As telephone-based 56k modems began losing popularity, some Internet service providers such as Netzero and Juno started using pre-compression to increase the throughput and maintain their customer base. As example, the Netscape ISP uses a compression program that squeezes images, text, and other objects at the modem server, just prior to sending them across the phone line. Certain content using lossy compression (e.g., images) may be recompressed (transcoded) using different parameters to the compression algorithm, making the transmitted content smaller but of lower quality. The server-side compression operates much more efficiently than the on-the-fly compression of V.44-enabled modems due to the fact that V.44 is a generalized compression algorithm whereas other compression techniques are application-specific (JPEG, MPEG, Vorbis, etc.). Typically Website text is compacted to 4% thus increasing effective throughput to approximately 1,300 kbit/s. The accelerator also pre-compresses Flash executables and images to approximately 30% and 12%, respectively.
The drawback of this approach is a loss in quality, where the GIF and JPEG images are lossy compressed, which causes the content to become pixelated and smeared. However the speed is dramatically improved such that Web pages load in less than 5 seconds, and the user can manually choose to view the uncompressed images at any time. The ISPs employing this approach advertise it as "surf 5× faster" or simply "accelerated dial-up".
