AT&T 7100 series, 7500 series, 2500 series, 7200 series, 7400 series, 7300 series manual Pvc, Pdm

GLOSSARY GL-19

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permanent switched	On the System 75 and Generic 1, a capability that establishes and
connection (PSC)	maintains a continuous switched connection between two data endpoints.
	PSCs are automatically established when the communications system is
	started or restarted, and are maintained until the system becomes inactive.
	If a PSC is inadvertently dropped, the system automatically reestablishes
	the call. When a trunk is involved in the PSC, one of the data endpoints is
	local to the controlling system and the other is on a remote system. Also
	called nailed-up connection. See also dedicated switched connection.
permanent virtual circuit	A continuous logical circuit between the processors of two
(PVC)	communications systems that carries distributed communications system
	(DCS) messages between the systems over a data communications
	interface unit (DCIU) or processor interface (PI) link. More than one PVC
	can be established on the same DCIU or PI link. PVCs are needed for
	proper operation of the DCS data features.
PDM	See processor data module.
port	A data- or voice-transmission access point on a device that is used for
	communicating with other devices.
premises distribution	A cabling system that consolidates wiring for a customer’s on-site and
system (PDS)	remote telephones and data terminals, and channels transmissions to the
	communications system.
PRI	See primary rate interface.
primary rate interface	A standard Integrated Services Digital Network (ISDN) frame format that
(PRI)	specifies the protocol used between two or more communications systems.
	PRI runs at 1.544 Mbps and, as used in North America, provides 23 64-
	kbps B-channels (voice or data) and one 64-kbps D-channel (signaling).
	The D-channel is the 24th channel of the interface and contains
	multiplexed signaling information for the other 23 channels.
primary high-usage trunk	A high-usage trunk group that is administered to provide service to first-
group	route call traffic only.
private branch exchange	See PBX.
processor data module	A device that provides an RS-232C data communications equipment
(PDM)	(DCE) interface for connecting to data terminals, applications processors
	(APs), and host computers; and provides a digital communications
	protocol (DCP) interface for connection to a communications system. See
	also modular processor data module.
protocol	A set of conventions governing the format and timing of message
	exchanges.