About ISA Server 2004

ISA Server 2004 SP2 Features
ISA Server 2004 SP2 provides BITS caching for Microsoft Update, HTTP compression with inspection, and packet prioritization using DiffServ.
BITS Caching
The Background Intelligent Transfer Service (BITS) helps you transfer large amounts of data without degrading network performance. It does this by transferring data in small chunks, utilizing unused bandwidth as it becomes available, and reassembling the data at the destination. ISA Server 2004 SP2 provides the caching mechanism for Microsoft Update data received through BITS.
Notes
· The use of BITS caching with servers other than Microsoft Update or Software Update Services servers is not supported.
· The Microsoft Update cache rule calculates the size of an object based on its content length, and does not include the length of the headers.
Microsoft Update Caching
Updating the Microsoft Windows® operating system and other Microsoft products on corporate computers from Microsoft Update can use a large portion of the available bandwidth. This problem is exacerbated in a low-bandwidth connection scenario, but can be an issue in higher bandwidth conditions as well. Updating Windows and other Microsoft software is an important security function, and should be expedited.
ISA Server 2004 SP2 provides the Microsoft Update caching feature that uses the SP2 BITS caching feature to efficiently cache the updates, so that the ISA Server cache can serve the requests. The update request can be completed over the Internet connection once, and then can be applied through the corporate network.
ISA Server Microsoft Update caching uses HTTP Range Requests to make the caching process even more efficient. Microsoft Update uses a mechanism that enables computers that use a specific version of Windows to request and receive only the ranges that contain the update information they need. Because ISA Server can cache those range requests, additional efficiency can result. For example, in a branch office where all of the client computers run Windows XP, only the Windows XP ranges of an update will be requested and cached. This results in quicker updates with lower bandwidth use and a more secure operating environment.
Note
For more information about how Microsoft Update enables computers to request and receive only specific ranges, see Using Binary Delta Compression (BDC) Technology to Update Windows Operating Systems at the Microsoft Download Center.
HTTP Compression
HTTP compression reduces file size by using algorithms to eliminate redundant data. Most common Web-related file types can safely be compressed. HTTP compression uses the industry standard GZIP and Deflate algorithms, which are built into Windows 2000 Server and later operating systems and Internet Explorer version 4 and later versions. These algorithms compress static files, and optionally perform on-demand compression of dynamically generated responses before sending them over the network. These same algorithms are again used to decompress the static files and dynamic responses on an HTTP 1.1 supported client. A client that is configured to use HTTP 1.1 will request compressed content from a Web server. Web servers indicate in their responses whether they support compression.
Note
In Internet Explorer, configure the use of HTTP 1.1 on the Advanced tab of Internet Options, by selecting Use HTTP 1.1 through proxy connections.
HTTP compression in ISA Server is a global HTTP policy setting. It applies to all HTTP traffic that passes through ISA Server to or from a specified network or network object, rather than to traffic handled by a specific rule. HTTP compression is provided by two Web filters:
· Compression Filter. This filter is responsible for compression and decompression of HTTP requests and responses. This filter has a high priority, and is high in the ordered list of Web filters. This is because the filter is responsible for decompression. If you choose to enable inspection of compressed content, decompression must take place before any other Web filters inspect the content.
· Caching Compressed Content Filter. This filter is responsible for caching of compressed content and serving a request from the compressed content in the cache. This filter has the lowest priority, and is low in the ordered list of Web filters, because caching can take place after all other filters have handled the content.
Do not change the default priority and order settings of these filters.
HTTP compression also provides a range compression feature, which is described in Range Compression in this document.