Interphase Tech RAS Communications Controller 5536 - Manual (Page 237)

Glossary
5536 PRI RAS Communications Controller Users Guide 217
X.21 bis ‹ (Packet data networking) International recommendation
that defines the most popular physical interface for X.25. Equivalent to
RS-232 and V.24.
X.21 (bis) link ‹ Commonly used in European countries, this is a pay
as you go link. When a signal is raised, the network automatically
establishes a link to the remote unit.
X.25 ‹ Packet switching protocol that lets computers communicate
via wide area packet switched data networks
XID ‹ See exchange identification.