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Glossary

101

MTPSR1-202ST

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 connec-

tor 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 telecommunica-

tions 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 manage-

ment.

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 56 Kbps. 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 discreet segments. This connection lasts for the duration of the call after which each seg-

ment may 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.

Synchronous Data Link Control (SDLC): A discipline conforming to subsets of the Advanced Data

Communications Control Procedures (ADCCP) of the American National Standards Institute (ANSI)

and High-level Data Link Control (HDLC) of the International Organization for Standardization, for

managing synchronous, code-transparent, serial-by-bit information transfer over a link connection.

Transmission exchanges may be duplex, or half-duplex over switched or nonswitched links. The

configuration of the link connection may be point-to-point, multipoint, or loop.

Synchronous Transmission: The transmission of data which involves sending a group of charac-

ters in a packet. This is a common method of transmission between computers on a network or

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