Internet and Overlay NetworksInternet and Overlay Networks

Ram KeralapuraRam KeralapuraECE DeptECE Dept

rkeralapura@ucdavis.edurkeralapura@ucdavis.edu

22

Layered ArchitectureLayered Architecture

Five main layersFive main layers• Application layerApplication layer• Transport layerTransport layer• Network (IP) layerNetwork (IP) layer• Link layerLink layer• Physical/Optical layerPhysical/Optical layer Optical switches

Optical fibers

Routers Virtual IP links

Applications/ComputersApplication layer links

33

IntroductionIntroduction

Internet Routing InfrastructureInternet Routing Infrastructure• Intra-domain routing (IGP) Intra-domain routing (IGP)

RIP, OSFP, ISIS, etc.RIP, OSFP, ISIS, etc.

• Inter-domain routing Inter-domain routing BGPBGP

Internet

Domain orAutonomous System

44

Intra-domain RoutingIntra-domain Routing

Links are assigned link costs/weightsLinks are assigned link costs/weights Path between two nodes inside a Path between two nodes inside a

domain follows shortest path (least domain follows shortest path (least cost path) cost path)

A

F E

B C

D

2

1

3

4

1

1

7

2

Dst A

F E

B C

D

55

Network PropertiesNetwork Properties

Important properties of networks that Important properties of networks that service providers look for:service providers look for:• ConnectivityConnectivity• PerformancePerformance• ResiliencyResiliency• Robustness in functionalityRobustness in functionality

Service availability – delivering a given Service availability – delivering a given packet from source to destinationpacket from source to destination

66

Characterizing NetworksCharacterizing Networks

Main causes for concern – resiliency Main causes for concern – resiliency and robustnessand robustness• How does the IGP protocol behave How does the IGP protocol behave

during network component failures?during network component failures?• How does the behavior impact the data How does the behavior impact the data

that the network carries?that the network carries?

77

Characterizing Networks (cont’d)Characterizing Networks (cont’d)

We have developed a model that We have developed a model that captures the dynamic behavior of the captures the dynamic behavior of the network protocols during link failures network protocols during link failures [Keralapura et al, 2004][Keralapura et al, 2004]

Protocol convergence depends on:Protocol convergence depends on:• Topology – nodes and connectivityTopology – nodes and connectivity• Protocol timer settingsProtocol timer settings• Number of entries to update in the Number of entries to update in the

forwarding tablesforwarding tables

88

Characterizing Networks (cont’d)Characterizing Networks (cont’d)

Metrics for service availabilityMetrics for service availability• Service disruption timeService disruption time• Traffic disruptionTraffic disruption

Based on the above metrics we Based on the above metrics we define “goodness factor” for the define “goodness factor” for the networknetwork

99

Results (cont’d)Results (cont’d)

Static properties (like node out-degree) do not capture operational conditions and network dynamics

Out Degree

Out Degree

Ingre

ss N

ode G

oodness

Ingre

ss N

ode G

oodness

1010

Network Diameter

Netw

ork

Goodness

Similar results were also found in the paper “Layered Complex Networks” by Kurant and Thiran

1111

Internet ArchitectureInternet Architecture

Tiered hierarchy in domainsTiered hierarchy in domains

Tier-1

A

Tier-1

A

Tier-1

B

Tier-1

B

Tier-2C

Tier-2C

Tier-2D

Tier-2D Tier-2

E

Tier-2E

Tier-2F

Tier-2F

Peering relationship

Customer-Provider relationship

1212

Inter-domain routingInter-domain routing

Policy-based routingPolicy-based routing• Ad-hoc and can change with agreements Ad-hoc and can change with agreements

with other domainswith other domains Can we capture these policies?Can we capture these policies?

• Domains do not disclose their connectivityDomains do not disclose their connectivity Policies can obstruct views and hinder Policies can obstruct views and hinder

domain-level topology discoverydomain-level topology discovery• Need multiple vantage points for more Need multiple vantage points for more

accurate topology informationaccurate topology information

1313

Application Layer NetworksApplication Layer Networks

Email NetworksEmail Networks World Wide Web (WWW)World Wide Web (WWW) Peer-to-Peer (p2p) NetworksPeer-to-Peer (p2p) Networks Several Content Delivery Networks Several Content Delivery Networks

(CDN)(CDN)

Overlay networks

1414

Background: Overlay NetworksBackground: Overlay Networks

A

A’

X

B

C

D

Y

C’

B’

D’

Domain-1

Domain-2

Domain-3

Domain-4

1515

Interaction between networksInteraction between networks

Overlay networks compete with IP Overlay networks compete with IP networks to provide routing servicenetworks to provide routing service

IP and overlay networks are unaware IP and overlay networks are unaware of key things happening at the other of key things happening at the other layerlayer

Multiple overlay networks co-exist Multiple overlay networks co-exist and make independent decisionsand make independent decisions

How does all this affect IP and How does all this affect IP and overlay networks?overlay networks?

1616

Interactions between NetworksInteractions between Networks

Identified some potential interactions Identified some potential interactions [Keralapura et al, 2005][Keralapura et al, 2005]• Traffic engineering in IP networksTraffic engineering in IP networks

Load balancing issuesLoad balancing issues IP layer traffic matrix estimationIP layer traffic matrix estimation

• Coupling of multiple domainsCoupling of multiple domains Defeats the objective of BGPDefeats the objective of BGP

• Multiple co-existing overlay networksMultiple co-existing overlay networks Traffic oscillationsTraffic oscillations Cascading reactionsCascading reactions

1717

A

BD

C

E

HG

F

NM

5

20

8

8

5

5

5 5

5

5

5 5

55

Load Balancing and TM EstimationLoad Balancing and TM Estimation

1818

Coupling Multiple AS DomainsCoupling Multiple AS Domains

A E

Domain-1 Domain-2

B

C

D H

F

GX

Defeats one of the objectives of BGP to decouple different domains

1919

Traffic OscillationsTraffic Oscillations

Time (ms)

Link

Util

izat

ion

Failure of link 10-12 Failure of link 2-5

Traffic Oscillations

2020

Open questionsOpen questions

Interactions need to be understood Interactions need to be understood better and we need to model thembetter and we need to model them

How to go about characterizing the How to go about characterizing the robustness of a network after we robustness of a network after we model such interactions?model such interactions?

Are there interactions between Are there interactions between networks at other layers?networks at other layers?• If yes, then how to we qualify, quantify, If yes, then how to we qualify, quantify,

and model them?and model them?