Just click here . Many users are confused by compression . The principles involved are quite simple. It is the number of compression types and thier names that causes some confusion. Let's first address compression that is external to the modem and the Internet.
Most files contain many repeated items of data.
Nearly any file can be compressed by using a single marker for similar repeated items of data. The file's size is substantially reduced. When decompressed, the markers are replaced with those correct data items, the file increases back to its original size and it now regains its functionality. They are more efficient. The degree of compression achieved can be massive.