Path Computation Element (PCE) Architecture (draft-ash-pce-architecture-01.txt)

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Path Computation Element (PCE) Architecture
(draft-ash-pce-architecture-01.txt)
Adrian Farrell Old Dog Consulting adrian_at_olddog.co
.uk
JP Vasseur Cisco Systems, Inc. jpv_at_cisco.com
Jerry Ash ATT gash_at_att.com
Outline

• PCE architecture summary
• provided in backup slides
• you read the draft
• I-D updates based on comments raised on list
• next step working group draft

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PCE Architecture Summary(see backup slides
attached)

• terminology
• assumptions
• motivation for PCE architecture
• PCE architectural considerations
• security confidentiality
• PCE evaluation metrics
• PCE architecture overview
• composite PCE
• external PCE
• multiple PCE path computation
• multiple PCE path computation with inter-PCE
  communication
• architecture non-goal to specify protocols
• protocol extensions will be worked out in other
  IDs

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Composite PCE Node
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External PCE Node
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Multiple PCE Path Computation
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Multiple PCE Path Computationwith Inter-PCE
Communication
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I-D Updates Based on Issues Raised on List

• PCE should advertise its capabilities, for
  example
• set of constraints it can account for (diversity,
  SRLGs, optical impairments, wavelength
  continuity, etc.)
• text added to Section 6.4
• path computation request include if near-disjoint
  paths acceptable
• text added to Section 6.6
• TED information can include info from sources
  other than IGP (e.g. LSP routes, reserved
  bandwidth, measured traffic volume)
• needed to perform LSP re-optimization
• needed to reconfigure virtual network topology
  (VNT) lower layer (e.g., optical) paths
• text added to Section 6.7
• elaborate on advantages of stateful PCE
  pitfalls of using stateful PCE in a distributed
  PCE environment
• text added to Section 6.8
• evaluation metrics should include TED
  synchronization speed impact on the data flows
• text added to Section 7

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I-D Updates Based on Issues Raised on List

• identify areas for standardization
• added Section 5.5 Areas for Standardization
• based on PCE Charter
• other editorial changes

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Next Steps

• propose draft as PCE WG draft

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Backup Slides
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Terminology

• path computation element (PCE)
• entity (component, application or network node)
  capable of computing a network path based on
  network graph computational constraints
• e.g., PCE computes path of a TE LSP by using TED
  bandwidth/other constraints
• path computation client (PCC)
• any client application requesting a path
  computation by the PCE
• domain
• any collection of network elements within a
  common sphere of address management or path
  computational responsibility
• e.g., IGP areas, AS, multiple ASs within a SP
  network, multiple ASs across multiple SP networks
• single PCE path computation single PCE computes
  a path in a domain
• multiple PCE path computation multiple PCEs
  compute a path in a domain
• centralized computation model all paths in a
  domain computed by a single, centralized PCE
• distributed computation model computation of
  paths in a domain shared among multiple PCEs

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Assumptions

• PCE may or may not be located at head-end
• e.g. nodes on path contribute to path computation
  (e.g., loose hops) making them PCEs
• path computation may be made by PCE physically
  distinct from the computed path
• path computed by PCE may be
• complete full explicit path of strict hops
• partial mix of strict loose hops (may be an
  abstract node such as an AS)
• PCE path computation can be used in conjunction
  with other path computation models
• e.g., inter-AS TE LSP may be computed using PCE
  in some domains but not others
• no assumptions made about PCE implementation
• e.g., could be implemented on a router, LSR,
  dedicated network server, etc.
• PCE function independent of forwarding capability
  of node on which it is implemente

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Motivation for PCE Architecture

• inter-area/AS optimal path computation (node has
  partial visibility)
• computation of inter-area/AS diverse path (node
  has partial visibility)
• CPU-intensive path computation/global
  optimization
• backup path computation for bandwidth protection
  with backup capacity optimization
• multi-layer networks e.g. TDM network provides
  connectivity for client-layer (IP, MPLS, L2,
  etc.)
• absence of TED or use of non-TE-enabled IGP
• node outside routing domain (e.g., CE to PE path
  computation)
• network element lacks control plan or routing
  capability

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PCE Architectural Considerations

• synchronization
• non-synchronized (e.g., PCE makes multiple
  individual path computations to generate set of
  paths)
• synchronized (e.g., single PCE invokes
  computations by other PCEs before supplying
  result to PCC
• PCE discovery load balancing
• detecting PCE liveness
• PCC-PCE PCE-PCE communication
• PCE TED synchronization
• stateful vs. stateless PCEs
• monitoring
• policy confidentiality
• must preserve confidentiality across multiple SPs
• must ensure confidentiality security of PCC-PCE
  PCE-PCE messages

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Security Confidentiality

• PCC-PCE communication
• subject to "usual" security issues
• snooping not a significant issue
• might want to encrypt
• spoofing is very serious
• must offer strong authentication
• protocol is P2P so this is relatively easy
• DoS important because of 'centralized' nature of
  PCE
• PCE-PCE communication
• same as for PCC-PCE, but add confidentiality
• confidentiality (protection of domain topology
  information)
• use loose routes
• PCE encrypts ERO segments
• decrypt on entry to domain
• replace ERO segment with cookie
• entry point to domain consults local PCE using
  cookie to retrieve next ERO segment

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PCE Evaluation Metrics

• optimality
• scalability
• load sharing
• multiple path computation
• reoptimization
• path computation time
• network stability
• synchronization
• between TED network topology/resource states
• speed of TED synchronization
• impact of synchronization on data flows