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

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 requirementsPCED extensions allowing a PCE to advertise a list of supported OFPCEP extensions allowing to carry an OF in a request/response

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 objectCarried in a PCReq message to indicate the desired OFCarried in a PCRep message to indicate the OF applied by the PCENew error type/value

Changes since last version

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

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)

Objective functions that apply to the computation of a single pathOF 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 requestsOF4: 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

Definition of Objective Functions 2/2

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 specificationOnly one expected change in next revision: Factorization of the OF

in the reply message with synchronized path requests

Running code

Adoption as WG doc?

Thanks

Questions?