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Background

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). Background.

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Background

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  1. Encoding of Objective Functions in PCE Communication and Discovery Protocolsdraft-leroux-pce-of-01.txtJ.L. Le Roux (France Telecom) J.P. Vasseur (Cisco Systems) Y. Lee (Huawei) IETF 69, PCE WG, Chicago

  2. 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

  3. 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

  4. Changes since last version • As agreed in Prague, we defined in this document the six mandatory objective functions listed in RFC4657

  5. Definition of Objective Functions 1/2 • Notation: • A network comprises a set of N links {Li, (i=1..N)} • A path P is a list of K links {Lpi,(i=1..K)} • Metric of link L is noted M(L) • The cost of a path P is noted C(P), C(P) = sum {M(Lpi), (i=1...K)}. • Residual bandwidth on link L is noted R(L) • Speed of link L is noted B(L)

  6. 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), i=1..K } ) is minimized • OF3: Maximum residual Bandwidth Path (MBP) • Find a path P such that ( Min { R(Lpi)), i=1..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), i=1..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), i=1..m}) is minimized

  7. 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?

  8. ThanksQuestions?

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