SSH Tectia Server (M) uses GNU ZLIB (LZ77) for compression. The zlib compression is described in RFC 1950 and in RFC 1951.
By default, compression is disabled. Compression can be enabled in the ssh2_config file:
Alternatively, compression can be enabled on the command line:
$ ssh2 +C username@remote
Compression is worth using if your connection is slow (for example, a modem connection). The efficiency of the compression depends on the type of the file, and varies widely. It is close to 0% for already compressed files like zip and often 50% or even more for text files.