High Performance Enabled SSH/SCP
from the Pittsburgh Supercomputing Center

hpn-ssh is a version of OpenSSH modified to support high-performance
bulk transfers (such as with scp or rsync).  These modifications are
required because:

  SCP and the underlying SSH protocol is network performance limited by
  statically defined internal flow control buffers. These buffers often
  end up acting as a brake on the network throughput of SCP especially
  on long and wide paths. Modifying the ssh code to allow the flow
  control buffers to be defined at run time eliminates this bottleneck.

WWW: http://www.psc.edu/networking/projects/hpn-ssh/