UUCP `x' Protocol
=================

   The `x' protocol is used in Europe (and probably elsewhere) with
machines that contain an builtin X.25 card and can send eight bit data
transparently across X.25 circuits, without interference from the X.28
or X.29 layers.  The protocol sends packets of 512 bytes, and relies on
a write of zero bytes being read as zero bytes without stopping
communication.  It first appeared in the original System V UUCP
implementation.