Enable/Disable Acceleration

Prefetch (client)

Prefetch (server)

The Prefetch feature reduces the time required to download and display web pages. The Prefetch client mechanism intercepts browser connections destined to ports 80 and 8080, and attempts to match them with connections already in the process of delivering content from the remote PacketShaper. The Prefetch server mechanism operates on the PacketShaper closest to the web server; it inspects all content returning from connections to ports 80 and 8080, tries to find and prefetch any embedded objects that the browser will probably request, and will immediately start pushing that content back towards the browser-side PacketShaper.

The Prefetch client and server can be enabled/disabled independently. For prefetching to work, Prefetch client support must be enabled on the PacketShaper closest to the browser machines, and Prefetch server support must be enabled on the PacketShaper closest to the web server. If there are web servers on both sides of the link and you want to provide prefetching for web connections in both directions, you can enable Prefetch client and server on both PacketShapers.

Notes:

• Prefetch works on HTTP traffic running on ports 80 or 8080.
• When Prefetch is enabled, the PacketShaper and partner must be configured with the address of at least one DNS server. If more than one DNS server is configured, the Prefetch logic will spread its requests equally among them. To configure DNS servers, see Reconfigure Basic Settings.
• Client Prefetch forces FastStart be enabled. If FastStart isn't already enabled when you turn on client Prefetch, FastStart will automatically be set to on and the following message will alert you to this situation: "Enabling client prefetch has also enabled FastStart."

The FastStart feature accelerates web downloads by reducing the time needed to establish each new HTTP connection. Using FastStart, Xpress acknowledges TCP connections immediately without waiting for a connection to be established to the web server. This immediate acknowledgment allows the browser to send its HTTP GET request right away. Xpress then combines the HTTP GET request with the XTP connection request. This process delivers the HTTP request to the web server one round-trip faster. For web pages that consist of large numbers of objects, FastStart greatly improves the responsiveness of the web page display.

FastStart is enabled by default. There is typically no need to disable FastStart unless you are using SCPS.

Notes:

• FastStart works on HTTP traffic running on ports 80 or 8080.
• Be aware that FastStart can result in false "connection established" messages

When SCPS (Space Communications Protocol Standards) is enabled, it becomes the transport protocol for the transmission of data over the satellite portion of the link. XTP provides higher performance than SCPS under most conditions, but SCPS is available for organizations that have standardized on SCPS as the required transport protocol.

Notes:

• FastStart and Prefetch are not available when using SCPS. If you enable SCPS when FastStart is enabled (or vice versa), a message appears that "Enabling SCPS prevents the use of FastStart."
  
  
• Turning SCPS on or off will terminate all active accelerated connections.
  
  
• Outbound link rate is not used.