IETF 69, PCE WG, Chicago 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 l The computation of one or a series of TE-LSPs is subject to an objective function (OF) è Unsynchronized computation: Minimum cost path, shortest widest path, widest shortest path, etc. è Synchronized computation: Minimize the load on the most loaded link, minimize the global bandwidth consumption, etc. l As spelled out in RFC 4674, it may be useful for a PCC to discover the set of objective functions supported by a PCE l 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 l This draft covers these requirements è PCED extensions allowing a PCE to advertise a list of supported OF è PCEP extensions allowing to carry an OF in a request/response

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

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

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

l Objective functions that apply to the computation of a single path è OF 1: Minimum Cost Path (MCP) –Find a path P such that C(P) is minimized è OF2: Minimum Load Path (MLP) –Find a path P such that ( Max {(B(Lpi) - R(Lpi)) / B(Lpi), i=1..K } ) is minimized è OF3: Maximum residual Bandwidth Path (MBP) –Find a path P such that ( Min { R(Lpi)), i=1..K } ) is maximized l Objective functions that apply to a set of path requests è OF4: Minimize aggregate Bandwidth Consumption (MBC) –Find a set of paths such that ( Sum {B(Li) - R(Li), i=..N} ) is minimized è 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. è 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 Definition of Objective Functions 2/2

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

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