Someone asked:
   "Can you explain rwin, mss, and mtu in the config.tel file?"

Sure, Rwin is the TCP sliding window.  The window allows transfers to
proceed without waiting for an acknowldgement for every packet, but
rather transmitting (up to) a window of data before waiting for
acknowlegments.  If the window size equals the mss, then there is no
window, because every packet must be acknowledged.  If large windows
are selected and data is lost, the entire window may have to be resent,
hence the warning that larger is not always better.  During a transfer,
both sides of the connection continually advertise what their free
space in the window is, so that the transfer side can control data flow
to only send what the receiving side can accept.

Mss is the maximum segment size that the TCP connection advertises to
the other side.  The other side then sends packets up to this size.  In FTP,
all of the data packets except the last will probably be this big.

Mtu is the maximum size of outgoing packets on the TCP connection.  When
transmitting FTP data to a host, packets will be this big, unless the
host advertizes a smaller mss.  For Telnet and the FTP control connection,
packets are sent per character, so this is never an issue.