H

Handhole
    A buried box whose lid is even with the surface of the ground.  It provides a space for splicing
    and terminating cables.

Hardwire
    To permanently connect by wire, two or more devices rather than to connect them temporarily
    through connectors or switches.

H Channel
    The ISDN packet switched channel on BRI (Basic Rate Interface) designed to carry user information
    streams at different speeds, depending on the type.

HDB3 - High Density Bipolar Three
     A line interface standard for E1 which is similar to B8ZS, which eliminates data streams with 8 or
    more consecutive zeros.  Allows for 64 Kbps clear channel capacity and still assures a minimum
    ones density required by E1 lines.

HDLC- High-level Data Link Control
     An ITU-T standard for a bit-oriented datalink-layer protocol on which most other bit oriented protocols
    are based.  If first line  is busy, rollover to the next available line in the group.

HDSL - High-bitrate Digital Subscriber Loop
     Circuit box that delivers copper wire T1's as opposed to fiber wire T1s.  Alternating two-way
    communication path  (one way at a time). Half duplex.

HDT - Host Data Terminal
    Part of the Tellabs Cablespan equipment, and located at the central office (or POP). Receives
    signals from multiple Remote Service Terminals (RST).

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

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

Hi-Cap - High Capacity Service
    A tariffed, digital-data transmission service equal to, or in excess of,  T-1 data rates (1.544 Mbps).

Holding Time
     The total time from you picking up the handset, to dialing a number, to waiting for it an answer,
    having a conversation on the  line, to hanging up and replacing the handset in its cradle. You are
    never billed for holding time. You are always billed for only  conversation time which is only part
    of the holding time. Although, holding time figures are nice to know when you are trying  to determine
    how many circuits you need. You will need sufficient circuits to support dialing, etc. - even though
    you're not  being billed for that time.

Homing
    When you dial a long distance number, your central office will choose a special set of trunks to send
    your call onto the next switching center for movement through the nationwide toll system.  Those trunks
    are said to be the "homing" trunks for your central office.

Hoot-n-Holler - also known as a shout down
     A voice only full time circuit that connects a speakerphone in one location to a speakerphone in a
    distant location. This type of circuit is normally open at all times to allow two-way communications
    without having to pick up the receiver or dial the  phone. Speakerphones used in this type of circuit
    are full duplex, transmit and receive units. This circuit is very similar to the  ARD and MRD and is
    also used by the financial industry.

HOP
     A network connection between two distant nodes.  Each short, individual trip that packets make
    many times over, from router  to router, on their way to their destinations.

Hop Count
    The number of hops it will take for a packet to make it from a source to a destination.  In TCP/IP
    networks, hop count is recorded in a special field in the IP packet header and packets are discarded
    when the hop count reaches a specified maximum value.

Host
    An intelligent device attached to a network.

Host Site
    In the transfer of files, the host site is the location receiving a file.  When two individuals are
    exchanging files, the one who receives the file first would be the host, the other would be
    considered the remote.

Host Switch
    An electronic switching machine that provides centralized control over most of the switching
    functions of a group of remote switches.

Hot Cut
    The conversion from an old to a new phone system; or, in the case of a circuit, from an old routing
    path to a new one.

House Cable
    Communication cable within a building or a complex of buildings which is owned and maintained by
    either the LEC/RBOC or the building owners.

Hub
    1. A term used to describe a device that serves as the center of a star-topology network.
    2. A group of circuits connected at one point on a network. Enables traffic concentration and economies
    of scale. Hubs are located in larger cities throughout a network for concentration and routing of calls from
    cities with lower traffic demands.

Hunt Group
    A series of telephone lines organized in such a way that if the first line is busy, the next line is hunted,
    and so on until a free line is found.

Hybrid
    A device used for converting a conversation coming in on two pairs (one pair for each direction of the
    conversation) onto one pair and vice versa.

Hybrid Key System
     A CPE system that has characteristics of both a key system and a PBX system.

Hybrid Object-Oriented System
     A computer system that combines object-oriented modeling and development methodology with
    non-object-oriented  techniques (such as relational databases). This approach complicates the
    development and maintenance process and does  not fully exploit the potential of object-oriented
    technology. It is a tactic that is used during the transition from legacy systems  to fully object-oriented,
    enterprise-wide software solutions.

Hydra
    A 25-pair cable that at one end has an Amphenol connector and at the other has many individual 2, 4,
    6 and 8 wire connectors, typically male RJ11s.

Hypertext
     Interactive on-line documentation technique. Allows the user to select (e.g. mouse click) certain words
    or phrases and  immediately display related information for the selected item. Hypertext requires a "tag"
    language (like Hypertext Markup  Language) to specify branch labels with a hypertext document.