www.isocore.com/mpls2013

Path Computation and Instantiation in Software Defined Networks Using Stateful

PCE

Siva Sivabalan Santiago Alvarez Cisco Systems

{ msiva@cisco.com, saalvare@cisco.com }

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Why PCE as an SDN Component?

•  SDN premise: programmatic, centralized control can contribute to greater network agility, optimization, customization and automation

•  PCE architecture already enables centralized path computation for large, multi-domain and multi-layer networks

•  PCE provides a good starting point for implementing an SDN model in WAN

•  Commercially available implementation of base functionality available for at least 5 years

•  Recent extensions (SDN driven): stateful PCE, PCE-initiated LSPs, Segment Routing support

PCE: One Piece of the SDN WAN Puzzle

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DC/Cloud Providers

Customers

DC SDN Customer SDN

Workflow Orchestration/Apps

Collector Programming

Application Engine

NGN WAN

Viz & Analytics

APPS

APIs

IP/MPLS Segment Routing

Multi-Layer

SDN WAN

APPS

Stateless and Stateful PCE

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PCEP

Stateful PCE

TED

LSP DB

Stateful PCC

•  More optimal centralized path computation (e.g. LSP state, resource usage, policy, network analytics, etc.)

•  Enables centralized path initiation and update control

•  Requires LSP state synchronization (LSP database)

•  Limited ability to optimize network resources •  No knowledge of previously established

paths •  Not well suited for SDN deployments •  Still useful for inter-domain MPLS-TE in

non-SDN deployments

PCEP

Stateless PCC

Stateless PCE

TED

PCEP

Passive Stateful PCE

TED

LSP DB

Stateful PCC

Active and Passive Stateful PCE

5 5

PCEP

Active Stateful PCE

TED

LSP DB

Stateful PCC

•  PCC or PCE may initiate path setup •  PCC may delegate update control to PCE •  PCC may revoke delegation •  PCE may return delegation

•  PCC initiates path setup •  PCC retains control on path updates •  PCE learns LSP state to optimize path

computation

PCE has update control over delegated

paths PCC maintains update control

over paths

Active Stateful PCE PCE-Initiated and PCC-Initiated LSPs

6 6

•  PCC may initiate path setup based on distributed network state

•  Can be used in conjunction with PCE-initiated paths

•  Tighter integration with application demands •  PCE can be part of controller architecture

determining what paths to set up and when

PCEP

PCC-Initiated (Active Stateful PCE)

TED

LSP DB

Stateful PCC

PCEP

PCE-Initiated (Active Stateful PCE)

TED

LSP DB

Stateful PCC

Application initiates LSP

via PCE

PCC initiates LSP based on

local policy

PCE Path Profiles

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•  Path computation profile centralized on PCE

•  PCC initiates LSP and only specifies destination and profile id

•  Path usage profiles preconfigured on PCC •  PCE initiates LSP and references usage

profile id to apply

PCC-Initiated (Active Stateful PCE)

TED

LSP DB

Stateful PCC

PCE-Initiated (Active Stateful PCE)

TED

LSP DB

Stateful PCC

PCEP Create / Initiate

Path computation parameters,

path profile 10

Path Comp

Path Usage

Path Comp

Path profile 10

PCEP Request

Destination, path profile 10

Path Comp

Path Usage

Path Comp

Path profile 10

Path profile 10

PCE Extensions for Segment Routing (SR)

•  Segment routing enables source routing based on segment ids distributed by IGP

•  PCE specifies path as list of segment ids

•  PCC forwards traffic by pushing segment id list on packets

•  No path signaling required •  Minimal forwarding state •  Maximum network forwarding

virtualization •  The state is no longer in the

network but in the packet

PCEP

Stateful PCE

TED

LSP DB

Stateful PCC

Node SID

Adjacency SID

Forwarding table remains constant

In Out Int L1 L1 Intf1 … … … L7 L7 Int3 L8 Pop Intf3 … … … L9 Pop Intf5

Application Path

Request

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Summary

•  Stateful PCE is an important SDN enabler providing centralized path computation optimization

•  Different degrees of centralization (computation, updates, initiation, configuration)

•  PCE and SR provide a very compelling SDN solution •  Tight application integration •  Maximum network forwarding

virtualization

PCE

Stateless Stateful

Passive Active

PCE Initiated paths

PCC Initiated paths

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References

•  A Path Computation Element (PCE)-Based Architecture RFC 4655

•  Applicability of Stateful Path Computation Element (PCE) draft-zhang-pce-stateful-pce-app

•  PCEP Extensions for Stateful PCE draft-ietf-pce-stateful-pce

•  PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model draft-crabbe-pce-pce-initiated-lsp

•  PCE Path Profiles draft-alvarez-pce-path-profiles

•  PCEP Extensions for Segment Routing draft-sivabalan-pce-segment-routing

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