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

GL-18GLOSSARY

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Open Systems	A logical model, consisting of seven levels of interfaces, created by the
Interconnection (OSI)	International Standards Organization (ISO) to show how interconnected
reference model	telecommunications systems should interface.
OSI	See Open Systems Interconnection reference model.
packet	A group of bytes — including a message (the data) and control
	information (the header) — transmitted as a discrete unit. In each packet,
	the message and control information are arranged in a specified format. In
	many systems, the packet is further encapsulated with additional header
	and trailer elements to form a frame. See also packet switching.
packet	A functional unit that enables data terminal equipment (DTE) not
assembler/disassembler	equipped for packet switching to access a packet-switched network.
(PAD)
packet switching	A data-transmission technique whereby user information is segmented and
	routed in discrete data envelopes called packets, each with its own
	appended control information for routing, sequencing, and error checking.
	Packet switching allows a channel to be occupied only during the
	transmission of a packet; on completion of the transmission, the channel is
	made available for the transfer of other packets. See also BX.25, packet,
	and X.25.
PAD	See packet assembler/disassembler.
parallel data transmission	An operation whereby a group of data bits is processed or transmitted
	simultaneously over essentially parallel paths.
parity	A method of checking and, in some cases, correcting the accuracy of bits.
partitioning	The capability to impose restrictions on each tenant’s users to limit their
	access to only a specified subset of the communications system’s facilities
	and services. Partitioning allows a multitenant system to comply with
	state or federal regulations and to provide security and cost allocation
	among tenants.
pattern	For Automatic Alternate Routing — Automatic Route Selection (AAR-
	ARS), a series of trunk groups arranged in a preferential order. Also
	called routing pattern.
PBX	See communications system.