User guide

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Glossary
Public Switched Telephone Network (PSTN): The group of
circuit-switching voice carriers, which are commonly used as
analog data communications services.
Pulse Code Modulation (PCM): 1. In data communication,
variation of a digital signal to represent information; for example,
by means of pulse amplitude modulation (PAM), pulse duration
modulation (PDM), or pulse position modulation (PPM). 2.
Transmissions of analog information in digital form through
sampling and encoding the samples with a fixed number of bits.
Pulse dialing: One of two methods of dialing a telephone,
usually associated with rotary-dial phones. Compare with “tone
dialing”.
Q
Quantizing: The process of analog-to-digital conversion by
assigning a range, from the contiguous analog values, to a
discrete number.
R
Random Access Memory (RAM): A computer’s primary
workspace. All data must be stored in RAM (even for a short
while), before software can use the processor to manipulate the
data. Before a PC can do anything useful it must move programs
from disk to RAM. When you turn it off, all information in RAM is
lost.
Rate Enforcement: The concept in frame relay where frames
sent faster than the CIR are to be carried only if the bandwidth is
available, otherwise they are to be discarded. (The frame relay
network assumes that anything exceeding the CIR is of low
priority.) Rate enforcement makes sure that the network will not
get so congested that it isn’t able to meet the agreed on CIR.
Recognized Private Operating Agency (RPOA): A corporation,
private or government-controlled, that provides
telecommunications services. RPOAs, such as AT&T, participate
as non-voting members in the CCITT.
Red Alarm: A T1 error condition generated when a local failure
(e.g., loss of synchronization) exists for 2.5 seconds, causing a
Carrier Group Alarm (CGA). See also “Blue Alarm” and “Yellow
Alarm”.
Request for Comment (RFC): A set of papers in which Internet
standards (published and proposed), along with generally-
accepted ideas, proposals, research results, etc. are published.
Ring Down Box: A device that emulates a CO by generating
POTS calls for testing and product demos.
Ring Down Circuit: A tie line connecting phones where picking
up one phone automatically rings another phone. A feature used
for emergencies to alert the person at the other phone of the
incoming call.
RJ-11: An industry standard interface used for connecting a
telephone to a modular wall outlet; comes in 4-and 6-wire
packages.
RJ-45: An 8-wire modular connector for voice and data circuits.
Robbed Bit Signaling: The popular T1 signaling mechanism
where the A and B bits are sent by each side of the T1
termination and are “buried” in the voice data of each voice
channel in the T1 circuit. Since the bits are “robbed” infrequently,
voice quality remains relatively uncompromised. See “bit
robbing”. The robbed-bit signaling technique is used in D4
channel banks to convey signaling information. The eighth (least
significant) bit of each of the 24 8-bit time slots is “robbed” every
sixth frame to convey voice-related signaling information such as
on-hook, off-hook, etc., for each channel.
Router: A device that connects two networks using the same
networking protocol. It operates at the Network Layer (Layer 3)
of the OSI model for forwarding decisions.
Routing Information Protocol (RIP): A distance vector-based
protocol that provides a measure of distance, or hops, from a
transmitting workstation to a receiving workstation.
RS-232C: An EIA standard for a serial interface between
computers and peripheral devices (modem, mouse, etc.). It uses
a 25-pin DB-25, or a 9-pin DB-9 connector. The RS-232 standard
defines the purposes, electrical characteristics and timing of the
signals for each of the 25 lines.
RS-422: The EIA standard for a balanced interface with no
accompanying physical connector. RS-422 products can use
screw terminals, DB-9 various DB-25 and DB-37 connectors.
RS-530: The EIA standard for the mechanical/electrical interface
between DCEs and DTEs transmitting synchronous or
asynchronous serial binary data. RS-530 provides for high data
rates with the same connector used for RS-232; however, it is
incompatible with RS-232.
S
Serial Port: The connector on a PC used to attach serial devices
(those that need to receive data one bit after another), such as a
mouse, a printer or a modem. This consists of a 9- or 25-pin
connector that sends data in sequence (bit by bit). Serial ports
are referred to as “COMx” ports, where x is 1 to 4 (i.e., COM1
through COM4). A serial port contains a conversion chip called a
“UART” which translates between internal parallel and external
serial formats.
Service: The requirements offered by an RPOA to its customers
to satisfy specific telecommunications needs.
Severely Errored Seconds (SES): Refers to a typical T1 error
event where an error burst occurs (a short term, high bit-error
rate that is self-clearing). Per the ITU-T (CCITT) G.821: any
second in which the BER is less than 1x10 -3 .
Signaling: The process of establishing, maintaining, accounting
for, and terminating a connection between two endpoints (e.g.,
the user premises and the telco CO). Central office signals to the
user premises can include ringing, dial tone, speech signals, etc.
Signals from the user’s telephone can include off-hook, dialing,
speech to far-end party, and on-hook signals. In-band signaling
techniques include pulse and tone dialing. With common channel
signaling, information is carried out-of-band.
Simple Network Management Protocol (SNMP): TCP/IP
protocol that allows network management.
Simultaneous Voice Data (SVD): A technology for letting a user
send data via a modem, and use a handset to talk to another
user at the same time over the same connection. The alternative,
making a second call, can be expensive or even impossible. The
uses for SVD are telecommuting, videoconferencing, distant
learning, tech support, etc.