When connecting from an OpenIndiana machine on a corporate LAN to a home machine on a domestic ADSL2+ line (also running OpenIndiana, via port forwarding), X window sessions over SSH (ssh -X) were so slow to render as to make working a total drag. Enabling the use of compression in the client’s SSH configuration file resulted in a considerable speed-up:
Add the following to /etc/ssh/ssh_config
Compression yes CompressionLevel 2
CompressionLevel ranges from 1 (fastest) to 9 (best).
As far as the server goes for allowing compression by clients, according to man sshd_config:
Controls whether the server allows the client to negoti‐
ate the use of compression. The default is yes.”