Access Port
The physical gateway between a customer's local loop and the frame relay network.

Amplifier
A device used to boost the strength of an electronic or optical signal, which is weakened (attenuated) as it passes through the transport network. Amplifiers add gain to the signal by an amount equal to the loss in the previous section of the network since last amplification.

Asymmetric Digital Subscriber Line (ADSL)
A new technology that allows more data to be sent over existing copper telephone lines. ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).

Asynchronous Transfer Mode (ATM)
A method of sending audio, visual and computer data at the same time over one high-speed digital line.

Atlantic Crossing (AC-1)
Part of the Global Crossing network. AC-1 links the United States, United Kingdom, Netherlands and Germany. It became operational in May 1998.

B

Backhaul Capacity
Capacity on terrestrial fiber optic cables from undersea cable landing stations to metropolitan areas.

Band
A range of frequencies between two defined limits.

Bandwidth
A measure of capacity of information-carrying capacity on a communications channel. Narrowband: Less than or equal to 64 Kbps. Wideband: Digital rates between 64 Kbps and 1.544 Mbps (DSI) or 2.048 Mbps (E1)-LANs, bulk files transfer, video conferencing, and multimedia. Broadband: Greater than 44.736 Mbps (D3) or 34.368 Mbps (E3).

Bidirectional Line Switched Ring (BLSR)
Commonly referred to as BLSR. It is a method of SONET transport in which half of the working network is sent counterclockwise over one fiber and the other half is sent clockwise over another fiber. BLSR offers bandwidth use advantages for distributed traffic in single-ring architectures.

Bit
A binary unit of information that can have either of two values, 0 or 1. Contraction of binary digit: kilobit = 1,000 bits; megabit = 1 million bits; gigabit = 1 billion bits; terabit = 1 trillion bits.

Border Gateway Protocol (BGP)
A routing protocol used in interdomain routing in large networks to maintain integrity of the network. It allows the routers to exchange only prespecified information with prespecified routers in other domains.

Bridge
A data communications device that connects two or more network segments and forwards packets between them. It also amplifies the carrier signal, and accepts data packets, (perhaps buffering them during periods of network congestion) and forwards them.

Broadband
A transmission channel usually carrying a tremendous amount of information at transmission speeds of 45 Mbps (45,000,000 bits per second) or greater. A communications channel with a bandwidth sufficiently large to carry voice, data and video on a signal channel. Any voice communications channel having a bandwidth greater than a voice-grade channel.

Burst Mode
A way of doing data transmission, usually faster than normal transmission mode, in which a continuous block is transferred between main memory and an input/output device without interruption until the transfer has been completed. Characteristically, burst mode is sustainable for only limited periods of time under special conditions.

C

Capacity
The information-carrying ability of a telecommunications system, as defined by its design (number of fibers, system length, and optoelectronic equipment) and its deployed equipment (amount of optoelectronics in the station) and measured in bits per second. Capacity is sold in discrete units, usually system interface levels such as DS-3s and STM-1s, that in the aggregate are the equivalent of total system capacity.

Carrier
A third-party provider of communications services by wire, fiber or radio. Common Carrier: A private company offering facilities or services to the general public on a non-discriminatory basis and regulated as to market entry, practices, and rates by various Federal and State authorities. Private Carrier: Services provided for internal use and free of most common carrier regulations to allow discrimination in service provision or pricing.

Challenge-Handshake Authentication Protocol (CHAP)
An authentication method that can be used when connecting to an Internet Service Provider. CHAP allows you to log in to your provider automatically, without the need for a terminal screen.

Channelization
The process of subdividing the bandwidth of a circuit into smaller increments called channels. Typically, each channel carries an individual transmission, e.g., a voice conversation, a data conversation, or a computer-to-computer session. This process is accomplished through a multiplexer, such as dense wavelength division multiplexers.

Compression
Algorithm that minimizes the redundancy in the signal to be transmitted.

Cryptography
The process of concealing the contents of a message from all except those who know the key. Cryptography is used to protect e-mail messages, credit card information, and corporate data. As the Internet and other forms of electronic communication become more prevalent, electronic security is also becoming increasingly important.

D

Dark Wavelength
Refers to a virtual channel in a fiber optic system utilizing DWDM. Each virtual channel is supported through a specific wavelength of light, with many channels riding over the same fiber. Once the fiber system is deployed and the DWDM equipment is activated, some of the wavelengths may be activated immediately and others may be left dark for future needs. When the need arises, those dark wavelengths are lit up.

Dense Wavelength Division Multiplexing (DWDM)
A technique which employs more than one light source and detector operating at different wavelengths and simultaneously transmits optical signals through the same fiber while message integrity of each signal is preserved.

Digital
Describes a method of storing, processing and transmitting information through the use of distinct electronic or optic pulses representing the binary digits 0 and 1. In communications they will modify a carrier at a selected frequency. The precise signal transitions preclude any distortion such as graininess or snow in the case of video transmission, or static or other background distortion in the case of audio transmission.

Digital Transmission
Method of storing, processing and transmitting information through the use of distinct electronic or optical pulses that represent the binary digits 0 and 1. Digital transmission and switching technologies employ a sequence of these pulses to represent information as opposed to a continuously variable analog signal. The precise digital numbers preclude any distortion such as graininess or snow in the case of video transmission, or static or other background distortion in the case of audio transmission.

Doped Fibers
Various impurities may be added to silica-based fiber optic strands as they are constructed to achieve specifically desired transmission or physical properties.

DSI
A digital transmission hierarchy supporting 1.544 million bits per second that may be used for "near-full motion" or compressed video, data or voice circuits (24, 48, or 96).

E

E-1
Similar to the North American T-1, E-1 is the European format for digital transmission. E-1 carries signals at 2.048 Mbps (32 channels at 64 Kbps), versus the T-1, which carries signals at 1.544 Mbps (24 channels at 64 Kbps). E-1 and T-1 lines may be interconnected for international use.

Erbium-Doped Fiber Amplifier (EDFA)
A purely optical (as opposed to electronic) device used to boost an optical signal. It contains several meters of glass fiber doped with erbium ions. When the erbium ions are excited to a high energy state, the doped fiber changes from a passive medium to an active amplifying medium.

F

Fault Tolerance
The ability of a system to respond gracefully to an unexpected hardware or software failure. There are many levels of fault tolerance, the lowest being the ability to continue operation in the event of a power failure.

Fiber Kilometers
The number of route kilometers installed multiplied by the number of fiber strands along the path.

Fiber Optics
Technology based on thin filaments of glass or other transparent materials used as the medium for transmitting coded light pulses that represent data, image and sound. Fiber-optic technology offers extremely fast transmission speeds.

Full Duplex
The simultaneous transmission of data in both directions, used when communicating between two computers. Full duplex is sometimes called "Echo On" by some communications programs.

G

Gbps (Gigabits per second)
A data rate of 1 Gbps corresponds to 1,000 million bits per second.

H

High Performance Parallel Interface (HIPPI)
HIPPI is used to network supercomputers, high-end workstations and peripherals using cross-bar type circuit switches. It provides for transfer rates of 800 Mbps over 32 twisted pair copper wires (single HIPPI) and 1,600 Mbps over 64 pairs (double HIPPI).

I

Indefeasible Right of Use (IRU)
A measure of currency in the undersea cable business. The owner of an IRU has the right to use the capacity for the time and bandwidth to which the IRU applies.

International Telecommunication Union (ITU)
The ITU is an intergovernmental agency of the United Nations within which the public and private sectors cooperate for the development of telecommunications. The ITU adopts international regulations governing the use of the radio spectrum and develops standards to facilitate the interconnection of telecommunications systems on a worldwide basis. It is headquartered in Geneva, Switzerland. In 1996, the ITU comprised 185 Member States and 363 members (scientific and industrial companies, public and private operators, broadcasters, regional and international organizations active in three sectors: Radio communications, Standardization and Development).

Internet
A fabric of interconnected computer networks, originally known as the DARPA network (Defense Advanced Research Projects Agency) connecting government and academic sites. It currently links about 50 million people worldwide who use it for everything from scientific research to simple e-mail.

Internet Protocol (IP) Address
An Internet address that is a unique number consisting of four parts separated by dots, sometimes called a "dotted quad." For example, 198.204.112.1. Every Internet computer has an IP address and most computers also are assigned one or more domain names that are easier to remember than the dotted quad.

ISP
Internet Service Provider.

L

Lambda
The 11th letter of the Greek alphabet. Lambda is used as the symbol for wavelength in lightwave systems. Fiber optic systems use multiple wavelengths of light through dense wavelength division multiplexing (DWDM). Each range of wavelength appears in a "window" roughly corresponding to a color in the visible light spectrum.

Latency
The amount of time it takes a packet to travel from source to destination. Together, latency and bandwidth define the speed and capacity of a network.

Local Loop
The physical facility, leased from a local exchange carrier (LEC), which provides connectivity between the customer's location and the carrier's point of presence.

Low Voltage Differential Signaling (LVDS)
A low noise, low power, low amplitude method for high-speed (gigabits per second) data transmission over copper wire.

M

Media Gateway Control Protocol (MGCP)
A proposed control and signal standard for the conversion of audio signals carried on telephone circuits to data packets carried over the Internet or other packet networks. Unlike regular phones, IP phones and devices are not fixed to a specific switch, so they must contain processors that enable them to function independently from a central switching location. MGCP eliminates the need for complex, processor-intense IP telephony devices, thus simplifying and lowering the cost of these terminals.

Megabits per second (Mbps)
One Mbps corresponds to a data rate of 1,000,000 bits per second.

Multicasting
The ability of one network node to send identical data to a number of end servers on the multicast backbone. For large amounts of data, IP multicasting is more efficient than normal Internet transmissions because the server can broadcast a message to multiple recipients simultaneously.

Multilink Point-to-Point Protocol (MP)
MP allows multiple physical connections between two points to be combined into a single logical connection called a bundle. MP supports dynamic bandwidth allocation, which means that physical links can be added or removed from the bundle as needed.

Multimedia
The electronic conversation between two or more people or groups of people in different places using two or more types of digitally integrated communication for voice, sound, text, data, graphics, video, image or presence at the same time. Applications include conferencing, presentations, training, referencing, games, etc.

Multiplexing
An electronic or optical process that combines two or more lower bandwidth transmissions onto one higher bandwidth signal by splitting the total available bandwidth into narrower bands (frequency division) or by allotting a common channel to several transmitting sources one at a time in sequence (time division).

Multipoint
Pertaining or referring to a communications line to which three or more stations are connected. It implies that the line physically extends from one station to another until all are connected.

MultiProtocol Label Switching (MPLS)
MPLS is a widely supported method of speeding up data communication over combined IP/ATM networks. This improves the speed of packet processing and enhances performance of the network.

O

Optical Fiber
Thin filaments of glass through which light beams are transmitted. Enormous capacity, low-cost, low-power consumption, small space, lightweight, insensitivity to electromagnetic interference characterize this transport media.

P

Packet
Generic term for a bundle of data, organized in a specific way for transmission. A packet consists of the data to be transmitted and certain control information, including the destination address.

Packet Switching
A process where messages are broken into finite-sized packets that are always accepted by the network. The message packets are sent across different circuit paths. The packets are reassembled into the original message at the end of the circuit.

Pipelining
In networking, pipelining is a technique used at the transport layer or data link layer in a layered network architecture that allows for the transmission of multiple frames without waiting to see if they are acknowledged on an individuals basis.

Point of Presence (POP)
The physical location within a LATA where an interexchange carrier's circuits interconnect with the local lines of telephone companies in that LATA.

Polling
Making continuous requests for data from another device. For example, modems that support polling can call another system and request data.

Protocols
Computer rules that provide uniform specifications so that computer hardware and operating systems can communicate.

R

Repeater
1. Equipment that receives a low-power signal, possibly converting it from light to electrical form, amplifying it or retiming and reconstructing it for transmission. It may need to be reconverted to light for retransmission. 2. An optoelectrical device used at each end and occasionally intermediate points of exceptionally long fiber optic span. Optical input is converted to electrical form to restore a clean signal, which drives lasers that fully restores the optical signal at the original signal strength.

Requests for Comments (RFCs)
Internet standards that have developed within the Internet community since 1969. They have grown to become a large series of numbered Internet informational documents and standards widely followed by commercial software and freeware in the Internet and Unix communities. Few RFCs are standards but all Internet standards are recorded in RFCs. Perhaps the single most influential RFC has been RFC 822, the Internet electronic-mail format standard. RFCs are unusual in that they are floated by technical experts acting on their own initiative and reviewed by the Internet at large, rather than formally promulgated through an institution such as ANSI (American National Standards Institute). For this reason, they remain known as RFCs even after they have been adopted as standards.

Router
A network device that connects two similar networks having the same network protocol. It also chooses the best path between two networks when there are multiple paths.

RFS (Ready for Service)
The data of provisional acceptance or commercial service of a cable system.

S

Serial Line Internet Protocol (SLIP)
An Internet protocol which is used to run IP over serial lines such as telephone circuits. It allows a packet to traverse multiple networks on the way to its final destination.

STM-1
The largest standard circuit unit of capacity, which consists of 155,500 Kbps (equal to 155 Mbps). Thus, each Gbps contains enough capacity for 6.4 STM-1 circuits. While capacity is sold to the largest telecommunications companies in minimum investment units equal to one STM-1 unit, most telecommunications companies buy smaller units at a price higher than the equivalent STM-1 price.

Synchronous Transfer Mode (STM)
New term for traditional TDM switching to distinguish it from ATM.

T

Time Division Multiplex (TDM)
A technique for transmitting a number of separate data, voice and/or video signals simultaneously over one communications medium by quickly interleaving a piece of each signal one after another.

V

Voice over IP (VoIP)
VoIP is voice communications transmitted over the Internet.

W

Wavelength
The distance between two crests of a signal or a carrier and is measured in terms of meters, millimeters, nanometers, etc. In lightwave applications, because of the extremely high frequencies, wavelength is measured in nanometers.

Wavelength Division Multiplexing (WDM)
A way of increasing the information-carrying capacity of an optical fiber by simultaneously operating at more than one wavelength. With WDM you can multiplex signals by transmitting them at different wavelengths through the same fiber.

X

xDSL
A term referring to a variety of new Digital Subscriber Line technologies. Some of these varieties are asymmetric with different data rates in the downstream and upstream directions. Others are symmetric. Downstream speeds range from 384 Kbps (or "SDSL") to 1.5-8 Mbps (or "ADSL").