Caching Issues

The WTE gets its Web-browsing capabilities from a component called the Web-browser control, which is the same component used by Microsoft Internet Explorer. Because they both use the Web-browser control, the WTE and Internet Explorer share many characteristics. One common characteristic is the caching behavior. Understanding how the Web-browser control performs caching is important because caching can prevent callers from accessing recently updated files in your application.

As a caller browses your application's Web site, the Web-browser control stores (caches) a copy of each accessed HTML file in the Temporary Internet Files folder (the cache) on the local disk. Whenever the control needs to access a file, it first looks in the cache. If it doesn't find the file in the cache, the control retrieves it from the Web server.

Outdated Cached HTML Files

Caching becomes an issue when you update files on your applications Web site. If you edit or replace an HTML file, the Web-browser control will not use the updated or new file if the cache contains a file with the same name. The control continues to use its cached file and never checks for a newer version.

Caching is not an issue when your application uses the File protocol to access a file (for example, File://\\MyWTEdir\start.HTM). In this case, the Web-browser control always gets the file from the local disk or network share. Because it does not cache files that are on the local disk or network share, the control always gets the newest version.

There are several ways you can ensure that the Web-browser control uses the latest versions of your application's files:

• Manually delete old versions of files from the cache.
• Author your application on your local disk if you don't need ASP pages. If you do need ASP pages, you can write an ASP expression on the first line of the file to prevent caching. For example:

  <% response.expires = 0 %>

• Use Internet Explorer to change the caching behavior of the Web-browser control. If you choose this option, keep in mind that you must change the caching behavior while you are logged on to the same account as the WTE or the changes will not affect your application. Also note that changing caching behavior through Internet Explorer alters the behavior for all subsequent Internet Explorer sessions on that account.

To change the caching behavior

1. Log on to the user account under which the Web telephony service is running.
2. Open an instance of Internet Explorer on the computer where the WTE is installed. From the Tools menu, select Internet Options.
3. From the General tab on the Internet Options property sheet, select Settings in the Temporary Internet Files dialog box.
4. From the Settings dialog box, under Check for newer versions of stored pages, choose one of the following:
   • Every visit to the page—The Web-browser control checks for the latest version with each page reference. It does this by checking the time on the file in the IIS server. If the file has not been changed, it will not be brought in again. This means that if the file was replaced by a file that had an earlier time stamp than the first one, the replacement file will not be brought in.
   • Every time you start Internet Explorer—The Web-browser control checks for new pages only after the Web telephony service has been restarted.

For a complete description of the caching options, see the Internet Explorer help file.

Outdated Cached Wave Files

The Web-browser control caches wave files in the same way that it caches HTML pages. The setting under Check for newer versions of stored pages in Internet Explorer also affects wave files. If the setting is Every visit to the page, the WTE checks for a newer version of a file on every reference to it. If the setting is Every time you start Internet Explorer or Automatically, the engine checks for a newer version only after the Web telephony service is restarted.