Adrian Farrel Old Dog Consulting adrianolddogcouk History of PCE We know where PCE comes from Simple CSPF computation of paths for MPLSTE But RFC 4655 was not quite so limited in its definition ID: 646651
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Slide1
Evolution of
Path Computation Towards Generalized Resource Computation
Adrian Farrel
Old Dog Consulting
adrian@olddog.co.ukSlide2
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
computationSlide3
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 advertisingSlide4
Taking Other Things into Account
Paths and networks have all sorts
of attributes and characteristicsA PCE can specialise
Optical networks
Wavelength continuity
Limited switching capabilities
Optical impairmentsMulti-layer networksSlide5
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 pathsSlide6
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, sewerageSlide7
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
N
etwork Operation (ABNO) architecture [RFC 7491]…Slide8
Active PCE with a Control Plane
PCE
TED
Orchestrator / ABNO Controller
Compute how to provide a connection
Instruct the head end to signal the connectionSlide9
PCE as the SDN Controller
Compute how to provide a connection
Instruct the network
PCE
TED
Orchestrator / ABNO ControllerSlide10
PCE as the SDN
Orchestrator
Determine what connections are needed
Compute how to provide
the connections
Instruct the
network
ABNO Controller
PCE
TED
ApplicationsSlide11
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 demandsThis makes PCE a network planning toolIt can also be used to coordinate resources to build virtual networksNetwork slicingSetting up paths through server networksSee Abstraction and Control of Transport
Networks (ACTN)
draft-
ceccarelli
-
actn
-framework
TE abstractiondraft-ietf-teas-interconnected-te-info-exchangeSlide12
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
]
nouna 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?*www.dictionary.comSlide13
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 nodesSlide14
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 loadsWho 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 linksSlide15
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?Slide16
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 IETFBut if I write some software that does generalized resource computation and I call it “OldDogCrop PCE” is it a PCE?
The Book of WisdomSlide17
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 ?Slide18
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 UnicornSidney the SDN Unicorn
The Griffon of PisaSlide19
Questions?