node (switch, router) – Link (fiber, copper, channel, virtual link, tunnel) – Buffers, bandwidth, timeslot, optical channel … resource [ree-sawrs, -sohrs, -zawrs, -zohrs, ri-sawrs, -sohrs, -zawrs, -zohrs] noun a source of supply, support, or aid, especially one that can be readily drawn upon when needed* So what about other resources? – Servers, CPU, rack space, power consumption, radio channels, mobile cells … – Can PCE make informed decisions related to these resources? *

PCE in SFC A service function chain is a path – Nodes are service functions on their specific service function nodes – Links are the tunnels between those nodes Path computation is about selecting – Which functions and in which order according to the needs of the traffic – Which service function node to use to realize the function – Which tunnels to use to link the service function nodes Additional constraints will include an understanding of – The size of the traffic flow – The bandwidth available for the various tunnels – The processing load and capabilities of the service function nodes

PCE in NFV In Network Function Virtualization the service functions are instantiated as software instances on servers in data centers (the cloud) The Service Function Chains still need to be built based on knowledge of loads and capabilities However, new service functions can be instantiated to handle current or predicted loads Who makes the decisions? – What are the predicted demands? – What new service function instantiations are needed? – Where should they be placed? These decisions are like the decisions used to create a virtual network utilising resources in a server network by building connections and presenting them as links

Generalized Resource Computation We see that there are many decisions in networking about the consumption and placement of resources These decisions are related to path computation – But they are not pure path computation issues There is a set of computation problems that select resources for use, activation, or placement in support of network services What engine performs these computations? – Is it a new server? – Is it PCE with new capabilities? – Is it new function but bundled with a PCE, and if so, what will be call it?

What Defines a PCE? Where do we go for an authoritative definition? – Perhaps RFC 4655 – Perhaps defined by the use of PCEP How do we know who is authoritative? – Perhaps the IETF But if I write some software that does generalized resource computation and I call it “OldDogCrop PCE” is it a PCE?

If We Change What a PCE Does is it Still a PCE? I really don’t want to invoke Wittgenstein, but… We can cause a lot of confusion by calling things by the wrong name – But we might be saved by the abbreviation, PCE – Provisioning Computation Element ?

Where Does that Leave Us? I have two unicorns Do I know what they are doing when I’m not watching? Do I know what they are for? Do I know their limits and capabilities? Can I teach them new tricks? Or should I invest in a griffon? Percy the PCE Unicorn Sidney the SDN Unicorn The Griffon of Pisa

Questions?