X has been used over TCP/IP, DECnet, and LAT over ethernet.
It has also been over SLIP, PPP,
and other proprietary protocols over serial lines.
The risks associated with TCP/IP
are discussed in Chapter 9.
There has been a mapping of X to the OSI protocol stack and services.
As yet, there are no commercially-available implementations
of X as an OSI Application Layer protocol.
When there are,
one would expect X to use the OSI security services,
which are under development.