Telecom Acronyms
AAL5 ATM Adaption Layer 5. AAL5 has been adapted by the ATM Forum for a
Class of Service called High Speed Data Transfer.
ADSL Asymmetric Digital Subscriber Line. A high-speed transmission technology using
existing twisted pair lines that permits simultaneous POTS and high-speed data
communication. A much higher data rate is employed downstream than upstream.
AMI Alternate Mark Inversion. A line coding technique used to accommodate the ones
density requirements of E1 or T1 lines.
ANSI American National Standards Institute. Accredits and implements standards.
Member of ISO.
ATM Asynchronous Transfer Mode. A high-bandwidth, low-delay, connection-oriented
switching and multiplexing technique using fixed-sized cells.
Attenuation The dissipation of the power of a transmitted signal as it travels over a
wire.
ATU ADSL Transceiver Unit. The ADSL Forum uses terminology for DSL equipment
based on the ADSL model for which the Forum was originally created. The DSL
endpoint is known as the ATU-R and the CO unit is known as the ATU-C. These terms
have since come to be used for other types of DSL services, including RADSL, MSDSL
and SDSL.
ATU-C ATU – Central Office. An ATU at the carrier’s central office in support of
ADSL-based services.
ATU-R ATU – Remote. Equipment placed at the customer premises in support of
ADSL-based services.
AWG American Wire Gauge. An indication of wire size. The heavier the gauge,
the lower the AWG number and the lower the impedance.
Bandwidth The difference between the highest and lowest frequencies of a band that
can be passed by a transmission medium without undue distortion.
BER Bit Error Ratio. Measure of transmission quality indicating the number of
bits incorrectly transmitted in a given bit stream compared to the total number of bits
transmitted in a given duration of time.
bps Bits per second. Indicates the speed at which bits are transmitted across a
data connection.
BRI Basic Rate Interface. An ISDN service rate of 144 kbps, provided as two
B-channels of 64 kbps for data transfer and one D-channel of 16 kbps for
control and signaling.
Bridge A network component that operates at OSI layer 2. Most often an Ethernet
bridge, which may forward or filter frames based on their type and destination.
Bridged tap Any part of the local loop that is not in the direct transmission path
between the CO and the service user.
Cable Binder A cable binder is used to bundle multiple insulated copper pairs together
in the telephone network.
CAP Carrierless Amplitude & Phase Modulation. A transmission technology for
implementing a DSL connection. Transmit and receive signals are modulated into two
wide-frequency bands using passband modulation techniques.
CAP Competitive Access Provider.
CAT5 Category 5. A level of unshielded twisted pair wiring performance as
defined by EIA/TIA-568.
CBR Constant Bit Rate (as used in ATM).
CLEC Competitive Local Exchange Carrier.
CO Central Office/Central Site. In North America, a CO houses one or more
switches to serve local telephone subscribers. Known as a public exchange elsewhere.
CPE Customer Premises Equipment. Terminal equipment supplied by either
the customer or supplier, which is connected to the telecommunications network.
Crosstalk Line distortion caused by wire pairs in the same bundle being used for
separate signal transmission.
CSA Carrier Serving Area.
CSU Channel Service Unit. A digital interface unit that connects service user
equipment to the local digital telephone loop.
DACS Digital Access & Cross-Connect System. A device that allows DS0
channels to be individually routed and reconfigured.
DCE Data Communications Equipment. The equipment that provides the signal
conversion between the DTE and the network.
DDS Digital Data Service. Private line digital service that provides digital
communication circuits.
DHCP Dynamic Host Configuration Protocol. A TCP/IP protocol that provides
static and dynamic address management.
DLC Digital Loop Carrier. Network transmission equipment, consisting of a CO
terminal and a remote terminal, used to provide a pair gain function.
DLCI Data Link Connection Identifier. The virtual circuit number corresponding
to a particular connection between two destinations. This number is used
as part of the frame relay header.
DMT Discrete MultiTone. DSL technology using digital signal processors to
divide the signal into 256 subchannels.
Downstream Refers to the transmission direction from the CO to the customer
premises.
DSL Digital Subscriber Line. The non-loaded, local-loop copper connection between
the NSP and the customer premises. DSL can provide simultaneous high-speed digital
data access and POTS service over the same twisted-pair wiring.
DSLAM Digital Subscriber Line Access Multiplexer. DSL Central Office
equipment that supports multiple users and includes the CO side of DSL modems.
DSU Digital Service Unit. Data communications equipment that transmits digital data
over a private line.
DTE Data Terminal Equipment. The equipment, such as a computer or
terminal, that provides data in the form of digital signals for transmission.
E1 A wideband digital interface operating at 2.048 Mbps, as defined by the ITU
recommendations G.703 and G.704. Generally available outside North America.
EIA/TIA Electronic Industries Association/Telecommunications Industry
Association. This organization provides standards for the data communications industry
to ensure uniformity of the interface between DTEs and DCEs.
Ethernet A type of network that supports high-speed communication among
systems. It is a widely-implemented standard for LANs.
ETSI European Telecommunications Standardization Institute. An organization
that produces technical standards in the area of telecommunications.
FDDI Fiber Distributed Data Interface. A LAN token ring standard using fiber
optic cable.
FDI Feeder Distribution Interfaces. Points where cable bundles from the
telephony switch use drop lines extended out to the customer premises.
FDM Frequency Division Multiplexing.
FEXT Far End CrossTalk. One category of Crosstalk that occurs at the remote
end of a link.
FRAD Frame Relay Assembler/Dissembler. A FRAD connects non-frame relay
devices to the frame relay network.
Frame Relay A high-speed connection-oriented packet switching WAN protocol using
variable-length frames.
HDB3 High Density Bipolar Three Zeros Substitution. A line coding technique
used to accommodate the ones density requirements of E1 lines.
HDSL High-bit-rate Digital Subscriber Line. A technique for high bandwidth,
bidirectional transmission over copper wire for T1 and E1 services.
Hertz Frequency measurement. 1 Hertz = 1 cycle per second.
HTU-C HDSL Terminal Unit – Central. The module at the CO or central site end
of an HDSL connection. Also known as a Line Termination Unit (LTU).
HTU-R HDSL Terminal Unit – Remote. The module at the customer premises end
of an HDSL connection. Also known as a Network Termination Unit (NTU).
IDC Insulation Displacement Connection. A wire connection device.
IDSL ISDN DSL. Uses 2B1Q line code.
IEEE Institute of Electrical and Electronics Engineers.
IETF Internet Engineering Task Force. The primary working body developing
TCP/IP standards for the Internet.
ILEC Incumbent Local Exchange Carrier. Refers to the primary existing central
office carrier, as distinguished from new competitive carriers established after
deregulation.
IP Internet Protocol. An open networking protocol used for Internet packet
delivery.
ISA Industry Standard Architecture. A standard for connections of personal
computer bus architecture.
ISDN Integrated Services Digital Network. Telecommunication service that uses
digital transmission and switching technology to provide voice and data communications
on a bearer channel while sending signaling on a data channel.
ISO International Standards Organization.
ISP Internet Service Provider. A vendor who provides direct access to the Internet.
ITU International Telecommunications Union. The telecommunications agency
of the United Nations, established to provide standardized communications
procedures. Formerly known as CCITT.
IXC IntereXchange Carrier. All long distance carriers; also known as Other
Common Carriers.
kbps Kilobits per second. One kilobit is usually taken to be 1,024 bits.
LAN Local Area Network. A privately owned and administered data communications
network limited to a small geographical area.
LAP-F Link Access Protocol – Frame Relay. Q-922 Framing.
Last mile Refers to the local loop and is the difference between a local telephone
company office and the customer premises; a distance of about 3 miles or 4 kilometers.
Layer OSI reference model. Each layer performs certain tasks to move the information
from the sender to the receiver. Protocols within the layers define the tasks for the
networks.
LEC Local Exchange Carrier. A company that provides intra-LATA (local
access transport area) telecommunications services.
Local loop The distance between the CO and the customer premises.
L2TP Layer Two Tunneling Protocol.
MAC Media-specific Access Control. Protocol for controlling access at the data link
Layer 2.
Mbps Megabits per second. One megabit is 1,048,576 bits.
MDF Main Distribution Frame. The point where all local loops are terminated
at a CO.
MUX Multiplexer. A device that can send several data streams over a single
physical line.
NAP Network Access Provider. The provider of the physical network that
permits connection of service subscribers to NSPs.
NEBS Network Equipment Building System. A set of requirements for the
reliability and usability of equipment, established by Bellcore.
NEXT Near End CrossTalk. Crosstalk in which the interfering signal is traveling
in the opposite direction as the desired signal.
NIC Network Interface Card. The circuit board or other hardware that provides
the interface between a DTE and a network.
NID Network Interface Device. A device that connects the local loop to the
customer premises and includes the demarcation point.
Node A connection or switching point on the network.
NSN Network Service Node.
NSP Network Service Provider. A vendor, such as an ISP, local telephone company,
CLEC or corporate LAN, that provides network services to subscribers.
NTU Network Termination Unit. Equipment at the customer premises which
terminates a network access point.
Nx64 Describes a continuous bit stream to an application at the Nx64 kbps rate.
OC Optical Carrier Usually described as a level n signal. The fundamental
transmission rate for SONET. For example, OC3 represents a transmission rate of about
155 Mbps. OSI Open Systems Interconnection. The OSI Reference Model is a seven-
layer network architecture model of data communication protocols developed by ISO
and ITU.
PBX Public Branch Exchange. Telephone switching equipment dedicated to one
customer. A PBX connects private telephones to each other and to the
public dial network.
PCI A standard interface for PC cards such as NICs for Pentium and newer PCs.
POP Point-of-Presence. An IXC’s or NSP’s equivalent of a CO.
POTS Plain Old Telephone Service. Standard telephone service over the PSTN,
with an analog bandwidth of less than 4 KHz.
POTS Splitter A device that filters out the DSL signal and allows the POTS frequencies
to pass through.
PPP Point to Point Protocol A protocol used for dial-up data connections for users
connecting to their ISP. Provides security and authentication services (PAP, CHAP).
PSTN Public Switched Telephone Network. A network shared among many users
who can use telephones to establish connections between two points. Also
known as the dial network.
PTT Postal Telephone & Telegraph. Provider of access services. A
governmental agency in many countries.
PVC Permanent Virtual Connection. A virtual connection established administratively.
Included in networks supporting ATM, frame relay, and X.25.
QAM Quadrature Amplitude Modulation. Modulation technique using variations
in signal amplitude.
QoS Quality of Service. Measures of quantitative (speed) and qualitative (delay, error
rates…) for a given networking connection.
RADSL Rate Adaptive Digital Subscriber Line. Transmission technology that
supports both asymmetric and symmetric applications on a single twisted pair telephone
line. Allows adaptive data rates up to 7 Mbps.
RFC Request for Comment A document submitted for standardization to the IETF.
RFC 1483 A standard encapsulation protocol that maps Ethernet or IP frames over
an ATM PVC.
RFI Radio Frequency Interference. All computer equipment generates radio
waves. Levels are regulated by the FCC.
Router A device that connects LANs by dynamically routing data according to
network Layer 3. Most often an IP protocol router used for internet access.
RT Remote Terminal. The local loop can be terminated at RTs. RTs are
intermediate points closer to the customer premises used to improve
service reliability.
RTU Remote Termination Unit. A device installed at the customer premises
that connects to the local loop. Also referred to as the ATU-R.
SDH Synchronous Digital Hierarchy. Based in part on SONET, SDH is an ITU
standard for the interworking of ANSI and ITU transmission techniques.
SDSL Symmetric Digital Subscriber Line. Provides high bandwidth,
bidirectional transmission over one copper wire pair for T1 or E1 services.
SMDS Switched Multimegabit Digital Services. A packet switching service
connecting LANs.
SNMP Simple Network Management Protocol. Protocol for open networking
management.
SOHO Small Office/Home Office.
SONET Synchronous Optical NETwork. An ANSI standard for the transmission of
digital data over optical networks.
STS-1 Synchronous Transport Signal 1. The fundamental SONET standard for
transmission over optical fiber at 51.84 Mbps.
SU Service User. The end user at the customer premises.
SVC Switched Virtual Connection A temporary connection setup by a user to a
specified endpoint to exchange data. Used by ATM and X.25.
TCP/IP Transmission Control Protocol/Internet Protocol. The dominant protocol
suite in the worldwide Internet, TCP is Layer 4, the transport layer. IP is Layer 3, the
network layer.
TDM Time Division Multiplexer. A device that enables the simultaneous
transmission of multiple independent data streams into a single high-speed
data stream.
Telnet Virtual terminal protocol in the Internet suite of protocols. Allows the user
of one host computer to log into a remote host computer.
10Base-T Standard for 10 Mbps Ethernet over twisted pair wiring.
TIMS Transmission Impairment Measurement Set.
T1 A term for a digital carrier facility used to transmit a DS1 formatted
digital signal at 1.544 Mbps. It is primarily used in the United States.
2B1Q Two Binary, one Quaternary. A line coding technique that compresses two
binary bits of data into one time state as a four-level code.
UAWG Universal ADSL Working Group.
UBR Unspecified Bit Rate (as used in ATM).
UNI User to Network Interface. Used in ATM networking from a switch to an end user
device.
Upstream Typically refers to the transmission speed from the customer premises
toward the telephone network.
URL Uniform Resource Locator. An Internet standard addressing protocol for
location and access of resources.
UTP Unshielded Twisted Pair. See CAT5.
VBR Variable Bit Rate (as used in ATM).
VC Virtual Circuit. A logical connection or packet-switching mechanism
established between two devices at the beginning of a transmission.
VDSL Very-high-bit rate DSL. Generally refers to a data transmission speed from
25 to 50+ Mbps over very short distances.
WAN Wide Area Network. A network that spans a large geographic area.
xDSL Refers to all DSL-based services and standards.
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