The Workshop on Internet Topology (WIT) Report

ACM SIGCOMM Computer Communication Review Volume

37 ,  Issue 1  (January 2007)

Dmitri Krioukov CAIDA

Fan Chung UCSD

kc claffy CAIDA

Marina Fomenkov CAIDA

Alessandro Vespignani Indiana University

Walter Willinger AT&T Research

What we need to know to understand Internet Topology

• As and router level topology generation mechanisms.

• Degree based methods (PLRG, BA, BRITE, BT, INET)

• Structural methods (GT-ITM)

• Canonical topologies

• General model of Random Graphs (GRG)

• Power law Random Graph (PLRG)

Outline

• Motivation of different people interested in this area

• Different models

• Different way for data collection

• Open Problems

• Recommendations

Motivationnetworking researchers

• what a node or a link represents• physically meaningful topologies ie router-level connectivity• logical constructs such as AS-level topology, or overlay networks

such as the WWW graph, email graph, P2P networks• how new technologies, policies, or economic conditions will impact

the Internet’s connectivity structure at different layers.

physicists

• Internet is just one of many examples of a complex network.• Physicists search for inherent principles shaping small and large-

scale network patterns. • They want to find universal laws on application domains.

MotivationMathematicians• Internet topology analysis, having mathematicians involved will

stimulate the development of suitable mathematical apparatuses.Engineers• need understand the Internet structure since performance of several

applications and protocols depends strongly on peculiarities of an underlying network.

• Ex: Recent research suggests that observed Internet-like topologies are particularly well-structured for routing efficiency (A. Brady and L. Cowen, “Compact routing on power-law graphs with additive stretch,” in ALENEX, 2006. ) but the existing Internet routing architecture does not exploit this efficiency. The knowledge and understanding of the topological properties of the Internet should help engineers to optimize future technological developments.

Data

• Mathematicians do not need data at all• Physicists are interested in data to support their

models, but are not especially concerned much about the data quality

They both rely on Networking community• Engineers are the closest to collecting actual data, at

least about their own networks. However, data ownership and stewardship are complex and highly charged issues with numerous social, political, liability, and security implications.

• It is the responsibility of all data users to educate themselves on the incompleteness, inaccuracy, and other deficiencies of these measurements and to avoid over interpretation.

Data Collection Techniques

• Simulation technique for random graph generator • Router level graph

– Trace route over months, over different monitoring points to collect data

• WHOIS database– Whois databases enable you to search for information about the

people, computers, organizations, and name servers. top-level domains ".com", ".net", and ".org" can be searched from their online database ie. http://www.whois.sc/

- Search domain names using partial word(s) in Domain Search.- Partial word(s) searching on active domain names ("bill gates")- IP address searching ("66.218.71.198")- Full domain ( nameintel.com goes directly to whois)

Data Collection Techniques

• What is AS? – IP with common Routing policies

• What is BGP? - organizations can run BGP using private AS numbers to an

ISP that connects all those organizations to the Internet • BGP data collection (Autonomous Systems AS level

graph) – BGP tables are collected from Oregon route Server, this

connects to the various ISP for collecting BGP table. http://www.routeviews.org

– The ability to infer AS peering relationship, from BGP routing tables depends largely on inter-AS business contracts. If a business contract does not permit a given inter-AS route to be used by a third party, BGP does not advertise this information to the global Internet.

– Internet Routing Registry (IRR) databases

Models

• Static - constructing statistical ensembles of random networks with certain characteristics matching values measured in the real Internet.

• Dynamic - trying to reproduce the details of the Internet evolution/growth

Networking researchers– descriptive in the sense of matching certain graph-

theoretic properties– provide context for known structural or architectural

features of InternetPhysicists and Mathematicians

– Lets leave it

(OPEN PROBLEMS) better Internet topology data

• Incompleteness of the data– classical Erd˝os-R´enyi random graphs, are extremely unlikely to represent real

Internet topologies measured from multiple vantage points– inference of probability distributions specifying possible quantitative deviations of

real topologies from measured ones remains largely an open problem– lack of observation points, finite number of destinations probed, inability to

capture other layers and disambiguate between high-degree nodes and opaque clouds

• We need targeted measurements focused on particular geographic areas.• Existing measurement tools have not demonstrated the ability to scale up to

measure link and/or node properties across realistic networks• Internet measurement would ideally progress from measuring only the intra-

and inter-AS topology at the router- and AS-level (“An empirical approach to modeling inter-AS traffic matrices,” in IMC, 2005.)

(OPEN PROBLEMS) Modeling

• Descriptive models strive to reproduce some graph-theoretic properties of the Internet and usually are not concerned with their network-specific interpretation. (“The Internet AS-level topology: Three data sources and one definitive metric,” Computer Communication Review, vol. 36, no. 1, 2006. )

• explanatory models acknowledge domain-specific constraints (traffic conditions, cost-minimization requirements, technological reality ) while attempting to simulate the fundamental principles and factors responsible for the structure and evolution of network topology. But which factors are critical is open problem.

(OPEN PROBLEMS) Modeling

• Future developments in the field of Internet modeling may include the following advancements – Annotated models of an ISP’s router-level topology, where

nodes are labeled with router capacity, type, or role, and link labels describe delay, distance, or bandwidth;

– annotated models of the Internet’s AS-level topology, where node labels include AS-specific information, e.g., number and/or locations of PoPs, customer base, and link labels reflect peering relationships

– models built around parameters closely related to real use of the network, e.g., routing models that define and utilize routing-related parameters such as robustness, fairness, outage, etc.

– dynamic, evolutionary models of the Internet deriving simple rules for network evolution from actual technological constraints, e.g., from known Cisco router characteristics.

(OPEN PROBLEMS) General Theory

Internet is complex engineered system because• At the AS level, the Internet topology is a result

of local business decisions independently made by each AS

• On the other hand, at the router level the Internet topology is a product of human-controlled technological optimizations aiming to minimize cost and maximize efficiency

(OPEN PROBLEMS) General Theory

• Traditional graph theory is not suitable for dealing with dynamic network structures that change over time.

• Multiple layers in the Internet protocol stack have their own corresponding topologies, i.e., fiber, optical, router, AS,Web, P2P graphs, that describe significantly different aspects of Internet connectivity.(Multiscale Modelling and Simulation, Springer, Berlin, 2004 )

• Need to development of new approaches, techniques, and tools for measuring or inferring, AS related traffic.

• Interplay political, social, economical, technological diversity– For example, is the router-level topology of a large Korean ISP different

because of their atypically high penetration of broadband deployment, or importance of gaming traffic?

– small Chinese Internet AS-level topology preserves the structural characteristics of the global Internet (Chinese Internet AS-level topology,” 2006, arXiv:cs.NI/0511101.)

RECOMMENDATIONS• Interdisciplinary communication remains a serious bottleneck,

important to read, try to understand, and cite publications from other fields

• A lack of comprehensive and high-quality topological and traffic data represents a serious obstacle to successful Internet topology modeling, and especially model validation.– outreach to Internet registries, e.g., ARIN, RIPE, and other databases

regarding access and use of their data for research purposes;– develop new techniques and tools to collect the data for the next

generation of Internet models– Concentrate on robustness– support repositories of publicly available topology and traffic data

• DatCat - facilitate sharing of data sets with researchers in pursuit of more reproducible scientific results (http://imdc.datcat.org.)

• convert theoretical results into practical solutions• Can a GENI-like facility help in tackling some of the research

challenges identified in this report, and if so, how?