Half-duplex transmission. A communications circuit that can transmit and receive information but not simultaneously.

Handover. The switching of a mobile signal from one channel or cell to another. There are two categories of handover, Internal handover and External handover.

Handset. The hand-held telephone terminal containing a transmitter and receiver.

Handshake. An exchange of signals between two connected devices to ensure that the connection is maintained.

H-ARQ (Hybrid Automatic Retransmission reQuest). Combines the best of ARQ and FEC to improve throughput. On detection of errors, the previous redundant code, plus extra code, is incrementally added to subsequent blocks, until the "errored" block is corrected.

HCS: Hierarchical Cell Structure. HCS is a technique that uses a combination of overlaid micro- and macro-cells to increase the capacity within a cellular network.

HDTV (High Definition Television). A digital TV format that combines high-resolution video and stereo-surround sound.

Header. Information attached to the first frame of a message. It carries information to the receiving device about the message itself, the message's destination, and routing information.

Headset. A device that contains the same technology as a handset but is worn on the head to keep the hands free.

HEC (Header Error Control). Using the fifth byte (octet) in the ATM cell header, ATM equipment may check for an error and corrects the contents of the header. The check is calculated using a CRC algorithm allowing a single-bit error in the header to be corrected or multiple errors to be detected.

HEO Satellites (High Earth Orbit Satellites).

HF (High Frequency) . Frequencies in the 300 to 30000 KHz range.

High frequency bands. Frequency bands above the audible frequencies.

High speed. Data transmission rates in excess of 9.6 Kb/s.

Hold. A feature that allows the called party to exit a call briefly without the call being disconnected.

Hop. In cellular telecommunications, a switch from one radio frequency RF channel to another.

Hertz. The measurement of bandwidth in analog devices.

HLR (Home Location Register). A database containing subscriber information files about the subscriber and the current location of a subscriber's mobile station.

HPA (High Power Amplifier). An amplifier that can handle very high RF power.

HSCSD: High Speed Circuit Switched Data. GPRS is a circuit switched data service developed for mobile communications systems that will support data rates of up to 57 kbps.

HTML (Hypertext Markup Language). HTML is a standard recommended by the W3C and defines a set of "markup" codes (or tags) that are inserted into a file which is intended to be displayed on a World Wide Web browser. The codes inform the browser how the text and images are displayed for the user.

HTTP (Hypertext Transfer Protocol). A protocol or set of rules for exchanging files including text, images, sound and video on the World Wide Web (WWW).