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Glossary
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.
RS232-C: 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.
Serial Line Internet Protocol (SLIP): An Internet protocol which is used to run IP over serial lines such as telephone
circuits.
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.
Simple Network Time Protocol (SNTP): A protocol used to allow network access to accurate clocks and other sources of
time-based information.
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.
Superframe (D4): A T1 transmission format that consists of 12 DS1 frames, or 2316 bits. A DS1 frame consists of 193 bit
positions. A frame overhead bit is in the first position, and it is used for frame and signaling phase alignment only.
Subscriber Loop: See "Local loop".
Switched 56: A circuit-switched (full duplex digital synchronous data transmission) service that lets you dial a number and
transmit data to it at 56K bps. It is a relatively low cost service, widely used in North America for telecommuting,
videoconferencing and high speed data transfers. Many phone companies are (or will be) phasing out Switched 56 in favor
of ISDN service.
Switched Virtual Circuit (SVC): A type of data transmission 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.
Switched Network: A network in which a temporary connection is established from one point via one or more segments.
MTASR3-200
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