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Glossary

PSTN

Public Switched Telephone Network: Colloquially referred to as

"plain old telephone service" (POTS). A term that describes the assortment
of telephone networks and services available globally.

PVC

permanent virtual circuit: In a Frame-Relay network, a logical con-

nection, defined in software, that is maintained permanently. Compare with:
SVC. See also: virtual circuit.

PVP

permanent virtual path: A virtual path made up of PVCs. See

also: PVC.

PVP tunneling

permanent virtual path tunneling: A technique that links

two private ATM networks across a public network using a virtual path;
wherein the public network transparently trunks the complete collection of
virtual channels in the virtual path between the two private networks.

PVST

Per-VLAN Spanning Tree: A Cisco proprietary implementation of STP.

PVST uses ISL and runs a separate instance of STP for each and every VLAN.

PVST+

Per-VLAN Spanning Tree+: Allows CST information to be passed

into PVST.

QoS

Quality of Service: A set of metrics used to measure the quality of

transmission and service availability of any given transmission system.

queue

Broadly, any list of elements arranged in an orderly fashion and

ready for processing, such as a line of people waiting to enter a movie the-
ater. In routing, it refers to a backlog of information packets waiting in line
to be transmitted over a router interface.

queuing

A quality of service process that allows packets to be forwarded

from the router based on administratively defined parameters. This may be
used for time-sensitive protocols, such as SNA.

R reference point

Used with ISDN networks to identify the connection

between an NT1 and an S/T device. The S/T device converts the 4-wire net-
work to the two-wire ISDN standard network.

RADIUS

Remote Access Dial-in User Service: A protocol that is used to

communicate between the remote access device and an authentication
server. Sometimes an authentication server running RADIUS will be called a
RADIUS server.

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