Glossary Z

X

X.25

An ITU-T packet-relay standard that defines communication between DTE and DCE network devices. X.25 uses a reliable Data Link layer protocol called LAPB. X.25 also uses PLP at the Network layer. X.25 has mostly been replaced by Frame Relay.

X.25 protocol

First packet-switching network, but now mostly used in Europe. Replaced in U.S. by Frame Relay.

XTAG

A locally significant numerical value assigned by the MLS-SE to each MLS-RP in the layer 2 network. See also: MLS-SE and MLS-RP.