Techniques

Web accelerators may use several techniques to achieve this reduction:
They may cache recently or frequently accessed documents so they may be sent to the client with less latency or at a faster transfer rate than the remote server could.
They may freshen objects in the cache ensuring that frequently accessed content is readily available for display.
They may preemptively resolve hostnames present in a document (HTML or Javascript) in order to reduce latency.
They may prefetch documents that are likely to be accessed in the near future.
They may compress documents to a smaller size, for example by reducing the quality of images or by sending only what's changed since the document was last requested.
They may optimize the code from certain documents (such as HTML or Javascript).
They may filter out ads and other undesirable objects so they are not sent to the client at all.
They may maintain persistent TCP connections between the client and the proxy server.
They may improve the performance via protocol level accelerations, such as TCP acceleration.