Web Characterization:

Status of this document

This document is a W3C Note reporting on the results of the HTTP-NG Web Characterization Group and the structure of the Web Characterization Activity. The work which was part of the W3C HTTP-NG Activity, phase I, is now continued in the Web Characterization Activity.

Review comments on this document should be sent to <www-wca@w3.org> which is the archived email list for the Web Characterization Activity. Information on how to subscribe to public W3C email lists can be found at the subscription request page.

This document is a NOTE made available by the W3C for discussion only. This indicates no endorsement of its content, nor that the Consortium has, is, or will be allocating any resources to the issues addressed by this NOTE.

Table of Content

Abstract

1. The HTTP-NG Web Characterization Group

1.1 Mission statement

1.2 Participants

1.3 Deliverables and Accomplishments

2. The Web Characterization Activity

2.1 The structure of the Activity

3. Example characterizations

3.1 The HTTP-NG testbed

4. WCG papers

5. Summary

Abstract

This document describes the experiences and results that came out of the Web Characterization Group as part of the W3C HTTP-NG Activity, and how that work is now continued in the Web Characterization Activity.

The HTTP-NG Working Group created a series of scenarios for the HTTP-NG protocol design group, which were implemented in the scope of the HTTP-NG testbed, and used to optimize its design.

The WCA started in November 1998, and will bring that work model to a wider audience.

1. Introduction

Web Characterization is concerned with looking at the overall patterns of Web structure and usage by measuring such aspects as server access patterns, the kind of data being accessed, bytes transferred, popularity of resources, etc. By better understanding the dynamics of the Web and how it grows we believe that W3C and the Web Community in general will be better suited to evolve the Web and to ensure its long term interoperability and robustness.

The purpose of the Activity is to define and implement a scalable mechanism for gathering data, boiling it down and to presenting it in efficient ways to content providers, service providers, user groups, researchers and technology designers and other groups.

The information used to characterize the Web is strictly concerned with general patterns of Web usage and does not focus on specific users or Web sites. The scope of this Activity is to characterize the Web as a distributed system and not on an individual basis.

1.1 Mission Statement

The HTTP-NG Web Characterization Group was chartered in August 1997 as a part of the HTTP-NG Activity. Its intent was to create a stable and comprehensive platform of knowledge and analysis of the Web, to enable the protocol designers to create a relevant and well-instructed solution. Previously, analysis of user behavior on the Web has often been based on spurious data, gathered in an ad-hoc manner. The HTTP-NG Web Characterization Group was an attempt at rectifying this.

It was set up to fulfill four primary goals:

1. To respond to the questions raised by the HTTP-NG Protocol Design Group regarding current usage of the World Wide Web.
2. To design and develop representative scenarios for use in the HTTP-NG testbed.
3. To make recommendations to the Protocol Design Group in issues concerning Web usage and characterization methods.
4. To devise a system and a methodology to make characterization of the Web easier and more reliable in the future.

1.2 Participants

The group consisted of members from Boston Universities Ocean group, Harvard Colleges Vino group, INRIA, Microsoft, Netscape, Virginia Techs Network Resource Group, and Xerox Parcs Webology group. Jim Pitkow, Xerox Parc, chaired the group.

1.3 Deliverables and Accomplishments

The HTTP-NG WCG has leveraged and helped focus existing research programs, which the group considers one of its major accomplishments.

During its charter, the group has responded to the questions of the HTTP-NG Protocol Design Group. This has been influential in the design of the HTTP-NG protocol. It has also created the HTTP-NG testbed, which operates by using SURGE (Scalable URL Generator) from Boston University Ocean Group. Scenario parameters derived from observed statistical regularities in the distribution of file sizes, reading times, and other metrics, were used to simulate client traffic in the testbed. SURGE used some aspects of Web traffic which were not taken into account by then current traffic generators.

The group has completed all the original requirements, with the exception of the redesign of the Common Log File Format and the recommendations for automatic re-sampling of the Web, which has been moved to the Web Characterization Activity.

2. The Web Characterization Activity

The W3C Web Characterization Activity was started in November 1998 with a workshop, gathering some 50 persons interested in the subject. Subsequently, a working group and an interest group has been started.

The purpose of the Activity is to define and implement a scalable mechanism for gathering data, boiling it down and to presenting it in efficient ways to content providers, service providers, user groups, researchers and technology designers and other groups.

The information used to characterize the Web is strictly concerned with general patterns of Web usage and does not focus on specific users or Web sites. The scope of this Activity is to characterize the Web as a distributed system and not on an individual basis.

The Web Characterization Group in the HTTP-NG Activity was a first phase in this project. It was completed in August 1998, and phase 2 begun. Its focus is to extend the Web Characterization work and to create an active knowledge base containing up-to-date information about the Web by broaden the scope of Web characterization, and providing information and test scenarios for the W3C Membership and the Web community in general about the Web and its use, both now and in the near future.

An important result of WCG is the identification of the three key groups in the characterization work and how they interact:

Bulk Data Providers

The Bulk Data Providers are typically server maintainers and ISPs providing server and proxy logs but can also be backbone providers gathering information directly from the Net or users running instrumented Web clients etc. Because of privacy concerns and because of the sheer size of log files, it is often preferred to have data providers running a set of characterization tools locally so that only the boiled down data sets and profiles are released.

The W3C Characterization Working Group

The WCG develops and maintains a set of characterization tools used by the data providers and defines the mechanism for exchanging boiled down data sets and profiles with the data providers in order to maintain confidentiality and trust. The collected data sets are used to develop characterization models and to provide characterization data to the third group, the reduced data consumers.

Reduced Data Consumers

The reduced data consumers use the profiles and data sets provided by the WCG and provide feedback and new questions to be asked. Primary data consumers are expected to be content providers, service providers, user groups, researchers and technology designers.

2.1 The structure of the Activity

The format for this Activity is to let the interaction between the reduced data consumers and bulk data providers take place through an Interest Group, with a new Web Characterization Working Group (WCG) functioning as the mediator, provider of analysis tools and disseminator of characterization information.

Web Characterization Interest Group

The role of the Interest Group is to be a discussion forum for bulk data providers and reduced data consumers, and to provide requests and feedback to the Working Group. It is expected that the tools and dissemination mechanism produced by the Working Group will benefit from a feedback mechanism with its immediate users, as well as their continuous review. All work will be discussed on the Web Characterization Activity Forum.

Participation in the Interest Group is open to everybody.

Web Characterization Workshop

The Activity was kicked off by the Web Characterization Workshop, November 5, 1998 in Boston, MA, with the intent of bringing together both W3C Members and Web characterization experts. As a results of the Workshop, the Interest Group was formed, and several organizations who wanted to participate in the Working Group were identified.

Web Characterization Working Group

The WCG is intended to work using a request/response based model similar to the one  used in the HTTP-NG Activity. Requests will be formally issued by the Interest Group and by W3C Activities and the WCG will respond with realistic time lines for when and how results can be made available.

The WCG will start its work by formally soliciting requests for characterization data needed by other W3C Working Groups and Activities. The solicitation process is intended to occur at six-month intervals, enough time for the Working Group to understand and respond to the requests of the other W3C Groups. Requests from the Interest Group will be dealt with on a case by case basis. All work will be discussed on the Web Characterization Activity Forum.

The working group has the following participants:

Further information about the work in progress can be found at the Web Characterization Activity Home Page

3. Example Characterizations

The following are examples of some of the findings of the HTTP-NG WCG and other researchers in the field of Web Characterization. This is by no means meant to be neither a complete listing of the findings of the HTTP-NG WCG, nor a representative sample of research in the field. Rather it contains results that the group found provocative and representative of the types of questions the HTTP-NG WCG found to be of interest.

• Question: Where do all the clicks go?
• Answer: Analysis of performed independently by Alexa Internet and by the HTTP-NG WCG analysis of AOL trace data indicates that only a few servers account for the majority of all clicks issued by users. The proportions may surprise you: 50% of the clicks go to only 1% of the WWW sites visited and 80% of the clicks go to only 26% of the sites!

Alexa Internet and WCG Analysis of AOL Data - December 1997

• Question: How fast is the Web growing?
• Answer: Not as quickly as during the early years of the Web. Although this calculation is a bit fuzzy given that the data sources used different methods to count the total number of servers and definitions of what a server actually is (virtual hosting, etc.), the rapid hyper-growth of the Web from 1992 to mid 1995 has slowed to roughly gaining an order of magnitude every 30 months

Source: W3C, Mark Gray, Netcraft Server Survey

• Question: How many WWW pages are there?
• Answer: During the spring of 1998, two independent research groups (NEC Research Institute and DEC Systems Research Center) employed the same theoretical foundation of set intersection to answer this question, but came up with different answers to the question! While the devil is in the details of the methodology employed by each study, the general procedure was take issue a set of queries to the major search engines and determine the number of same pages returned by the engines. This tells us the number of pages that all the search engines agree exist and the degree to which each search engine contains pages the others do not. From this NEC reports that there are 320 million pages while DEC reports that there are 275 million pages. Our analysis of the AOL log files point to approximately 200 - 250 million pages as of this writing.
• Question: How often are broken links encountered? Redirections? POSTS? GETs with appended content?
• Answer: Primarily based on analysis of AOL data, we have found that the number of broken links encountered while users surf the Web is between 5 and 8% of all clicks. The occurrence rate of redirections (when a site automatically sends your request to another locations as often occurs with advertising and legacy servers) is approximately 6 to 7% of the time. The HTTP header POST only occurred 1% of the time whereas GET requests with appended material occurred around 10% of the time. These headers are significant in they are used to carry user data back to the server. This is useful for searching, ordering, counters on pages that say how many times a page has been visited, etc. Secure links (using SSL) occupies 152 000 out of 300 million links (0.05%).

3.1 The HTTP-NG testbed

The HTTP-NG testbed was designed for the specific purpose of making reliable and convincing claims that the performance of HTTP-NG would be comparable to prior HTTP implementations. It was designed in close cooperation with the HTTP-NG Protocol Design Group.

An analysis of the current practice in load generation tools left the HTTP-NG WCG concerned with the representativeness of the traffic being generated.

Essentially, three types of traffic generation models exist: Stress testing, trace replay, and statistically derived models. Many current traffic generators follow the first model, by varying the number of requests per second that are issued to the server. While this approach does test the capacity of the server as measured by the number of HTTP operations per second, it does not produce traffic patterns that have actually been observed.

The second model for traffic generation utilizes packet traces collected from various servers and protocol analyzers. If this method had been used in the test bed, the group would have had to acquire traces from representative servers. Apart from determining what is representative, it also presents the problem of which servers to include, and obtain permission to use their log file information. Each Web site will also need to be recreated, due to e.g. the effect of the file system configuration on performance.

Consequently, the group selected to statistically model HTTP traffic. The users were segmented into three strata: Corporate users, ISP users, and educational users. To create models for the behavior of each strata, the group obtained full log files from America Online (major ISP), AltaVista (search engine/mixed user group), and Boston University (educational users). From Microsoft (Corporate usage) a distribution of usage was obtained. All data sets except for the AltaVista data were used to generate scenarios for the testbed. The log file analysis tools used were based on the prior work of the group members, and the personal connections of the group members were instrumental in obtaining these data sets.

The HTTP-NG testbed is designed as the diagram below shows:

The HTTP-NG testbed was thus able to take both network characteristics and user behavior into account, inserting a simulated network between the robot simulating the client and the server. The statistical traffic generator takes a set of parameters to create a mock server with the associated file system, and a set of simulated clients that make statistically based requests for files.

The model characterizes sites as containing Web pages with embedded media and Web pages without embedded media. Using a model that characterizes pages, rather than just objects, makes alteration in the composition of sites easier. This facilitates determining the effect of new technologies, like Cascading Style Sheets (CSS).

4. WCG Papers

Throughout the year of the WCG's existence, various group members have contributed papers, articles, and presentations to the group and the Web characterization community. Given the limited focus of the HTTP-NG project effort, it is not surprising that these items are focused on characterizations and representative testbed designs.

5. Summary

The group has achieved its objectives, creating feedback for the HTTP-NG Protocol Design Group by answering the questions this group had about the Web, and by creating the HTTP-NG testbed, which enabled the creation of an optimized and efficient design of the next generation of the Hypertext Transfer Protocol. The Web characterization work is now being continued in the Web Characterization Activity.