Telecommunications and Networks
Business value of networks
The Internet
Network components
Chapter
6
Network Concepts
• Computer Network
– An interconnected chain , group or system of computers and other
devices
• Number of possible connections on a network is N * (N-1)
– Where N = number of nodes (points of connections on the network)
– Example, if there are 10 computers on a network, there are 10 * 9 =
90 possible connections
• This type of mathematical growth is called exponential. This
term just means that the growth in number of connections is
many times greater than the number of nodes.
• Metcalfe’s law states that the usefulness, or utility, of a
network equals the square of the number of users.
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Telecommunications network
• Telecommunications
– Exchange of information in any form (voice, data,
text, images, audio, video) over networks
– Any arrangement where a sender transmits a
message to a receiver over a channel consisting of
some type of medium
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Telecommunications network components
• Terminals: any input/output device that uses networks to
transmit or receive data
• Telecommunications Processors: devices that support
data transmission and reception
• Telecommunications Channels: media over which data are
transmitted and received
• Computers: all sizes and types;
• Telecommunications Control Software: programs that
control telecommunications activities
– telecommunications monitors for mainframe,
– network operatings ystems for network servers,
– Web browsers for microcomputers.
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Telecommunications network model
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Types of Telecommunications Networks
•
•
•
•
•
•
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Internet,
intranet,
extranet,
wide area,
local area,
client/server,
peer-to-peer
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The Internet
• the Internet is a network made up of millions of
smaller private networks, each with the ability to
operate independent of, and in harmony with, all the
other millions of networks connected to the Internet.
• No central computer system
• No governing body
• No one owns it
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Internet Service Provider
• ISP
– A company that specializes in providing easy access
to the Internet
– For a monthly fee, you get software, user name,
password and access
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Popular uses of the Internet
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An Intranet
• A network inside an organization
• That uses Internet technologies (such as Web browsers
and servers, TCP/IP protocols, HTML, etc.)
• To provide an Internet-like environment within the
organization
• For information sharing, communications, collaboration
and support of business processes
• Protected by security measures such as passwords,
encryption, and firewalls,
• Can be accessed by authorized users through the
Internet
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Enterprise Information Portal
6-11
Extranet
• Network links that use Internet technologies To
connect the Intranet of a business with its
customers, suppliers or other business partners
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Extranet Uses
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Wide Area Network (WAN)
• Telecommunications network that covers a large
geographic area
Source: Courtesy of Cisco Systems
6-14Inc.
Metropolitan Area Networks
• a wide area network optimized a specific
geographical area
• Such networks can range from several blocks of
buildings to entire cities.
• A local telephone company is probably operating
on a MAN.
• MANs will often provide means for
internetworking of local area networks.
6-15
Local Area Network (LAN)
• Connect computers within a limited physical area
such as an office, classroom, or building
• Most LANs use a more powerful microcomputer
with a large hard disk capacity, called a file server
or network server , that contains a network
operating system program that controls
telecommunications and the sharing of network
resources.
6-16
Local Area Network (LAN)
6-17
Virtual Private Networks (VPN)
• A secure intranets and extranets, that uses the
Internet as its backbone but relies on firewalls,
encryption and other security
• A pipe traveling through the Internet , so we can
send and receive our data without anyone
outside the pipe being able to see or access our
transmissions.
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VPN
6-19
Client/Server networks (two-tier model)
• Clients (PCs or networked computers workstations)
are Interconnected by LANs and share application
processing with network servers.
1. Clients: Provide user interface, perform
some/most processing on an application.
2. Network Servers: Shared computation,
application control, distributed databases.
6-20
Client/Server networks(three-tier model)
1.Thin clients: provide a browser-based user
interface for processing small application
programs.
2.Application servers for multi-user operating
systems, Web server software, and application
software applets.
3.Database servers for Internet/intranet Web
databases, operational databases, and database
management software.
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Client/Server Network
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Peer-to-peer networks
• Networks that connect from one PC to another PC
• two major models of peer-to-peer networking technology:
– The pure peer-to-peer network architecture
– the central server architecture
• Common use is the downloading and trading of files
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Peer-to-Peer Network
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Telecommunications Media
• Wired Technologies
– Twisted-Pair Wire
– Coaxial Cable
– Fiber Optics
• Wireless Technologies
–
–
–
–
–
Terrestrial Microwave
Communications Satellites
Cellular Systems
Wireless LANs
Bluetooth
6-25
Wired Technologies
• Twisted-pair wire:
– Ordinary telephone wire
– Copper wire twisted into pairs
– the most widely used medium
for telecommunications.
Source: Phil Degginger/Getty6-26
Images.
Wired Technologies
• Coaxial cable:
– Sturdy copper or aluminum wire
wrapped with spacers to insulate and
protect it
– they can be placed underground and
laid on the floors of lakes and
oceans.
– They allow high-speed data
transmission and are used instead of
twisted-pair wire lines in high-service
metropolitan areas, for cable
television systems, and for shortdistance connections of computers
and peripheral devices.
Source: Ryan McVay/Getty 6-27
Images.
Wired Technologies
• Fiber-optic cable:
– One or more hair-thin filaments
of glass fiber wrapped in a
protective jacket
– They can conduct pulses of
visible light elements (photons)
generated by lasers at
transmission rates as high as
trillions of bits per second .
– This speed is hundreds of times
faster than coaxial cable and
thousands of times better than
twisted-pair wire lines.
Source: CMCD/Getty 6-28
Images.
Problem of “The Last Mile”
• Network providers use fiber optic to provide backbone
• But houses are connected to the backbone via twistedpair
• Cannot get the benefit of the faster, better technology
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Wireless Technologies
Wireless telecommunications technologies rely on radio wave,
microwave, infrared, and visible light pulses to transport digital
communications without wires between communications devices.
• Terrestrial microwave
– Earthbound microwave systems that transmit high-speed radio signals
in a line-of-sight path
– Between relay systems spaced approximately 30-miles apart
– Microwave antennas are usually placed on top of buildings, towers,
hills, and mountain peaks
– a popular medium for both long-distance and metropolitan area
networks.
• Communications satellites
– Satellite serves as relay stations for communications signals
– Uses microwave radio signals
6-30
Wireless Technologies
• Cellular systems
– Divide the geographic area into small areas or cells
– Each cell has transmitter or radio relay antenna to send
message from one cell to another
• Wireless LANs (WiFi)
– Radio signals within an office or building
– Connect PCs to networks
• Bluetooth
– Short-range wireless technology
– To connect PC to peripherals such as printer
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Telecommunications Processors
• Modems
• Internetwork Processors
– Hub
– Switch
– Router
– Gateway
• Multiplexers
6-32
Modems
• Modems: Convert digital signals from a computer
into Analog frequencies that can be transmitted
over ordinary telephone lines.
• In analog systems: the quantity is as an electrical
voltage or current.
– For example, if the temperature being measured is 83
degrees then quantity could be 83 volt or 8.3 volt or
any other voltage proportional to the temperature.
• In a digital systems: the quantity is expressed as a
number.
– For example , the 83 is the binary number 1010011, 0
could be represented by 0 volts, and 1 by 5 volts.
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Internetwork Processors
• Hub and Switch – port switching communications
processors that make connections between different
network devices (computers, other processors, etc.)
• Router and Gateway – intelligent communications
processors that interconnects networks based on
different protocols and different communications
architectures
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Communications Processors
6-35
Telecommunications Processors
• Multiplexer
– Allows a single communications channel to carry
simultaneous data transmissions from many
terminals
• This process is accomplished in two basic ways.
1. frequency division multiplexing (FDM): multiplexer
effectively divides a high-speed channel into
multiple slow-speed channels.
2. time division multiplexing (TDM): the multiplexer
divides the time so each terminal can use the highspeed line into very short time slots,
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Telecommunications Software
• Used by PCs, servers and communications processors
like multiplexers and routers. to manage network
performance, for example:
– Network Operating Systems
– Middleware: which can help diverse networks
communicate with one another.
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Telecommunications Software functions
• Traffic Management – manage network
resources and traffic to avoid congestion and
optimize service levels to users
• Security – provide authentication, encryption,
firewall, auditing and enforcement
• Network Monitoring – troubleshoot and watch
over the network, informing network
administrators of potential problems before
they occur
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Network Topologies
• Topology: structure of a network
• Star: ties end user computers to a central computer
• Ring: ties local computer processors together in a
ring
• Bus: in which local processors share the same
communications channel
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Network Topologies
6-40
Network Architectures & Protocols
• Protocol: standard set of rules and procedures for the control
of communications in a network
• Network Model: is a standard description for how messages
should be transmitted between any two points in a
telecommunications network.
• The main idea in any network model is that the process of
communication between two endpoints in a
telecommunication network can be divided into layers, with
each layer adding its own set of special, related functions.
• Two main type of Network Model:
– OSI model
– TCP/IP model
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OSI & TCP/IP Models
• Open Systems Interconnection (OSI)
– A seven-layer model that serves as a standard
model for network architectures
• Transmission Control Protocol / Internet
Protocol (TCP/IP)
– A five layer telecommunications protocol used by
the Internet
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OSI & TCP/IP Models
6-43
Bandwidth
• Bandwidth
– Frequency range of a telecommunications channel
– Determines transmission rate (speed) and represents the
capacity of the connection.
– measured in bits per second (bps)
• Transmission Rates:
– Narrow-band channels provide low-speed
– Broadband channels provide high-speed
6-44
Transmission Speeds (bandwidth) of
various network technologies.
6-45
Switching Alternatives
• Circuit Switching
– Switch opens a circuit to establish a link between a
sender and receiver
– it remains open until the communication session is
completed
• Packet Switching
– Break messages into groups called packets
– Transmit packets separately
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Internet Telephony: Voice over IP (VoIP)
• Using an Internet connection to pass voice data
using IP
• Advantage: Skips standard long-distance phone
charges
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Voice Over IP
• VoIP works by
– Digitizing a voice signal,
– Chopping it into packets, and
– Sending them over a company’s network or the
Internet
– Packets are reassembled at the destination
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