The Cable Center

This glossary of cable and telecommunications terms is intended to enhance your understanding of this dynamic industry. We are able to present this information with the generous help of CableLabs - consult their website for the most up-to-date information about cable technology.

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H.323
An ITU-T standard for transmitting and controlling audio and video information. The H.323 standard requires the use of the H.225/H.245 protocol for communication control between a “gateway” audio/video endpoint and a “gatekeeper” function.

Half Duplex
Two-way transmission, one way at a time.

Halo
Most commonly, a dark area surrounding an unusually bright object, caused by overloading of the camera tube. Reflection of studio lights from a piece of jewelry, for example, might cause this effect. With certain camera tube operating adjustments, a white area may surround dark objects.

Hardware
The equipment involved in production, storage, distribution or reception of electronic signals. In cable television it means the headend, the coaxial cable network, amplifiers, the television receiver and production equipment like cameras and videotape recorders.

Harmonic Distortion
Form of interference involving the generation of harmonics according to the frequency relationship f=nf1 for each frequency present, where n is a whole number equal to 2 or more.

Harmonic Related Carrier (HRC)
A method of spacing television channels on a cable television system in exact 6-MHz increments, with all carrier frequencies harmonically related to a common reference.

Hashed Message Authentication Code (HMAC)
A message authentication algorithm, based on either SHA-1 or MD5.

HDSL
High-speed digital subscriber line that utilizes existing copper infrastructure of the telephone companies. HDSL offers video and data transmission rates of 1.5 Mbps up to 12,000 feet. See also DSL.

Headend
The control center of a cable television system, where incoming signals are amplified, converted, processed and combined into a common cable along with any original cablecasting, for transmission to subscribers. The system usually includes antennas, preamplifiers, frequency converters, demodulators, modulators, processors and other related equipment. Or the central location on the cable network that is responsible for injecting broadcast video and other signals in the downstream direction. See also Master Headend, Distribution Hub.

Headend Router
The computer, at the cable headend, responsible for gateway operations between the headend and the internet.

Header
Protocol control information located at the beginning of a protocol data unit.

Hertz (Hz)
A unit of frequency equivalent to one cycle per second. See also megahertz and gigahertz.

Heterodyne
A process of the shifting of a signal of interest down to a frequency at which it may be processed more easily to extract information.

High Band
TV channels 7 through 13.

High-bandwidth Digital Content Protection (HDCP)
A specified method from Intel for protecting copyrighted digital entertainment content that uses the Digital Video Interface (DVI) by encrypting its transmission between the video source and the digital display (receiver). The video source might be a computer, set-top box, or DVD player, and the digital display might be an LCD display, television, plasma panel or projector.

High Definition Multimedia Interface (HDMI)
A specification that combines video and audio into a single digital interface for use with DVD players, digital television (DTV) players, set-top boxes, and other audiovisual devices. The basis for HDMI is High Bandwidth Digital Content Protection (HDCP) and the core technology of Digital Visual Interface (DVI). HDCP is an Intel specification used to protect digital content transmitted and received by DVI-compliant displays.

High Definition Television (HDTV)
A television signal with greater detail and fidelity than the current TV systems used. The USA currently uses a system called NTSC. HDTV provides a picture with twice the visual resolution as NTSC as well as CD-quality audio. Or television that substantially exceeds NTSC, PAL or SECAM in resolution and quality.

High Electron Mobility (HEMT)
A transistor that yields the lowest noise figures in single FET devices.

High Frequency (HF)
Used here to refer to the entire subsplit (5-30 MHz) and extended subsplit (5-42 MHz) band used in reverse channel communications over the cable television network.

High Q
A fiber circuit with a great deal of selectivity.

High Return
A frequency division scheme that allows bi-directional traffic on a single coaxial cable. Reverse channel signals propagate to the headend above the downstream passband.

High Split
When the upstream frequencies are 5-150/174-750 MHz; this split provides the greatest amount of return path.

High VHF Band
Part of the frequency band which the FCC allocates to VHF broadcasting, including channels 7 through 13, or 174 through 216 MHz.

Home Audio/Video interoperability (HAVi) architecture
A specification defined by a consumer electronics industry consortium. It is composed of a set of API’s allowing for the development of applications for a home networked environment.

Home Page
The default Web page that is displayed when you open your browser. The browser may be configured to automatically load this page on start-up, or not until the home button is pressed. It also refers to the main page of a Web site.

Homes Passed
Total number of homes which have the potential for being hooked up to the cable system.

Horizontal (Hum) Bars
Relatively broad horizontal bars, alternately black and white, which extend over the entire picture. They may be stationary, or may move up or down. Sometimes referred to as a “venetian blind” effect. Caused by approximate 60-cycle interfering frequency, or one of its harmonic frequencies.

Host Device
A host device refers to the set-top or receiver containing and executing the OpenCable Application Platform implementation. It is also host to the CableCARD device.

House Drop
The coaxial cable that connects each building or home to the nearest feeder line of the cable network.

Hub
Device used to connect segments of a network. A hub offers bandwidth on demand to shared resources vs. being fixed to all accessible ports. A signal distribution point for part of an overall system. Larger cable systems are often served by multiple hub sites, with each hub in turn linked to the main headend with a transportation link such as fiber optics, coaxial supertrunk, or microwave. A hardware device that interconnects computers on a Local Area Network and acts as a central distribution point for the communications lines.

Hue
Corresponds to “color” in everyday use; i.e., red, blue, etc. Black, white and gray do not have hue.

Hum Modulation
Undesired modulation of the television visual carrier by the fundamental or low-order harmonics of the power supply frequency, or other low-frequency disturbances.

Hybrid Fiber/Coax(ial [cable]) (HFC)
HFC system is a broadband bi-directional shared media transmission system using fiber trunks between the headend and the fiber nodes, and coaxial distribution from the fiber nodes to the customer locations.

HyperText Markup Language (HTML)
The language used to create and display Web documents. It uses “tags” to identify the components of a document (text, graphics, multimedia) and how those components should behave.

HyperText Transfer Protocol (HTTP)
The standard for exchanging files (text, graphics, and multimedia) on the World Wide Web. Or HTTP is the transport layer for HTML documents over the Internet Protocol (IP).

HyperText Transfer Protocol Secure (HTTPS)
An extension of HTTP developed by Netscape to enable security on a Web site. HTTPS encrypts and decrypts your page requests and the data returned to you by a Web server.