Glossary
V.120— One of the terminal rate adaptation protocols for the ISDN B-channel. V.120 is more software-intensive than the V.110 B-channel standard.
Videotex— A two-way information-retrieval service that can be accessed by terminals and by a TV set (with installed decoder). Allows interactive retrieval of information pages from a central resource. See also ISDN.
virtual circuit— A logical connection. Used in packet switching wherin a logical connection is established between two devices at the start of transmission. All information packets follow the same route and arrive in sequence (but do not necessarily carry a complete address).
X
X.25— ITU-T’s definition of a three-level packet-switching protocol to be used between packet-mode DTEs and network DCEs. X.25 corresponds with layer 3 of the 7-layer OSI model.
X.75— An ITU-T standard for linking X.25 packet-switched networks. X.75 defines the connection between public networks, i.e., for a gateway between X.25 networks.
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