by Dinesh Thakur
Category: Computer Network
Modem is abbreviation for Modulator – Demodulator. Modems are used for data transfer from one computer
network to another computer network through telephone lines. The
computer network works in digital mode, while analog technology is used
for carrying massages across phone lines.
by Dinesh Thakur
Category: Computer Network
Computer Networks
fall into three classes regarding the size, distance and the structure
namely: LAN (Local Area Network), MAN (Metropolitan Area Network), WAN
(Wide Area Network). Before we discussing about type of network we can
discuss about what is a network.
What is Network?
In the today world, Two devices are in network if a process in one device is able to exchange information with a process in another device. Networks are known as a medium of connections between nodes (set of devices) or computers. A network is consist of group of computer systems, servers, networking devices are linked together to share resources, including a printer or a file server. The connections is established by using either cable media or wireless media.
by Dinesh Thakur
Category: Computer Network
Switching is the most valuable asset of computer networking. Every time in computer network you access the internet
or another computer network outside your immediate location, or your
messages are sent through a maze of transmission media and connection
devices. The mechanism for exchange of information
between different computer networks and network segments is called
switching in Networking. On the other words we can say that any type
signal or data element directing or Switching toward a particular
hardware address or hardware pieces.
by Dinesh Thakur
Category: Computer Network
During 20th century the most important technology has been the information
gathering, its processing and distribution. The computers and
communications have been merged together and their merger has had a
profound effect on the manner in which computer systems are organized.
by Dinesh Thakur
Category: Computer Network
Protocol Definition: It is a digital language through which we communicate with others on the Internet. protocol meaning is that it a set of mutually accepted and implemented rules at both ends of the communications channel for the proper exchange of information.
By adopting these rules, two devices can communicate with each other
and can interchange information. We can't even think of using the
Internet without Protocols. Each protocol is defined in
different terms and different use with unique name. Message travel from
sender to reciever via a medium (The medium is the physical path over
which a message travels) using a protocol.
by Dinesh Thakur
Category: Computer Network
A computer network consists of two or more computers that are linked in order to share resources such as printers
and CD-ROMs, exchange files, or allow electronic communications. The
computers on a computer network may be linked through cables, telephone
lines, radio waves, satellites, or infrared light beams.
by Dinesh Thakur
Category: Computer Network
There are different types of communications connection in existence between two endpoints.,
Home networks, and the Internet is the one of the most commonly used
examples. Many type of devices are and several different methods are
used connecting to these type of network architectures.
There
are different advantages and disadvantages to this type of network
architectures. Connecting computers to a these type of networks, we
requires some networking framework to create the connections. The two
different computer
network connection types are getting discussed in this page are
Point-to-Point Connection and multipoint connection. The main difference
between them we can getting discussed with the help of below
definition.
by Dinesh Thakur
Category: Computer Network
The term Network Topology defines the geographic Physical or logical arrangement of computer networking devices . The term Topology refers
to the way in which the various nodes or computers of a network are
linked together. It describes the actual layout of the computer network
hardware. Two or more devices connect to a link; two or more links form a
topology. Topology determines the data paths that may be used between
any pair of devices of the network.
by Dinesh Thakur
Category: Computer Network
IEEE 802.4 Token Bus : In token bus Computer network station must have possession of a token before it can transmit on the computer network. The IEEE 802.4 Committee has defined token bus
standards as broadband computer networks, as opposed to Ethernet's
baseband transmission technique. Physically, the token bus is a linear
or tree-shape cable to which the stations are attached.
by Dinesh Thakur
Category: Computer Network
There
are many type of Serves in the Computer Networking World. Server is a
machine, that can be design for interconnecting the machines with each
other.Many type of the functions are performed by the servers to
facilitate different uses. Let us discussed first, what is a server
before getting discuss about type of servers.
by Dinesh Thakur
Category: Computer Network
Internetworking started as a way to connect disparate types of computer
networking technology. Computer network term is used to describe two or
more computers that are linked to each other. When two or more
computer LANs or WANs or computer network segments are connected using
devices such as a router and configure by logical addressing scheme with a protocol such as IP, then it is called as computer internetworking.
by Dinesh Thakur
Category: Computer Network
what is lan: It actually stands for local area network. A network is a group of computers and other devices connected together so they can pass information back and forth. The
local area network (LAN) is a network which is designed to operate over
a small physical area such as an office, factory or a group of
buildings. LANs are very widely used in a variety of applications.
by Dinesh Thakur
Category: Computer Network
What is router: Router is a network layer (Layer 3) of the OSI reference model device that means it can connect multiple computer
networks via wired or wireless connections. Network router can receive,
analyze, perform the traffic directing functions and forwards data
packet from one network to its destination node. A router is a device
that forwards packets between networks by processing the routing information included in the packet.
by Dinesh Thakur
Category: Computer Network
Ethernet : IEEE 802.3 Local Area Network (LAN) Protocols : Ethernet protocols refer to the family of local-area network (LAN) technology covered by the IEEE 802.3.
It is working examplc of the more general carrier sense multiple access
with collision detect (CSMA/CD). In the Ethernet Computer Network
standard, there are two modes of operation: half-duplex and full-duplex modes.
In the half duplex mode, data are transmitted using the popular
Carrier-SenseMultiple Access/Collision Detection (CSMA/CD) protocol on
as hared medium.
by Dinesh Thakur
Category: Computer Network
The
transmission means, is that sending a signal from one location to
another. Transmission technologies refer to the physical layer protocol
such as modulation, demodulation, line coding, error control etc. The
transmission technology can be categorized broadly into two types:
Broadcast networks
•
Broadcast networks have a single communication channel that is shared
or used by all the machines on the network. Short messages called
packets sent by any machine are received by all the others.
by Dinesh Thakur
Category: Computer Network
- In the peer to peer computer network model we simply use the same Workgroup for all the computers and a unique name for each computer in a computer network.
- There is no master or controller or central server in this computer network and computers join hands to share files, printers and Internet access.
- It is practical for workgroups of a dozen or less computers making it common environments, where each PC acts as an independent workstation and maintaining its own security that stores data on its own disk but which can share it with all other PCs on the network.
- Software for peer-to-peer network is included with most modern desktop operating systems such as Windows and Mac OS.
by Dinesh Thakur
Category: Computer Network
WAN is the acronym for, Wide Area Network
and refers to a network used to connect different equipments from
remote areas. This technology connects sites that are in diverse
locations. Wide Area Networks (WANs) connect larger geographic area,
such as New York, Canada, or the world. The geographical limit of WAN is
unlimited. Dedicated transoceanic cabling or satellite uplinks may be
used to connect this type of network. Hence, a WAN may be defined as a
data communications network that covers a relatively broad geographic
area to connect LANs together between different cities with the help of
transmission facilities provided by common carriers, such as telephone
companies. WAN technologies function at the lower three layers.
by Dinesh Thakur
Category: Computer Network
• A Computer networking model where one or more powerful computers (servers) provide the different computer
network services and all other user'of computer network (clients)
access those services to perform user's tasks is known as client/server
computer networking model.
• In such networks, there exists a central controller called server. A server is a specialized computer that controls the network resources and provides services to other computers in the network.
• In such networks, there exists a central controller called server. A server is a specialized computer that controls the network resources and provides services to other computers in the network.
by Dinesh Thakur
Category: Computer Network
Types of Computer Networks can
be classified on various properties. The Computer networks can also be
classified on the basis of Computer network technology used by them.
There are two types of Computer networks in this category.
by Dinesh Thakur
Category: Computer Network
The
IEEE 802.3 standard is popularly called as Ethernet. It is a bus based
broadcast network with decentralized control. It can operate at 10 Mbps
or 100 Mbps or above. Computers on an Ethernet can transmit whenever
they want to do so. If two or more machines transmit simultaneously,
then their packets collide. Then the transmitting computers just wait
for an arbitrary time and retransmit their signal. There are various
technologies available in the LAN market but the most popular one of
them is Ethernet.
by Dinesh Thakur
Category: Computer Network
In
"frequency shift keying (FSK)", the frequency of a sinusoidal carrier
is shifted between two discrete values. One of these frequencies (f1) represents a binary "1" and the other value (f0)
represents a binary "0". The representation of digital data using FSK
is as shown in Fig. Note that there is no change in the amplitude of the
carrier.
by Dinesh Thakur
Category: Computer Network
The
point-to-point scheme provides separate communication channels for each
pair of computers. When more than two computers need to communicate
with one another, the number of connections grows very quickly as number
of computer
increases. Above figure illustrates that two computers need only one
connection, three computers need three connections and four computers
need six connections.
Modem- Classification of Modems
by Dinesh Thakur
Category: Computer Network
Modem
word came from the combination of two words modulator and demodulator.A
modem is a hardware device that enables the computers to transmit data
over cable or satellite connection.A modem converts signals between
modulator and demodulator vice versa. The outgoing digital signals from a
computer a modem can modulates to an analog signals
and in the demodulation in reverse analog signal are converts back to a
digital signal.The modems can be classified according to their
characteristics as below:
by Dinesh Thakur
Category: Computer Network
The term computer networks resulted from the 'combination of two major areas, namely computers and communications.
by Dinesh Thakur
Category: Computer Network
A
Metropolitan Area Network (MAN) covers larger geographic area such as
cities or districts. By interconnecting smaller networks within a large
geographic area, information
is easily disseminated throughout the network. Local libraries and
government agencies often use a MAN to connect to citizens and private
industries. It may also connect MANs together within a larger area than
LAN. The geographical limit of a MAN may span a city.
by Dinesh Thakur
Category: Computer Network
• Hybrid networks are the networks that are based on both peer-to-peer & client-server relationship.
• Hybrid networks incorporate the best features of workgroups in peer-to-peer networks with the performance, security and reliability of server-based networks.
• Hybrid networks still provide all of the centralized services of servers, but they also allow users to share and manage their own resources within the workgroup.
• Hybrid networks incorporate the best features of workgroups in peer-to-peer networks with the performance, security and reliability of server-based networks.
• Hybrid networks still provide all of the centralized services of servers, but they also allow users to share and manage their own resources within the workgroup.
by Dinesh Thakur
Category: Computer Network
Broadcast: Any
form of communication in which a single sender transmits messages to
many receivers at once, the most familiar examples being the television
and public radio systems. The opposite of broadcast is POINT-TO-POINT or
narrowcast communication, between just a single transmitter and a
single receiver - a telephone conversation for example. When such a
multiple connection is made via a network cable as opposed to wireless,
such communication is often called MULTIPOINT, as opposed to a
point-to-point or UNICAST. Communication channel is shared by all the
machines on the network in broadcast network.
by Dinesh Thakur
Category: Computer Network
The term network is
defined as a set of computers of different types, terminals,
telephones, and other communication equipments, connected by data
communication links, which allow the network components to work
together. The network components may be located within a small area or
spread over many remote locations. In any case, data communications hold
the network together.
What is baud rate?
by Dinesh Thakur
Category: Computer Network
baud, baud rate A
baud is the number of signaling elements per second sent by a
communications device such as a modem, In theory, a modem with a high
baud rate means fast transmission. The baud rate is therefore equal to the bit rate only if each signal element represents one bit of information.
by Dinesh Thakur
Category: Computer Network
Client Computer: A personal computer in networking that connects to the server and uses the network services to perform user's tasks is a client computer.
by Dinesh Thakur
Category: Computer Network
In computer
networking Switches (also called switching hub, bridging hub,and more
correctly called a network switch) and Bridges are the layer 2 computer
networking devices. Once the number of users began to push the limits of
a single computer network segment, there was a need to create a new
segment to link two computer networks together a device called bridges
accomplished this. basically the bridges have 2 ports, one for each
computer networks, bridges actually inspect the data that passes through
them and make decisions about whether to send it to the other computer
network or not. Switch takes data from one network device and forwards
it to the destination node based on MAC address.
by Dinesh Thakur
Category: Computer Network
The
distinguishing feature of star topology is that all nodes are joined at
a single point, as shown in Figure. This single point is called as a
central node, hub, or switch, to which all other devices are attached
directly, generally via UTP or STP. This topology is frequently used for
networks in which control of the network is located in the central
node. This method is optimal when the bulk of communication is between
the central and outlying nodes. If traffic is high between outlying
nodes, an undue switching burden is placed on the central node.
by Dinesh Thakur
Category: Computer Network
TCP/IP encapsulate upper layers using headers for the purpose of exchanging control and status information about the progress of the communication because its protocols
also engage in peer talk by encapsulating data with protocol headers
before submitting it to the underlying layer for subsequent delivery to
the network. The data communication using TCP/IP and Ethernet as it is passed down the layers by an application on node X to node Y across the network.
by Dinesh Thakur
Category: Computer Network
Bus topologies
are multipoint electrical circuits that can be implemented using
coaxial cable, UTP, or STP. Data transmission is bidirectional, with the
attached devices transmitting in both directions. While generally
operating at a raw data rate of 10 Mbps, actual throughput is much less.
by Dinesh Thakur
Category: Computer Network
A Distributed computing is a model of computation that is firmly related to Distributed Systems, refers to as multiple computer
systems located at different places linked together over a network and
use to solve higher level computation without having to use an expensive
supercomputer.
Distributed system is called, When collection of various computers
seems a single coherent system to its client, then it is called distributed system.
by Dinesh Thakur
Category: Computer Network
To
access Internet Through a Cable TV. Computer Network requires a cable
Modem. It has two interfaces on it one for computer and other for Cable
Network The Computer side interface is usually is a USB Interface or
10Mbps Ethernet And The Cable Network is common cable wire interface.
by Dinesh Thakur
Category: Computer Network
A LAN Operating System, or Network Operating System (NOS), is software that provides the network with multi-user, multitasking capabilities. The operating system
facilitates communications and resource sharing, thereby providing the
basic framework for the operation of the LAN. The operating system
consists of modules that are distributed throughout the LAN environment.
Some NOS modules reside in servers, while other modules reside in the
clients.
by Dinesh Thakur
Category: Computer Network
Connectionless service is a self-contained action and does not include establishment, maintenance and releasing a connection.
• Each message carries the full destination address and is treated and routed independently of all other messages.
by Dinesh Thakur
Category: Computer Network
A packet is the unit of data that is routed between an origin of computer
or device to another on the Internet or any other packet-switched
network. When any file (e-mail message, HTML file, Graphics Interchange
Format file, Uniform Resource Locator request, and so forth) is sent
from one place of network to another place of network on the Internet,
the Transmission Control Protocol (TCP) layer of TCP/IP of network.
by Dinesh Thakur
Category: Computer Network
Amplitude Shift Keying (ASK) is the simplest type of digital CW modulation. Here the carrier is a sinewave of frequency fc. We can represent the carrier signal mathematically as follows:
by Dinesh Thakur
Category: Computer Network
The
ring architecture is a distributed architecture, with minimal
connectivity and a topology of two links connected to every node as
shown in Figure and forms unbroken circular configuration. Figure shows a
network laid out in a physical ring, or closed loop, configuration.
Transmitted messages travel from node to node around the ring. Each node
must be able to recognize its own address in order to accept messages.
SMDS - What is Switched Multimegabit Data Service (SMDS)?
by Dinesh Thakur
Category: Computer Network
•
The SMDS is designed to connect the multiple LANs together. This is the
first high speed broadband service offered to the public.
• Fig.(a) shows the interconnection of four LANs using six high speed leased lines. But this interconnection is expensive.
by Dinesh Thakur
Category: Computer Network
Availability of different operating systems,
hardware platforms and the geographical dispersion of the computing
resources necessitated the need of networking in such a manner that
computers of all sizes can communicate with each other, regardless of
the vendor, the operating system, the hardware platform, or geographical
proximity. Therefore, we may say that internetworking is a scheme for
interconnecting multiple networks of dissimilar technologies. To
interconnect multiple networks of dissimilar technologies use both
additional hardware and software. This additional hardware is positioned
between networks and software on each attached computer. Thus, system of interconnected networks is called an inter network or an Internet.
by Dinesh Thakur
Category: Computer Network
The
idea at the basis of the wavelength routing network consists of maximum
reuse the same wavelengths. The figure illustrates a node of a routing
network wherein wavelengths of the same wavelength are used repeatedly.
by Dinesh Thakur
Category: Computer Network
The
physical layer represents the first level of the hierarchy of the
reference model. This level is responsible for transporting the bits on
physical media varied. To access a support, use an access interface.
by Dinesh Thakur
Category: Computer Network
The acronym bps stands for bits per second, which is a measurement of how fast information
(data) travels between two devices. When two modems converse via the
telephone line, the speed of modem communications is measured in bps.
(When people talk about modems, they often use the word "baud" to mean
the same thing as bps, though technically the two terms are not
synonymous.
by Dinesh Thakur
Category: Computer Network
Shared Ethernet Networks
implementing technical standard access to physical media by the IEEE
802.3 working group under the name MAC access (Medium Access Control).
MAC uses a general technique called random access.
by Dinesh Thakur
Category: Computer Network
The Optical Switches
are used to connect optical links between them. At incoming optical
fibers correspond outgoing optical fibers. If the switch uses an
electrical part, the switch is said optoelectronics and not only
optical. These switches are based on the interconnection of switching
elements, that is to say, switches which have two input gates and two
output ports as shown in Figure. Connected in series, these elementary
switches allow making great switches. The design of these devices,
however, poses many problems.
by Dinesh Thakur
Category: Communication Networks
Transmission media is a pathway that carries the information from sender to receiver. We use different types of cables or waves to transmit data. Data is transmitted normally through electrical or electromagnetic signals.
by Dinesh Thakur
Category: Communication Networks
Definition Data Transmission: When we enter data into the computer
via keyboard, each keyed element is encoded by the electronics within
the keyboard into an equivalent binary coded pattern, using one of the
standard coding schemes that are used for the interchange of information.
To represent all characters of the keyboard, a unique pattern of 7 or 8
bits in size is used. The use of 7 bits means that 128 different
elements can be represented, while 8 bits can represent 256 elements. A
similar procedure is followed at the receiver that decodes every
received binary pattern into the corresponding character.
by Dinesh Thakur
Category: Communication Networks
ALOHA: ALOHA
is a system for coordinating and arbitrating access to a shared
communication Networks channel. It was developed in the 1970s by Norman
Abramson and his colleagues at the University of Hawaii. The original
system used for ground based radio broadcasting, but the system has been
implemented in satellite communication systems.
by Dinesh Thakur
Category: Communication Networks
Data communication
refers to the exchange of data between a source and a receiver via form
of transmission media such as a wire cable. Data communication is said
to be local if communicating devices are in the same building or a
similarly restricted geographical area.
by Dinesh Thakur
Category: Communication Networks
Congestion
is an important issue that can arise in packet switched network.
Congestion is a situation in Communication Networks in which too many
packets are present in a part of the subnet, performance degrades.
Congestion in a network may occur when the load on the network (i.e. the number of packets sent to the network) is greater than the capacity of the network (i.e. the number of packets a network can handle.). Network congestion occurs in case of traffic overloading.
by Dinesh Thakur
Category: Communication Networks
The
first layer (physical layer) of Communication Networks the OSI Seven
layer model is dedicated to the transmission media. Due to the variety
of transmission media and network wiring methods, selecting the most
appropriate media can be confusing - what is the optimal cost-effective
solution. When choosing the transmission media, what are the factors to
be considered?
• Transmission Rate
• Distances
• Cost and Ease of Installation
• Resistance to Environmental Conditions
• Transmission Rate
• Distances
• Cost and Ease of Installation
• Resistance to Environmental Conditions
There are two types of transmission media :
• Guided
• Unguided
• Unguided
Guided Media :
• Unshielded Twisted Pair (UTP)
• Shielded Twisted Pair
• Coaxial Cable
• Optical Fiber
• Shielded Twisted Pair
• Coaxial Cable
• Optical Fiber
Two-wire Open Lines
The
simplest transmission media is a two-wire transmission line. There are
two wires insulated from each other, open to free space. This type of
media is suitable for connecting equipments that are separated less than
50 meters. This media can support data rate up to a theoretical maximum
of 19 Kbps. A two-wire transmission media can directly connect two
computers. However, if a computer
is to be connected to a communicating device like a modem, multiple
communication lines are required. In this case, a number of separate
insulated wires are moulded in the form of a flat ribbon with
terminating connectors as shown in Figure (b).
The
limitations of this transmission media are their poor noise
characteristics, failure to provide connectivity over long distances,
low bit rate. This type of transmission media is often used in telephone
networks.
Unshielded Twisted Pair (UTP) : UTP
is the copper media, inherited from telephony, which is being used for
increasingly higher data rates, and is rapidly becoming the de facto
standard for horizontal wiring, the connection between, and including,
the outlet and the termination in the communication closet.
A Twisted Pair is
a pair of copper wires, with diameters of 0.4-0.8 mm, twisted together
and wrapped with a plastic coating. The twisting increases the
electrical noise immunity, and reduces the bit error rate (BER) of the
data transmission. A UTP cable contains from 2 to 4200 twisted pairs.
UTP
is a very flexible, low cost media, and can be used for either voice or
data communications. Its greatest disadvantage is the limited
bandwidth, which restricts long distance transmission with low error
rates.
Shielded Twisted Pair (STP) : STP
is heavier and more difficult to manufacture, but it can greatly
improve the signaling rate in a given transmission scheme Twisting
provides cancellation of magnetically induced fields and currents on a
pair of conductors.
Magnetic
fields arise around other heavy current-carrying conductors and around
large electric motors. Various grades of copper cables are available,
with Grade 5 being the best and most expensive.
Grade
5 copper, appropriate for use in 100-Mbps applications, has more twists
per inch than lower grades. More twists per inch means more linear feet
of copper wire used to make up a cable run, and more copper means more
money.
Shielding
provides a means to reflect or absorb electric fields that are present
around cables. Shielding comes in a variety of forms from copperbraiding
or copper meshes to aluminized.
Mylar tape wrapped around each conductor and again around the twisted pair.
Coaxial Cable: Coaxial
cable is a two-conductor cable in which one conductor forms an
electromagnetic shield around the other. The two conductors are
separated by insulation. It is a constant impedance transmission cable.
This media is used in base band and broadband transmission. Coaxial
cables do not produce external electric and magnetic fields and are not
affected by them. This makes them ideally suited, although more
expensive, for transmitting signals.
Optical Fiber : Optical fiber consists of thin glass fibers that can carry information
at frequencies in the visible light spectrum and beyond. The typical
optical fiber consists of a very narrow strand of glass called the core.
Around the core is a concentric layer of glass called the cladding.
A
typical core diameter is 62.5 microns .Typically cladding has a
diameter of 125 microns. Coating the cladding is a protective coating
consisting of plastic, it is called the Jacket. An important
characteristic of fiber optics is refraction. Refraction is the
characteristic of a material to either pass or reflect light. When light
passes through a medium, it “bends” as it passes from one medium to the
other. An example of this is when we look into a pond of water If the
angle of incidence is small, the light rays are reflected and do not
pass into the water.
If
the angle of incident is great, light passes through the media but is
bent or refracted. Optical fibers work on the principle that the core
refracts the light and the cladding reflects the light. The core
refracts the light and guides the light along its path. The cladding
reflects any light back into the core and stops light from escaping
through it - it bounds the medium!
Unguided Media : Transmission
media then looking at analysis of using them unguided transmission
media is data signals that flow through the air. They are not guided or
bound to a channel to follow. Following are unguided media used for data
communication.
• Radio Transmission
• Microwave
• Satellite Communication
• Microwave
• Satellite Communication
• RF Propagation: There are three types of RF (radio frequency) propagation :
• Ground Wave
• Ionospheric
• Line of Sight (LOS)
• Ionospheric
• Line of Sight (LOS)
Ground
wave propagation follows the curvature of the Earth. Ground waves have
carrier frequencies up to 2 MHz. AM radio is an example of ground wave
propagation. Ionospheric propagation bounces off of the Earth’s
ionospheric layer in the upper atmosphere.
It
is sometimes called double hop propagation. It operates in the
frequency range of 30 - 85 MHz. Because it depends on the Earth’s
ionosphere, it changes with the weather and time of day. The signal
bounces off of the ionosphere and back to earth. Ham radios operate in
this range.
Line
of sight propagation transmits exactly in the line of sight. The
receive station must be in the view of the transmit station. It is
sometimes called space waves or tropospheric propagation. It is limited
by the curvature of the Earth for ground-based stations (100 km, from
horizon to horizon). Reflected waves can cause problems. Examples of
line of sight propagation are: FM radio, microwave and satellite.
Radio Frequencies : The
frequency spectrum operates from 0 Hz (DC) to gamma rays (1019 Hz).
Radio frequencies are in the range of 300 kHz to 10 GHz. We are seeing
an emerging technology called wireless LANs. Some use radio frequencies
to connect the workstations together, some use infrared technology.
Microwave : Microwave
transmission is line of sight transmission. The transmit station must
be in visible contact with the receive station. This sets a limit on the
distance between stations depending on the local geography. Typically
the line of sight due to the Earth’s curvature is only 50 km to the
horizon! Repeater stations must be placed so the data signal can hop,
skip and jump across the country.
Microwaves
operate at high operating frequencies of 3 to 10 GHz. This allows them
to carry large quantities of data due to their large bandwidth.
Advantages :
(a) They require no right of way acquisition between towers.
(b) They can carry high quantities of information due to their high operating frequencies.
(c) Low cost land purchase: each tower occupies only a small area.
(d) High frequency/short wavelength signals require small antennae.
Disadvantages :
(a) Attenuation by solid objects: birds, rain, snow and fog.
(b) Reflected from flat surfaces like water and metal.
(c) Diffracted (split) around solid objects.
(d) Reflected by atmosphere, thus causing beam to be projected away from receiver.
Satellite : Satellites
are transponders (units that receive on one frequency and retransmit on
another) that are set in geostationary orbits directly over the
equator. These geostationary orbits are 36,000 km from the Earth’s
surface. At this point, the gravitational pull of the Earth and the
centrifugal force of Earth’s rotation are balanced and cancel each other
out. Centrifugal force is the rotational f0rce placed on the satellite
that wants to fling it out into space.
The
uplink is the transmitter of data to the satellite. The downlink is the
receiver of data. Uplinks and downlinks are also called Earth stations
because they are located on the Earth. The footprint is the “shadow”
that the satellite can transmit to, the shadow being the area that can
receive the satellite’s transmitted signal.
by Dinesh Thakur
Category: Communication Networks
The term Transmission Mode defines the direction of the flow of information between two communication devices i.e. it tells the direction of signal flow between the two devices.
There are three ways or modes of data transmission: Simplex, Half duplex (HDX), Full duplex (FDX)
by Dinesh Thakur
Category: Communication Networks
Firstly
we understand the concept of what is broadband connection in
communication networks. Broadband is a high-capacity high-speed Data
transmission medium. This can be done on a single cable by establishing
different bandwidth channels. Broadband technology can be used to
transmit voice, data and video over long distances simultaneously.
by Dinesh Thakur
Category: Communication Networks
Error detection and correction has great practical importance in maintaining data (information) integrity across noisy Communication Networks channels and lessthan- reliable storage media.
by Dinesh Thakur
Category: Communication Networks
Cyclic Redundancy Check (CRC)
An error detection mechanism in which a special number is appended to a
block of data in order to detect any changes introduced during storage
(or transmission). The CRe is recalculated on retrieval (or reception)
and compared to the value originally transmitted, which can reveal
certain types of error. For example, a single corrupted bit in the data
results in a one-bit change in the calculated CRC, but multiple corrupt
bits may cancel each other out.
by Dinesh Thakur
Category: Communication Networks
• In sliding window method, multiple frames are sent by sender at a time before needing an acknowledgment.
• Multiple frames sent by source are acknowledged by receiver using a single ACK frame.
by Dinesh Thakur
Category: Communication Networks
The Media Access Control (MAC) data communication Networks protocol
sub-layer, also known as the Medium Access Control, is a sub-layer of
the data link layer specified in the seven-layer OSI model. The medium
access layer was made necessary by systems that share a common
communications medium. Typically these are local area networks. The MAC
layer is the "low" part of the second OSI layer, the layer of the "data
link". In fact, the IEEE divided this layer into two layers "above" is
the control layer the logical connection (Logical Link Control, LLC) and
"down" the control layer The medium access (MAC).
Bluetooth Architecture
2. Scatternet
by Dinesh Thakur
Category: Communication Networks
Open System Interconnection (OSI) model, an ISO standard for worldwide communication Networks that defines a networking framework for implementing protocols in seven layers. Layering the communications process means breaking down the communication process into Smaller and Easier to handle interdependent categories. The convention and rules used in such communications are collectively known as Layer protocol. Open Systems Interconnection (OSI) model is developed by ISO (International organization for standardization) in 1984. ISO is the organization dedicated to defining global communication and standards.
by Dinesh Thakur
Category: Communication Networks
The
pair of twisted is the simplest transmission medium. it consists of one
or more pairs of electrical son arranged spiral. This type of support
is suitable for transmission both analog and digital.
by Dinesh Thakur
Category: Communication Networks
Coaxial cables
are the guided media that carnes the signal of higher frequency range
compared to twisted pair cable. Coaxial cables are also called coax.
(short form). Two types of coaxial cables are widely used: 50 ohm cable
and 75 ohm cable. 50 ohm cable is used for digital transmission and 75
ohm cable is used for analog transmission. Due to the shield provided,
this cable has excellent noise immunity. It has a large bandwidth and
low losses. Co-axial cables are easy to install. They are often
installed either in a device to device daisy chain (Ethernet) or a star
(ARC net).
by Dinesh Thakur
Category: Communication Networks
•
Bluetooth is, with the infrared, one of the major wireless technologies
developed to achieve WPAN. Bluetooth is a wireless LAN technology used
to connect devices of different functions such as telephones, computers (laptop or desktop), notebooks, cameras, printers and so on. Bluetooth is an example of personal area network.
• Bluetooth project was started by SIG (Special Interest Group) formed by four companies IBM, Intel, Nokia and Toshiba for interconnecting computing and communicating devices using short-range, lower-power, inexpensive wireless radios.
• The project was named Bluetooth after the name of Viking king – Harald Blaatand who unified Denmark and Norway in 10th century.
• Nowadays, Bluetooth technology is used for several computer and non computer application:
• Bluetooth project was started by SIG (Special Interest Group) formed by four companies IBM, Intel, Nokia and Toshiba for interconnecting computing and communicating devices using short-range, lower-power, inexpensive wireless radios.
• The project was named Bluetooth after the name of Viking king – Harald Blaatand who unified Denmark and Norway in 10th century.
• Nowadays, Bluetooth technology is used for several computer and non computer application:
1. It is used for providing communication between peripheral devices like wireless mouse or keyboard with the computer.
2. It is used by modern healthcare devices to send signals to monitors.
3. It is used by modern communicating devices like mobile phone, PDAs, palmtops etc to transfer data rapidly.
4. It is used for dial up networking. Thus allowing a notebook computer to call via a mobile phone.
5. It is used for cordless telephoning to connect a handset and its local base station.
6. It also allows hands-free voice comml1nication with headset.
7. It also enables a mobile computer to connect to a fixed LAN.
8. It can also be used for file transfer operations from one mobile phone to another.
9. Bluetoothusesomnidirectionalradio waves that can through wallsor othernon-metalbarriers.
2. It is used by modern healthcare devices to send signals to monitors.
3. It is used by modern communicating devices like mobile phone, PDAs, palmtops etc to transfer data rapidly.
4. It is used for dial up networking. Thus allowing a notebook computer to call via a mobile phone.
5. It is used for cordless telephoning to connect a handset and its local base station.
6. It also allows hands-free voice comml1nication with headset.
7. It also enables a mobile computer to connect to a fixed LAN.
8. It can also be used for file transfer operations from one mobile phone to another.
9. Bluetoothusesomnidirectionalradio waves that can through wallsor othernon-metalbarriers.
Bluetooth devices have a built-in short range radio transmitter. The rate provided is 1Mbps and uses 2.4 GHz bandwidth.
Bluetooth is that when the device is with in the scope of a other devices automatically start the transfer information without the user noticing. a small network between the devices is created and the user can accessed as if there were cables.
Bluetooth Architecture
Bluetooth architecture defines two types of networks:
1. Piconet
2. Scattemet
1. Piconet
• Piconet is a Bluetooth network that consists of one primary (master) node and seven active secondary (slave) nodes.
• Thus, piconet can have upto eight active nodes (1 master and 7 slaves) or stations within the distance of 10 meters.
• There can be only one primary or master station in each piconet.
• The communication between the primary and the secondary can be one-to-one or one-to-many.
• All communication is between master and a slave. Salve-slave communication is not possible.
•
In addition to seven active slave station, a piconet can have upto 255
parked nodes. These parked nodes are secondary or slave stations and
cannot take part in communication until it is moved from parked state to
active state.
2. Scatternet
• Scattemet is formed by combining various piconets.
• A slave in one piconet can act as a master or primary in other piconet.
•
Such a station or node can receive messages from the master in the
first piconet and deliver the message to its slaves in other piconet
where it is acting as master. This node is also called bridge slave.
• Thus a station can be a member of two piconets.
• A station cannot be a master in two piconets.
Bluetooth layers and Protocol Stack
• Bluetooth standard has many protocols that are organized into different layers.
• The layer structure of Bluetooth does not follow OS1 model, TCP/IP model or any other known model.
• The different layers and Bluetooth protocol architecture.
Radio Layer
• The Bluetooth radio layer corresponds to the physical layer of OSI model.
• It deals with ratio transmission and modulation.
• The radio layer moves data from master to slave or vice versa.
• It is a low power system that uses 2.4 GHz ISM band in a range of 10 meters.
•
This band is divided into 79 channels of 1MHz each. Bluetooth uses the
Frequency Hopping Spread Spectrum (FHSS) method in the physical layer to
avoid interference from other devices or networks.
• Bluetooth hops 1600 times per second, i.e. each device changes its modulation frequency 1600 times per second.
• In order to change bits into a signal, it uses a version of FSK called GFSK i.e. FSK with Gaussian bandwidth filtering.
Baseband Layer
• Baseband layer is equivalent to the MAC sublayer in LANs.
• Bluetooth uses a form of TDMA called TDD-TDMA (time division duplex TDMA).
• Master and slave stations communicate with each other using time slots.
• The master in each piconet defines the time slot of 625 µsec.
• In TDD- TDMA, communication is half duplex in which receiver can send and receive data but not at the same time.
•
If the piconet has only no slave; the master uses even numbered slots
(0, 2, 4, ...) and the slave uses odd-numbered slots (1, 3, 5, .... ).
Both master and slave communicate in half duplex mode. In slot 0, master
sends & secondary receives; in slot 1, secondary sends and primary
receives.
•
If piconet has more than one slave, the master uses even numbered
slots. The slave sends in the next odd-numbered slot if the packet in
the previous slot was addressed to it.
• In Baseband layer, two types of links can be created between a master and slave. These are:
1. Asynchronous Connection-less (ACL)
• It is used for packet switched data that is available at irregular intervals.
• ACL delivers traffic on a best effort basis. Frames can be lost & may have to be retransmitted.
• A slave can have only one ACL link to its master.
• Thus ACL link is used where correct delivery is preferred over fast delivery.
• The ACL can achieve a maximum data rate of 721 kbps by using one, three or more slots.
2. Synchronous Connection Oriented (SCO)
• sco is used for real time data such as sound. It is used where fast delivery is preferred over accurate delivery.
• In an sco link, a physical link is created between the master and slave by reserving specific slots at regular intervals.
• Damaged packet; are not retransmitted over sco links.
• A slave can have three sco links with the master and can send data at 64 Kbps.
Logical Link, Control Adaptation Protocol Layer (L2CAP)
• The logical unit link control adaptation protocol is equivalent to logical link control sublayer of LAN.
• The ACL link uses L2CAP for data exchange but sco channel does not use it.
• The various function of L2CAP is:
1. Segmentation and reassembly
• L2CAP receives the packets of upto 64 KB from upper layers and divides them into frames for transmission.
• It adds extra information to define the location of frame in the original packet.
• The L2CAP reassembles the frame into packets again at the destination.
2. Multiplexing
• L2CAP performs multiplexing at sender side and demultiplexing at receiver side.
• At the sender site, it accepts data from one of the upper layer protocols frames them and deliver them to the Baseband layer.
•
At the receiver site, it accepts a frame from the baseband layer,
extracts the data, and delivers them to the appropriate protocol1ayer.
3. Quality of Service (QOS)
• L2CAP handles quality of service requirements, both when links are established and during normal operation.
• It also enables the devices to negotiate the maximum payload size during connection establishment.
Bluetooth Frame Format
The various fields of blue tooth frame format are:
1. Access Code: It is 72 bit field that contains synchronization bits. It identifies the master.
2. Header: This is 54-bit field. It contain 18 bit pattern that is repeated for 3 time.
The header field contains following subfields:
(i) Address:
This 3 bit field can define upto seven slaves (1 to 7). If the address
is zero, it is used for broadcast communication from primary to all
secondaries.
(ii)Type: This 4 bit field identifies the type of data coming from upper layers.
(iii) F: This flow bit is used for flow control. When set to 1, it means the device is unable to receive more frames.
(iv) A: This bit is used for acknowledgement.
(v) S:
This bit contains a sequence number of the frame to detect
retransmission. As stop and wait protocol is used, one bit is
sufficient.
(vi) Checksum: This 8 bit field contains checksum to detect errors in header.
3. Data: This field can be 0 to 2744 bits long. It contains data or control information coming from upper layers
by Dinesh Thakur
Category: Communication Networks
Unshielded Twisted Pair (UTP) : UTP
is the copper media, inherited from telephony, which is being used for
increasingly higher data rates, and is rapidly becoming the de facto
standard for horizontal wiring, the connection between, and including,
the outlet and the termination in the communication closet.
by Dinesh Thakur
Category: Communication Networks
Hamming
code is technique developed by R.W. Hamming for error correction. This
method corrects the error by finding the state at which the error has
occurred.
by Dinesh Thakur
Category: Communication Networks
• In this method of flow control, the sender sends a single frame to receiver & waits for an acknowledgment.
• The next frame is sent by sender only when acknowledgment of previous frame is received.
by Dinesh Thakur
Category: Communication Networks
• In all practical situations, the transmission of data needs to be bi-directional. This is called as full-duplex transmission.
• We can achieve this full duplex transmission i.e. by having two separate channels-one for forward data transfer and the other for separate transfer i.e. for acknowledgements.
by Dinesh Thakur
Category: Communication Networks
Data
link layer is the second layer in OSI reference model and lies above
the physical layer. The data link layer performs the following
functions.
1. Data link layer receives the data from the network layer & divide it into manageable units called frames.
by Dinesh Thakur
Category: Communication Networks
We
are talking of Wireless LAN (WLAN) that is to say, "Wireless LAN", not
to be confused with WAN course. Also referred Radio LAN (WLAN) if the
communication medium is the radio (not light infrared for example).The
stations of the wireless network can communicate directly with each
other, we called Ad Hoc network type, or via relay terminals called APs
(Access Points, PA) then it is an infrastructure network. the second
type is by far the most common in business.
by Dinesh Thakur
Category: Communication Networks
Analog
is best explained by the transmission of signal such as sound or human
speech, over an electrified copper wire. In its native form, human
speech is an oscillatory disturbance in the air. Which varies in terms
of its volume or power (amplitude) and its pitch or tone (frequency)?
Analogous variations in electrical or radio waves are created in order
to transmit the analog information signal for video or audio or both over a network from a transmitter (TV station or CATV source) to a receiver (TV set, computer connected with antenna). At the receiving end an approximation (analog) of the original information is presented.
by Dinesh Thakur
Category: Communication Networks
IEEE
802.5 Token Ring: Token ring is the IEEE 802.5 standard for a
token-passing ring in Communication networks. A ring consists of a
collection of ring interfaces connected by point-to-point lines i.e. ring
interface of one station is connected to the ring interfaces of its
left station as well as right station. Internally, signals travel around
the Communication network from one station to the next in a ring.
by Dinesh Thakur
Category: Communication Networks
Computers are digital in nature. Computers process, store, and communicate information in binary form, i.e. in the combination of 1s and 0s which has specific meaning in computer language. A binary digit (bit) is an individual 1 or O. Multiple bit streams are used in a computer network.
by Dinesh Thakur
Category: Communication Networks
Hubs/Repeaters
are used to connect together two or more network segments of any media
type. In larger design, signal quality begins to deteriorate as segment
exceeds their maximum length. A hub provides the signal amplification
required to allow a segment to be extended a greater distance.
by Dinesh Thakur
Category: Communication Networks
Transmission is the method by which computer
networks send electrical signals. Data communication is concerned with
the process of exchanging data electronically between two communication
devices. In a local area network, all communication functions are
performed through direct cables. Computers located far away are
connected through a special form of data communication link. The
existing telephone or telegraphic network may also be used for
connecting computers located at remote locations.
by Dinesh Thakur
Category: Communication Networks
Definition: Optical fiber consists of thin glass fibres
or plastic or any dielectric medium which can carry light signals from
one end to the other. Optical fiber refers to the medium and the
technology which is related, or you can say that it is connected with
the transmission of information
in the form of light impulses and this transmission is done along with a
glass or plastic wire or fiber. The wires of fiber optic cable can
carry much more information than any other conventional copper wire. The
typical optical fiber consists of a very narrow strand of glass called the core. Around the core is a concentric layer of glass called the cladding.
Optical fibres make use of light to send information through the optical medium.
Optical fibres make use of light to send information through the optical medium.
by Dinesh Thakur
Category: Communication Networks
Bound Transmission Media
in Communication Networks are the cables that are tangible or have
physical existence and are limited by the physical geography. Also
known as Conducted systems, wired media generally employ a metallic or
glass conductor which serves to conduct, some form of electromagnetic
energy.
by Dinesh Thakur
Category: Communication Networks
Microwave radio,
a form of radio transmission that use. Ultra-high frequencies developed
out of experiments with radar (radio detecting and ranging) during the
period preceding World War II. There are several frequency ranges
assigned to microwave systems, all of which are in the Giga Hertz (GHz)
range and the wavelength in the millimeter range. This very short
wavelength gives rise to the term microwave. Such high frequency signals
are especially susceptible to attenuation and, therefore must be
amplified or repeated after a particular distance.
by Dinesh Thakur
Category: Communication Networks
When
data is being transmitted from one machine to another, it may be
possible that data become corrupted on its, way. Some of the bits may be
altered, damaged or lost during transmission. Such a condition is known
as error.
by Dinesh Thakur
Category: Communication Networks
Unbound transmission media
extend beyond the limiting confines of cabling. They provide an
excellent Communication Networks alternative for WANS. The lack of
physical restrictions provides larger bandwidth as well as wide area
capabilities. Unbound media typically operate at very high frequencies. The three types of unbound transmission media are: Radio wave, Micro wave, Infrared.
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