Amplifier - A device the boosts the strength of
an electronic signal. In a cable system, amplifiers are spaced at regular
intervals throughout the system to keep signals picture-perfect regardless
of how far your live from the Head-End.
Attenuation - The dissipation of the power of a
transmitted signal as it travels over a wire.
Bandwidth - A measure of the information-carrying
capacity of a communication channel. The bandwidth corresponds to the
difference between the lowest and highest frequency signal which can be
carried by the channel.
Carrier Sense Multiple Access Collision Detection (CSMA/CD)
- The Ethernet media access method. All network devices contend equally
for access to transmit. If a device detects another device's signal while
it is transmitting, it aborts transmission and retries after a brief pause.
Channel - A signal path of specified bandwidth for
conveying information.
Channel Capacity - The number of channels available
for current or future use on a cable system.
Coaxial cable - Actual line of transmission for
carrying television signals . Its principal conductor is either copper
or copper-coated wire surrounded by insulation and then encased in aluminium.
Crosstalk - Line distortion caused by wire pairs
in the same bundle being used for separate signal transmission.
Demodulation - The extraction of the modulation
or information from a radio-frequency current.
Digital Set Top Box - A device which accepts digital
encoded television broadcasts and converts them to display on an analog
television set.
Distribution system - Part of a cable system consisting
of trunk and feeder cables.
DOCSIS - (Data Over Cable Service Interface Specifications)
Specification for transmission of data over a cable network that has been
approved by the ITU as an international standard. DOCSIS was developed
by MCNS, a consortium consisting of CableLabs and a consortium of North
American multi-system operators.
Downstream - Signals transmitted to a subscriber.
Drop - The cable and hardware from tap to subscriber
is called the drop.
Drop Cable - Generally 330 feet or less of coaxial
cable, starting at a tap and continuing on to the subscriber's connection.
Dual cable - Two independent distribution systems
operating side by side, providing double the channel capacity of a single
cable.
Duplex - In a communications channel, the ability
to transmit in both directions.
Ethernet - The name of the local area network originally
invented by the Xerox Corporation Palo Alto Research Center. It operates
using the CSMA/CD medium access control method. It is the most popular
LAN technology used today.
Feeder Cables - The cables that take signals from
the trunk line to the subscriber area and to which the subscriber taps
are attached.
Fiber Optics - A method of transmitting signals
over light waves sent through extremely thin fibers spun from glass.
Frequency - The number of times a complete electromagnetic
wave cycle occurs in a fixed unit of time, usually one second. The rate
at which a current alternates, measured in Hertz on a telecommunications
medium.
Frequency Modulation (FM) - A common method of transmitting
information over a carrier wave by changing its frequency.
Head-End - The control center of a cable television
system, where incoming signals are amplified, converted, processed and
combined into a common cable along with any original cablecasting, for
transmission to subscribers. The system usually includes antennas, preamplifiers,
frequency converters, demodulators, modulators, processors and other related
equipment.
Head-End Router - The computer, at the cable Head-End,
responsible for gateway operations between the Head-End and the Internet.
Hybrid Fiber Coax (HFC) - A network consisting of
fiber optical cables and coaxial cables.
IEEE - Institute of Electrical and Electronics Engineers.
MAC Address - An address that identifies a particular
medium access control (MAC) sub-layer service access point.
MCNS (Multimedia Cable Network System) - A consortium
of CableLabs and North American Multi-system operators that developed
DOCSIS, a specification for the transmission of data over a cable network
that has been approved by the ITU as an international standard.
Medium Access Control (MAC) Protocol - In a subnetwork,
that part of the protocol that governs access to the transmission medium,
independent of the physical characteristics of the medium , but taking
into account the topological aspects of the subnetworks in order to enable
the exchange of data between nodes.
MegaHertz (MHz) - One million cycles per second.
Modulation - When some characteristics of an electromagnetic
wave are deliberately changed or manipulated for the purpose of transmitting
information.
Multiple System Operator (MSO) - A company that
owns and operates more than one cable system.
Multiplexer - A device that allows several users
to share a single circuit. It funnels different data streams into a single
stream. At the other end of the communications link, another multiplexer
reverses the process by splitting the data stream back into the original
streams.
Multiplexing - Transmitting multiple signals simultaneously
on a single chain.
Narrowband - Generally refers to delivery channels
capable of carrying sub T1 speeds.
National Cable Television Association (NCTA) - The
major trade association for the cable television industry.
Network Congestion - A state of overload within
a network, where there is a risk of service degradation.
On-demand Service - A type of telecommunication
service in which the communication path is established almost immediately
in response to a user request brought about by means of a user-network
signalling.
Optical Fiber - An extremely thin, flexible thread
of pure glass, able to carry one thousand times the information possible
with traditional copper wire.
Packet - A series of bits containing data and control
information, including source and destination node addresses, formatted
for transmission from one node to another.
Physical Layer - Layer 1, the lowest layer of the
OSI model, is implemented by the physical channel. The Physical layer
insulates Layer 2, the Data Link layer, from medium-dependent physical
characteristics such as baseband, broadband or fiber-optic transmission.
Layer 1 defines the protocols that govern transmission media and signals.
Point of Presence (POP) - The point where the inter-exchange
carrier's responsibilities for the line begin and the local exchange carrier's
responsibility ends. Location of a communications carrier's switching
or terminal equipment.
Public Access - A non-commercial channel set aside
by a cable system for use by the public, on a first come first serve,
non-discriminatory basis.
Quality of Service (QoS) - The accumulation of the
cell loss, delay, and delay variation incurred by the cells belonging
to a particular ATM connection.
Radio Frequency (RF) - Analog electrical signals
sent over the cable. Conventional (broadcast) television and radio, as
well as cable TV, deliver RF signals to your television/radio. RF is quickly
becoming yesterday's news to many cable TV providers who are installing
fiber-optic lines that will replace today's cables.
Ranging - The process by which a cable modem learns
its distance from the Head-End. Ranging is a continual process, due to
the expanding and contracting of cable that occurs during the day.
Repeater - A repeater is a network device that repeats
signals from one cable onto one or more other cables, while restoring
signal timing and waveforms.
Receiver - Electronic device which can convert electromagnetic
waves into either visual or aural signals, or both. For cable television,
usually the subscriber's television set.
Return Path - or Upstream, or Reverse Path - The
term used to describe traffic and paths that go from the subscriber to
the Head-End.
Reverse Path Forwarding - A technique where a router
receives a packet, then floods the packet out on all paths, except the
path on which it received the packet.
Router - A device used to interconnect two or more
local area networks, each of which operates with a different medium access
control method.
Service user (Subscriber) - A person, organization,
or telecommunications system that accesses the network in order to communicate
via the services provided by the network.
Set-Top Box - A part of the Network Access which
performs application-specific functions such as decoding digital TV.
Share - The percent of television households tuned
to a particular program or category of programming.
Signalling - The process by which an end system
notifies a network that it wants service.
Splitters - Passive devices that divide the traffic
on trunk cables and send it down feeder cables.
Subscriber - A household or business that legally
receives and pays for cable and/or pay television service for its own
use.
Subsplit - A frequency division scheme that allows
bi-directional traffic on a single cable. Return path signals come to
the Head-End from 5 to 30 MHz. Forward path signals go from the Head-End
from 54 to the upper frequency limit.
Switch - A mechanical or electric device that is
used to deliberately interrupt, or alter the path of the current through
the circuit.
Switched Network - Any network in which switching
is present and is used to direct messages from the sender to the ultimate
recipient. Usually switching is accomplished by connecting and reconnecting
lines in different configurations in order to set up a continuous pathway
between the sender and the recipient.
System Integrators (SI) - Companies that provide
installation of networking equipment and possibly other services such
as training or network management.
Tap - A tap is a device which splits off a portion
of the feeder line signal for the subscriber.
Telecommunications - Communicating over a distance
through wire, radio, optical or other electromagnetic means.
Transmission Control Protocol/Internet Protocol (TCP/IP)
- Are the standard network protocols used over the Internet. It is also
used as the standard communications protocol in private networks called
Intranets and Extranets.
Trunk Amplifiers - The amplifiers along the trunk
line responsible for maintaining signal strength.
Trunk Cable - Cables that carry the signal from
the Head-End to groups of subscribers.
Trunk Line - Radiating out from the Head-End are
trunk lines which carry the main CATV signal to be distributed.
Upstream - or Reverse Path or Return Path. The term
used to describe traffic and paths that go from the subscriber to the
Head-End.
Wide Area Network (WAN) - A computer network which
usually spans larger geographic area, such as cities, counties, states,
nations and planets. WAN's usually employ telephone-type topologies, like
T1, T3 and ATM etc. The Internet is held together by lots of WAN's which
hold together LAN's, which network computers.
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Network SecurityInterGate Policy Manager
