MPLS Protection Routing: A Tutorial Zartash Afzal Uzmi.

MPLS Protection Routing: A Tutorial

Zartash Afzal Uzmi

Jan 13, 2006 Lahore University of Management Sciences 2

First slide…

Questions?Ask when you have them!


Outline Background

Network Services and QoS Architectural Requirements IP and MPLS

Introduction to protection and restoration routing Terminology Local Protection: Types of Backup Paths Fault Models Backup Bandwidth Sharing Activation sets

Protection routing framework Components Typical example Evaluation and Experimentation


Outline Background





Network Traffic and Services Network Traffic today

Not what it was 10 years ago Multimedia intensive

New and interactive applications are emerging Internet telephony Videoconferencing Streaming media (voice and video) Remote collaboration (e.g., remote desktop)

Many new applications are real-time More and more users of these applications

Burstiness behavior has changed over the years!


Current Network Architecture Internet is popular because

It is inexpensive Internet is inexpensive because

It uses resource sharing by means of statistical multiplexing

Current Internet architecture Uses packet switches with buffers Required buffer size is primarily determined by a

random traffic pattern Buffer size optimization

Too low High drop rate Too high High delay


Architectural Requirements

Emerging applications Two-way interactive communications One-way streaming media type applications

Under normal conditions We are worried about the buffers used in two-way

interactive applications When resources fail

We are also worried about the one-way applications Current Internet architecture is not suitable

for new and emerging applications New architectures are being researched


Architectural Requirements New network architectures

All circuit-switched? Mix of packet-switch and “circuit-switch-like”

Experience with networks Bigger buffers are required when there is more

randomness and more aggregation Should use circuits at places where we see more

aggregation Example: 100x100 project

Edge network is packet-switched Core network is virtual-circuits


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)


Outline Background





Protection and Restoration

Restoration On-demand recovery – no preset backup paths Example: existing recovery in IP networks

Protection Pre-determined recovery – backup paths “in advance” Primary and backup are provisioned at the same time

IP supports restoration Because it is datagram service

MPLS supports restoration as well as protection Because it is virtual-circuit service


Restoration in IP network

In traditional IP, what happens when a link or node fails? Failure 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 protection possibilities in an MPLS network, but… First we need to look at the QoS

requirements


QoS Requirements Bandwidth Guaranteed Primary Paths

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

Minimal “Protection or Restoration Latency” Protection/Restoration latency is the time that

elapses between: “the occurrence of a failure”, and “the diversion of network traffic on a new path”

Restoration is generally SLOWER than protection


Protection in MPLS First we define Protection level

Path protection Also called end-to-end protection For each primary LSP, a node-disjoint backup LSP is set up Upon failure, ingress node diverts traffic on the backup path

Local Protection Upon failure, node immediately upstream the failed element

diverts the traffic on a “local” backup path

Path Protection More LatencyLocal Protection Less Latency


Protection in MPLS

S 1 2 3 D

Primary PathBackup Path

Path Protection

This type of “path Protection” still takes 100s of ms.We may explore “Local Protection” to quickly switch onto backup paths!


Local Protection: Fault Models

A B C DLink Protection

A B C D

A B C D

Node Protection

Element Protection


Protection Modes 1+1 protection

Flow sent on two separate disjoint paths Receiver responsible for choosing one of the two

1:1 protection A backup path protects a single LSP (or a portion of

a single LSP) N:1 protection

A backup path protects one link or one node or both Overlapping portions of many LSPs are protected by

a single backup path Applicable for local protection only

N:M protection (M<N)


nhop and nnhop paths


All links and all nodes are protected!

A B C D E

PLRPLR: Point of Local Repair: Point of Local Repair

nnhop

nhop

LOCAL PROTECTION


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

LSP1LSP1

LSP2LSP2

BW: XBW: X


XX XXXX

YY YYX+Y

Sharing


Activation Sets

A

B

C

D

E

Activation set for node B

Activation set for link (A,B)

A

B

C

D

E


Outline Background





Protection 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 primary LSPs that can be placed on the network


Evaluation & Experimentation Traffic Generation

Use existing or emerging traffic models Consider call holding times and multi-service traffic

Rejected Requests Experiments Generate a set of LSP requests Measure the number of rejected requests Simulate on various topologies

Network Loading Experiments Set link capacities to infinity Measure the total bandwidth required to service a

given set of LSP requests Simulate on various topologies


Recent Trends Preemption of lower class traffic Multilayer recovery

We can “almost” deal with recovery at a single protocol layer

What if we intend to provide recovery at multiple protocol layers?

For multilayer recovery, we need to consider these additional issues: Interworking of layers Local information stored at each node of each layer Recovery provided by each individual layer Signaling mechanism from one layer to another Effects on bandwidth sharing (if sharing is used)


We are not done, yet…Questions & Answers


Extra Stuff!Example: A Protection Routing

Architecture


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 Rij: Bandwidth remaining on link (i, j)

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

backup paths spanning link (i, j) Also propagate Gij and Rij

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


Single Link Protection: Network 1


Single Node Protection: Network 1


Single Element Protection: Network 1


More Extra Stuff!Bandwidth Sharing Model for

oAIS


A Bandwidth Sharing Model


All links 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


Last slide…

Thank you!Questions?

MPLS Protection Routing: A Tutorial Zartash Afzal Uzmi.

Documents

Transcript of MPLS Protection Routing: A Tutorial Zartash Afzal Uzmi.