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Michael S. Borella
Designing documents that will be viewed from remote locations via a network requires an understanding of traditional document and interaction design issues, plus an understanding of how network delays will impact document delivery. Unfortunately, being aware of networking issues is not always sufficient since designers usually have no way of viewing their documents as if those documents were being delivered to a remote site. This paper describes a set of tools that allow designers to view documents stored locally while experiencing response time delays as if the documents were delivered from a different location on the network. By using measured network latencies to drive an instrumented World-Wide Web server, we allow designers to view the documents they create from the perspective of someone sitting down the hall, across the country, or across an ocean.
document design, network delays, response time, WWW
© 1997 Copyright on this material is held by the authors.
Recently there has been a dramatic increase in the use of distributed documents. Many organizations are hiring designers to develop their 'on-line presence.' The resulting documents are often filled with eye-catching graphics, animation, or embedded software written using languages such as Java or JavaScript.
Many of these documents are created on high-power workstations sitting next to the designer's desk. While in-house demos are often impressive, many documents fail when placed on the Internet [1]. Some documents that were eye-catching are now just slow. As a result, some potential visitors, annoyed by the delays, move on before the document fully loads. The result may be that a person never visits the site again due a poor first impression [2].
Designers creating documents that will be used over a network must consider not only the traditional rules of document and interaction design, but must also consider network delays. Unfortunately, network delays are highly variable and depend on many factors beyond the control of the document designer. So how can designers experience their documents in the same way their users will?
The key is to introduce realistic network delays that allow designers to understand how the documents will be experienced by users. At least two alternatives exist:
The first strategy causes documents to make an extra round-trip on the network causing unrealistic delays. The second strategy forces designers to move copies of the documents around the network. The single biggest drawback to both methods is that designers can only experience current network conditions. Network delays vary dramatically depending on the time of day, day of the week, and week of the year. For example, the same 9K document may take 600 msec to download at one point during the day and 1900 msec at another. If it is 5PM and the designer wants to see how their documents will look at 3AM, these strategies force them to wait ten hours.
This research is the first to study the simulation of realistic network delays for distributed documents. A set of tools (WANDS: Wide-Area Network Delay Simulator) was developed that allows designers to view their documents as if they were located at other sites on a network. These tools run on a single machine, allowing network delays to be simulated under controlled conditions. They also allow designers to experience different network conditions without having to wait. Midnight can be simulated at noon. August can be simulated in January.
WANDS consists of three tools. The WANDS Crawler is used to capture delay characteristics between various points on the network. Given several parameters, including the starting URL, the Crawler automatically retrieves remote documents. For each document, its size and the delay between when the document was requested and when it arrived is recorded. Links from this document to additional documents are followed, allowing the Crawler to automatically retrieve numerous documents given only a single URL. The WANDS Analyzer processes the output of the Crawler to generate the data used to drive a server. The Analyzer divides documents into groups based on their size. Delays are analyzed for each group of documents resulting in a delay distribution for each document size. This data is fed into the WANDS Server.
The WANDS Server is an instrumented WWW server which allows designers to experience realistic network delays when retrieving documents from a local machine. As designers request documents, the server automatically delays each document based on the delay distributions generated by the Analyzer.
By collecting network delay statistics at different times of the day, days of the week, or weeks of the year, one set of documents can be viewed under different circumstances. In addition, alternative sets of documents can be viewed under the same conditions.
A WWW site was created and placed on a computer at Florida International University (FIU). The site consisted of 53 HTML documents and 273 subdocuments (e.g. graphics). Using the Crawler, we gathered network delay statistics by retrieving these documents from DePaul University. The data was processed using the Analyzer and the results fed into the WANDS Server.
Since the goal is to allow designers to retrieve documents in any order, documents were retrieved in a random order during the simulations. Under these conditions, the important question is: was the overall experience similar to the original experience over the Internet? In other words, if documents of a particular size tended to be slow on the Internet, were they slow during the simulation?
Due to the volume of data generated during the simulations, the results for one typical simulation are presented in a graphical format. The following graph indicates how frequently delays of various magnitudes were experienced over the Internet and during simulation using the FIU data. Similar results were obtained for other experiments. To date individuals that have used the WANDS Server and have been unable to differentiate between the local simulation and retrieving documents from remote locations [2].
Using the WANDS tools designers can, for the first time, experience their documents as their users will. Network delay statistics are captured, processed, and used to drive the WANDS Server. The server automatically adds appropriate delays based on document size. The end result is an experience much like what a user would encounter if they retrieved the documents over a network. Capturing network statistics at different times or over different networks allows designers to evaluate how their documents would appear under different circumstances. Designers can view alternative sets of documents under the same circumstances to determine which set would be more appropriate. In summary, the WANDS tools allow designers to evaluate the effectiveness of distributed documents while experiencing realistic network delays.
1. Fox, R. News Track: Designers Jump on the Web, Communications of the ACM 39, 1 (1996), 9.
2. Sears, A., Jacko, J. A., & Borella, M. S. (1997) Internet delay effects: How users perceive quality, organization, and ease of use of information. Technical Report #97-02, School of Computer Science, DePaul University, Chicago, IL.
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