| Term |
Definition |
| H.110 |
A TDM bus standard developed by ECTF to provide backward compatibility to existing TDM busses with more bandwidth and potential for development. H.100 has a total bandwidth of 256 Mbps. On a compact PCI platform, the name H.110 is used for this bus, which keeps the same logical characteristics but different electrical ones. |
| H.261 |
Videophone video compression standard. |
| H.323 |
An Internet standard that allows dissimilar communication devices to communicate with each other by using a standardized communication protocol. H.323 defines a common set of CODECs, call setup and negotiating procedures, and basic data transport methods. |
| H0 Channel |
A channel with a bandwidth of one-quarter that of a T1 trunk or 384kb/s. |
| H11 Channel |
The North American primary rate bandwidth of 1.536Mb/s allocated as a single channel. |
| H12 Channel |
The European primary rate bandwidth of 1.920Mb/s allocated as a single channel. |
| Half Duplex |
The process whereby a device can receive or transmit but never do both at the same time. |
| Hamming Code |
A code using redundant bits as a means of detecting transmission errors. |
| Hard Wired |
Describes a connection between two or more devices which is direct and permanent. |
| Harmonic Distortion |
The distortion of a signal as it passes through a transmission medium which is caused by the creation additional, harmonic, frequencies. |
| HCMOS |
High-density Complementary Metal-Oxide Semiconductor. |
| HDLC |
High-Level Data Link Control - An encapsulation protocol that defines specific bit patterns as delimiters and thus allows transmission of data over a serial link. |
| HDSL |
High bitrate digital subscriber line - A symmetric DSL technology that provides a maximum bandwidth of 1.5 megabits per second in each direction over two phone lines, or 2 Megabits per second over three phone lines. |
| HDTV |
High Definition Television. |
| HDX |
Half Duplex. |
| Headend |
The equipment in a cable system which receives the various program source signals, processes them, and retransmits them to subscribers. In the 10Broad36 Ethernet media system, the location that serves as the root for the branching tree of the physical medium; the point to which all inbound signals converge and the point from which all outbound signals emanate. |
| Headend Convertor |
A device used in broadband transmission systems which receives signals at one frequency performs amplification and then transmits them at a different frequency. |
| Heartbeat |
In an IEEE 802.3 network a circuit (normally part of the transceiver) which generates a collision signal at the end of a transmission. This signal is used by the controller interface for self testing purposes. |
| HER |
High Efficiency Red - As in an LED. |
| Heuristic Routing |
A routing method which examines the delays suffered by in-coming packages (in a packet switched Network) and then forwards them along routes which will optimize their end to end transmission time. |
| HF |
High Frequency - Transmission frequencies in the range 3 to 30 megahertz. |
| HIC |
Hybrid Integrated Circuit. |
| High Capacity Service |
Generally used to describe "public" available tariffed digital transmission service at speeds greater than T1. |
| High Definition Television |
The generally agreed upon definition of HDTV is approximately twice the vertical and horizontal picture resolution of today's NTSC TV, which essentially makes the picture twice as sharp. HDTV also has a screen ratio of 16:9 as compared with most of today's TV screens, which have a screen ratio of 4:3. HDTV offers reduced motion artifacts (i.e. ghosting, dot crawl), and offers 5.1 independent channels of CD-quality stereo surround sound, (also referred to as AC-3). |
| High Pass |
A frequency level above which an analog filter allows all frequencies to pass. |
| Highpass Filter |
A circuit that passes frequencies above a specific frequency (the cutoff frequency). Frequencies below the cutoff frequency are reduced in amplitude to eliminate them. |
| Highway |
A common path or a set of parallel paths over which signals from a number of channels pass with separation achieved by time division. |
| HMOS |
High-density Metal Oxide Semiconductor. |
| Hop |
A general term used to describe a single point to point connection within a network. |
| Hot Potato Routing |
A packet switching routing technique which retransmits a package as soon as possible after reception even if this means making a poor (based on time, cost, etc) routing choice. |
| Hub |
A device from which a number of transmission links radiate. The network so formed has the same configuration as a star topology. |
| HVDC |
High Voltage Direct Current. |
| HVPS |
High Voltage Power Supply. |
