Algorithms for computing Maximally Redundant Trees for IP/LDP
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A lia Atlas (Juniper Networks) Gabor Enyedi , Andras Csaszar (Ericsson) IETF 83, Paris, France PowerPoint PPT Presentation


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Algorithms for computing Maximally Redundant Trees for IP/LDP Fast-Reroute draft-enyedi-rtgwg-mrt-frr-algorithm-01. A lia Atlas (Juniper Networks) Gabor Enyedi , Andras Csaszar (Ericsson) IETF 83, Paris, France. Agenda. Briefly about the algorithm Problem Avoid using a node

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A lia Atlas (Juniper Networks) Gabor Enyedi , Andras Csaszar (Ericsson) IETF 83, Paris, France

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A lia atlas juniper networks gabor enyedi andras csaszar ericsson ietf 83 paris france

Algorithms for computing Maximally Redundant Trees for IP/LDPFast-Reroutedraft-enyedi-rtgwg-mrt-frr-algorithm-01

Alia Atlas (Juniper Networks)

Gabor Enyedi, Andras Csaszar (Ericsson)

IETF 83, Paris, France


Agenda

Agenda

  • Briefly about the algorithm

  • Problem

  • Avoid using a node

  • Non-2-connected networks


Agenda1

Agenda

  • Briefly about the algorithm

  • Problem

  • Avoid using a node

  • Non-2-connected networks


Adag and partial order

ADAG and partial order

E

G

D

Root

C

S

B

A

H


Adag and partial order1

ADAG and partial order

  • Almost DAG (ADAG)

  • A<<B if there is a path from A to B

  • Root is both the shortest and the greatest

E

G

D

Root

C

S

B

A

H


Adag and partial order2

ADAG and partial order

  • S<<E

    • Blue path: increasing [S, E]

    • Red path: decreasing [Root, S] and [E, Root]

E

G

D

Root

C

S

B

A

H


Adag and partial order3

ADAG and partial order

  • S>>A

    • Blue path: increasing [S,Root] and [Root, A]

    • Red path: decreasing [A, S]

E

G

D

Root

C

S

B

A

H


Adag and partial order4

ADAG and partial order

  • S and C are not ordered

    • Blue path: [S, E] and [C, E]

    • Red path: [A, S] and [A, C]

E

G

D

Root

C

S

B

A

H


Agenda2

Agenda

  • Briefly about the algorithm

  • Problem

  • Avoid using a node

  • Non-2-connected networks


Three trees

Three trees

  • We have tree trees

    • SPT

    • Two MRTs

  • There is no connection between SPT and MRTs

  • Impossible to find a redundant pair for SPT

  • Example:

Shortest path

1

C

D

10

1

Dest

S

No redundant pair for that!

1

10

1

B

A

1


Agenda3

Agenda

  • Briefly about the algorithm

  • Problem

  • Avoid using a node

  • Non-2-connected networks


Total order

Total order

  • Partial order can compare any X only with S

    • We need to compare any two nodes

  • Make a total order as well

    • If A<<B, let A<B

    • If A and B are not ordered select either A<B or B<A

    • This can be done with a topological oder after converting the ADAG into a DAG

  • Results:

    • If A<B, either A<<B or A and B are not ordered


A possible total order

A possible total order

  • Numbers are written next to nodes

8

7

E

G

6

D

Root

C

S

4

5

0

3

B

A

H

1

2


Possible cases

Possible cases

  • If dst>>src, failed node F

If S<<F<E, it may be on the BLUEpath

8

7

E

G

6

D

Root

C

S

4

5

0

3

B

Otherwise: it may be on the REDpath

A

H

1

2


Possible cases1

Possible cases

  • If dst<<src, failed node F

Otherwise: it may be on the BLUEpath

8

7

E

G

6

D

Root

C

S

4

5

0

3

If A<F<<S, it may be on the RED path

B

A

H

1

2


Possible cases2

Possible cases

  • If dst and src are not ordered

    • There are four sub-paths

If F>>src, it may be on the first part of the RED path

If F and src are not ordered, and F>dest, it may be on the second part of the RED path

7

8

E

G

6

D

4

Root

C

S

5

0

3

F and src are not ordered, and F<dest, it may be on the second part of BLUE path

B

If F<<src, it may be on the first part of the BLUE path

A

H

1

2


Agenda4

Agenda

  • Briefly about the algorithm

  • Problem

  • Avoid using a node

  • Non-2-connected networks


Non 2 connected problem

Non-2-connected problem

  • In this case we don’t have a single order

    • Neither a partial order

    • Nor a total order

  • Convert the GADAG into an ADAG!

C

A

Non-root block

X

Local root block

D

B


Non 2 connected problem1

Non-2-connected problem

  • In this case we don’t have a single order

    • Neither a partial order

    • Nor a total order

  • Convert the GADAG into an ADAG!

C

A

X1

Non-root block

Local root block

X2

D

B


A lia atlas juniper networks gabor enyedi andras csaszar ericsson ietf 83 paris france

Thank you!


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