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Glossary
Primitive: An abstract representation of interaction across the access points indicating that information is being passed
between the service user and the service provider. The OSI Reference Model defines four types of primitives: Request,
Indication, Response and Confirm.
Private Branch Exchange (PBX): A telephone exchange located on the customer's premises. The PBX provides a circuit
switching facility for telephone extension lines within the building and access to the public telephone network. See also
"Exchange".
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.
ProxyServer: A secure gateway that provides multiple LAN users with high performance Internet access by functioning as a
TCP/IP proxy server that resides on the outer edge of a firewall.
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 (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 is 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, e.g., on-hook, off-hook, etc., for each channel.
MTPSR1-202ST
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