In addition, caching a document that many users need can save considerable network cost and connection time. Caching can also reduce the amount of disk space browsers use because many local browsers can use a single copy of a cached document. If you want, you can also configure the proxy server to use only the local cache. For instance, you can provide Internet documents to local browsers that do not have an internet connection. Determining when documents should be updated or deleted can be a difficult task.
Some documents can remain stable for a very long time and then suddenly change.
Other documents can change on a weekly or a daily basis. This means you need to decide carefully how often to refresh or delete the documents held in cache. The individual departments have control over the server and cache. These departmental proxy servers can connect to a proxy server on a firewall between the Internet and the organization. This proxy server talks to the Internet as shown in Figure 31 .