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Glossary
Systems Network Architecture (SNA): The description of the logical structure, formats, protocols, and operational
sequences for transmitting information units through, and controlling the configuration and operation of networks.
T
Tariff: The rate/availability schedule for telephone and ISDN services from a regulated service provider.
TCP/IP: A set of communication protocols that support peer-to-peer connectivity functions for both local and wide area
networks.
T Carrier: The generic name for a digitally multiplexed carrier system. In the North American digital hierarchy, a T is used to
designate a DS (digital signal) level hierarchy. Examples: T1 (DS1) is a 1.544 M bps 24-channel designation. In Europe, T1
is called E1. The T Carrier system was originally designed for transmitting digitized voice signals, but has since been
adapted for digital data applications.
T1: A digital transmission link capable of 1.544M bps. T1 uses two pairs of normal UTP, and can handle 24 voice
conversations, each digitized at 64 Kbps. T1 is a standard for digital transmission in the U.S., Canada, Japan and Hong
Kong. T1 is the access method for high-speed services such as ATM, frame relay, and SMDS. See also T Carrier, T1 line
and FT1.
T1 Channel Tests: A set of diagnostics that vary by carrier, used to verify a T1 channel operation. Can include Tone, Noise
Level, Impulse Noise Level, Echo Cancellers, Gain, and Crosstalk testing.
T1 Framing: To digitize and encode analog voice signals requires 8000 samples per second (twice the highest voice
frequency of 4000 Hz). Encoding in an 8-bit word provides the basic T1 block of 64 Kbps for voice transmission. This "Level
0 Signal, as its called, is represented by "DS-0", or Digital Signal at Level 0. 24 of these voice channels are combined into a
serial bit stream (using TDM), on a frame-by-frame basis. A frame is a sample of all 24 channels; so adding in a framing bit
gives a block of 193 bits (24x8+1=193). Frames are transmitted at 8000 per second (the required sample rate), creating a
1.544M (8000x193=1.544M) transmission rate.
T1 Line: A digital communications facility that functions as a 24-channel pathway for data or voice. A T1 line is composed of
two separate elements: the Access element and the Long Haul element.
T1 Mux: A device used to carry many sources of data on a T1 line. The T1 mux assigns each data source to distinct DS0
time slots within the T1 signal. Wide bandwidth signals take more than one time slot. Normal voice traffic or 56/64 Kbps
data channels take one time slot. The T1 mux may use an internal or external T1 DSU; a "channel bank" device typically
uses an external T1 CSU.
Transmission Control Protocol / Internet Program (TCP/IP): A multilayer set of protocols developed by the US
Department of Defense to link dissimilar computers across dissimilar and unreliable LANs.
Terminal: The screen and keyboard device used in a mainframe environment for interactive data entry. Terminals have no
"box", which is to say they have no file storage or processing capabilities.
Terminal Adapter (TA): An ISDN DTE device for connecting a non-ISDN terminal device to the ISDN network. Similar to a
protocol converter or an interface converter, a TA connects a non-ISDN device between the R and S interfaces. Typically a
PC card.
Terminal Endpoint Identifier (TEI): Up to eight devices can be connected to one ISDN BRI line. The TEI defines for a
given message which of the eight devices is communicating with the Central Office switch. In general, more than one of the
eight may be communicating.
Tie line: A dedicated circuit linking two points without having to dial a phone number (i.e., the line may be accessed by
lifting the telephone handset or by pushing a button).
Time-Division Multiplexing (TDM): Division of a transmission facility into two or more channels by allotting the common
channel to several different information channels, one at a time.
Time Slot: One of 24 channels within a T1 line. Each channel has a 64 Kbps maximum bandwidth. "Time slot" implies the
time division multiplexing organization of the T1 signal.
Toll Call: A call to a location outside of your local service area (i.e., a long distance call).
Tone dialing: One of two methods of dialing a telephone, usually associated with Touch-Tone® (push button) phones.
Compare with pulse dialing.
Topology: Physical layout of network components (cables, stations, gateways, and hubs). Three basic interconnection
topologies are star, ring, and bus networks.
Transmission Control Protocol (TCP): A communications protocol used in Internet and in any network that follows the US
Department of Defense standards for internetwork protocol. TCP provides a reliable host-to-host protocol between hosts in
packet-switched communications networks and in interconnected systems of such networks. It assumes that the Internet
protocol is the underlying protocol.
MTPSR1-202ST
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