Restoration Routing in MPLS Networks

Restoration Routing in MPLS Networks

Zartash Afzal UzmiComputer Science and Engineering

Lahore University of Management Sciences

Sept 17, 2005 Lahore University of Management Sciences 2

Outline

Background: Quick overview of MPLS Introduction to restoration routing

QoS Requirements: Why restoration routing? Local Restoration: Types of Backup Paths Local Restoration: Fault Models

Backup Bandwidth Sharing Activation sets Typical example of restoration routing frameworks

Optimized aggregate information scenario (oAIS) Experiments, simulations, and results


IP versus MPLS

In IP Routing, each router makes its own routing and forwarding decisions In MPLS, source router makes the routing decision Intermediate routers make forwarding decisions

A path is computed and a “virtual circuit” is established from ingress router to egress router

An MPLS path or virtual circuit from source to destination is called an LSP (label switched path)


Restoration in IP network

In traditional IP, what happens when a link or node fails? Information needs to be disseminated in the

network During this time, packets may go in loops Restoration latency is in the order of seconds

We look for restoration possibilities in an MPLS network


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


Restoration in MPLS

S 1 2 3 D

Primary Path

Backup Path

Path Protection

This type of “path Protection” still takes 100s of ms.

We need to explore “Local Protection” to quickly switch onto backup paths!


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)


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


nnhop path that spans (i, j)


Local Restoration: Fault Models

A B C DLink Protection

A B C D

A B C D

Node Protection

Element Protection


nhop and nnhop paths

Primary Path

Backup Path All links and all nodes are protected!

A B C D E


nnhop

nhop


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?


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


Activation Sets

A

B

C

D

E

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

A

B

C

D

E


Restoration Routing Frameworks

We look to answer the following questions? Who computes the primary path? What is the fault model (link, node, or element protection)? Where do the backup paths originate? Who computes the backup path? At what point do the backup paths merge back with the primary

path What information is stored locally in the nodes/routers What information is propagated through routing protocols What if a primary path can not be fully protected

The goal is almost always to maximize bandwidth sharing Performance criteria is almost always the maximum number of

LSPs that can be placed on the network


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


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


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


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


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

A

F

D E

B C

G

FAB=9

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

HAB=5


A Bandwidth Sharing Model

Primary Path

Backup Path All links and all nodes are protected!

(Simplified for the Link Protection Fault Model)Recall the definition of nhop paths

A B C DLink Protection


Bandwidth Sharing Model

Previous: Aij:= Set of all primaries traversing through (i, j)

Buv:= Set of all backups traversing through (u, v)

New definition (specialized for link protection case): Aij:= Set of all primaries traversing through (i, j)

Buv:= Set of all nhop paths traversing through (u, v)

µij:= Set of all nhop paths that span (i, j)

ijuv:= Buv ∩ µij (set of paths falling on (u,v) if (i,j) fails)



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, nhij

b}|| ij

uv || = 2 + 7 = 9 (Un-shareable)Shareable = Guv - || ij

uv || = 10 - 9 = 1



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


Simulation Experiments

Rejected Requests Experiments Measure the number of rejected LSPs for each

information scenario Simulated on two topologies

Network Loading Experiments Link capacities set to infinity Measure the total bandwidth required to service a

given set of LSPs for each information scenario Simulated on two topologies


Single Link Protection: Network 1


Single Node Protection: Network 1


Single Element Protection: Network 1


Questions & Answers


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

Restoration Routing in MPLS Networks

Documents

Transcript of Restoration Routing in MPLS Networks