Subnet Level Internet Topology Generator

Mehmet Burak AKGUN

CS790 Complex Networks

OUTLINE

•Introduction

•Literature Review

•Subnet Level Generator Design Targets

•References

2

Introduction

Internet is not always available for experimental purposes. Thus researchers use network simulators.

In order to evaluate new algorithms and protocols, network researchers need realistic network topologies to be used in the simulation environment

General purpose of internet topology generators is to synthesize realistic and highly configurable internet topologies in a reasonable time.

3

4

Why not use Existing topologies?

By Stephen G. Eick - http://www.bell-labs.com/user/eick/index.html 

Why not use Existing topologies?•Internet is growing in a distributed and

uncontrolled fashion•Achieving a deep understanding of

internet topology is a challenging task.•Operators do not want to publish the

details of the existing topology•AS-level connectivity is based on the

complex business relationships and routing policies among service provider companies

5

Topology Discovery Studies

•Many studies were carried out to map the actual internet topology through Trace-Route.

However no one is completely successful.- Aliasing issues- Load Balancing Routers

- Unresponsive Routers

-It takes a long time to tracert huge number the paths.

6

Literature Review

•Before 1999▫There is a strong belief that internet is

hierarchical•1999-2001

▫Discovery of internet’s degree distribution to be power law

•2001-▫Attention shifted again from local properties

to large scale properties which are better represented by hierarchical generators.

7

Routing of Multipoint Connections B.M. Waxman 1988

Produces random graphs using Erdos-Renyi random graph model

Nodes are uniformly distributed on a planeExistence of an edge between two nodes is

a probabilistic function of the distance between nodes. (inversely affected by distance)

8

TiersM. Doar. A Better Model for Generating Test Networks 1996•A multi-tier network topology generator

▫WAN, MAN, LAN•Three level hierarchical structure•Only one WAN per random topology•For each level of hierarchy, user specifies

number of nodes•Minimum spanning tree is calculated

9

GT-ITMHow to Model an Internetwork, E.W.Zagura et.al. 1996•Two types of hierarchical graphs(n-level, TS)

▫Transit-stub reproduces the hierarchical structure of internet.

▫Firstly a connected random graph is generated▫Each node is considered as a transit domain

and each transit domain is expanded to form another connected random graph

▫After running expanding operation for levels, A number of random graphs are generated and connected to each node in the network as Stubs

10

On Power-LawRelationships of the Internet Topology. C. Faloutsos, P. Faloutsos, and M. Faloutsos. 1999.•Measurements on internet

▫AS level (Autonomous Systems as nodes)▫Router level (Routers as nodes)

•Found out that Degree Distribution of these graphs are power laws

•Led to a new generation of topology generators which does not model the hierarchical structure of internet and focus on the node degrees

11

Degree Based Topology Generators•These generators assume the fact that, it

is more important to match the local properties of internet (like degree distribution) rather than large scale hierarchical structure

12

Heuristics for Internet Map Discovery, R. Govindan, H. Tangmunarunkit, Infocom 2000•Measurements conducted by Bell-labs

using 284806 nodes and 449306 edges.•System named MERCATOR•All measurements are router level, i.e, no

end hosts (which may be up to billions)•Connection degree is lower than 0,001 %

13

14

A map of the Internet as discovered by the Bell-labs.Links painted with different colors represent different geographical

locations.

Internet Node Degree Distribution by Bell-Labs 97% correlation with ideal power law distribution

15

Inet: Internet Topology GeneratorCheng Jin, Qian Chen, Sugih Jamin 2000

•AS level generator•User specifies target size•Inet assigns degree for each node

according to the power degree distribution

•Forms the spanning tree using the number of edges decided for each node

16

BRITE: An Approach to Universal Topology Generation

Alberto Medina, Anukool Lakhina, Ibrahim Matta, and John Byers,2001• Argue that preferential connectivity and

incremental growth are the primary reasons of the power law distribution of internet

• Skewed node placement▫ Area is divided into HSxHS squares and nodes

distributed (one node is selected for backbone)▫ Each square is further divided into LSxLS squares

nodes are uniformly distributed among squares

• Locality based preferential network connections (uses Waxman probabilistic

function)• Degree distribution is also preserved for nodes

17

Controversy

•Internet is growing in hierarchical structure

•Opposite to our intuitions, internet topology generators using power law degree distribution(BRITE and INET), perform better than structural generators(TIERS).

18

Network Topology Generators: Degree based vs Structural H. Tangmunarunkit SIGCOMM 2002•Arguing that modeling large scale

structure of internet(hierarchical structure) should be more important than local properties(degree distribution)

•Defined metrics to compare degree based and structural generators.

•Degree based generators are surprisingly perform well for large scale metrics.

19

IGen: Generation of Router-level InternetTopologies through Network Design HeuristicsB. Quoitin et.al. 2009• Router level topology generator• Most of the previous internet topology

generators use random networks, which is not a realistic assumption

• Internet topology is highly engineered, optimized for costs and affected by business relations among Autonomous Systems.

• Topology design is a complex issue. O(n^5)• Engineers use heuristics (MENTOR,

MENTour,Delaunay triangulation and two-trees.

• IGen tries to mimic the engineering approach by using these heuristics.

20

21

Subnet Level Topology Generation•Objectives

▫Subnet level design (unique for now)▫Realistic Topologies(may use heuristics as

in Igen)▫Compatible to famous simulators (NS-2)▫Highly configurable to fit various network

applications and satisfy user needs.▫User-friendly gui

22

References• A. Medina, A.Lakhina, I. Matta, J. Byers, “ BRITE: Universal Topology Generation from a User`s

Perspective” Ninth IEEE International Symposium on Modeling, Analysis, and Simulation of Computer and Telecommunications Systems (MASCOTS`01), Cincinnati, Ohio, 2001.

• B. Quoitin, V.V.D. Schrieck, P. Francois and O. Bonaventure, “IGen: Generation of Router-Level Internet Topologies through Network Design Heuristics” 21st international Teletraffic Congress,Paris, France 2009

• C. Jin, Q. Chen, S. Jamin, “Inet, Internet Topology Generator” , ACM SIGCOMM Computer Communication Review, vol.32 Issue 4, pp.147-159, October 2002.

• H. Tangmunarunkit, R. Govinan, S. Jamin, S. Shenker, W. Willinger, “Network Topologies, Power Laws, and Hierarchy”, ACM Sigcimm Computer Communication Review, vol.32, Issue 1, pp.76-76, 2002.

• V. Paxson, S. Floyd, “” why we don’t know how to simulate the internet”, Proceedings of 29 th conference on Winter Simulation, pp.1037-1044, Atlanta, Georgia, United States, 1997.

• H. Haddadi, S. Uhlig, A. Moore, R. Mortier, M. Rio, “Modeling Internet Topology Dynamics”, ACM SIGCOMM Computer Communication Review, vol.38, Issue 2, pp.65-68, April 2008

• M.B. Doar, “A Better Model for Generating Test Networks”, GLOBECOM Global Telecommunications Coference, pp.86-93, London, Novenber 1996.

• R. Govindan, H. Tangmunarunkit, “Heuristics for Internet Map Discovery” , INFOCOM 2000• B.M. Waxman, “Routing of Multipoint Connections”, IEEE Journal of selected Areas in

Communications, vol.6, no:9, pp.1617-1622, December 1988. http://www.math.uu.se/research/telecom/software/stgraphs.html

23

Thank you

Questions

?

24