NETWORKING
In the world of computers, networking is the
practice of linking two or more computing
devices together for the purpose of sharing data.
Networks are built with a mix of computer
hardware and computer software.
Area Networks
Networks can be categorized in several different
ways. One approach defines the type of network
according to the geographic area it spans. Local
area networks (LANs), for example, typically
reach across a single home, whereas wide area
networks (WANs), reach across cities, states, or
even across the world. The Internet is the
world's largest public WAN.
Network Design
Computer networks also differ in their design.
The two types of high-level network design are
called client-server and peer-to-peer. Clientserver networks feature centralized server
computers that store email, Web pages, files
and or applications. On a peer-to-peer network,
conversely, all computers tend to support the
same functions. Client-server networks are
much more common in business and peer-topeer networks much more common in homes.
A network topology represents its layout or
structure from the point of view of data flow. In
so-called bus networks, for example, all of the
computers share and communicate across one
common conduit, whereas in a star network, all
data flows through one centralized device.
Common types of network topologies include
bus, star, ring and mesh.
Network Protocols
In networking, the communication language
used by computer devices is called the protocol.
Yet another way to classify computer networks
is by the set of protocols they support. Networks
often implement multiple protocols to support
specific applications. Popular protocols include
TCP/IP, the most common protocol found on
the Internet and in home networks.
Wired vs Wireless Networking
Many of the same network protocols, like
TCP/IP, work in both wired and wireless
networks. Networks with Ethernet cables
predominated in businesses, schools, and
homes for several decades. Recently, however,
wireless networking alternatives have emerged
as the premier technology for building new
computer networks.
Wireless Computer Networking
Wireless networks utilize radio waves and/or
microwaves to maintain communication
channels between computers. Wireless
networking is a more modern alternative to
wired networking that relies on copper and/or
fiber optic cabling between network devices.
A wireless network offers advantages and
disadvantages compared to a wired network.
Advantages of wireless include mobility and
elimination of unsightly cables. Disadvantages
of wireless include the potential for radio
interference due to weather, other wireless
devices, or obstructions like walls.
Wireless is rapidly gaining in popularity for
both home and business networking. Wireless
technology continues to improve, and the cost
of wireless products continues to decrease.
Popular wireless local area networking (WLAN)
products conform to the 802.11 "Wi-Fi"
standards. The gear a person needs to build
wireless networks includes network adapters
(NICs), access points (APs), and routers.
Network topologies
are categorized into the following basic types:
bus
ring
star
Hybrid
Bus Network Topology
This diagram illustrates the bus network
topology. A bus topology such as 10Base-2 or
10Base-5 Ethernet uses a single communication
backbone for all devices.
Ring Network Topology
This diagram illustrates the ring network
topology. A ring topology such as FDDI or
SONET sends messages clockwise or
counterclockwise through the shared link.
Star Network Topology
This diagram illustrates the star network
topology. A star topology typically uses a
network hub or switch and is common in home
networks.
HYBRID TOPOLOGY
What is Data Communications?
The distance over which data moves within a
computer may vary from a few thousandths of
an inch, as is the case within a single IC chip, to
as much as several feet along the backplane of
the main circuit board. Over such small
distances, digital data may be transmitted as
direct, two-level electrical signals over simple
copper conductors. Except for the fastest
computers, circuit designers are not very
concerned about the shape of the conductor or
the analog characteristics of signal
transmission.
Frequently, however, data must be sent beyond
the local circuitry that constitutes a computer.
In many cases, the distances involved may be
enormous. Unfortunately, as the distance
between the source of a message and its
destination increases, accurate transmission
becomes increasingly difficult. This results from
the electrical distortion of signals traveling
through long conductors, and from noise added
to the signal as it propagates through a
transmission medium. Although some
precautions must be taken for data exchange
within a computer, the biggest problems occur
when data is transferred to devices outside the
computer's circuitry. In this case, distortion and
noise can become so severe that information is
lost.
Data Communications concerns the
transmission of digital messages to devices
external to the message source. "External"
devices are generally thought of as being
independently powered circuitry that exists
beyond the chassis of a computer or other
digital message source. As a rule, the maximum
permissible transmission rate of a message is
directly proportional to signal power and
inversely proportional to channel noise. It is the
aim of any communications system to provide
the highest possible transmission rate at the
lowest possible power and with the least
possible noise.
Communications Channels
A communications channel is a pathway over
which information can be conveyed. It may be
defined by a physical wire that connects
communicating devices, or by a radio, laser, or
other radiated energy source that has no
obvious physical presence. Information sent
through a communications channel has a source
from which the information originates, and a
destination to which the information is
delivered. Although information originates
from a single source, there may be more than
one destination, depending upon how many
receive stations are linked to the channel and
how much energy the transmitted signal
possesses.
In a digital communications channel, the
information is represented by individual data
bits, which may be encapsulated into multibit
message units. A byte, which consists of eight
bits, is an example of a message unit that may
be conveyed through a digital communications
channel. A collection of bytes may itself be
grouped into a frame or other higher-level
message unit. Such multiple levels of
encapsulation facilitate the handling of
messages in a complex data communications
network.
Any communications channel has a direction
associated with it:
Simplex channel
The message source is the transmitter, and the
destination is the receiver. A channel whose
direction of transmission is unchanging is
referred to as a simplex channel. For example, a
radio station is a simplex channel because it
always transmits the signal to its listeners and
never allows them to transmit back.
A half-duplex channel is a single physical
channel in which the direction may be reversed.
Messages may flow in two directions, but never
at the same time, in a half-duplex system. In a
telephone call, one party speaks while the other
listens. After a pause, the other party speaks
and the first party listens. Speaking
simultaneously results in garbled sound that
cannot be understood.
A full-duplex channel allows simultaneous
message exchange in both directions. It really
consists of two simplex channels, a forward
channel and a reverse channel, linking the same
points. The transmission rate of the reverse
channel may be slower if it is used only for flow
control of the forward channel.
Analog Communication
Analog Communication is a data transmitting
technique in a format that utilizes continuous
signals to transmit data including voice, image,
video, electrons etc. An analog signal is a
variable signal continuous in both time and
amplitude which is generally carried by use of
modulation.
Analog circuits do not involve quantisation of
information unlike the digital circuits and
consequently have a primary disadvantage of
random variation and signal degradation,
particularly resulting in adding noise to the
audio or video quality over a distance.
Data is represented by physical quantities that
are added or removed to alter data. Analog
transmission is inexpensive and enables
information to be transmitted from point-topoint or from one point to many. Once the data
has arrived at the receiving end, it is converted
back into digital form so that it can be
processed by the receiving computer.
Analog
Analog signals are signals with continuous
values. Analog signals are used in many
systems, although the use of analog signals has
declined with the advent of cheap digital
signals.
Digital
Digital signals are signals that are represented
by binary numbers, "1" or "0". The 1 and 0
values can correspond to different discrete
voltage values, and any signal that doesnt quite
fit into the scheme just gets rounded off.
Demodulation
(Electronics) Electronics the act or process by
which an output wave or signal is obtained
having the characteristics of the original
modulating wave or signal; the reverse of
modulation
Modulation
(Electronics) the transmission of a signal by
using it to vary a carrier wave; changing the
carrier's amplitude or frequency or phase