Transcript Chapter 6

Chapter 6:
Telecommunications and Networks
Agenda - I
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What Is Telecommunications?
What Is Data Communications?
What are the Electromagnetic Waves?
What is Electromagnetic Signal Frequency?
What is a Communication Line Bandwidth?
Digital Versus Analog Data
Components of Communication Networks
Contacted and Radiated Media
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Twisted Pair Wire
Coaxial Cable
Fiber-Optic Cable
Broadcast Radio
Microwave
Satellite Microwave
Agenda - II
– Cellular Radio
– Infrared Transmission
 Selection of Media
 Transmission Modes
 Telecommunications Devices
 Telecommunications Carriers and Services
 Networks: LANs and WANS
 Terminal-to-Host, File Server, and Client/Server Systems
 Network Topologies
– Star Topology
– Bus Topology
– Ring Topology
 Coordinating Data Communications
 Popular Communication Protocols
 Home and Small Business Networks
What Is Telecommunications?
Telecommunications is the electronic transmission of
signals for communications between a sender and a
receiver. The methods include telephone, radio, and
television, etc.
What Is Data Communications?
 Data communications is a specialized subset of
telecommunications that refers to electronic collecting,
processing, and distributing of data between computer
system devices. This definition excludes the transmission
of data to local peripherals such as disk, tape, and printers.
 Data communications is sometimes called networking
because it involves the transmission of data over a
network.
What are the Electromagnetic Waves?
 The motion of electrically charged particles produces electromagnetic
waves. These waves are also called "electromagnetic radiation"
because they radiate from the electrically charged particles.
 Radio waves, microwaves, visible light, and x rays are all examples of
electromagnetic waves that differ from each other in wave length.
 Electromagnetic waves need no material medium for transmission.
Light and radio waves can travel through interplanetary and interstellar
space from the sun and stars to the earth. Regardless of their frequency
and wavelength, electromagnetic waves travel at a speed of 299,792
km (186,282 mi) per second in a vacuum.
What is Electromagnetic Signal Frequency?
 Frequency refers to the number of times a current
(electromagnetic wave) passes through a complete cycle.
The measure of frequency is a Hertz (Hz), which
represents one cycle per second.
 Frequencies are represented from a number from 0 Hertz
to 300 GHz (called the electromagnetic spectrum).
K=Kilo=1,000, M=Mega=1,000,000,
G=Giga=1,000,000,000
What is a Communication Line Bandwidth?
 Communication line bandwidth is the difference between
the minimum and maximum range of frequencies allowed
by the communication line.
 Bandwidth = higher frequency - lower frequency. For
example: A wire transmits in a frequency range from 100
Hz to 2,500 Hz. Its bandwidth is 2,400 Hz.
 Bandwidth is important because it indicates how much
data can be transmitted over a specific channel. A wider
bandwidth allows more data to be transmitted at a given
time.
Digital Versus Analog Data
 Analog signals are represented by rising and falling
voltages (waves) such as light, voice, video signals that are
in a continuous form.
 Digital signals are represented pulse of fixed voltages such
as binary signals (o or 1) that are in a discrete form and can
be used by computer.
Components of Communication Networks
 In order for communication to occur, there must be a
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source, a medium, a receiver and a message.
The source (sender) is the device that sends the message
(transmitter) and is any device that can be connected to the
network like a PC or a telephone.
The medium connects the source with the receiver and can
be a copper cable, a fiber-optic cable, airwaves or another
physical path.
The receiver is the device that accepts the message.
The message can be a file, a request, a response, a status
message, a control message or correspondence. The
message must be understandable.
Contacted and Radiated Media
 A Communication network cannot exist without a medium
to connect the source and receiver. If this medium can be
seen physically, it is considered a contacted medium.
 Radiated media, or wireless media, do not use physical
wires to transmit data. With radiated media, the signal is
radiated through the air, water and vacuum of space.
Twisted Pair Wire
 Twisted pair wire consists of two wires twisted together a specific
number of times to create a magnetic field that reduces the amount of
interference in the line.
 In shielded twisted pair (STP), the twisted core is placed into a cladding
shield, which is wrapped with wires to absorb any interference. Used
when you have to pack many wires together in a small space or in an
environment with a lot of electrical equipment. STP wires are reliable in
high-speed areas.
 In unshielded twisted pair (UTP), the twisted core is just covered with
the plastic material without the use of cladding material. Often used in
telephone systems.
UTP lines are grouped into categories based on their quality and use.
Coaxial Cable
 Coaxial cable is composed of a single copper wire (the inner conductor),
surrounded by a insulating cladding material called a shell. The shell is
then surrounded by a second conductor (usually a braided copper shield),
which gives the cable the ability to transmit much more data than a
twisted pair wire. Finally, the entire cable is enclosed in a rubber outer
cladding called the jacket.
 Coaxial cables allow the use of broadband and baseband transmission. In
broadband transmission, a single cable is divided into many channels,
each of which can carry a different transmission. The carrier wave is
divided into bandwidths and separated by guardbands to prevent
interference between the signals. In baseband transmission, only a single
signal is transmitted over the cable.
 A single coaxial cable can carry 1,000 simultaneous voice and data
transmissions.
Fiber-Optic Cable
 Fiber-optic cable uses light to transmit data signals. The
core of the fiber-optic cable is composed of one or more
thin tubes of glass or plastic. Each tube is called the optical
fiber and is as thin as the human hair. A light-emitting
diode (LED) or a laser is used to send light through the
fibers.
Broadcast Radio
 Broadcast radio involves sending signals through the air
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between transmitters, at frequencies from 30 to 300 MHz.
Amplitude modulation (AM) radio uses a low frequency
and allows it to broadcast its signal far (530-1605 KHz).
Frequency modulation (FM) radio uses a higher frequency
and the signal travels shorter distances (87.6-108 MHz).
Short wave radios transmit signals over long distances and
utilize specific restricted frequency ranges.
Television stations use the ultra-high frequency (UHF)
channels and very-high frequency (VHF) channels to
transmit TV programs in the ranges 400-900 MHz and 50225 MHz respectively.
Microwave
 Microwave transmission uses very-high frequency signals (3,000 MHz to
30 GHz) to transmit signals between stations. The high frequency permits
large amounts of data to be transmitted. Unlike broadcast radio signals,
which are omnidirectional, microwave transmission is focused and
unidirectional. That means means that microwave stations use line-of-sight
transmission and signals travel in straight line. The two types of
microwave transmission are terrestrial and satellite:
 Terrestrial microwave transmissions are sent between two microwave
stations on the earth (earth station). It is the most common form of longdistance communication.
 Satellite microwave transmissions involve sending microwave
transmissions between two or more earth-based microwave stations and a
satellite.
Satellite Microwave
 Most communications satellites are placed into orbit 22,300 miles above
the earth's surface. The earth's gravity keeps the satellite in orbit at the
same rate as the earth (geosynchronous orbit). Such satellites are called
geosynchronous orbiting satellites (GEOS).
 Low earth orbiting satellites (LEOS) orbit the earth at a height of 3251,000 miles and they orbit around the poles (not in a fixed position
relative to the earth).
 Medium earth orbiting satellites (MEOS) are similar to LEOS but are
positioned at 6,000-10,000 miles above the earth.
 Because microwaves use line-of-sight, the satellite signal can only reach
a part of the earth. This area is called a footprint.
Cellular Radio
 Cellular telephones actually are radio devices that use cellular radio
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(form of broadcast radio with restrictions on how far the signal is
transmitted) to transmit voice and data. The broadcast area of a cellular
radio system is divided into cells. Here is how it works:
1. Using a cellular phone, the caller dials a number. The signal is sent
from the cell phone's antenna to the cellular antenna located in cell 1.
2. The signal is sent to the regional cellular phone switching office.
3. The signal is switched to the local Telephone Company switching
station.
4. The signal is now in the regular phone system and the call is switched
to the number dialed.
Infrared Transmission
 Infrareds (IR) transmission involves sending light signals
at a frequency between visible light and radio waves.
Commonly used in TV remote controls, now is used to
provide LAN connections.
 It is a line-of-sight transmission and has a maximum
coverage of 30 to 80 feet.
 Increasingly, computers and devices such as printers come
with IrDA ports, which enable the transfer of data without
the use of cables.
Selection of Media
 In developing any network, the designer must take into
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account:
The cost of the medium
The speed at which it can transmit
The error rate that should be expected using the medium
The security of the data transmitted over the medium
The transmission distance
The availability of the medium
The environmental constraints
Transmission Modes
Signals can be transmitted though telecommunications
media in a number of different ways:
 In simplex transmission, data can flow only in one
direction
 In half-duplex transmission, data can flow in both
directions but it can only flow in one direction at any point
in time
 In full-duplex transmission, data can flow in both
directions at the same time
Telecommunications Devices
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Telecommunication devices are hardware devices that
allow electronic communication to occur.
Modems translate data from digital to analog and vice
versa
Fax devices allow the transmission of text, graphs and
other digital files via telephone lines
Multiplexers allow several signals to be sent over one
channel
Communication processors are computers devoted to
communications management
Bridges, Routers, Gateways, and Switches
Telecommunications Carriers and Services
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Several companies provide telecommunications media, devices and
services called telecommunications carriers
Switched lines are standard telephone lines provided by telephone
companies
Dedicated lines provide a constant connection between two points
Private Branch Exchange (PBX) is a communications system that can
manage both voice and data transfer within a building and an outside line
Wide-area Telecommunications Service (WATS) is a billing method for
heavy users of voiceband media (the 1-800 lines)
Integrated Serviced Digital Network (ISDN) is a technology that uses
existing common-carrier lines to simultaneously transmit voice, video
and image data in digital form
Digital Subscriber Line (DSL) uses existing phone wires to provide
transmission speeds exceeding 500 Kbps.
T1 carrier increases the number of voice calls through the existing cables
Networks: LANs and WANS
 A Computer Network is a collection of computers and
peripherals linked together so that they can share
applications, data, and resources such as printers, modems,
and CD-ROMs.
 A Local Area Network (LAN) enables computer users to
transfer files, manipulate data, and share resources within
the same office or building.
 A Wide Area Network (WAN) ties together large
geographic regions using microwave, satellite, or
telephone lines.
Home and Small Business Networks
Terminal-to-Host, File Server, and
Client/Server Systems
 In a Terminal-to-Host network, the application and
database reside on one host computer and the user interacts
with the application and data using a “dump” terminal.
 In the File and Client/Server model, certain machines and
devices on the network are dedicated to providing services
to the network. (cost, performance, security, privacy, virus,
multi-vendor)
 A Peer-to-peer network allows personal computers to be
linked together to share their resources. In such an
arrangement, a single peripheral as a printer connected to a
workstation can be used by other network users. Users can
also share programs and data.
Network Topologies
The Topology of the Network is the network’s physical
layout. This is what defines the path that information must
take to move from one place to another on the network. The
3 basic topologies are: Star, Bus, and Ring
Star Topology
 In a Star topology, all of the workstations and servers are
connected to a centrally located device called a hub. The
hub controls and directs messages.
Bus Topology
 In a Bus or linear network topology, all workstations and
servers are connected to a single cable called the bus. At
the ends of the network circuit, a device called terminator
is installed to complete the network circuit.
Ring Topology
 In a Ring topology, all workstations and servers are
chained together in much the same way as they are in a bus
network. The exception is that the cables at the ends of the
network are connected together rather than terminated.
Coordinating Data Communications
 Polling is a procedure in which the main computer checks
each device one at a time to see if there are any messages
waiting to be communicated to other network devices.
 Token passing is a technique in which an electronic
"token" is passed from one device to another. If a device
has the token and a message, the message can be
transmitted.
 Contention is a procedure in which a device checks to see
if a message is currently being transmitted. If there are no
messages being transmitted, the device starts the messagesending sequence.
Popular Communications Protocols
 Ethernet is the most widely used networking protocol in use today,
mainly because of the low cost of implementing the network and the
lack of need for centralized control. Ethernet can be used to link many
different types of computers together. Ethernet can run on coax,
twisted pair, and fiber optic cabling. All cabling schemes support 10
Mbps speeds but the latest (10baseF) can also support 100 Mbps.
 The Transmission Control Protocol/Internet Protocol (TCP/IP) was
developed in 1973 for use in the APRANet network. Over time,
TCP/IP has developed to be a suite network protocols that will support
remote log-in capabilities, file transfer, e-mail, and routing. It is most
commonly associated with the Internet since in 1983 TCP/IP was
adopted as the Internet standard.
 Bluetooth is a communications standard using short-range radio wave
that defined by Ericsson for wireless communications
Communications Software
 Network operating system (NOS)
 Network management software
– Simple Network Management Protocol (SNMP)
– Fault detection
– Performance management
Points to Remember - I
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What Is Telecommunications?
What Is Data Communications?
What are the Electromagnetic Waves?
What is Electromagnetic Signal Frequency?
What is a Communication Line Bandwidth?
Digital Versus Analog Data
Components of Communication Networks
Contacted and Radiated Media
–
–
–
–
–
–
Twisted Pair Wire
Coaxial Cable
Fiber-Optic Cable
Broadcast Radio
Microwave
Satellite Microwave
Points to Remember - II
– Cellular Radio
– Infrared Transmission
 Selection of Media
 Transmission Modes
 Telecommunications Devices
 Telecommunications Carriers and Services
 Networks: LANs and WANS
 Terminal-to-Host, File Server, and Client/Server Systems
 Network Topologies
– Star Topology
– Bus Topology
– Ring Topology
 Coordinating Data Communications
 Popular Communication Protocols
 Home and Small Business Networks