Encoding of Objective Functions in PCE Communication and Discovery Protocols draft-leroux-pce-of-01.txt

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Encoding of Objective Functions in
PCE Communication and Discovery
Protocols
draft-leroux-pce-of-01.txt



J.L. Le Roux (France Telecom)
J.P. Vasseur (Cisco
Systems) Y. Lee
(Huawei)
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Background

• The computation of one or a series of TE-LSPs is
  subject to an objective function (OF)
• Unsynchronized computation Minimum cost path,
  shortest widest path, widest shortest path, etc.
• Synchronized computation Minimize the load on
  the most loaded link, minimize the global
  bandwidth consumption, etc.
• As spelled out in RFC 4674, it may be useful for
  a PCC to discover the set of objective functions
  supported by a PCE
• As spelled out in RFC 4657, a PCC must be able to
  indicate in a request a required objective
  function as well as optional parameters
• This draft covers these requirements
• PCED extensions allowing a PCE to advertise a
  list of supported OF
• PCEP extensions allowing to carry an OF in a
  request/response

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Solution Overview

• A common Objective Function Code Point Registry
  is defined for both PCE communication and
  discovery protocols
• 16 bit code point registry to be managed by IANA
• PCE Discovery Extension A new sub-TLV, OF-List,
  carried in the PCED TLV
• Carries the list of supported objective functions
• PCEP Extension A new PCEP OF object
• Carried in a PCReq message to indicate the
  desired OF
• Carried in a PCRep message to indicate the OF
  applied by the PCE
• New error type/value

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Changes since last version

• As agreed in Prague, we defined in this document
  the six mandatory objective functions listed in
  RFC4657

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Definition of Objective Functions 1/2

• Notation
• A network comprises a set of N links Li,
  (i1..N)
• A path P is a list of K links Lpi,(i1..K)
• Metric of link L is noted M(L)
• The cost of a path P is noted C(P), C(P) sum
  M(Lpi), (i1...K).
• Residual bandwidth on link L is noted R(L)
• Speed of link L is noted B(L)

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Definition of Objective Functions 2/2

• Objective functions that apply to the computation
  of a single path
• OF 1 Minimum Cost Path (MCP)
• Find a path P such that C(P) is minimized
• OF2 Minimum Load Path (MLP)
• Find a path P such that ( Max (B(Lpi) - R(Lpi))
  / B(Lpi), i1..K ) is minimized
• OF3 Maximum residual Bandwidth Path (MBP)
• Find a path P such that ( Min R(Lpi)), i1..K
  ) is maximized
• Objective functions that apply to a set of path
  requests
• OF4 Minimize aggregate Bandwidth Consumption
  (MBC)
• Find a set of paths such that ( Sum B(Li) -
  R(Li), i..N ) is minimized
• OF5 Minimize the Load of the most loaded Link
  (MLL)
• Find a set of paths such that ( Max B(Li) -
  R(Li)) / B(Li), i1..N) is minimized.
• OF6 Minimize the Cumulative Cost of a set of
  paths (MCC)
• Find a set of paths P1..Pm such that (Sum
  C(Pi), i1..m) is minimized

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Next Steps

• Straightforward PCED and PCEP extensions
• We covered the major point raised in Prague, i.e.
  the definition of the six mandatory objective
  functions
• Stable specification
• Only one expected change in next revision
  Factorization of the OF in the reply message with
  synchronized path requests
• Running code
• Adoption as WG doc?

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ThanksQuestions?