Quick Navigator:

A  B  C  D  E  F   G  H  I  J  K  L  M   N  O  P  Q  R  S  T   U  V  W  X  Y  Z  #

A

AAL5
ATM Adaptation Layer 5. AAL5 has been adopted by the ATM Forum for a Class of Service called High Speed Data Transfer.

Access Method
The method by which networked stations determine when they can transmit data on a shared transmission medium. Also, the software within an SNA processor that controls the flow of information through a network.

Access Provider
Organization providing and maintaining network services for subscribers.

Access Rate
The transmission speed, in bits per second, of the physical access circuit between the end user and the network.

ADSL (Asymmetric Digital Subscriber Line)
A new method of transmitting at speeds up to 7 Mbps in one direction over a single copper telephone line, with up to 640 kbps in the other direction.

AIX
Advanced Interactive Executive. IBM's implementation of UNIX.

AMI
Alternative Mark Inversion. The line-coding format in T1 transmission services.

AN
Access Node. See node.

ANSI
American National Standards Institute. Accredits and Implements standards developed by other organizations. Member of ISO.

ANSI T1.403
The performance-monitoring, data-link, and network-interface requirements for ESF CSUs as defined by the Exchange Carriers Standards Association. T1.403 specifies automatic performance reports transmitted to the network once per second via the data link. (In an E1 environment, Performance Monitor is the equivalent of T1.403).

ANSI T1.413
The interface standard for DMT ADSL.

Asymmetric Transmission
Transmission which sends data at different rates in each direction, faster downstream than upstream.

ATM
Asynchronous Transfer Mode. High bandwidth, low-delay, connection-oriented, packet-like switching and multiplexing technique requiring 53-byte fixed-sized cells.

Attenuation
The dissipation of the power of a transmitted signal as it travels over the copper wire line.

ATU
ADSL Transceiver Unit. The ADSL Forum uses terminology for DSL equipment based on the ADSL model for which the Forum was originally created. Thus, 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, like RADSL and SDSL. ATU generally represents xDSL services.

ATU-C
ATU-Central Office. ATU Equipment placed in carriers central office in support of DSL-based services.

ATU-R
ATU-Remote. Equipment placed in customer location in support of DSL-based services.

AWG
American Wire Gauge. Gauge is a measure of the thickness of a cable where the lower the number, the heavier the gauge. Heavier gauge wire has lower impedance and is used for electrical wiring where heat buildup is a factor.

Back to Quick Navigator

B

B Channel
In ISDN, a full duplex, 64 kbps channel for sending data.

Backbone
Equipment that provides connectivity for users of distributed networks and includes all the network infrastructure required to provide connectivity between the edge vehicles.

Backbone LAN
A transmission facility designed to interconnect two or more local area network segments.

Backbone network
The main artery or link for a private or public network. Typically the backbone carries the lion's share of traffic (data, voice, video or some combination), is capable of carrying significant bandwidth and it is the network to which small/remote networks/links are attached.

Bandwidth
A term now used to describe the capacity or amount of traffic (data, voice or video) a certain communications line is capable of accommodating.

Baseband
Transmission scheme in which the entire bandwidth, or data-carrying capacity, of a medium (such as coaxial cable) is used to carry a single digital pulse, or a signal, between multiple users. Because digital signals are not modulated, only one kind of data can be transmitted at a time. Contrast with broadband.

BER (Basic Encoding Rate)
Rule for encoding data units described in ANS.1.

BER (Bit Error Rate)
The ratio of received bits that are in error.

Bits Per Second (bps)
The number of bits passing a point every second. The transmission rate for digital information.

BRI (Basic Rate Interface)
An ISDN interface that provides each user with two 64 kbps bearer channels and one 16kbps data channel (2B+D).

Bridged tap
Any part of the local loop that is not in the direct talking path between the CO and the service user.

Bridge/Router
A device that can provide the functions of a bridge, router or both concurrently. Bridge/router can route one or more protocols, such as TCP/IP and/or XNS, and bridge all other traffic.

Broadband
Data transmission at a high rate, generally greater than T1 speeds (1.5 Mbps). This allows the transmission of voice, data and video signals over a single medium.

Back to Quick Navigator

C

Cable Binder
In the telephone network, multiple insulated copper pairs are bundled together into a cable called a cable binder.

Cable modem
Cable Modems are the cable television companies answer to high-speed data access.   This technology shares the same connection that your cable television uses.  A special signal splitter is installed to filter out the television signals and a special cable modem is installed near your computer.  This type of connection is always on and has the potential for very high-speeds but it has several inherent draw backs.

This is a shared service.  This means that you share your Internet connection with everyone else in your area (usually 1000-2000 users are put on the same connection).   This means that it is less secure since you are sharing your connection with other users.  It also means that the speed you get will depend on how many other users are currently on and what they are using their connection for.  As more and more of your neighbors connect and surf the Internet your connection speed will get less and less.

The other drawback is that this is a residential service only.  There is currently no business version of this service.

Campus Area Network
A network which encompasses interconnectivity between floors of a building and/or buildings in a confined geographic area such as a campus or industrial park. Such networks would not require public rights-of-way and operate over fairly short distances.

CAP
Carrier less Amplitude & Phase Modulation. A transmission technology for implementing a Digital Subscriber Line (DSL). The transmit and receive signals are modulated into two wide-frequency bands using Passband modulation techniques. CAP is bandwidth-efficient and supports ADSL, HDSL, RADSL, and SDSL line coding.

CAP (Competitive Access Provider)
Alternative provider to Local Exchange Carrier (LEC). See also CLEC.

CAT5
Category 5. Specifications from EIA/TIA-570 refer to CAT5 and Grade UTP5 unshielded twisted pair wiring.

CBR
Committed Bit Rate.

CCITT (Consultative Committee for International Telegraph and Telephone)
The former name of an international organization that develops communications standards such as Recommendation X.25. Now called ITU-T.

Central Office
A local telephone company office which connects to the main system where circuit switching of customer lines occurs.

CEU
Commercial End User. See SU, service user.

Channel
A communication path. Multiple channels can be multiplexed over a single cable in certain environments. The term is also used to describe the specific path between large computers and attached peripherals.

Churn
The term used to describe turnover in subscribers of various media such as magazines, newspapers, cable, and videotex services. Churn is an important measure of a medium's success in holding on to customers after they have been signed up as subscribers.

Circuit-Switched Network
Network that establishes a physical circuit temporarily, until it receives a disconnect signal.

Circuit Switching
Switching system in which a dedicated physical circuit path must exist between sender and receiver for the duration of the "call". Used heavily in the phone company network, circuit switching often is contrasted with contention and token passing as a channel-access method, and with message switching and packet switching as a switching technique.

CLEC (Competitive Local Exchange Carrier)
Alternative provider to Local Exchange Carrier (LEC). See also CAP.

Client/Server
A distributed system model of computing that brings computing power to the desktop, where users ("clients") access resources from servers.

CO
Central Office. In North America, a CO location houses one or more switches to serve local telephone subscribers. Known as public exchange elsewhere.

Codec (Coder/Decoder)
Equipment to convert between analog and digital information format. Also may provide digital information format. Also, may provide digital compression functions.

Common Carrier
Licensed utility that provides communications services at government-regulated rates.

Compression
Reducing the size of a data set to lower the bandwidth or space required for transmission or storage.

Concentrator
Device that serves as a wiring hub in star-topology network. Sometimes refers to a device containing multiple modules of network equipment.

Conditioned Analog Line
Analog line to which devices have been added to improve the electrical signal.

Copper Optics
A PairGain trademark referring to the functionality of the company's xDSL technology. In essence, with PairGain xDSL products, users can achieve fiber optic-quality signal transmission over copper cable.

CPE (Customer Premises Equipment)
Terminating equipment, such as terminals, phones, routers and modems, supplied by the phone company, installed at customer sites, and connected to the phone company network.

Crosstalk
Line static that can occur when wire pairs within the same bundles are used for separate signal transmission. Especially evident with repeated T1/E1 transmission.

CSA
Carrier Serving Area.

CSU/DSU (Channel Service Unit/Data Service Unit)
A digital interface unit that connects end user equipment to the local digital telephone loop.

Back to Quick Navigator

D

DACS
Digital Access & Cross-Connect Systems. A digital cross-connect device for routing lines among multiple ports. The connections are typically set up in advance of the call.

D Channel
Full duplex 16 kbps (basic rate) or 64 kbps (primary rate) ISDN channel.

DCE (Data Circuit-terminating Equipment)
Equipment that resides at the customer end of a transmission link and provides all necessary termination functions for that link. May be owned by the customer or by the service provider.

DCE (Data Communications Equipment)
The devices and connections of a communications network that connect the communication circuit with the end device (data terminal equipment). A modem can be considered a DCE.

DDS
Digital Data Service. Private line digital service with data rates of 56/64 kbps.

DECNET
Digital Equipment Corporation's proprietary network architecture.

Dedicated Line
A transmission circuit installed between two sites of a private network and "open," or available, at all times.

Demodulation
Opposite of modulation; the process of retrieving data from a modulated carrier wave.

DHCP (Dynamic Host Control Protocol)
A TCP/IP protocol.

Dial up
A type of communication that is established by a switched-circuit connection using the telephone network.

DLC (Digital Loop Carrier)
Network transmission equipment used to provide a pair gain function. Consists of a CO terminal and a remote terminal.

DLCI (Data Link Connection Identifier)
The Frame Relay virtual circuit number used in internetworking to denote the port to which the destination LAN is attached.

DMT (Discrete Multitone)
In DMT, a large number of low-rate carrier frequencies are QAM-modulated at a low rate to transmit a single high-rate data stream. DMT is used for ADSL and proposed for VDSL.

Downstream
Refers to transmission speed from the CO to the service user.

DRAM
Dynamic Random Access Memory. Memory used to store data in PCs and other devices.

Drop Cable
A cable that connects a network device such as a computer to a physical medium such as an Ethernet network. Drop cable is also called transceiver cable because it runs from the network node to a transceiver (a transmit/receiver) attached to the trunk cable.

DS-0 (Digital Signal 0)
(1) North American Digital Hierarchy signaling standard for transmission at 64 kbps.
(2) Digital Signal Level 0 is the worldwide standard transmission rate (64 kbps) for PCM digitized voice channels. 24 DSOs exist in each DS1 (T1) signal.

DS-1 (Digital Signal 1)
North American Digital Hierarchy signaling standard for transmission at 1.544 Mbps. Supports 24 simultaneous DS-O signals. Term often used interchangeably with T-1, although DS-1 signals may be exchanged over other transmission systems.

DSL (Digital Subscriber Line)
Another name for an ISDN BRI channel. Operated at the Basic Rate Interface (with two 64 kbps circuit switched channels and one 16 kbps packet switched channel), the DSL can carry both voice and data signal at the same time, in both directions, as well as the signaling data used for call information and customer data.

DSLAM
Digital Subscriber Line Access Multiplexer. Provides high-speed Internet or Intranet access over traditional twisted-Pair telephone wiring through the use of RADSL technology. Provides simultaneous high-speed digital data access and POTS analog service over the same twisted-pair telephone line. Can be installed in the CO or at an ISP adjacent to the CO.

DSP (Digital Signal Processing)
The processing of signal transmission using digital techniques.

DSP (Digital Signal Processor)
A specialized computer chip designed to perform speedy complex operations on digitized waveforms.

DSU
Digital Service Unit. Digital loop device residing on customer premises providing interface to customer's DTE.

DTE (Data Terminal Equipment)
The part of a data station that serves as a data source, destination, or both, and that provides for the data communications control function according to protocol. DTE includes computers, protocol translators, and multiplexers.

Back to Quick Navigator

E

E1
The term for a digital facility used for transmitting data over a telephone network at 2.048 Mbps. The European equivalent of T1.

E3
The highest transmission rate generally available in the European digital infrastructure (34 Mbps).

Echo Cancellation
Process by which a transmitter/receiver cancels out the transmitted signal as to "hear" the received signal better.

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.

EMS
Element Management System. A management system that provides functions at the element management layer.

Enterprise Network
A large typical corporate network under the auspices of one organization.

Ethernet
A baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. Ethernet networks operate at 10 Mbps using CSMA/CD to run over coaxial cable. Ethernet has become a series of standards produced by IEEE referred to as IEEE 802.3.

ETSI
European Telecommunications Standards Institute.

Back to Quick Navigator

F

FCC
Federal Communications Commission. The United States federal regulatory agency responsible for regulating interstate and international communications.

FDDI
Fiber Distributed Digital Interface. A LAN Token Ring standard using fiber optic cable.

FDI
Feeder Distribution Interfaces. Points where cable bundles from the telephone switch use drop lines extended out to service users.

FDM
Frequency Division Multiplexing.

FEXT
Far End Crosstalk. One strategy of Crosstalk, the other being Near End Crosstalk of NEXT.

Fiber Optics
A method for the transmission of information (sound, pictures, data). Light is modulated and transmitted over high purity, hair-thin fibers of glass. The bandwidth capacity of fiber optic cable is much greater than that of conventional cable or copper wire.

Fiber Optic Cable
A transmission medium that uses glass or plastic fibers, rather than copper wire, to transport data or voice signals. The signal is imposed on the fiber via pulses (modulation) of light from a laser or a light-emitting diode (LED). Because of its high bandwidth and lack of susceptibility to interference, fiber-optic cable is used in long-haul or noisy applications.

Fractional T1
A WAN communications service that provides the user with some portion of a T1 circuit which has been divided into 24 separate 64 kbps channels.

FRAD
Frame Relay Access Device.

Frame Relay
A streamlined packet switching protocol designed to provide high-speed frame or packet switching with minimal delay and efficient bandwidth usage.

FRF
Frame Relay Forum.

FRSP
Frame Relay Service Provider.

FTP
File Transfer Protocol. Internet tool for accessing files linked to the Internet.

Back to Quick Navigator

G

GBPS (Gigabits Per Second)
1,000,000,000 bits per second. A measure of transmission speed.

GUI
Graphical User Interface.

Back to Quick Navigator

H

HDB3
High Density Bipolor-3 zeros. A bipolar coding method that does not allow more than three consecutive zeros.

HDSL (High-bit-rate Digital Subscriber Line)
Designed to be a cost-effective method of delivering T1/E1 line speeds over unconditioned copper cable, without the use of repeaters.

HDSL2
Same as description for HDSL (see above) but it supports full T1 over a single pair, it is interoperable with other vendors and it is ANSI standard based.

Headend
The source end of a coaxial cable TV system. Often, the site for signal processing equipment essential to proper functioning of a cable system.

Hertz
Frequency measurement, 1 Hertz = 1 cycle per second.

HTML
HyperText Markup Language. The standard authoring language used on World Wide Web pages. HTML is basically ASCII text surrounded by commands known as "tags".

HTU-C
HDSL Transceiver Unit-Central Office.

HTU-R
HDSL Transceiver Unit-Remote.

Back to Quick Navigator

I

IDC
Insulation Displacement Connection. A type of wire connection device in which a wire is punched down into a metal holder that strips away the insulation to achieve electrical connection.

IDSL
ISDN DSL using 2B1Q line code.

IEEE (Institute of Electrical and Electronic Engineers)
Professional organization that defines network standards. IEEE LAN standards are the predominant LAN standards today, including protocols similar or virtually equivalent to Ethernet and Token Ring.

IETF (Internet Engineering Task Force)
The primary working body developing new TCP/IP standards for the Internet.

ILEC
Incumbent Local Exchange Carrier. Refers to the primary existing carrier, as distinguished from new competitive carriers with the advent of telecom deregulation.

Interoperability
The ability of equipment from multiple vendors to communicate using standardized protocols.

Interface
(1) The point at which two systems or pieces of equipment are connected. (2) A connection between two systems or devices. A shared boundary defined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals.

Intranet
A private network that uses Internet software and standards.

IP
Internet Protocol. A standard describing software that keeps track of the Internetwork addresses for different nodes, routes outgoing messages, and recognizes incoming messages.

IPX
Internetwork Packet Exchange. LAN communications protocol used to move data between server and/or workstation programs running on different network nodes.

ISA
Industry Standard Architecture. A personal computer bus architecture.

ISDN (Integrated Services Digital Network)
A CCITT networking standard devised to provide end-to-end, simultaneous handling of digitized voice and data traffic on the same link.  Integrated Services Digital Network.  This is the predecessor to DSL technology.   It combines voice and data on the same copper telephone line.  It usually runs at speeds of either 64k or 128k and it is a measured service.  This means you pay per minute for your actual usage.

ISO (International Standards Organization)
Founded in 1946 to facilitate the development of industrial standards.

ISP
Internet Service Provider

ITU (International Telecommunications Union)
Produces technical standards for all internationally controlled aspects of analog and digital communications. Formerly known as CCITT.

IXC (Interexchange Carrier)
(1) A long-distance telephone company offering circuit-switched, leased-line or packet-switched service or some combination.
(2) Any individual, partnership, association, joint-stock company, trust, governmental entity or corporation engaged for hire in interstate or foreign communication by wire or radio, between two or more exchanges.

Back to Quick Navigator

J

Back to Quick Navigator

K

Kbps (kilobits per second)
1,000 bits per second. A measure of transmission speed.  Kilo Bits Per Second.  A measure of time relating to telecommunications speeds.   1kbps is 1,000 bits of information, the higher the number, the faster the speed.

Back to Quick Navigator

L

LAN (Local Area Network)
The means by which a local community of users and workgroups can share information and resources electronically. Many communications protocols are used to accomplish this, the most prevalent of which are Ethernet and Token Ring.

LANE
LAN Emulation. Typically used in LANE over ATM.

LATA (Local Area Transport Area)
(1) A geographic area established for the provision and administration of communications service. It encompasses one or more designated exchanges, which are grouped to serve common social, economic and other purposes.
(2) Contiguous local exchange areas that include every point served by a LEC within an existing community of interest and that serve as the dividing line for the allocation of assets and liabilities between the IXC and the LEC.
(3) A telephone company term that defines a geographic area; sometimes corresponds to an area code.

Last mile
A reference to the local loop, the distance between a local telco office and the subscriber, a distance actually about 0 to 3 miles (0 to 4 kilometers).

Layer
OSI reference model. Each layer performs certain tasks to move the information from the sender of the receiver. Protocols within the layers define the tasks for the networks but not how the tasks are accomplished.

Leased Line
A transmission line reserved by a communications carrier for the private use of a customer.

LEC
Local Exchange Carrier. LEC's provide local transmission services.

Lifeline POTS
A minimal telephone service designed to extend a "lifeline" to the telephone system in case of emergency, particularly when electric power is lost.

Line code
Any method of converting digital information to analog form for transmission on a telephone line. 2B1Q, DMT, and CAP are all line codes.

Link
Physical connection between two nodes in a network. It can consist of a data communication circuit or a direct channel (cable) connection. Also an LED signal that indicates connection has been established.

Local Loop
Refers to the physical copper pair or loop of wire from Central Office to the subscriber.

L2TP
Layer Two Tunneling Protocol.

Back to Quick Navigator

M

MAC
Media Access Control. A method of controlling access to a transmission medium (e.g., Ethernet, Token Ring, FDDI).

MAN (Metropolitan Area Network)
A data communication network covering the geographic area of a city. Often used by a CAP to carry backbone traffic in their serving area.

Mbps
Megabit per second. 1,000,000 bits per second.  A measure of time relating to transmission rates.  1Mbps is 1 million bits of information, the higher the number, the faster the speed.

MDF
Main Distribution Frame. Central point where all local loops terminate in the CO.

MIB
Management Information Database.

Modulation
Process by which signal characteristics are transformed to represent information. Types of modulation include frequency modulation (FM), where signals of different frequencies represent different data values.

MPEG
Motion Picture Experts Group. Group developing emerging ISO standard for the compression and coding of motion video.

MSO
Multiple System Operator. A company that operates more than one cable TV system.

MTBF
Mean time between failure.

MTSO
Mobile Telephone Switching Office. A generic name for the main cellular switching center which supports multiple base stations.

MUX (Multiplexer)
A technique that enables several data streams to be sent over a single physical line. It is also a function by which one connection from a layer is used to support more than one connection to the next higher layer.
(2) A device for combining several channels to be carried by one line or fiber.

Back to Quick Navigator

N

NAP
Network Access Provider. The NAP provides a transit network service permitting connection of service subscribers to NSPs. The NAP is typical the network provider that has access to the copper twisted pairs over which the DSL-based service operates.

NDIS (Network Design Interface Specification)
Used for all communication with network adapters. Works primarily with LAN manager and allows multiple protocol stacks to share a single NIC.

NEBS
Network Equipment Building System.

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 installed in a PC that provides the interface between a communicating PC and the network.

NID
Network Interface Device. An electronic device that connects the telephone line and the POTS splitter to the local loop.

NMS (Network Management System)
A system responsible for managing at least part of a network. NMSs communicate with agents to help keep track of network statistics and resources.

Node
A node on a network is usually formed by the presence of a router and user access equipment. Often, several leased lines are joined together at network node.

NSN
Network Service Node.

NSP
Network Service Provider. Can include a local telephone company, ISP, or CLE.

NTU
Network Termination Unit. Equipment at the customer premises which terminates a network access interface.

Nx64
Describes a contiguous bit stream at the Nx64 kbps rate to application. Examples are LAN interconnect a point-to-point videoconferencing.

Back to Quick Navigator

O

OCn
Optical carrier level n signal. The fundamental transmission rate for SONET. For example, OC3 operates at 1.55 Mbps.

OPTIS (Overlapped Pulse Amplitude Modulated Transmission with Interlocking Spectra)
The technology developed by PairGain and ultimately adopted by the ANSI standards committee as the line coding technique for HDSL2. ANSI committee members all agree that PairGain’s OPTIS line code is far superior to any others proposed, such as SC-PAM. The performance characteristics and spectral compatibility are unmatched.

OSI (Open Systems Interconnection)
A 7-layer architecture model for communications systems developed by ISO and used as a reference model for most network architectures.

Back to Quick Navigator

P

Packet
(1) A logical grouping of information that includes a header and (usually) user data. (2) Continuous sequence of binary digits of information is switched through the network and an integral unit.

Packet Switched Network
A network in which data is transmitted in units called packets. The packets can be routed individually over the best available network connection and reassembled to form a complete message at the destination.

Pair gain
The multiplexing of x phone conversations over a lesser number of physical capacities. "Pair gain" is the number of conversations obtained, divided by the number of wire pairs used by the system.

PBX
Public Branch Exchange.

POP
Point-of-Presence. A POP refers to a node of an ISP or other NSP. A POP is usually a network node.

POTS
Plain Old Telephone Service. Restricted to less than 4000 Hertz of the frequency spectrum.

POTS Splitter
A device that rejects the DSL signal and allows the POTS frequencies to pass through.

PSC
Public Service Commission.

PSTN
Public Switched Telephone Network. The generic term for the collection of networks which provide public telephone switching service.

PTO
Public Telephone Operator.

PTT (Postal, Telegraph and Telephone Company)
Generic term for a provider of these services. A governmental agency in many countries.

PVC (Permanent Virtual Circuit)
A defined virtual link with fixed end-points that are set-up by the network manager. A single virtual path may support multiple PVCs.

Back to Quick Navigator

Q

QAM
Quadrature Amplified Modulation. A two-dimensional modulation used for ADSL, cable modems and proposed for VDSL. CAP is a special case of QAM. In QAM, a single carrier frequency is modulated in both sine and cosine components.

QoS
Quality of Service. Term for the set of parameters and their values which determine the performance of a given virtual circuit.

Back to Quick Navigator

R

RADSL
Rate-Adaptive ADSL. A simple extension of ADSL to encompass a wide variety of data rates depending on the line's transmission capability. RADSL can be either CAP or DMT ADSL.

RBOC (Regional Bell Operating Companies)
Seven LEC telephone companies created after AT&T divestiture.

Remote LAN Access
A data communications such as a corporate or campus environment in which the computer networks can be accessed remotely via public telecommunications networks.

Repeater
An electronic device used to regenerate digital signals and restore signal quality across a certain distance of cable.

RFI
Radio Frequency Interference. Radio frequency is the electromagnetic spectrum from 3 kHz to 300 GHz.

Router
A device that Interconnects LANs that can dynamically route data at Layer 3, the network layer, based on destination and routes available.

RSVP
Resource Reservation Setup Protocol. A reservation setup protocol for the Internet.

RT
Remote Terminal. Local loop terminates at Remote Terminal intermediate points closer to the service user to improve service reliability.

RTU
Remote Termination Unit. A device installed at the service user site that connects to the local loop to provide high-speed connectivity. Also referred to as the ATU-R.

Back to Quick Navigator

S

SDH
Synchronous Digital Hierarchy. An international standard for transmission in SONET.

SDSL
Symmetric Digital Subscriber Line.  SDSL is a variation of DSL that uses one pair of copper cable for transmission.  It was designed for applications requiring fast transfer speeds in both directions.  It's typical to see this type of DSL in speeds from 144kbps all the way up to 1.1Mbps in both directions making it well suited for large file transfers and web site hosting.

S-HDSL
Single pair transmission using HDSL technology, normally 2B1Q.

SIP
SMDS Interface Protocol (SIP). Formal name given to each layer of the SMDS network interface.

SMDS
Switched Multimegabit Digital Services.

SNA
Systems Network Architecture. IBM's vendor specific connection-oriented, virtual circuit network architecture for terminal/host communication.

SNMP (Simple Network Management Protocol)
A network management standard initially established to allow multi-vendor networking devices to be managed more easily with common management tools.

SOHO
Small Office/Home Office.

SONET (Synchronous Optical Network)
A recently emerging networking standard that utilizes fiber optics to create backbone networks, capable of transmitting at extremely high speeds and accommodating gigabit-level bandwidth.

Spanning Tree
An algorithm, the original version of which was invented by Digital Equipment Corporation, used to prevent bridging loops by creating a spanning tree. The algorithm is now documented in the IEEE 802.1d specification, although the Digital algorithm and the IEEE 802.1d algorithm are not the same, nor are they compatible.

STS-1
Synchronous Transport Signal 1. A SONET standard for transmission over OC-1 optical fiber at 51.84 Mbps.

SU
Service User. The end user at the customer premises.

SVC (Switched Virtual Circuit)
A virtual link, with variable end-points, established through an ATM network. With a SVC, the user defines the end-points when the call is initiated that are subsequently terminated at the end of the call. With a Permanent Virtual Circuit (PVC), the end-points are predefined by the network manager. A single virtual path may support multiple SVCs.

SWC
Service Wire Center.

Symmetric Transmission
Transmission in which a channel sends and receives data with the same signaling rate.

Back to Quick Navigator

T

T1
Digital transmission facility operating with a nominal bandwidth of 1.544 Mbps. Also known as Digital Signal Level 1 (D1). Composed of 24 DS-0 channels in many cases. The T1 digital transmission system is the primary digital communication system in North America. 

T2/T3
A digital facility used to transmit a DS1 formatted digital signal.

T3
Digital transmission facility operating at 45 Mbps bandwidth. Composed of 28 DS-1 channels in many cases. Also known as DS-3.

TCP/IP (Transmission Control Protocol/Internet Protocol)
A reliable, full duplex, connection-oriented end to end transport protocol running on top of IP.

TDM
Time Division Multiplexing. Technique where data from multiple channels may be allocated bandwidth on a single wire pair based on time slot assignment.

Telecommuter
Person who performs work at home while linked to the office by means of a telecommunications-equipped computer system.

Telnet
A program that lets you connect to other computers on the Internet.

TIMS
Transmission Impairment Measurement Set.

Transparent LAN Service
Service offered by a provider that is used to connect LANs at geographically separated sites. "Transparent" means the connection is invisible to the user and typically runs at the same speed as the LAN.

Twisted Pair
Cable consisting of two 18 to 24 AWG (American Wire Gauge) solid copper strands twisted around each other. The twisting provides a measure of protection from electromagnetic and radio-frequency interference.

Back to Quick Navigator

U

Upstream
Refers typically to the transmission speed from the service user to the telephone network.

URL
Uniform Resource Locator. Used with the World Wide Web as an address.

UTP
Unshielded twisted pair. See CAT5.

Back to Quick Navigator

V

VC
Virtual Circuit. A logical connection or packet-switching mechanism established between two devices at the start of transmission.

VDSL
Very-high-bit rate DSL. Generally refers to 25 to 50+ Mbps transmission over very short distances.

VLAN
Virtual LAN. Workstations connected to an intelligent device which provides capabilities to define LAN membership.

VLSI
Very Large Scale Integration.

VOD
Video On Demand

VPN
Virtual Private Network.

Back to Quick Navigator

W

WAN (Wide Area Network)
A network which encompasses interconnectivity between devices over a wide geographic area.

WIPO
World Intellectual Property Organization. 

Back to Quick Navigator

X, Y, Z

xDSL
Another way of referring generically to any of the DSL variants: ADSL, HDSL, SDSL, RADSL, IDSL, VDSL.

Back to Quick Navigator

#, 1, 2, 3, ...

10BASE-T
The Institute of Electrical and Electronic Engineers (IEEE) 802.3 specification for ethernet over thin coaxial cable.

2B1Q
2 binary, one quarternary. A one-dimensional modulation for transmitting 2 bits per symbol. 2B1Q is a 4-level PAM (pulse amplitude modulation) system used for HDSL, S-HDSL, and ISDN BRI.

Back to Quick Navigator