SSH Tectia Server for IBM z/OS 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.