1. PCE-based Computation Procedure for P2MP Inter-domain TE LSP draft-zhao-pce-pcep-inter-domain-p2mp-procedures-06
Quintin Zhao,
Zafar Ali,
Tarek Saad,
Daniel King,
Ramon Casellas,
Siva Sivabalan,
IETF 79 - Beijing

2. Updates in this version
Two new authors have joined this work: Ramon Casellas from CTTC and Siva Sivabalan from Cisco.
Fixed some spotted typos and unified a couple of redundant paragraphs
Added a couple of figures for core tree and domain tree examples.
Updated some definitions.
Added paragraphs to address the scalability of the Core Path procedure along with the hint that it could be computed offline for a large network or it could be computed inline for a small network.
Added a section on parallelism (section 7.6):
In order to minimize latency in path computation in multi-domain networks, intra-domain path segments and intra-domain sub-trees SHOULD be computed in parallel when possible.
IETF 79 - Beijing

3. Quick Review for the procedures introduced in this draft
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4. Inter-Domain P2MP Path Computation Procedures Example: How to build a P2MP Tree?
Maybe combine slides 15 & 16
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree.
- Phase 2 - Grafting destinations to the P2MP LSP Core Tree
PCE1 will now pass request message with all the destination nodes and also the CT to its child PCE
If the current PCE is not the leaf PCE, then it will rebuild the request message pass the message down to its child PCE
The leaf PCE will graft all the destination nodes belonging to the leaf domain to the entry node of the Core-Tree and reply it to its parent PCE
When a PCE receives the reply with the CT, it will graft all the destination nodes belonging to the current domain to the entry node of the Core-Tree and reply to its parent PCE
For the PCE1, when it receives all the replies from its child PCEs it will merge all the sub trees into the final Core-Tree and graft all the destination nodes belong to the root PCE to the entry node from the final Core Tree.
Once the final Core-Tree is complete (the P2MP LSP path tree) it will reply to the PCC with the complete P2MP LSP path.
Domain6 4 4 4

5. Inter-Domain P2MP Path Computation Procedures Phase1:Build the Core Tree
PCE4
PCE1 D1
PCE3 T A W E P M Q R
PCE2 X Z
Maybe combine slides 15 & 16
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree.
- Phase 2 - Grafting destinations to the P2MP LSP Core Tree
PCE1 will now pass request message with all the destination nodes and also the CT to its child PCE
If the current PCE is not the leaf PCE, then it will rebuild the request message pass the message down to its child PCE
The leaf PCE will graft all the destination nodes belonging to the leaf domain to the entry node of the Core-Tree and reply it to its parent PCE
When a PCE receives the reply with the CT, it will graft all the destination nodes belonging to the current domain to the entry node of the Core-Tree and reply to its parent PCE
For the PCE1, when it receives all the replies from its child PCEs it will merge all the sub trees into the final Core-Tree and graft all the destination nodes belong to the root PCE to the entry node from the final Core Tree.
Once the final Core-Tree is complete (the P2MP LSP path tree) it will reply to the PCC with the complete P2MP LSP path.
PCE5 U
PCE6 D2 5 5 5

6. Inter-Domain P2MP Path Computation Procedures Phase2: Compute the sub-tree for each individual domains
PCE4
PCE1 D1
PCE3 T
PCE2
Maybe combine slides 15 & 16
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree.
- Phase 2 - Grafting destinations to the P2MP LSP Core Tree
PCE1 will now pass request message with all the destination nodes and also the CT to its child PCE
If the current PCE is not the leaf PCE, then it will rebuild the request message pass the message down to its child PCE
The leaf PCE will graft all the destination nodes belonging to the leaf domain to the entry node of the Core-Tree and reply it to its parent PCE
When a PCE receives the reply with the CT, it will graft all the destination nodes belonging to the current domain to the entry node of the Core-Tree and reply to its parent PCE
For the PCE1, when it receives all the replies from its child PCEs it will merge all the sub trees into the final Core-Tree and graft all the destination nodes belong to the root PCE to the entry node from the final Core Tree.
Once the final Core-Tree is complete (the P2MP LSP path tree) it will reply to the PCC with the complete P2MP LSP path.
PCE5 U
PCE6 D2 6 6 6

7. Inter-Domain P2MP Path Computation Procedures Phase3: Grafting sub-tree into the core-tree
PCE4
PCE1 D1
PCE3 T A W E P M Q R
PCE2 X Z
Maybe combine slides 15 & 16
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree.
- Phase 2 - Grafting destinations to the P2MP LSP Core Tree
PCE1 will now pass request message with all the destination nodes and also the CT to its child PCE
If the current PCE is not the leaf PCE, then it will rebuild the request message pass the message down to its child PCE
The leaf PCE will graft all the destination nodes belonging to the leaf domain to the entry node of the Core-Tree and reply it to its parent PCE
When a PCE receives the reply with the CT, it will graft all the destination nodes belonging to the current domain to the entry node of the Core-Tree and reply to its parent PCE
For the PCE1, when it receives all the replies from its child PCEs it will merge all the sub trees into the final Core-Tree and graft all the destination nodes belong to the root PCE to the entry node from the final Core Tree.
Once the final Core-Tree is complete (the P2MP LSP path tree) it will reply to the PCC with the complete P2MP LSP path.
PCE5 U
PCE6 D2 7 7 7

8. Core-Tree Computation: VSPT for D1
PCE 4 computes D1 (1)
PCE 4 supplies {D1(1)}
PCE4
PCE 3 computes
V-T-D1 (3)
W-T-D1 (3)
PCE 3 supplies {VTD1(3), WTD1(3)}
PCE1 D1
PCE3 V T A
PCE 2 computes E-F-G-V-T-D1 (5) E-P-Q-R-M-W-T-D1 (7) H-P-E-F-G-V-T-D1 (7) H-P-Q-R-M-W-T-D1 (7) PCE 2 supplies {EGVTD1(5), EMWTD1(7),
HGVTD1(7), HMWTD1(7)} B
PCE2 G W C F E P M 2 Q R S A E G V T J
Sub-path (D1-1) 4 H
Sub-path (D1-2) S A E
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree.
- Phase 1 - Build the P2MP LSP Core Tree
The root PCE receives the request from the PCC and sends the request message to its PCE children
Each PCE will send the Border Node (BN) information which belongs to the current domain associated to it
The PCE then passes the request to its child PCE with their corresponding destinations
Once the destination domain with the leaf PCE is reached , we calculate the Virtual SPT (VSPT) for each entry node of each leaf domain, we call this node a leaf Node within the core tree.
When the root PCE receives all the VSPTs, from each domain it will build the necessary P2MP LSP Core M W T D1 K 2 2 S B C H E G
Sub-path (D1-3) V T S B C H M
Sub-path (D1-4) W T
PCE 1 computes VSPT(D1) 8 8 8

9. Core-Tree Computation: VSPT for D2
PCE 6 computes U-D2 (1)
PCE 6 supplies {UD2(1)}
PCE 5 computes
X-Z-U-D2 (3)
Y-U-D2 (3)
PCE 5 supplies {XUD2(3), YUD2(3)}
PCE1 A B
PCE2 G
PCE 2 computes E-P-Q-R-M-X-U-D2 (8) E-P-H-J-K-Y-U-D2(7) H-P-Q-R-M-X-Z-U-D2 (8) H-J-K-Y-U-D2(5) PCE 2 supplies {EMXUD2(8), EHYUD2(7),
HMXZUD2(8), HKYUD2(5)} C F E P M Q R J X 4 2
Sub-path (D2-1) S A E M X U
PCE5 Z H
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree. 2 2 K
Sub-path (D2-2) S A E H K Y U D2 Y 4 2 S B U
Sub-path (D2-3) C H M X U 2 D2
Sub-path (2-4) S B C H K Y U
PCE6
PCE 1 computes VSPT(D2) 9 9 9

10. Core-Tree Computation: Merging VSPTs
Merging two sub-path from each VSPTs into a Core Tree
Take a sub-path(D1-i) from VSPT(D1) and a sub-path(D2-j) from VSPT(D2).
Merge them into a Core Tree(D1-i-D2-j)
Compute the cost for the Core Tree (D1-i-D2-j)
Repeat (1) to (3) for all the i and j combinations to generate all the possible Core Trees
Evaluate and identify the Core Tree with the minimum cost among all the Core Trees
- Discuss how we select the final Core Tree 10 10

11. Core-Tree Computation: Merging VSPTs
Take a sub-path(D1-1) from VSPT(D1): 2
Sub-path (D1-1) S A E G V T 4
Sub-path (D1-2) S A E M W T 2 D1 2
Sub-path (D1-3) S B C H E G V T
Sub-path (D1-4) S B C H M W T
Core Tree (D1-1-D2-2) (cost: 14)
VSPT(D1) 2 D1 S A E G V T
Take a sub-path(D2-2) from VSPT(D2) 2 2 H K Y U D2 4 2
Sub-path (D2-1) S A E M X U 2 2
Sub-path (D2-2)
- Discuss how we select the final Core Tree S A E H K Y U D2 4 2
Sub-path (D2-3) S B C H M X U 2
Sub-path (D2-4) S B C H K Y U
VSPT(D2) 11 11

12. Core-Tree Computation: Merging VSPTs
Take a sub-path(D1-1) from VSPT(D1): 2
Sub-path (D1-1) S A E G V T 4
Sub-path (D1-2) S A E M W T D1 2 2
Sub-path (D1-3) S B C H E G V T
Sub-path (D1-4) S B C H M W T
Core Tree (D1-2-D2-2) (cost: 13)
VSPT(D1) 4 D1 S A E M W T
Take a sub-path(D2-2) from VSPT(D2) 2 x U D2 4
Sub-path (D2-1) S A E M X U 2 2 2
Sub-path (D2-2) S A E H K
- Discuss how we select the final Core Tree Y U D2 4 2
Sub-path (D2-3) S B C H M X U 2
Sub-path (D2-4) S B C H K Y U
VSPT(D2) 12 12

13. Inter-Domain P2MP Path Computation Final Core Tree
PCE4
Final Core Tree (D1-2-D2-1) with a minimum cost: 13
PCE1 4 D1 D1
PCE3 S A E M W T T A X U 2
PCE2 D2 W E P M Q R X
PCE5 Z
- Highlight the selection of the core tree with a cost of 13 U D2
PCE6 13 13 13

14. Inter-Domain P2MP Path Computation Procedures Final P2MP Tree
PCE4
PCE1 D1
PCE3 T A W E P M Q R
PCE2 X Z
Maybe combine slides 15 & 16
We will build a CoreTree for the topology illustrated to the right
The computation of the Core Tree is subject to an objective function of Shortest path tree.
- Phase 2 - Grafting destinations to the P2MP LSP Core Tree
PCE1 will now pass request message with all the destination nodes and also the CT to its child PCE
If the current PCE is not the leaf PCE, then it will rebuild the request message pass the message down to its child PCE
The leaf PCE will graft all the destination nodes belonging to the leaf domain to the entry node of the Core-Tree and reply it to its parent PCE
When a PCE receives the reply with the CT, it will graft all the destination nodes belonging to the current domain to the entry node of the Core-Tree and reply to its parent PCE
For the PCE1, when it receives all the replies from its child PCEs it will merge all the sub trees into the final Core-Tree and graft all the destination nodes belong to the root PCE to the entry node from the final Core Tree.
Once the final Core-Tree is complete (the P2MP LSP path tree) it will reply to the PCC with the complete P2MP LSP path.
PCE5 U
PCE6 D2 14 14 14

15. Core-Tree Based Inter-Domain P2MP Path Computation
A Core-Tree is a path tree with Boundary Nodes (BNs) from each domain corresponding to the PCE topology which satisfies the following conditions:
The root of the core tree is the ingress LSR in the root domain
The leaf of the core tree is the entry node in the leaf domain
The transit and branch node are from the transit and branch domains.
A Sub-Tree is a path tree within a domain with all of its sub root node, transit node and leaf node within the same domain.
The sub-tree within each domain is optimized subject to the OF.
The Computing each sub-tree is independent of the domain sequences
The grafting and pruning of multicast destinations in a domain has no impact on other domains and no impact on the core-tree
The initial overview of the Core Tree solution
- The root of the core tree is the ingress LSR in the root domain
- The leaf of the core tree is the entry node in the leaf domain
- The transit and branch node are from the entry and exit nodes from the transit and branch domains 15 15 15

16. Core-Tree Based Inter-Domain P2MP Path Computation
Core-Tree Based Procedures are done in three phases:
Procedure Phase 1: P2MP LSP Core Tree Building for the Boundary Nodes (BNs)
Based on Backward Recursive Path Computation (BRPC) procedures, builds a Extended Shortest Path Tree (VSPT) which has the egress as the root and the ingress as the leaf;
The source PCE builds all possible Core-Trees based on the VSPT computed from previous step;
Find out the optimal Core-Tree based on the OF;
Procedure Phase 2: In each leaf domain, using domain specific algorithm such as CSPF to compute the sub-tree which has the entry BN as the root and each individual destination as leave of the sub-tree.
Procedure Phase 3: Grafting destinations or the sub-trees in each domain to the P2MP LSP Core Tree computed from phase1.
The initial overview of the Core Tree solution
- The root of the core tree is the ingress LSR in the root domain
- The leaf of the core tree is the entry node in the leaf domain
- The transit and branch node are from the entry and exit nodes from the transit and branch domains 16 16 16

17. Core-Tree based solution has the following advantages;
Conclusions
Core-Tree based solution has the following advantages;
It computes the optimal inter-domain P2MP path which satisfies the OF for the path, and also the path is remerge free;
Domain confidentiality is kept;
Policy for each individual domain can be applied individually;
Each domain can has its own algorithms for its sub-tree computation;
The individual destination’s pruning and graphing is independent of the core-tree computing;
The solution is scalable; 17

18. Next Steps
We ask the working group to adopt this draft as working group document.
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