| DSL Glossary
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
ADSL - Asymmetric Digital Subscriber Line Simultaneous high-speed data and POTS (voice) service over the same telephone line. Downstream speed ranges between 128Kbps and 8 Mbps. Upstream is usually lower than the downstream (hence, asymmetrical). The upstream rate varies from 64 Kbps to 640 Kbps. ADSL is appropriate for residential use as most home users require faster downstream speeds for file downloads, internet traffic, and video. There are 3 predominant industry standards for ADSL, all based on the DMT line code.
ADSL Forum An organization that proposes DSL standards.
ADSL Lite A type of DSL based on the G.Lite standard supporting up to 1.5 Mbps downstream and 512 Kbps upstream. This version of ADSL was designed to simplify user installation.
American Wire Gauge (AWG) Measurement of thickness for copper wiring. The lower the AWG, the longer is the distance that the wire can support. Telephone lines are typically 26 gauge (1/26" in diameter), or 24 gauge (1/24" in diameter). 24 gauge is thicker and conducts electricity better than 26 gauge (for like materials and conditions).
Asynchronous Data communication in which transmission is not related to specific timing between communicating devices.
Asynchronous Transfer Mode (ATM) A high-bandwidth, low-delay, standard for digital backbone networks.
Attenuation Lowering a signal's strength, or amplitude is called attenuation. Signals weaken, or are attenuated, as it travels over a wire.
ATU-C - ADSL Termination Unit - Central OfficeThe
device at the end of the ADSL line located in the telephone central office. Now most commonly called a DSLAM.
ATU-R - ADSL Termination Unit - Remote The device at the end of the ADSL line in the end-user's location. Now most commonly called CPE, also known as the modem, or gateway.
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Backbone The part of the network that carries traffic between network endpoints. Bandwidth The capacity of a medium to transmit a signal. More informally, the "size" of a data pipe, and its capacity to carry the files and messages.
Baud rate The actual symbol frequency being used to transmit data. Different amounts of data can be transferred per BAUD.
Bit The smallest unit of information in a binary number system. A bit can be a "0", or a "1". Four bits together for a single character is called a nibble. 8 bits together is called a byte. 16 bits together is known as a word.
Bits per second (bps) The speed at which bits (digital electronic signals) are transmitted. The bps rate may be equal to or greater than the baud rate.
Bridge A device that connects two networks into a single network using the same networking protocol, such as TCP/IP.
Bridge Tap An extension to a local loop (branches off the main line) used to attach a remote user to a central office. Bridge taps can limit the speed of DSL.
Byte A group of 8 bits which represent one data character.
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Cable Modem A modem that operates over cable TV lines (coax) and is one of the main broadband competitors to DSL. Cable networks share their data bandwidth between all of the users
on a specific cable node.
Central Office (CO) A telephone company faciliy where the local telephone lines terminate. The CO houses the equipment required for switching voice communications across the telephone network. Special equipment is set up at the CO to support DSL service.
Circuit The path through a network from source to destination and back.
Client An intelligent workstation that makes requests to other computers known as servers. PC computers on a LAN can be clients.
CPE - Customer Premises Equipment The DSL equipment located at the customer premises, which is either a DSL modem or router, for Internet access.
Crosstalk Line distortion caused by wire pairs in the same bundle being used for separate signal transmission. The signals from one line can affect the signals on another, adjacent line.
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Data Protocols Describe rules and conventions that determine how devices on a network exchange information.
DHCP (Dynamic Host Configuration Protocol) A protocol that allows remote clients to request configuration information, such as IP host addresses, from a server.
Dial-up Refers to data connectivity using the Public Switched Telephone Network (PSTN). Dial-up uses modems to connect client computers to remote LAN access routers.
Digital Loop Carrier (DLC)Also called a "remote terminal", a DLC extends the reach of communications from a central office to the home. DLCs can present a problem for DSL provisioning. The back-end connection (from the DLC to the CO) is typically T1, which does not have enough bandwidth for many users. There is also limited space and power available in the DLC. The ILECs are beginning to solve this problem by installing cards with DSLAM-like functionality, and adding Fiber back haul to the CO.
Domain Part of an Internet naming hierarchy. An Internet domain name consists of a sequence of names (labels) separated by periods; for example "ubiz.com".
DNS (Domain Name Service) DNS is a distributed database used by TCP/IP applications to map between hostnames and IP addresses, and.
Downstream Data Data that travels from the Internet to a local computer. For typical, residential Internet use, the downstream data rate is usually higher than the upstream data rate.
DSLDigital Subscriber Line. The generic term that refers to the entire family of DSL technologies, such as SDSL, ISDL, and ADSL. Subscriber line refers to the client (subscriber) local phone line.
DSLAM (Digital Subscriber Line Access Multiplexer) Terminates
the client DSL modem. Consolidates data traffic from individual DSL connections into large high-capacity backbone networks that connect to ISPs or corporate networks. This is the CO side modem and data concentrator.
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Electronic Mail (Email) A communications tool which is the electronic equivalent of postal mail. Because of the sheer speed of email (the ability to reach a destination in a matter of seconds), this form of communication has gained tremendous popularity.
Ethernet A type of local area network (LAN). Ethernet was originally designed for data transmission at speeds up to 10Mbps (million bits per second). Today's Ethernet can operate at 10, 100, and even 1Gbps (billion bits per second).
Ethernet Modem An external modem that connects to the PC via a 10/100baseT Ethernet connection. The users PC must support Ethernet to use this modem. The users PC must have
10/100baseT included, or the user must install an Ethernet NIC.
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Far End Crosstalk (FEXT) Crosstalk is Interference between conductors, such as phone lines. FEXT is interference measured at the far end (opposite end) of where a signal drives the line.
File Transfer Protocol (FTP) FTP enables you to transfer files between your computer and a remote computer. A common use of FTP on the Internet is to download software programs. It is a common protocol that can be used between different types of computers.
Filter (Micro-filter) User installable devices that are placed on all of the phone devices on an ADSL phone line. The in-line filter is used for RJ"2"1 connected handsets, answering machines, fax machines, caller ID boxes, V.90 modems, etc. The wall filter is used for wall mounted phones. It is placed between the wall jack and the phone. Not all homes will need this wall filter. Using micro-filters instead of a Splitter is called a "distributed filter" installation.
Firmware Firmware is software stored locally in a device's memory (such as in ROM - read only memory). This is the program that controls the device.
Fractional T1 T1 service offered in fractional amounts based on 64-Kbps increments. Full T1 is 1.544Mbps.
Frame Relay A packet based data networking service offered by phone companies. Frame relay takes advantage of shared bandwidth, and allows over subscription. Frame relay services are being replaced in favor of ATM.
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Gateway A computer system that reformats and transfers data between applications or networks that use
different protocols. Gateways provide an address translation service.
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HDSL (High-data-rate DSL) HDSL-2Uses four wires (two pairs) rather than the standard two wires and is typically used to replace T1 lines. Supports symmetric service at 1.54 Mbps but does not support POTS. Some versions go up to 2.3Mbps. There is no industry standard for HDSL. HDSL-2 provides similar speed capabilities as HDSL but utilizes a single wire pair. HDSL-2 also minimizes interference with other communication technologies. There will be an industry standard for HDSL-2.
Hertz The basic unit of frequency measurement described in the number of cycles per second.
Host A single, addressable device on a network. Computers, networked printers, and routers are hosts.
Hub A hub is a LAN device that serves as a central "meeting place" for communications from computers, servers, and peripherals. Hubs typically "repeat" signals from one computer to the others on the LAN.
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IDSL (ISDN DSL) This is an "always on" alternative to dial-up ISDN service with a capacity of up to 144 Kbps. IDSL has a larger reach than other DSL types. IDSL can be used at distances upwards of 26,000 feet.
Incumbent Local Exchange Carrier (ILEC) The primary telephone companies that handle voice and data connections. There are seven primary ILECS - Pacific Bell, US West, Bell Atlantic, Bell South, Southwestern Bell, Ameritech, and GTE.
Internet The largest computer network in the world, using the IP protocol suite. The Internet provides file transfer, remote login, email, news, and other services and is becoming the predominant method of connecting people and businesses' computers.
IP (Internet Protocol) IP allows a data packet to traverse multiple networks on the way to its final destination. Internet Protocol (IP) Address A 32-bit number assigned to
any computing device that uses the Internet Protocol (4 decimal fields separated by periods, e.g., 123.4.567.8.
Intranet An internal Internet designed to be used within the confines of a company, university or organization (outside users cannot access the entity's Intranet).
ISDN Integrated Services Digital Network An early dial-up predecessor of the DSL family that uses ISDN transmission technology to support up to 128 Kbps symmetrical service. ISDN is a usage-based service (tarriffed) offered by the telephone companies and is very expensive relative to DSL.
ISP (Internet Service Provider)An ISP is a telecommunications company that sells Internet access services and other products to end users.
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Kilobits per second (Kbps)Kilobits-per-second means thousands of bits per second. This is a way of describing the speed of an Internet connection (representing the number of bits transmitted per second). Typical modems operate at speeds between 9.6 Kbps and 56.0 Kbps.
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Latency The time it takes a data packet to move across a network connection.
Leased Line A dedicated circuit (private telephone line) between two locations, available full time for transmission of data or voice.
Load Coil A device used to extend the voice reach of a local loop beyond 18,000 feet. All load coils must be removed from a line in order for DSL to work.
Local Access and Transport Area (LATA) Defines the geographic area over which the LEC may provide toll calls. There are about 192 LATA's defined in the US.
Local Area Network (LAN) Typically a LAN is used within a single location, building, or set of buildings. It enables communication between computers and the sharing of local resources such as printers, CD readers, databases, and file servers.
Local Loop A pair of twisted wires between the telephone company's central office and the end-user's location. The local loop provides the user with access to the international telecommunications infrastructure.
Loop Qualification The process used to determine whether a specific phone line will support DSL.
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Megabits per second (Mbps) Megabits per second means millions of bits per second. Ethernet LANs operate at
speeds up to 1Gbps. A T1 WAN connection operates at 1.544 Mbps.
Modem Stands for modulator/demodulator. A modem is a data communications device that connects a computer to the telephone network. A modem converts analog waveforms into digital data and vice versa. Digital or ISDN modems, also called Terminal Adapters, are used to connect computers to digital ISDN lines.
Multimedia Anything using more than one medium; graphics, sound, animation, text, and/or video combined into one "presentation" on screen.
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Near-end Cross Talk (NEXT) Interference between pairs of lines at the same end of the line where the signal source is located.
Network Interface Card (NIC) A standard Ethernet card (10baseT, or 100baseT) used to connect to an Ethernet modem, an Ethernet connected ADSL router, or other Ethernet connected interface device. "NIC" does not refer to an ADSL modem.
Network Interface Device (NID) A device that terminates copper pair from the central office at the user's destination. Usually the "demarcation between the telephone companies equipment, and the users equipment.
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Packet A formatted unit of data transmitted on a network. Usually a piece of a larger file.
PCI Modem Sometimes referred to as an ADSL NIC, this modem connects inside the PC, into a PCI slot.
Plain Old Telephone Service (POTS) Basic voice telephone service is called POTS.
Point-to-Point Protocol The TCP/IP protocol that enables point to point connectivity to the Internet.
Port A location for passing data in and out of a device.
Point-to-Point Protocol over Ethernet (PPPoE) Point to Point
data connectivity over Ethernet. Can be used by one or multiple computers to share a single DSL connection.
Protocol An explanation of message formats along with the rules systems must follow to exchange messages. Standard protocols enable different computers to communicate.
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(QoS) Quality of Service QoS is the measure of the quality of service provided by a communications company.
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RADSL (Rate-Adaptive DSL) Automatic rate adaption which allows actual data transmission rates to adjust to
line conditions and distance. This term is not used frequently. RADSL typically refers to CAP (type of line code) based ADSL, which is not standardized.
Regional Bell Operating Company (RBOC) The U.S. telephone companies that resulted from the break up of AT&T.
RIP (Routing Information Protocol) A protocol used for the transmission of IP routing information.
RJ"2"1 A telephone-industry standard connector type, usually contains four pins, for two pairs (telephone lines)
RJ-45 A telephone-industry standard connector type, usually containing eight pins.
Router A device that connects (routes) multiple computer networks through IP addressing information contained in the IP packet. A DSL router routes packet data between a network and the Internet via the DSL connection.
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SDSL - Symmetrical Digital Subscriber Line A symmetrical member of the DSL family that supports data speeds from 144 Kbps to 1.5 Mbps. SDSL technology is best suited for two-way data traffic needs of businesses, and for video conferencing. SDSL does not support the use of POTS phone service on the same line. There is no industry standard for SDSL.
Serial PortA port found on most computers through which data flows to and from a serial device. Typically used for low speed communications to peripherals.
Server A device or system, which has been specifically configured to provide a service or information, usually to a group of clients.
SNMP (Simple Network Management Protocol) A protocol used for communication between management consoles and network devices.
Splitter The filter device that is professionally installed (via truck roll) on a user’s home to allow POTS and ADSL service on a single copper pair. The splitter
separates the POTS and data signal into two separate lines. The separated POTS connects to the traditional voice circuit in the home. The data line goes to the user’s ADSL modem. The splitter is usually installed at the
customer’s "NID", or network interface, which is typically located outside the user’s home. A splitter is a filter (actually 2 filters in one box) that is only installed professionally. A splitter can also be professionally
installed inside the home to provide the same function.
Splitterless DSLA term for DSL which does not require a splitter at the NID. G.lite ADSL is a "splitterless" technology. Splitterless DSL may require micro-filters, small filters located at each phone device (except for the DSL modem). Distributed Splitters are where the customer installs in-line microfilters at every existing telephone extension (except for the DSL modem).
Subnet A subnet extends the IP addressing scheme.
Subnet Mask A 32-bit number to specify which part of an address is the network number, and which part is the host address.
Swapper The swapper is placed between the RJ"2"1 phone jack, and the DSL modem. It will change, or swap pins 4 & 5, to pins 2 & 3. This allows a wall jack wired for DSL on pins 4 & 5 to connect to the ADSL modem that expects the DSL on pins 3 & 4. If a customer has two phone lines, his DSL modem line may be on pins 4 & 5 and require a swapper. A swapper may be needed even if a user does not have a second line. Sometimes, when a splitter is installed (by the service provider), the installer may place regular voice (POTs) on pins 3 & 4, and the DSL data on pins 4&5. A swapper will be needed in these cases.
Synchronous Data communications in which transmissions are sent with the sending and receiving devices synchronized.
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T1 A dedicated leased line service offered by the telephone companies that deliver data at 1.54 Mbps (divided into 24 64-Kbps channels). This service costs significantly more than DSL.
T3 A dedicated leased line service offered by the telephone companies that deliver data at 45 Mbps, equivalent to 28 T1 lines.
Terminal Adapter (TA) A Terminal Adapter is to an ISDN line what a modem is to a normal analog telephone line. It is a "modem" device which connects a client computer to an ISDN circuit.
TCP/IP (Transmission Control Protocol/Internet Protocol) Protocols developed by the U.S. Department of Defense in the 1970s to connect different computer networks. Essentially, these protocols are the basis of the Internet.
Telnet A virtual terminal protocol that enables the user to connect to other computers on the Internet.
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(UADSL) Universal Asymmetric Digital Subscriber Line The newest member of the DSL family now called the G.Lite standard (ITU 992.2). UADSL is an asymmetric service that delivers data up to 1.5 Mbps upstream and up to 512 Kbps upstream. This DSL service is targeted at the consumer market.
Upstream Data Data that travels from a local computer to the Internet.
USB Modem This is an external modem that connects to the PC via USB. There is a USB cable used between the PC and the modem.
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VDSL (Very-high-bit-rate DSL) Asymmetric DSL that supports up to 51 Mbps at very short distances (1,000 feet - 5,000 feet). Standards are still evolving for VDSL.
(VPN) Virtual Private Network A VPN is a software defined private network. A way to deliver private data safely over a public network, such as the Internet. The data traveling between two hosts are encrypted for privacy.
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Wall Jack A small outlet used to tap into telephone wall cable. An RJ"2"1 wall jack usually has four pins;
an RJ-45 wall jack usually has eight pins.
Wide-Area Network (WAN) A WAN is typically constructed to span cities and countries and links business network nodes. The Internet is considered a wide area network.
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"Y" Adapter ("T" Adapter)A "2 for 1" adapter that allows two devices (like a modem, and phone) to be
connected to a single phone jack. It is "parallel" wired - all of the pins on the (2) female jacks connect to the corresponding pins on the male side. This is a passive device that has no filtering or other function to it.
It can be used with a filter, but is not a filter by itself. There are "3 for 1" and "4 for 1" jacks available as well.
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