Relayed CSPF for Multi-Area Multi-AS PCEdraft-lu-relayed-cspf-00.txt

IETF 79 - Beijing, ChinaNovember 7-12, 2010

Wenhu Lu, Sriganesh Kini, Srikanth Narayanan

Agenda

• Solutions analysis• CSPF seed, heap, and relay• Mathematical base• PCE Elect• PCEP Extension• Relay Timer• Multi-AS

Existing Solutions

• Global TED– Too big, negating the purpose of having multiple areas or ASes;– violates the information hiding and confidentiality requirement and is

unacceptable by ISPs

• Crankback– Not scale– Not optimal– Labor intensive

• RBPC – RFC5441– Assume tailend is location-known, not always true– Can’t handle multi-homed cases– Complexity - Virtual Shortest Path Tree (VSPT)

We look for

• Solutions with– optimality– Scalability– simplicity

Divide & Conquer

• Path Tree Path TreesHeadend

Tailend Tailend

Headend

Area-3

Area-2

Area-1

Global TED

CSPF Seed

• The initial node for CSPF, or SPF– Seed to the heap

• SPF is a seed based algorithm• The entire Shortest Path Tree (SPT) is built

upon this seed.

Multiple Seeds

• A heap can have >1 seeds• In SPF expansion, the heap contains many

nodes– can be perceived as seeds for further expansion.

Heap Equivalence• A heap with one initial seed– is equivalent to that with multiple intermediate seeds

in any SPF stages for the destinations that have not yet been reached.

• The deposit time of seeds– is insensitive to destinations that have not yet been

reached, provided that the seeds carry correct attributes values such as cost and nexthop.

• The multiple seeds in property 1– can further be reduced to those that constitute a set

of nodes besides which the destinations are not viable.

Simple Case1. For convenience, assume every

router is also a PCE2. Start from Area “North” where

Headend “H” resides3. Compute paths to “A” and “B”

1. Note that “C” is not used4. PCE-North sends “relay” request

to PCE-South, say “B”5. PCE-South uses “A” and “B” as

seeds for CSPF in area “South”1. Note that “A” and “B” have non-zero

initial cost, hop-count, etc.6. These two seeds will be the base

to reach tailend “T”7. PCE-South replys to PCE-North

which stitch the paths

HH

CC

BBAA

TT

North

South

PCE Elect

• For an exit area– Only one BN is necessary– Either “A” or “B” will work

• Can be achieved through IGP-TE extension– draft-lu-ospf-area-tlv-00.txt

Multi-Exit-Areas• Two paths avaible• Race condition

A

D

C

B

H T

D

F

EC

B

A

PCReqPCReq

PCRep

PCRep

Relay Timer

• To collect multiple PCRep• Timeout to avoid infinite wait

PCEP Seed TLV

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Len | Node-ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Node-ID (Cont) | Sub-Type | Sub-Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Seg-ID | Cost | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cost (Cont) | Hops | Sub-Type | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-Type #1 | | | // // | Sub-Type #M | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Multi-AS Path Computation

• Information Hiding– Loose EROs– Loose ERO recovery method• Pre-computed EROs• Re-Query

• Transit Link– Included in the seed attributes

Thank You