
X.21 ◆
X.21 bis ◆ (Packet data networking) International recommendation that defines the most popular physical interface for X.25. Equivalent to
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 (XID).
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