Background
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Transcript of Background
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?