TCP/IP Explained
An easy to understand, comprehensive, and high-level introduction to TCP/IP.
TABLE OF CONTENTS TCP/IP Explained
Section 22.2: Compression
22.2 Compression
One of the problems associated with communications over slow serial links, is that we need to be able to squeeze as much usable bandwidth from them as possible. For instance, if we consider the case of Internet access from remote locations over dial up lines, we will probably be using at best 14.4 or 28.8kbps modems. This would be the case for a home or mobile user. If we now consider that the user may wish to download large files (or graphics as in the case of World Wide Web access), the need to conserve bandwidth is apparent.
22.2.1 Van Jacobson Compression
To overcome some of the bandwidth that is consumed by bulk transfers, Van Jacobson suggested (in RFC 1144) a compression technique that is widely used today. Known simply as Van Jacobson or VJ Compression, or when associated with SLIP - CSLIP, the compression method is attractive through its simplicity.
While some of the actual mathematics behind Van Jacobson's arguments are extremely complex and beyond the scope of this book, Van Jacobson argues that it is possible to make significant savings in bandwidth by simply compressing the headers associated with common Internet protocols. In actual fact VJ Compression only works with TCP/IP headers. The argument here is that in the case of UDP/IP the datagrams are either less frequent, or the amount of data carried outweighs the usefulness of compression at all. In particular, to see the effects of overhead in an IP environment, we should look...
Copyright Butterworth-Heinemann 1997 under license agreement with Books24x7
