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Antenna (radio)
Most simply, an antenna (U.S.)
or aerial (UK)
is an electronic component
designed to transmit or receive
radio waves.
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Bandwidth
(Analog)
For
analog signals,
bandwidth is the width, usually
measured in
hertz, of a frequency
band f2 − f1.
It can also be used to describe
a signal, in which case the
meaning is the width of the
smallest frequency band within
which the signal can fit.
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Bandwidth (Digital)
For
digital signals and
by extension from the above, the
word bandwidth is also used to
mean the amount of
data that can be
transferred through a digital
connection in a given time
period (i.e., the connection's
bit rate). In such
cases, bandwidth is usually
measured in
bits or
bytes per second.
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WiFi
Wi-Fi (or Wi-fi, Wi-Fi, Wifi,
wifi), short for "Wireless
Fidelity" (truthful
connection to a source), is a set
of product compatibility
standards for
wireless
local area networks
(WLAN)
based on the
IEEE
802.11
specifications. New standards
beyond the
802.11
specifications, such as
802.16 (WiMAX), are
currently in the works and offer
many enhancements, anywhere from
longer range to greater transfer
speeds.
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WiMAX
WiMAX, an acronym that stands
for Worldwide Interoperability
for Microwave Access, is a
certification mark for products
that pass conformity and
interoperability tests for the
IEEE 802.16 standards. IEEE
802.16 is working group number
16 of
IEEE 802,
specializing in
point-to-multipoint
broadband wireless access.
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FCC
The Federal Communications
Commission (FCC) is an
independent
United States
government
agency, created,
directed, and empowered by
Congressional
statute. The FCC was established
by the
Communications Act of 1934
as the successor to the
Federal Radio Commission
and is charged with
regulating all
non-Federal Government use of
the
radio
spectrum (including
radio and
television
broadcasting), and all
interstate
telecommunications (wire,
satellite and
cable) as well as all
international
communications that
originate or terminate in the
United States. The FCC took over
wire communication regulation
from the
Interstate Commerce Commission.
The FCC's jurisdiction covers
the 50 states, the District of
Columbia, and U.S. possessions.
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IEEE
The Institute of Electrical and
Electronics Engineers or IEEE
(pronounced as eye-triple-ee) is
an international
non-profit,
professional organization
for the advancement of
technology related to
electricity. It is the largest
technical professional
organization in the world (in
number of members), with more
than 360,000 members in around
175 countries (as of
2005). IEEE's
Constitution defines the
purposes of the organization as
"scientific and educational,
directed toward the advancement
of the theory and practice of
electrical, electronics,
communications
and
computer engineering,
as well as
computer science, the
allied branches of engineering
and the related
arts and
sciences." In
pursuing these goals, the IEEE
serves as a major publisher of
scientific journals
and a
conferences
organizer. It is also a leading
developer of industrial
standards in a broad
range of disciplines, including
electric power and
energy,
biomedical technology
and
healthcare,
information technology,
information assurance,
telecommunications, consumer
electronics, transportation,
aerospace, and
nanotechnology. IEEE
develops and participates in
educational activities such as
accreditation of
electrical engineering programs
in institutes of higher
learning.
IEEE 802
IEEE 802 refers to a family of
IEEE
standards about
local area networks
and
metropolitan area networks.
More specifically, the IEEE 802
standards are restricted to
networks carrying variable-size
packets. (By contrast, in
cell-based networks data is
transmitted in short, uniformly
sized units called cells.
Isochronous networks, where data
is transmitted as a steady
stream of octets, or groups of
octets, at regular time
intervals, are also out of the
scope of this standard).
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IEEE
802.11
IEEE 802.11 or
WiFi denotes a set of
Wireless LAN
standards developed by working
group 11 of the
IEEE LAN/MAN
Standards Committee (IEEE
802). The term is
also used to refer to the
original 802.11, which is now
sometimes called
"802.11legacy".The 802.11 family
currently includes six
over-the-air
modulation
techniques that all use
the same protocol, the most
popular (and prolific)
techniques are those defined by
the a, b, and g amendments to
the original standard; security
was originally included, and was
later enhanced via the 802.11i
amendment. Other standards in
the family (c–f, h–j, n) are
service enhancement and
extensions, or corrections to
previous specifications. 802.11b
was the first widely accepted
wireless networking standard,
followed (somewhat counter
intuitively) by 802.11a and
802.11g.
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IEEE
802.11a
The 802.11a amendment to the
original standard was ratified
in
1999. The 802.11a
standard uses the same core
protocol as the original
standard, operates in 5 GHz
band, and uses a 52-subcarrier
orthogonal frequency-division
multiplexing
(OFDM) with a maximum raw
data rate of 54 Mbit/s, which
yields realistic net achievable
throughput in the mid-20 Mbit/s.
The data rate is reduced to 48,
36, 24, 18, 12, 9 then 6 Mbit/s
if required. 802.11a has 12
non-overlapping channels, 8
dedicated to indoor and 4 to
point to point. It is not
interoperable with 802.11b,
except if using equipment that
implements both standards.
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IEEE
802.11b
The 802.11b amendment to the
original standard was ratified
in
1999. 802.11b has a
maximum raw data rate of 11 Mbit/s
and uses the same
CSMA/CA
media access method
defined in the original
standard. Due to the CSMA/CA
protocol overhead, in practice
the maximum 802.11b throughput
that an application can achieve
is about 5.9 Mbit/s over
TCP and 7.1 Mbit/s
over
UDP.802.11b products
appeared on the market very
quickly, since 802.11b is a
direct extension of the
DSSS modulation
technique defined in the
original standard. Hence,
chipsets and products were
easily upgraded to support the
802.11b enhancements. The
dramatic increase in throughput
of 802.11b (compared to the
original standard) along with
substantial price reductions led
to the rapid acceptance of
802.11b as the definitive
WLAN technology.
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IEEE
802.11g
In June 2003, a third modulation
standard was ratified: 802.11g.
This fly our works in the 2.4
GHz band (like 802.11b) but
operates at a maximum raw data
rate of 54 Mbit/s, or about 24.7
Mbit/s net throughput like
802.11a. It is fully backwards
compatible with b and uses the
same frequencies. Details of
making b and g work well
together occupied much of the
lingering technical process. In
older networks the presence of
an 802.11b participant
significantly reduces the speed
of an 802.11g network.
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IEEE
802.11i
IEEE 802.11i (also known as
WPA2) is an amendment to the
802.11 standard
specifying security mechanisms
for
wireless networks.
The draft standard was ratified
on
June 24h,
2004, and supersedes
the previous security
specification,
Wired Equivalent Privacy
(WEP), which was shown to have
severe security weaknesses.
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It implemented a subset of
802.11i; the Wi-Fi Alliance also
refer to the new standard as
WPA2 which is their approved
interoperable implementation of
802.11i. 802.11i makes use of
the
advanced encryption Standard
(AES)
block cipher; WEP and
WPA use only the
RC4
stream cipher.
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T1
The most common legacy of this
whole system is the line rate
designations. A "T1" now seems
to mean any data circuit that
runs at the original 1.544 Mbit/s
line rate. Originally the T1
format carried 24
pulse-code modulated,
time-division multiplexed
speech signals each encoded in
64 kbit/s streams, leaving 8
kbit/s of framing information
which facilitates the
synchronization and
demultiplexing at the receiver.
T2 and T3 circuit channels carry
multiple T1 channels
multiplexed, resulting in
transmission rates of up to
44.736 Mbit/s.
E1
An E1 link operates over two
separate sets of wires, usually
coaxial cable. A nominal 2.4
volt signal is encoded with
pulses using a method that
avoids long periods without
polarity changes. The line data
rate is 2.048
Mbit/s which is split
into 32 time slots, each being
allocated 8 bits in turn. Thus
each time slot sends and
receives an 8-bit sample 8000
times per second (8 x 8000 x 32
= 2,048,000). This is ideal for
voice telephone calls where the
voice is sampled into an 8 bit
number at that data rate and
reconstructed at the other end.
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OC-1
OC-1 (optical carrier one) is a
SONET line with
transmission speed of 51.84
Mbit/s
using
optical fiber.
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OC-3
OC-3 (Optical Carrier 3) is a
network line with transmission
speed of 155.52Mbit/s
(payload 150.336Mbit/s) using
fiber optics.
Depending on the system OC-3 is
also known as
STS-3 (electrical
level) and
STM-1 (SDH). When
OC-3 is not
multiplexed by
carrying the data from a single
source the letter c
(standing for concatenated) is
appended. Therefore becoming
OC-3c.
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Mesh
networking
Mesh networking is a way to
route data, voice and
instructions between nodes. It
allows for continuous
connections and reconfiguration
around blocked paths by
"hopping" from node to node
until a connection can be
established. Mesh networks are
self-healing: the network can
still operate even when a node
breaks down or a connection goes
bad. As a result, a very
reliable network is formed.
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Star
network
Star network is one of the most
common
computer network
topologies. In its
simplest form, star network
consists of one central, or
hub computer which
acts as a
router to transmit
messages. It is easy to
implement and extend, even in
large networks
Well suited for temporary
networks (quick setup). The
failure of a non-central node
will not have major effects on
the functionality of the
network. It has limited
cable length and number of
stations and its
maintenance costs may be higher
in the long run. Failure of the
central node can disable the
entire network.
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Router
A router is a
computer networking device
that forwards data packets
toward their destinations
through a process known as
routing. Routing
occurs at layer 3 (Network
layer) of the model.
Routing is most commonly
associated with the
Internet Protocol,
although other less-popular
routed protocols remain in use.
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Roaming
Roaming is a general term in
wireless
telecommunications
that refers to the extending of
connectivity service in a
network that is different than
the network with which a station
is registered.
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Network interface card (NIC)
A network card (also called
network adapter, network
interface card, NIC, etc.) is a
piece of
computer hardware
designed to provide for
computer communication
over a network. Whereas network
cards used to be
expansion cards to
plug into a computer bus, most
newer computers have a network
interface built into the
motherboard, so a
separate network card is not
required unless multiple
interfaces are needed or some
other type of network is used.
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SOHO
network
A SOHO network is a
Small office/home office
local area network.
SOHO networks generally are
confined to a single room. Such
networks generally use a small
Ethernet
switch or
hub and
cat 5 cabling, or a
WiFi wireless
network. Generally SOHO networks
are used to share files and
other information as well as to
share an
Internet access
connection. A SOHO network may
also have a server which needs
to be accessed. A wireless
network may be enough to satisfy
these requirements but a wired
network may be both more
efficient and more secure.
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Hotspot
(WiFi)
A
hotspot is a
WiFi access point or
area, in particular for
connecting to
Internet. Hotspots
are found near restaurants,
train stations, airports, cafes,
libraries and other public
places. Most hotspot equipment
is 802.11b or 802.11g WiFi
compliant and offers some level
of security like WPA. Hotspot
Access Points are different from
normal access points.
They feature:
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A
captive portal
where users are redirected
to for authentication and
payment
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A payment option using
credit card, Paypal, iPass
etc.
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A Walled Garden feature that
allows free access to
certain sites
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Wireless access point (WAP or
AP)
A wireless access point (WAP or
AP) is a device that "connects"
wireless communication devices
together to create a
wireless network. The
WAP is usually connected to a
wired network, and
can relay data between devices
on each side.
Many WAPs can be connected
together to create a larger
network that allows "roaming".
In contrast, a network where the
client devices manage themselves
is called an
ad-hoc network.
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Virtual private network (VPN)
A Virtual Private Network, or
VPN, is a private
communications network
usually used within a company,
or by several different
companies or organizations,
communicating over a public
network. VPN message traffic is
carried on public networking
infrastructure (e.g. the
Internet) using
standard (often insecure)
protocols.
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Digital Subscriber Line (DSL)
Digital Subscriber Line, or DSL,
is a family of technologies that
provide a digital connection
over the
copper wires of the
local
telephone network.
Its origin dates back to
1988, when an
engineer at
Bell Labs devised a
way to carry a digital signal
over the unused frequency
spectrum. This allows an
ordinary phone line to provide
digital communication without
blocking access to voice
services. Bell's management,
however, were not enthusiastic
about it, as it was not as
profitable as renting out a
second line for those consumers
who preferred to still have
access to the phone when dialing
out. This changed in the late
1990s when cable
companies started marketing
broadband Internet access.
Realizing that most consumers
would prefer broadband Internet
to a second dial out line, Bell
companies rushed out the DSL
technology that they had been
sitting on for the past decade
as an attempt to slow broadband
Internet access uptake, to win
market share against the cable
companies. As of
2005, DSL provides
the principal competition to
cable modems for
providing
high speed Internet
access to home consumers in
Europe and
North America;
although on average, cable is
much faster than DSL in most
commercial situations.
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Asymmetric Digital Subscriber
Line (ADSL)
Asymmetric Digital Subscriber
Line (ADSL) is a form of
DSL, a data
communications technology that
enables faster data transmission
over
copper
telephone lines than
a conventional
modem can provide.
ADSL has the distinguishing
characteristic that the data can
flow faster in one direction
than the other, i.e.,
asymmetrically. Providers
usually market ADSL as a service
for people to connect to the
Internet in a
relatively passive mode: able to
use the higher speed direction
for the "download" from the
Internet but not needing to run
servers that would require
bandwidth in the other
direction.
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Symmetric Digital Subscriber
Line (SDSL)
Symmetric Digital Subscriber
Line (SDSL) is a
Digital Subscriber Line
(DSL) variant with
E1-like data rates
(72 to 2320 kbit/s). It runs
over one pair of copper wires,
with a maximum range of about 3
kilometers. The main difference
between
ADSL and SDSL is that
SDSL has the same upstream data
transfer rate as downstream (symmetrical),
whereas ADSL always has smaller
upstream bandwidth (asymmetrical).
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Dial-up
access
Dial-up access is an inexpensive
but relatively slow form of
internet access in
which the client uses a
modem to dial the
internet service provider's
(ISP) node, a dialup server type
such as the
Point-to-Point Protocol
and
TCP/IP
protocols to
establish a modem-to-modem link,
which is then
routed
to the
internet. It is now
regarded as legacy technology
given the advent of widely
available
broadband Internet access
in the Western World.
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Voice over IP (VoIP)
Voice over IP (also called VoIP,
IP Telephony, and Internet
telephony) is the
routing of
voice conversations
over the
Internet or any other
IP
network. The voice data
flows over a general-purpose
packet-switched
network, instead of the
traditional dedicated,
circuit-switched
voice transmission lines. This
arrangement has several
advantages over traditional
telephony:
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Wider range of features and
facilities.
In addition to the basic
end-to-end voice
conversation, more
information and control
about each call can easily
be provided. This includes
sending and receiving
messages or data files in
parallel with the voice
conversation, audio
conferencing, managing
address books and passing
presence information about
whether friends/colleague
are available online to
interested parties.
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Freer innovation.
Innovation progresses at
market rates rather than the
slow pace of the
multilateral
International
Telecommunications Union
(ITU) committee process,
resulting in more new
advanced features.
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Lower per-call costs.
Once the capital costs of
terminals and/or computers
and the operating costs of a
data network connection are
in place, there are no
additional charges for usage
unless the destination is
outside the IP network.
However, this must be offset
by the higher costs of
telephony equipment.
Services from VoIP providers
are not always cheaper than
from conventional telephone
service providers.
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Higher quality voice
is an option where higher
bandwidth voice encoding can
be selected to improve
end-to-end quality. However,
often high compression
techniques are used to save
bandwidth and potential
result in slightly poorer
quality than traditional
telephony circuits.
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Lower infrastructure costs.
VoIP reduces the traditional
scheme—two separate wiring
systems, one for voice and
one for network—to a single
connection.
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"Future
proof" hardware.
Functionality is software
(protocol) based, allowing
for changes in software
coding without requiring a
"forklift" or component
upgrade.
Point of sale (POS)
POS or PoS is an
acronym for
point-of-sale (or point of
service or point of purchase).
This can mean a retail
shop, a checkout
counter in a shop, or a variable
location where a
transaction occurs.
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Radio frequency (RF)
Radio
frequency, or RF,
refers to that portion of the
electromagnetic spectrum
in which electromagnetic waves
can be generated by
alternating current
fed to an
antenna.
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Gateway (telecommunications)
In a
communications network,
a network
node
equipped for interfacing
with another network that uses
different protocols. A gateway
may contain devices such as
protocol translators,
impedance matching
devices, rate converters,
fault isolators, or
signal translators as
necessary to provide
system
interoperability. It
also requires the establishment
of mutually acceptable
administrative procedures
between the two networks. A
protocol translation/mapping
gateway interconnects networks
with different network protocol
technologies by performing the
required protocol conversions.
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Internet Protocol (IP)
The Internet Protocol (IP) is a
data-oriented protocol used by
source and destination
hosts for
communicating data across a
packet-switched
internetwork. Data in
an IP internetwork are sent in
blocks referred to as
packets
or
datagrams (the terms
are basically synonymous in IP).
In particular, in IP no setup is
needed before a host tries to
send packets to a host it has
previously not communicated
with.
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Dynamic Host Configuration
Protocol (DHCP)
Dynamic Host Configuration
Protocol (DHCP) is a
client-server
networking protocol.
Most organizations use DHCP. A
DHCP server provides
configuration parameters
specific to the DHCP client host
requesting, generally,
information required by the host
to participate on the Internet
network. DHCP also provides a
mechanism for allocation of
IP addresses to
hosts.
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Local area network
A local area network (LAN) is a
computer network
covering a local area, like a
home, office or small group of
buildings such as a college.
When using
Ethernet the
computers are usually wired to a
hub or to a
switch. This
constitutes the
physical layer. A
number of network
protocols may use the
basic physical layer including
TCP/IP. In this case
DHCP is a convenient
way to obtain an
IP address rather
than using fixed addressing.
LANs can be interlinked by
connections to form a Wide area
network. A
router is used to
make the connection between
LANs.LANs are distinguished from
other kinds of networks by three
characteristics:
Internet protocol suite (TCP/IP)
The Internet protocol suite is
the set of
communications protocols
that implement the
protocol stack on
which the
Internet runs. It is
sometimes called the TCP/IP
protocol suite, after the two
most important protocols in it:
the
Transmission Control Protocol
(TCP) and the
Internet Protocol
(IP). The internet protocol
suite can be described by
analogy with the
OSI model, which
describes the layers of a
protocol stack, not
all of which correspond well
with internet practice. In a
protocol stack, each layer
solves a set of problems
involving the transmission of
data, and provides a
well-defined service to the
higher layers. Higher layers are
logically closer to the user and
deal with more abstract data,
relying on lower layers to
translate data into forms that
can eventually be physically
manipulated.
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Network address translation
(NAT)
In
computer networking,
network address translation
(NAT, also known as network
masquerading or IP-masquerading)
is a technique in which the
source and/or destination
addresses of IP
packets are rewritten as they
pass through a
router or
firewall. It is most
commonly used to enable multiple
hosts on a private network to
access the
Internet using a
single public IP address.
According to specifications,
routers should not act in this
way, but it is a convenient and
widely-used technique.
Nonetheless, NAT can introduce
complications in communication
between hosts.
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Wireless LAN (WLAN)
A wireless LAN or WLAN is a
wireless
local area network that
uses
radio waves as its
carrier: the last link with the
users is wireless, to give a
network connection to all users
in the surrounding area. Areas
may range from a single room to
an entire campus. The backbone
network usually uses cables,
with one or more
wireless access points
connecting the wireless users to
the wired network. WLAN is
expected to continue to be an
important form of connection in
many business areas. The market
is expected to grow as the
benefits of WLAN are recognized.
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So far WLANs have been installed
in universities, airports, and
other major public places.
Decreasing costs of WLAN
equipment has also brought it to
many homes. Large future markets
are estimated to be in health
care, corporate offices and the
downtown area of major cities.
New York City has
even begun a pilot program to
cover all five boroughs of the
city with wireless Internet.
WLAN is also used as an
alternative to cabled LAN in
places where cabling was
difficult or impossible, Such
places could be old protected
buildings or classrooms.
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Point-to-point
Point-to-Point
telecommunications is most
recently (2003)
referenced regarding wireless
data communications for
Internet
or
Voice over IP via
radio frequencies in
the multi-gigahertz range. It
also includes technologies such
as
laser for
telecommunications
but in all cases expects that
the transmission medium is line
of sight and capable of being
fairly tightly beamed from
transmitter to
receiver. Point-to-Point is
sometimes incorrectly referred
to the peer-to-peer initializes
P2P, or Pt2Pt, or variations of
this.
P2P refers to
peer-to-peer
file sharing
networks. Point-to-Point is
distinct from
point-to-multipoint
and broadcast. In the
telecommunications signal
typically is bi-directional,
either
Time domain
Multi-plexed
or
channelized. In hubs
and switches, a hub provides a
point-to-multipoint (or simply
multipoint) circuit which
divides the total bandwidth
supplied by the hub among each
connected client node. A switch
on the other hand provides a
series of point-to-point
circuits, via
micro segmentation,
which allows each client node to
have a dedicated circuit and the
added advantage of having
full-duplex
connections.
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Point-to-multipoint
Point-to-multipoint (PT2MP)
telecommunications is
most typically (2003)
used in wireless
Internet and
IP Telephony via
gigahertz
radio
frequencies.PT2MP systems have
been designed both as single and
bi-directional systems. A
central antenna or antenna array
broadcasts to several receiving
antennae and the system uses a
form of
Time-domain
Multiplexing
to allow for the
back-channel
traffic.
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