Half-Duplex
A circuit designed for data
transmission in both directions, but not at the same time.
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.
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