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Glossary
Multi-Tech Systems, Inc. MT5634ZPX User Guide 58
PROM (Programmable Read Only Memory - pronounced
“prom”): A permanent memory chip that can be programmed or
filled by the customer after by the manufacturer has set initial
values. Contrast with ROM.
Protocol: 1. A set of semantic and syntactic rules that determines
the behavior of functional units in achieving communication. 2. In
Open Systems Interconnection architecture, a set of semantic and
syntactic rules that determine the behavior of entities in the same
layer in performing communication functions. 3. In SNA, the
meanings of and the sequencing rules for requests and responses
used for managing the network, transferring data, and
synchronizing the states of network components. 4. Synonymous
with line control discipline.
PSTN (Public Switched Telephone Network): A worldwide public
voice telephone network that is used as a telecommunications
medium for the transmission of voice, data and other information.
Public Data Network (PDN): A packet-switched network that is
available to the public for individual (“subscriber”) use. Typically,
controlled by a government or a national monopoly.
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.
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.
Root Hub: A Universal Serial Bus hub directly attached to the host
controller. This hub is attached to the host; tier 0.
Root Port: The upstream port on a hub.
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, DB9, various DB25, and DB37 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.
Stop Bit: One of the variables used for timing in asynchronous
data transmission. Depending on the devices, each character may
be trailed by 1, 1.5, or 2 stop bits.
Switched Virtual Circuit (SVC): A data transmission type where
the connection is maintained only until the call is cleared.
Switched Line: In communications, a physical channel
established by dynamically connecting one or more discrete
segments. This connection lasts for the duration of the call, after
which each segment can be used as part of a different channel.
Contrast with leased line.