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446 GLOSSARY
preview dialing Automated dialing feature in which CTI software queues the next call to
be made but allows you to check and activate the call.
PRI Primary Rate Interface. An ISDN service for users with large bandwidth
requirements, such as large PBXs or high performance video desktop
conferencing systems; the ISDN equivalent of a T1 circuit.
protocol A set of rules governing the information flow within a communications
infrastructure. A protocol typically specifies the structure of parameters
like format, timing, and error correction.
protocol converter A device that translates between two protocols to facilitate
communications between different computers or different systems.
PSTN Public-Switched Telephone Network. The term describes the national
telephone network.
punch-down block Telephony term describing the connector arrangements for distributing
and connecting unshielded and shielded twisted pair wiring inside a
building. Typically found in telephone wiring closets.
Q.921/931 ITU-TS “Q Series” Recommendations describing Lap-D, the Layer 2
protocol for an ISDN D-channel. See OSI model
.
reconfiguration The process of physically altering the location or functionality of network
or system elements. Automatic configuration describes the way
sophisticated networks can readjust themselves in the event of a link or
device failing, enabling the network to continue operation.
redundancy In data transmission, this refers to characters and bits that can be
removed from a transmission without affecting the message. In data
processing and data communications, it means providing backup for
components so that if one of them fails, the system continues to run
without interruption.
REN Ringer Equivalency Number. A number that indicates how much power is
required by a telephone to make it ring. When connecting telephones to
a telephone line, the sum of the RENs of the telephones must be less than
the rated REN capacity of the telephone line.
repeater A device that extends the maximum length of cable that can be used in a
single network.