A web accelerator is a proxy server that reduces web site access time. They can be a self-contained hardware appliance or installable software.
Web accelerators may be installed on the client computer or mobile device, on ISP servers, on the server computer/network, or a combination. Accelerating delivery through compression requires some type of host-based server to collect, compress and then deliver content to a client computer.
Web accelerators may use several techniques to achieve this reduction in access time:
- 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.
- freshen objects in the cache ensuring that frequently accessed content is readily available for display.
- prefetch documents that are likely to be accessed in the near future.
- 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.
- filter out ads and other undesirable objects so they are not sent to the client at all.
- maintain persistent TCP connections between the client and the proxy server.
- improve the performance via protocol level accelerations, such as TCP acceleration.
Web client accelerator
From July 2006, these applications generally serve to improve dial-up, broadband and other connections from which users may not be getting the best speed. Many users can achieve a 2- to 10-times speed increase in average browsing experience, while some report a 5- to 20-times speed increases for specific web sites and pages. Many ISPs offer web accelerators as a part of their dial up and broadband services. Web accelerators are typically designed for web browsing and, sometimes, for e-mailing and can not improve speeds of streaming, gaming, P2P downloads or many other Internet applications. However, there is substantial work being done on client-side Web Accelerators for Application Delivery Networks by several companies including Cisco Systems and F5 Networks as the demand for SaaS and PaaS look set to grow among small and medium enterprises.
Web server accelerator
Other web accelerators are targeted at the web site or web application owners. This type of web accelerator is installed in front of web servers and application servers and use a variety of the above techniques to improve performance to all users accessing the accelerated web sites or web applications. Web server accelerators are sometimes referred to as reverse proxies or Application Delivery Controllers. This type of server side accelerator has the added benefit of off-loading transactions and connection managements from the web or applications servers and hence, reducing its CPU utilization and increasing web server or application scalability to handle more users with less bandwidth.
There may be two sections to the proxy as well - a server portion sits in front of the web server and captures the input and output from the server and a client portion sits in front of the end-user's web browser to capture the input and output from the browser. An example would be Opera Turbo.