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| Glossary of Communications Terms |
Attenuation
The decrease in a signal’s power from transmission to reception. The received signal is lower in power because of such factors as line resistance, distance and network configuration.
Backbone
The part of the network used as the main path for carrying traffic between network endpoints.
CO (central office)
A telephone company facility serving a specific area. One or more phone lines run from a subscriber’s home or office to a CO.
Crosstalk
Interference on analog lines created by cables that are too close together. Crosstalk may produce static, buzzing, or multiple conversations on one line.
DOCSIS (Data Over Cable Service Interface Specification)
A relatively new industry standard defining how cable modems communicate over cable TV lines. Any DOCSIS modem will work on any
DOCSIS-compatible cable data network.
DSL (digital subscriber line)
A technology that provides high-speed, two-way data communications over analog phone lines. DSL operates on a higher frequency and doesn’t interfere with existing phone service. The most widely deployed variety is ADSP (asymmetric
DSL), which provides downstream speeds of 144 Kbps to 2.2 Mbps and upstream channels from 90 to 640 Kbps, depending on the distance from the CO. See
HDSL, IDSL, and VDSL.
Firewall
Software or hardware that filters or blocks traffic from a public or private network, preventing unauthorized or unrecognized access.
HDSL (high-bit-rate digital subscriber line)
A flavor of DSL that delivers up to 1.544 Mbps of data symmetrically over two copper twisted-pair lines. The range of HDSL is limited to 12,000 feet; signal repeaters extend the service farther from the CO.
IDSL (ISDN digital subscriber line)
A form of DSL providing a symmetrical speed of 144 Kbps over the copper wire provisioned for ISDN. Repeaters enable service up to 35,000 feet from the CO.
IP address
A numerical identifier for a device on a TCP/IP network. The IP address format is a string of four numbers, each from 0 to 255, separated by periods.
ISDN (Integrated Services Digital Network)
An all-digital replacement for analog telephone service, ISDN provides two 64-Kbps channels, called B-channels, over a single phone line, which can be used together or independently to carry voice or data. The data signaling channel, or D-channel, carries signaling and limited packet communications at either 16 or 64 Kbps, depending on the service.
SDSL (symmetric digital subscriber line)
A form of DSL that transfers data upstream and downstream at symmetric rates of up to 2.3 Mbps over a single copper twisted-pair line.
T1
A digital carrier technology used for transmitting data through the telephone system at 1.544 Mbps.
T3
A digital carrier facility used for transmitting data through the telephone system at 45 Mbps.
VDSL (very high data rate digital subscriber line)
An evolving form of DSL that can deliver data at a rate of 13 to 52 Mbps downstream and 1.5 to 2.3 Mbps upstream over a single copper twisted-pair line. The operating range of VDSL is up to 4,500 feet from the CO.
VPN (virtual private network)
An authentication, encryption, and data packaging technology that lets private network traffic travel over the public networks. VPNs provide remote offices and telecommuters with secure access to a corporate LAN or WAN. Because VPN traffic is encrypted, it cannot be deciphered as it travels over the Internet.
WLL (wireless local loop)
A broadband connection system that uses high frequency radio links to deliver voice and data without the problems of gaining right-of-way for the fiber-optic cable installation or finding adequate copper connections for
DSL. Also known as fixed-point wireless. |
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