1. Relayed CSPF for Multi-Area Multi-AS PCE draft-lu-relayed-cspf-00.txt IETF 79 - Beijing, China November 7-12, 2010 Wenhu Lu, Sriganesh Kini, Srikanth Narayanan

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

3. 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)

4. We look for Solutions with – optimality – Scalability – simplicity

5. Divide & Conquer Path TreePath Trees Headend Tailend Headend Area-3 Area-2 Area-1 Global TED

6. 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.

7. Multiple Seeds A heap can have >1 seeds In SPF expansion, the heap contains many nodes – can be perceived as seeds for further expansion.

8. 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.

9. Simple Case 1.For convenience, assume every router is also a PCE 2.Start from Area “North” where Headend “H” resides 3.Compute paths to “A” and “B” 1.Note that “C” is not used 4.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 H H C C B B A A T T North South

10. 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

11. Multi-Exit-Areas Two paths avaible Race condition A D C B HT D F E C B A PCReq PCRep

12. Relay Timer To collect multiple PCRep Timeout to avoid infinite wait

13. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

14. Multi-AS Path Computation Information Hiding – Loose EROs – Loose ERO recovery method Pre-computed EROs Re-Query Transit Link – Included in the seed attributes

15. Thank You