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Transcript
Chapter 5
Connectivity, the Wireless Revolution and Communications
Objectives:
In this chapter we will discuss the following topics:

Connectivity, the wireless revolution and communications.

Physical and wireless communications channels.

Conventional modems, T1, ISDN, DSL, cable modem, and satellite connections.

Bandwidth, serial versus parallel transmission, direction of data transmission, and
protocols.

Network architecture – configurations and strategies.

Local area, metropolitan area, and wide area networks.
Learning outcomes:
At the end of the chapter, students will be able to:
1. Explain what is meant by connectivity, the wireless revolution and communications.
2. Differentiate between physical and wireless communications channels.
3. Define what is conventional modems, T1, ISDN, DSL, cable modem, and satellite
connections.
4. Understand the term bandwidth, the difference between serial and parallel
transmission, direction of data transmission, and protocols.
5. Describe what is a network architecture, network configurations and strategies.
6. Explain the difference between a local area, metropolitan area, and wide area networks.
5.1
Connectivity, the wireless revolution and communications.
In this new millennium, computers are connected to each other on a network to fulfill the
computing requirements of the users. As users’ requirements get more and more sophisticated,
they no longer can work alone. They need to collaborate and interact with each other. As such
their computers need to be connected. Hence connectivity gradually becomes a ‘must’.
1
Connectivity refers to the use of computer networks to link to people and resources [1]. We can
link or connect to large computers and the Internet providing access to world-wide information
resources just by sitting in front of and clicking on our computer. Connectivity may also refer to
the internet bandwidth coming into and going out of a country, and the quality of the
infrastructure within the country for linking to the internet.
Being connected is no longer sufficient. Users need to be connected and yet at the same time
they want to be mobile. It is now cumbersome to have wires rooting them down at the
computer table. Users want to be connected to the Internet and the network, but without
wires limiting their movements. This is where wireless technology comes in handy. Wireless is a
term used to describe telecommunications in which electromagnetic waves (rather than some
form of wire) carry the signal over part or the entire communication path. Some monitoring
devices, such as intrusion alarms, employ acoustic waves at frequencies above the range of
human hearing; these are also sometimes classified as wireless.
The first wireless transmitters went on the air in the early 20th century using radiotelegraphy
(Morse code). Later, as modulation made it possible to transmit voices and music via wireless,
the medium came to be called "radio." With the advent of television, fax, data communication,
and the effective use of a larger portion of the spectrum, the term "wireless" has been
resurrected. Common examples of wireless equipment in use today include:

cellular phones and pagers -- provide connectivity for portable and mobile applications,
both personal and business

Global Positioning System (GPS) -- allows drivers of cars and trucks, captains of boats and
ships, and pilots of aircraft to ascertain their location anywhere on earth

Cordless computer peripherals -- the cordless mouse is a common example; keyboards
and printers can also be linked to a computer via wireless

Cordless telephone sets -- these are limited-range devices, not to be confused with cell
phones
2

Home-entertainment-system control boxes -- the VCR control and the TV channel control
are the most common examples; some hi-fi sound systems and FM broadcast receivers
also use this technology

Remote garage-door openers -- one of the oldest wireless devices in common use by
consumers; usually operates at radio frequencies

Two-way radios -- this includes Amateur and Citizens Radio Service, as well as business,
marine, and military communications

Baby monitors -- these devices are simplified radio transmitter/receiver units with limited
range

satellite television -- allows viewers in almost any location to select from hundreds of
channels

wireless LANs or local area networks -- provide flexibility and reliability for business
computer users
Wireless technology is rapidly evolving, and is playing an increasing role in the lives of people
throughout the world [2]. In addition, ever-larger numbers of people are relying on the
technology directly or indirectly. (It has been suggested that wireless is overused in some
situations, creating a social nuisance.) More specialized and exotic examples of wireless
communications and control include:

Global System for Mobile Communication (GSM) -- a digital mobile telephone system used
in Europe and other parts of the world [3]; the de facto wireless telephone standard in
Europe

General Packet Radio Service (GPRS) -- a packet-based wireless communication service
that provides continuous connection to the Internet for mobile phone and computer
users

Enhanced Data GSM Environment (EDGE) -- a faster version of the Global System for
Mobile (GSM) wireless service
3

Universal Mobile Telecommunications System (UMTS) -- a broadband, packet-based
system offering a consistent set of services to mobile computer and phone users no
matter where they are located in the world

Wireless Application Protocol (WAP) -- a set of communication protocols to standardize
the way that wireless devices, such as cellular telephones and radio transceivers, can be
used for Internet access [4]

i-Mode -- the world's first "smart phone" for Web browsing, first introduced in Japan;
provides color and video over telephone sets [5].
5.2
Physical and wireless communications channels.
Wireless communication channels [6] can be divided into:

fixed wireless -- the operation of wireless devices or systems in homes and offices, and
in particular, equipment connected to the Internet via specialized modems

Mobile wireless -- the use of wireless devices or systems aboard motorized, moving
vehicles; examples include the automotive cell phone and PCS (personal
communications services)

Portable wireless -- the operation of autonomous, battery-powered wireless devices or
systems outside the office, home, or vehicle; examples include handheld cell phones
and PCS units

IR wireless -- the use of devices that convey data via IR (infrared) radiation; employed in
certain limited-range communications and control systems
5.3 Conventional modems, T1, ISDN, DSL, cable modem, and satellite connections.
Conventional Modems
A device that comprises both a modulator that changes a signal in some way in the forward
direction and a demodulator that changes the signal back to its original form in the backward
direction, essentially reversing the modulation process. A conventional modem is a signal
conversion device that interfaces a digital device to an analog circuit or channel [7]. On the
transmit side of the connection, a modem accepts an incoming digital signal and modulates
4
(i.e., changes or varies) the characteristics of an electromagnetic waveform in some way to
represent that signal over an analog carrier. The modulation technique generally involves
amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), or some
combination. On the receive side of the connection, a modem with matching capabilities
accepts the modulated signal over the analog carrier and demodulates the signal to extract the
information and recreate the original digital signal. Many modems are capable of operating in
full duplex, simultaneously modulating signals as they transmit them and demodulating signals
as they receive them.
T1
T1 is a high-speed digital network (1.544 mbps) developed by American Telephone & Telegraph
(AT&T) in 1957 [8]. This technology was implemented in the early 1960s to support long-haul,
pulse-code modulation (PCM) voice transmission. During its inception, the main innovation of
T1 was that it introduced ‘digitized’ voice, thus creating a network that was fully capable of
digitally representing what was until then a fully analog telephone system.
ISDN
It stands for ‘integrated services digital network’ [9]. A set of recommendations describing a set
of interfaces for access to a digital public switched telephone network (PSTN) intended to
provide ubiquitous access to a wide range of services, including voice, data, video, and
multimedia.
Cable modem
A technology for connecting users to the Internet through the TV-cable network and has the
advantage of high-speed bandwidth 10-50 times as high (up to 5 megabits per second) as dialup modems, which have 56 kilobits per second and use the telephone networks. TV-cable
providers have to upgrade their network infrastructure to offer the service, whereas the dial-up
modems need just a telephone line for connectivity. An alternative to the usage of cable-
5
modems is DSL (Digital Subscription Line). DSL makes use of existing telephony lines and
achieves approximately the same transmission speeds as cable modems [10].
Satellite connections
A satellite Internet connection [11] is an arrangement in which the upstream (outgoing) and the
downstream (incoming) data are sent from, and arrive at, a computer through a satellite. Each
subscriber's hardware includes a satellite dish antenna and a transceiver (transmitter/receiver)
that operates in the microwave portion of the radio spectrum.
In a two-way satellite Internet connection, the upstream data is usually sent at a slower speed
than the downstream data arrives. Thus, the connection is asymmetric. A dish antenna,
measuring about two feet high by three feet wide by three feet deep, transmits and receives
signals. Uplink speeds are nominally 50 to 150 Kbps for a subscriber using a single computer.
The downlink occurs at speeds ranging from about 150 Kbps to more than 1200 Kbps,
depending on factors such as Internet traffic, the capacity of the server, and the sizes of
downloaded files.
Satellite Internet systems are an excellent, although rather pricey, option for people in rural
areas where Digital Subscriber Line (DSL) and cable modem connections are not available. A
satellite installation can be used even where the most basic utilities are lacking, if there is a
generator or battery power supply that can produce enough electricity to run a desktop
computer system. The two-way satellite Internet option offers an always-on connection that
bypasses the dial-up process. In this respect, the satellite system resembles a cable modem
Internet connection. But this asset can also be a liability, unless a firewall is used to protect the
computer against hack attempts.
5.4 Bandwidth, serial versus parallel transmission, direction of data transmission, and
protocols.
6
Bandwidth
In computer networks, bandwidth is often used as a synonym for data transfer rate [12] - the
amount of data that can be carried from one point to another in a given time period (usually a
second). This kind of bandwidth is usually expressed in bits (of data) per second (bps).
Occasionally, it is expressed as bytes per second (Bps). A modem that works at 57,600 bps has
twice the bandwidth of a modem that works at 28,800 bps. In general, a link with a high
bandwidth is one that may be able to carry enough information to sustain the succession of
images in a video presentation.
Serial versus Parallel Transmission
Data are transmitted along a communications medium either in serial or in parallel [13]. Most
microcomputer owners know that their machines are equipped with serial and parallel ports.
These enable the computer to transmit both serial and parallel digital signals. In both serial and
parallel transmission, the bytes corresponding to each message are sent along a medium, one
after another.
Thus, for the one-word message: SALMAN. The byte representation of the "S" is sent first, then
"A" then "L," and so on. Serial and parallel transmission differs in that, in serial transmission,
the bits of each byte are sent along a single path one after another. In parallel transmission,
separate, parallel paths correspond to each bit of a byte so that all the bits arrive at the
destination simultaneously.
Because parallel transmission can get messages to its destinations sooner, it is faster than serial
transmission. But, because more wiring is needed to set up the extra bit paths, parallel
transmission is much more expensive. Often, devices that are located within a few feet of each
other will communicate in serial. For example, a microcomputer may use parallel transmission
to send a word-processing document to a printer that is connected to it.
Direction of Data Transmission
7
Besides the previously mentioned ways in which data may travel, there are three directional
modes of travel in data transmission.

Simplex Communication: Simplex communication [14] is a mode in which data only
flows in one direction. Because most modern communications require a two-way
interchange of data and information, this mode of transmission is not as popular as it once
was. However, one current usage of simplex communications in business involves certain
point-of-sale terminals in which sales data is entered without a corresponding reply.

Half-duplex Communication: Half-duplex communication [15] adds an ability for a twoway flow of data between computer terminals. In this directional mode, data travels in two
directions, but not simultaneously. Data can only move in one direction when data is not
being received from the other direction. This mode is commonly used for linking computers
together over telephone lines.

Full-duplex Communication: The fastest directional mode of communication is fullduplex communication [16]. Here, data is transmitted in both directions simultaneously on
the same channel. Thus, this type of communication can be thought of as similar to
automobile traffic on a two-lane road. Full-duplex communication is made possible by
devices called multiplexers. Full-duplex communication is primarily limited to mainframe
computers because of the expensive hardware required to support this directional mode.
Protocols
In the field of telecommunications, a communications protocol [17] is the set of standard rules
for data representation, signaling, authentication and error detection required to send
information over a communications channel. An example of a simple communications protocol
adapted to voice communication is the case of a radio dispatcher talking to mobile stations. The
communication protocols for digital computer network communication have many features
intended to ensure reliable interchange of data over an imperfect communication channel.
Communication protocol is basically following certain rules so that the system works properly.
8
5.5
Network architecture – configurations and strategies.
A network architecture [18] is a blueprint of the complete computer communication network,
which provides a framework and technology foundation for designing, building and managing a
communication network. It typically has a layered structure. Layering is a modern network
design principle which divides the communication tasks into a number of smaller parts, each
part accomplishing a particular sub-task and interacting with the other parts in a small number
of well-defined ways. Layering allows the parts of a communication to be designed and tested
without a combinatorial explosion of cases, keeping each design relatively simple.
Open Systems Interconnection (OSI) network architecture, developed by International
Organization for Standardization, is an open standard for communication in the network across
different equipment and applications by different vendors. Though not widely deployed, the
OSI 7 layer model is considered the primary network architectural model for inter-computing
and inter-networking communications.
In addition to the OSI network architecture model, there exist other network architecture
models by many vendors, such as IBM SNA (Systems Network Architecture), Digital Equipment
Corporation (DEC; now part of HP) DNA (Digital Network Architecture), Apple computer’s
AppleTalk, and Novell’s NetWare.
5.6
Local area, metropolitan area, and wide area networks
Local Area Network (LAN)
The components in a Local Area Network [19] can be connected in a few ways, which is call LAN
topologies. Figure 5.6 describes the 4 basic LAN topologies:
Star: All stations are connected by cable (or wireless) to a central point, such as hub or a switch.
If the central node is operating in a broadcast fashion such as a Hub, transmission of a frame
9
from one station to the node is retransmitted on all of the outgoing links. In this case, although
the arrangement is physically a star, it is logically a bus. In the case of the central node acting as
switch, an incoming frame is processed in the node and then retransmitted on an outgoing link
to the destination station. Ethernet protocols (IEEE 802.3) are often used in the Star topology
LAN.
Ring: All nodes on the LAN are connected in a loop and their Network Interface Cards (NIC) are
working as repeaters. There is no starting or ending point. Each node will repeat any signal that
is on the network regardless its destination. The destination station recognizes its address and
copies the frame into a local buffer as it goes by. The frame continues to circulate until it
returns to the source station, where it is removed. Token Ring (IEEE 802.5) is the most popular
Ring topology protocol. FDDI (IEEE 802.6) is another protocol used in the Ring topology, which
is based on the Token Ring [19].
Bus: All nodes on the LAN are connected by one linear cable, which is called the shared
medium. Every node on this cable segment sees transmissions from every other station on the
same segment. At each end of the bus [19] is a terminator, which absorbs any signal, removing
it from the bus. This medium cable apparently is the single point of failure. Ethernet (IEEE
802.3) is the protocols used for this type of LAN.
Tree: The tree topology 19] is a logical extension of the bus topology. The transmission medium
is a branching cable with no closed loops. The tree layout begins at a point called the head-end,
where one or more cables start, and each of these may have branches. The branches in turn
may have additional branches to allow quite complex layouts.
10
Figure 5.6: LAN Architecture and Topologies: Bus, Star, Ring and Tree
Metropolitan Area Network (MAN)
A Metropolitan Area Network (MAN)[19] is a large computer network that spans a
metropolitan area or campus. Its geographic scope falls between a WAN and LAN. MANs
provide Internet connectivity for LANs in a metropolitan region, and connect them to wider
area networks like the Internet. A MAN is optimized for a larger geographical area than a LAN,
ranging from several blocks of buildings to entire cities. MANs can also depend on
communications channels of moderate-to-high data rates. A MAN might be owned and
operated by a single organization, but it usually will be used by many individuals and
organizations. MANs might also be owned and operated as public utilities. They will often
provide means for internetworking of local networks. Metropolitan area networks can span up
to 50km, devices used are modem and wire/cable
Summary
Connectivity refers to the use of computer networks to link to people and resources. Users
need to be connected and yet at the same time they want to be mobile. . Wireless is a term
11
used to describe telecommunications in which electromagnetic waves carry the signal over part
or the entire communication path.
Wireless communication channels can be fixed wireless, Mobile wireless, Portable wireless or IR
wireless. A conventional modem is a signal conversion device that interfaces a digital device to
an analog circuit or channel. T1 is a high-speed digital network implemented in the early 1960s
to support long-haul, pulse-code modulation (PCM) voice transmission. ISDN is a set of
recommendations describing a set of interfaces for access to a digital public switched telephone
network to provide ubiquitous access to a wide range of services, including voice, data, video,
and multimedia. Cable modem is a technology for connecting users to the Internet through the
TV-cable network. A satellite Internet connection is an arrangement in which the upstream
(outgoing) and the downstream (incoming) data are sent from, and arrive at, a computer
through a satellite.
Bandwidth is the amount of data that can be carried from one point to another in a given time
period. Parallel transmission is faster than serial transmission. There are three directional
modes of travel in data transmission: Simplex Communication, Half-duplex Communication and
Full-duplex Communication. , A communications protocol is the set of standard rules for data
representation, signaling, authentication and error detection required to send information over
a communications channel.
A network architecture is a blueprint of the complete computer communication network, which
provides a framework and technology foundation for designing, building and managing a
communication network. a Local Area Network can be connected in four different topologies:
star, bus, ring and tree. A Metropolitan Area Network (MAN) is a large computer network that
spans a metropolitan area or campus.
Exercises
12
Fill in the blanks.
1. …… may also refer to the internet bandwidth coming into and going out of a country, and
the quality of the infrastructure within the country for linking to the internet.
2. A ……. is a large computer network that spans a metropolitan area or campus.
3. In the …… topology, every node on this cable segment sees transmissions from every other
station on the same segment.
4. The …….. network architecture, is an open standard for communication in the network
across different equipment and applications by different vendors.
5. A ……… is the set of standard rules for data representation, signaling, authentication and
error detection required to send information over a communications channel.
6. …….. communication is primarily limited to mainframe computers because of the expensive
hardware required to support this directional mode.
7. In …… transmission, separate, parallel paths correspond to each bit of a byte so that all the
bits arrive at the destination simultaneously.
8. …… is the amount of data that can be carried from one point to another in a given time
period (usually a second).
9. ….. is a set of recommendations describing a set of interfaces for access to a digital public
switched telephone network (PSTN) intended to provide ubiquitous access to a wide range
of services, including voice, data, video, and multimedia.
10. …….the use of wireless devices or systems aboard motorized, moving vehicles; examples
include the automotive cell phone and personal communications services.
11. ….. is a term used to describe telecommunications in which electromagnetic waves carry the
signal over part or the entire communication path.
Answers:
1. Connectivity
2. Metropolitan Area Network (MAN)
3. Tree
13
4. Open Systems Interconnection (OSI)
5. communications protocol
6. Full-duplex
7. Parallel
8. Bandwidth
9. integrated services digital network
10. Mobile wireless
11. Wireless
References:
Books:
1. Diane M. Coyle, Computers Are Your Future, Complete, 10/E, Prentice Hall, 2009. ISBN-10:
0135045118, ISBN-13: 9780135045114.
2. John Preston, Sally Preston and Robert L. Ferrett, Computer Literacy for IC3, Prentice Hall,
2009. ISBN-10: 0131498649, ISBN-13: 9780131498648.
3. Alan Evans, Mary Ann Poatsy and Kendall Martin, Technology in Action, Introductory, 5/E,
Prentice Hall, 2009. ISBN-10: 0135137667, ISBN-13: 9780135137666.
4. Brian K.Williams and Stacey Sawyer, Using Information Technology: A Practical Introduction
to Computers and Communications, 7th Edition, McGraw-Hill, 2007. ISBN-13
9780072260717.
5. James A. O'Brien and George Marakas, Introduction to Information Systems, 13th Edition,
McGraw-Hill, 2007, ISBN-13 9780073043555.
Online References:
[1]
http://en.wikipedia.org/wiki/Connectivity_(computer_science)
[2]
http://www.wordinfo.info/words/index/info/view_unit/4003
14
[3]
http://en.wikipedia.org/wiki/GSM
[4]
http://www.webopedia.com/TERM/W/WAP.html
[5]
http://www.cbc.ca/technology/story/2009/01/07/f-forbes-smartphones.html
[6]
http://en.wikipedia.org/wiki/Channel_(communications)
[7]
http://www.yourdictionary.com/modem
[8]
http://www.yourdictionary.com/t1-and-t3
[9]
http://hea-www.harvard.edu/~fine/ISDN/overview.html
[10]
http://en.wikipedia.org/wiki/Cable_modem
[11]
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci528672,00.html
[12]
http://www.cyberindian.com/web-hosting/bandwidth-management.php
[13]
http://www.blurtit.com/q511025.html
[14]
http://en.wikipedia.org/wiki/Duplex_(telecommunications)
[15]
http://www.webopedia.com/TERM/H/half_duplex.html
[16]
http://home.olemiss.edu/~misbook/cdtddts.htm
[17]
http://en.wikipedia.org/wiki/Communications_protocol
[18]
http://www.edrawsoft.com/Network-Architecture.php
[19]
http://compnetworking.about.com/cs/lanvlanwan/g/bldef_lan.htm
15