Bandwidth

Bandwidth is the term used to relate the speed at which data can be transferred from one computer to another. The amount of data passed in response to a client request directly affects the response time. For example, the size and color depth of an image on a Web page impacts the speed at which a client can download and open the page. When developing network applications, consider the speed at which your clients connect to the server. On an intranet, network speeds are generally much faster than on the global Internet.

Strategies to Limit Bandwidth Impact

When designing content for use over the Web, there are a number of strategies a designer of a Web page can use to limit the impact of low bandwidth.

Show text first

Showing text first is the default when using Microsoft Internet Explorer. When a Web page is opened, the text for the page is loaded and displayed to the user first. Then, while the user begins reading the text, any included images are downloaded and displayed.

Alternative text

You can interrupt and cancel a Web page while it is being downloaded to your computer. Although an incomplete Web page may appear in the browser, your Web page can still provide information in the location that graphics would normally appear. For example, you may cancel a Web page that is loading in a browser. When the downloading is interrupted , the graphics will not continue to load, but labels for the graphics may have already been loaded, and they will appear in the graphic's place. Also, Web browsers such as Internet Explorer can provide a pop-up ToolTip describing what the graphic represents as long as alternative text has been provided for the graphic.

Example

In this HTML code example, the Next button is displayed. The alt parameter is used to specify what text should be shown to the user.

 <img src="Next.gif" alt="Next Page"> 

Multiple images instead of large image map

If a Web page will provide the user with a number of links to other pages, consider using separate, smaller image files for each link instead of a large image map graphic. An image map provides a single graphic that has "hot spots" that track where the user clicks. For example, if you use a map of a continent as your image map, the location on the graphic where the user clicks determines which country's home page is loaded. In a low bandwidth environment, downloading a single large image is not as effective as presenting the user with a number of smaller images representing each country.

Interlaced GIFs

Instead of making the client wait for all data to download before showing it, your application can use interlaced GIFs to return partial results and minimize bandwidth limitations. A client can view an interlaced GIF image as it downloads. The image is "blurry" image but becomes increasingly sharp as the image data is fully retrieved.