MPLS Local Restoration using Optimized

Aggregate Information

Zartash Afzal UzmiComputer Science and Engineering

Lahore University of Management Sciences

May 18, 2005 Lahore University of Management Sciences 2

Outline

Introduction QoS Requirements Local Restoration: Types of Backup Paths Local Restoration: Fault Models

Backup Bandwidth Sharing Activation sets The new model for bandwidth sharing Optimized aggregate information scenario (oAIS) Experiments, simulations, and results

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QoS Requirements Bandwidth Guaranteed Primary Paths

Bandwidth Guaranteed Backup Paths BW remains provisioned in case of network failure

Minimal “Restoration Latency” Restoration latency is the time that elapses between the

occurrence of a failure and the diversion of network traffic on a new path

Path Restoration More LatencyLocal Restoration Less Latency

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Types of Backup Paths

A next hop (nhop) path that spans a link (i, j) is a backup path which: originates at node i, and provides restoration for a primary LSP that traverses (i, j), if

(i, j) fails.

i j

PLRPLR: Point of Local Repair: Point of Local Repair

nhop path that spans (i, j)

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Types of Backup Paths

A next next hop (nnhop) path that spans a link (i, j) is a backup path which: originates at node i, and provides restoration for a primary LSP that traverses (i, j), if

either (i, j) or node j fails.

i j

PLRPLR: Point of Local Repair: Point of Local Repair

nnhop path that spans (i, j)

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Local Restoration: Fault Models

A B C DLink Protection

A B C D

A B C D

Node Protection

Element Protection

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nhop and nnhop paths

Primary Path

Backup Path All links and all nodes are protected!

A B C D E

PLRPLR: Point of Local Repair: Point of Local Repair

nnhop

nhop

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Opportunity cost of backup paths

Local Protection requires that backup paths are setup in advance Upon failure, traffic is promptly switched onto

preset backup paths

Bandwidth must be reserved for all backup paths This results in a reduction in the number of Primary LSPs

that can otherwise be placed on the network

Can we reduce the amount of “backup bandwidth” but still provide guaranteed backups?

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BW Sharing in backup Paths

Example:

max(X, Y)

BW: Y

A B

C D

E F G

L1L1

L2L2

BW: XBW: X

Primary Path

Backup Path

XX XXXX

YY YYX+Y

SharingSharing

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Activation Sets

A

B

C

D

E

Activation set for node B Activation set for link (A,B)

A

B

C

D

E

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Extent of BW Sharing: oAIS

Aggregate Information Scenario (AIS) Fij: Bandwidth reserved on link (i, j) for all primary LSPs Gij: Bandwidth reserved on link (i, j) for all backup LSPs

Optimized AIS (oAIS) – (Hij instead of Fij) Hij: Maximum bandwidth reserved on any one link by all

backup paths spanning link (i, j)

More Information propagated More potential for BW sharing

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oAIS versus AIS: ExampleLSP Request-1 (src, dst, bw) = (A, C, 4)

A

F

D E

B C

G

FAB=4

HAB=4

GAF=4

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oAIS ExampleLSP Request-2 (src, dst, bw) = (A, C, 5)

A

F

D E

B C

G

FAB=9

HAB=5

GAF=4

GAG=5

FAB=4

HAB=4

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oAIS ExampleLSP Request-3 (src, dst, bw) = (D, E, 7)

A

F

D E

B C

G

FAB=9

HAB=5

GAF=4

GAG=5

FDE=7

GAF=7

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oAIS ExampleLSP Request-4 (src, dst, bw) = (A, C, 6)

A

F

D E

B C

G

FAB=9

HAB=5

GAF=7

GAG=5

FDE=7Need to Evaluate cost of all possible backup paths?How much BW is shareable on (A, F)?

AIS:Shareable = max(0, GAF - FAB) = GAF - min(GAF, FAB) = 0Additional resv = 6

oAIS: (HAB ≤ FAB)Shareable = GAF - min(GAF, HAB) = 2Additional resv = 6 - 2 = 4

CIS: (link (A,B) knows BWred)Shareable = GAF - BWred = 7 - 4 = 3Additional resv = 6 - 3 = 3

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Bandwidth Sharing Model

Previous: Aij:= Set of all primaries traversing through (i, j) Bij:= Set of all backups traversing through (u, v)

Our definition (for link protection case): Aij:= Set of all primaries traversing through (i, j) Bij:= Set of all nhop paths traversing through (u, v) µij:= Set of all nhop paths that span (i, j) ij

uv:= Buv ∩ µij

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Bandwidth Sharing Model

i

u v

j k

RED=7BLU=2

3

OLD MODEL:Aij = {R, B}Buv = {R, B, …}Aij ∩ Buv= {R, B}|| Aij ∩ Buv || = 2+7 = 9Un-shareable = 9Shareable = 10 - 9 = 1

GRN=3 (New Request)Guv = 10

NEW MODEL:Aij = {R, B}Buv = {nhij

r, nhijb, …} (nhops through (u, v))

µij = {nhijr, nhij

b, …} (nhops spanning (i, j))ij

uv = µij ∩ Buv= {nhijr}

|| ijuv || = 2 + 7 = 9 (Un-shareable)

Shareable = Guv - || ijuv || = 10 - 9 = 1

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Bandwidth Sharing Model

i

u v

j k

RED=7BLU=2

3

OLD MODEL:Aij = {R, B}Buv = {R, B, …}Aij ∩ Buv= {R, B}|| Aij ∩ Buv || = 2+7 = 9Un-shareable = 9Shareable = 10 - 9 = 1

NEW MODEL:Aij = {R, B}Buv = {nhij

r, nhjkb, …} (nhops through (u, v))

µij = {nhijr, nhij

b, …} (nhops spanning (i, j))ij

uv = µij ∩ Buv= {nhijr}

|| ijuv || = 7 (Un-shareable)

Shareable = Guv - || ijuv || = 10 - 7 = 3

GRN=3 (New Request)Guv = 10

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Simulation Experiments

Rejected Requests Experiments Simulated on two topologies Measure the number of rejected LSPs for each

information scenario Network Loading Experiments

Simulated on two topologies Link capacities set to infinity Measure the total bandwidth required to service a

given set of LSPs for each information scenario

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Single Link Protection: Network 1

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Single Link Protection: Network 1

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Single Link Protection: Network 2

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Single Link Protection: Network 2

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Single Node Protection: Network 1

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Single Element Protection: Network 1

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Questions & Answers

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Restoration in MPLS

Primary Path

Backup Path

Path Protection

MPLS path Protection may take 100s of ms, whereas MPLS Local protection takes less than 10 ms.

A B C D E