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Basic Advanced TCP/IP Wireless
VT2400/VT2500 Series Voice Gateway User Guide
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H.323
A suite of protocols created by the ITU for interactive video-conferencing, data sharing, and audio
applications such as VoIP.
half-duplex
Network where only one device at a time can transmit data. See also
full-duplex
.
headend
A location that receives TV programming, radio programming, data, and telephone calls that it
modulates onto the HFC network. It also sends return data and telephone transmissions. Headend
equipment includes transmitters, preamplifiers, frequency terminals, demodulators, modulators, and
other devices that amplify, filter, and convert incoming broadcast TV signals to wireless and cable
channels.
header
The data at the beginning of a packet that identifies what is in the packet.
hexadecimal
A base-sixteen numbering system that uses sixteen sequential numbers (0 to 9 and the letters A to F)
as base units before adding a new position. On computers, hexadecimal is a convenient way to
express binary numbers.
HFC
A hybrid fiber/coaxial cable network uses fiber-optic cable as the trunk and coaxial cable to the
subscriber premises.
hop
The interval between two routers on an IP network. The number of hops a packet traverses toward its
destination (called the hop count) is saved in the packet header. For example, a hop count of six
means the packet has traversed six routers. The packet hop count increases as the time-to-live (TTL)
value decreases.
host
In IP, a host is any computer supporting end-user applications or services with full two-way network
access. Each host has a unique host number that combined with the network number forms its IP
address.
Host also can mean:
•
A computer running a web server that serves pages for one or more web sites belonging to
organization(s) or individuals
•
A company that provides this service
•
In IBM environments, a mainframe computer
HTML
Hyper Text Markup Language
HTTP
HyperText Transfer Protocol. The client-server TCP/IP used for exchanging HTML documents on the
World Wide Web.
hub
On a LAN, a hub is a device that connects multiple hosts to the LAN. A hub performs no data filtering.
See also
bridge
and
router
. An IP hub is typically a unit on a rack or desktop.
On an HFC network, a hub is a scaled-down headend that performs some or all headend functions for
part of the system.
Hz
Hertz — one cycle per second. The unit to measure the frequency that an alternating electromagnetic
signal cycles through its highest and lowest states. Used to define the bands of the electromagnetic
spectrum used in voice and data communications, or to define the bandwidth of a transmission
medium.
IANA
The Internet Numbering Address Authority (IANA) is an organization under the Internet Architecture
Board (IAB) of the Internet Society that oversees IP address allocation. It is under a contract from the
U.S. government.
ICMP
Internet Control Message Protocol is a protocol used for error, problem, and informational messages
sent between IP hosts and gateways. ICMP messages are processed by the IP software and are not
usually apparent to the end-user.
