ICS124

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ICS124 Session 4 Introduction to Networking
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• Objectives
• By the end of this session, the student will be
  able to
• Describe how data is represented for transmission
• Decode a bit pattern from transmitted data
• List the two methods modems use to modulate a
  carrier wave
• Diagrammatically represent data streams using the
  two modulation types
• Define Bandwidth
• Rank various communications types in order of
  bandwidth
• List the two methods of modem synchronization
• Contrast the modem synchronization methods in
  relation to speed and content
• List the three modes of data flow
• Provide an analogy of each of these methods to
  demonstrate how each method functions
• List three ways users can interact with a
  computer system
• Distinguish each of these through discussion of
  how the data is accessed, and where the data is
  processed
• List the three network topologies
• Diagram each of the topologies and show where
  each will fail
• List four components of a network
• Describe the purpose of each component
• Define the term protocol

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Introduction to Networking

• Background
• There are various ways that users can interact
  with a computer system.
• terminal to multi-user system
• PC to multi-user system
• PC on a network
• The basics are the same for each of these
  methods. As the complexity of these methods
  increases, the user is provided more access to
  the data in the computer system.

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Introduction to Networking, continued

• How data is represented
• Computers store data in binary form. We have
  looked at the storage of binary data in RAM and
  ROM as the states of switches
• a switch turned on represents a 1 bit
• a switch turned off represents a 0 bit
• This binary form can also be represented using
  electrical pulses, where
• the presence of a voltage represents a 1
• the absence of a voltage represents a 0
• 5V-
• 0V-
• In this waveform do we have
• 00101011001100? or
• 0000110011001111000011110000? or
• something else?

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Introduction to Networking, continued
How data is represented, continued The only way
to know is by measuring the waveform against
time 1 0 seconds IF we are transmitting at
a rate of 1 bit per second, then the bit stream
would be 00101011001100 2 bits per second, then
the bit stream would be 00001100110011110000111100
00 Serial port During the first week we briefly
mentioned the serial port on a PC. Its function
is to transmit or receive one bit at a time. The
typical maximum rate of serial ports on PCs is
115,400 bits per second, or 115,400 baud The
serial port is only able to transmit data about
15.3m (50') before the electrical properties of
the wire seriously degrade the signal (at 20Kbps).
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Introduction to Networking, continued

• Modems
• A means to send data over longer distances has
  been devised using older technologies (such as
  the phone) and newer technologies that are
  specifically designed for computer equipment.
• A modem is a device that modulates a digital data
  onto an analog signal, and demodulates the analog
  signal, providing digital data.
• An analog signal, called a carrier, can be
  modulated in two basic ways
• amplitude
• frequency

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Introduction to Networking, continued

• Modems, continued
• amplitude - two wave-forms with different
  amplitude
• The crests and troughs line up.
• The height, amplitude, of the waves are different
  (12)

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Introduction to Networking, continued

• Modems, continued
• frequency - two wave-forms with different
  frequency
• The amplitude of the waves are the same
• The number of repetitions per unit time,
  frequency, are different (11.5)

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Introduction to Networking, continued
Modems, continued By altering the amplitude or
the frequency of the carrier wave, information
can be transmitted. These are how the two types
are radio transmissions are classified. The AM
radio uses Amplitude Modulation to transmit the
audio, and the FM radio uses Frequency
Modulation. This is an example of how digital
information may be transmitted on a carrier
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Introduction to Networking, continued

• Bandwidth
• Although the PC can transmit data at very high
  rates, modems are restricted in their speed due
  to the limitations of the phone system.
• The amount of data that can be transmitted per
  second using any particular medium is defines its
  bandwidth.
• The greater the bandwidth, the more data that can
  be transmitted in time.
• Other communications types
• There are other communications types that yield
  better bandwidth
• ISDN (Integrated Services Digital Network)
• ADSL (Asymmetric Digital Subscriber Line)
• cable
• T1
• Each of these technologies require more expensive
  equipment to be installed.

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Introduction to Networking, continued

• Other communications types, continued
• The approximate speed of each of these
  technologies is
• ISDN - 128Kbps
• 1M DSL - 1Mbps
• cable - 1.2Mbps
• T1 - 1.5Mbps
• Synchronization
• When talking about the number of bits per second
  being transmitted, a means for each side of the
  communications link needs to be synchronized so
  that the bits are properly interpreted.
• There are two schemes to transmit data that takes
  the synchronization into account
• asynchronous transmission
• synchronous transmission

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Introduction to Networking, continued
Asynchronous/Synchronous transmissions A
representation of the two transmissions methods
is Because there are no start and stop
bits for each character in synchronous
transmission, it is faster than asynchronous
transmissions. Asynchronous transmission
increases the number of bits sent by a factor of
10/8 (1.25) assuming 8 bits, no parity, 1 stop
bit. To send 1KB of data 8192 data
bits 2048 start and stop bits 10240
total bits sent The serial port on a PC is
asynchronous.
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Introduction to Networking, continued

• Data flow directions
• The data in a communications link can flow in
  one-way or two-way directions. This is defined
  by the terms
• Simplex
• Half-duplex
• Full-duplex
• Simplex
• The data flows in one direction only. This is
  like listening to the radio in your car, all the
  information flows to you. You don't send
  information back through the radio.
• Half-Duplex
• The data flows in two directions, but only not
  simultaneously. This is like a polite
  conversion. The first person talks while the
  second person listens. When the first person
  stop talking the second person is then free to
  talk, while the first person listens.

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Introduction to Networking, continued
Full-Duplex The data flows in both directions
simultaneously. Each side of the conversation
can listen and talk at the same time.
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Introduction to Networking, continued

• Background, revisited
• There are various ways that users can interact
  with a computer system.
• terminal to multi-user system
• PC to multi-user system
• PC on a network
• Terminal to multi-user computer
• A terminal is a specialized piece of hardware
  that contains the monitor and keyboard and some
  means of data transmission.
• The terminal has no processing or storage
  capabilities. It simply provides an interface to
  a multi-user, central computer system.
• All processing and storage is on the central
  computer.
• Predominate technology up to the mid to
  late-eighties.

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Introduction to Networking, continued
Terminal to multi-user computer
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Introduction to Networking, continued

• PC to multi-user computer
• Once PCs made their appearance in the workplace,
  they provided a means for users to perform some
  local processing and storage. However, the
  mainframe or multi-user system still provided
  centralized processing and storage, the PC was
  just an adjunct.
• Data is commonly transferred between the PC and
  the mainframe. To transfer from PC to mainframe
  is to upload, the reverse is to download.
• File transfers can be accomplished using
  standardized protocols such as Xmodem, Ymodem,
  Zmodem and Kermit.
• In this type of environment, the PC needs to run
  specialized software that emulates the older
  terminals. For UNIX systems the terminal type
  that is most commonly emulated is the VT100. For
  IBM mainframes, the 3270 terminal.
• VT100 - can be emulated using HyperTerminal
  (distributed with Windows)
• 3270 - can be emulated using IBM Communications
  Manager (licensed software)

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Introduction to Networking, continued
PC to multi-user computer
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Introduction to Networking, continued
PC on a network Although mainframe and multi-user
computers are still very much a part of business
today as they still outperform the best PCs.
However, by networking computers data can be
shared and processed outside of the
mainframe. The following sections deal with the
technology of networking.
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Introduction to Networking, continued

• Network topologies
• A computer can be connected to only one other
  computer, or it can be connected to a network of
  computers. The network can be laid out in
  different arrangements, or topologies.
• The topologies that we will look at are
• Star network
• Ring network
• Bus network
• There are variations on these networks.
• Star network
• A central computer is responsible for controlling
  all activity on the network. The workstations
  communicate with the central computer for all
  requests.
• The problem with this arrangement is if the
  central computer fails, the network fails. Also,
  the speed of the network will be restricted by
  the speed of the central computer.

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Introduction to Networking, continued
Ring network The computers are arranged in a
ring, where a computer only talks to the computer
beside it. The problem with this arrangement is
that if one computer fails, then the ring is
broken and the network fails. The advantage of
the ring network is that there is no risk that
messages will collide with each other (see Bus
Network). Bus network The computers are all
connected to a common line. Any computer can
talk to any other computer in this network. The
advantage of the bus network is that if any
computer fails, the network continues to operate.
The problem with this network is if more than
one machine sends a message at the same time
(collision). The problem of collisions is why
the ring network can support more computers than
the bus network.
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Introduction to Networking, continued
Network topologies, continued This is a diagram
of each of the network topologies
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Introduction to Networking, continued

• Classification of networks
• A network can be classified as either
• Wide Area Network (WAN)
• Local Area Network (LAN)
• A WAN refers to a network that spans a large
  geographic area, from the size of a city to a
  global network.
• A LAN refers to a network that spans a small
  geographic area, from an office to complex of
  buildings such as a school campus.
• Components of networks
• There are various devices that are part of
  connecting computers and networks together. The
  short list discussed here is
• Network Interface card
• Bridge
• Gateway
• Router

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Introduction to Networking, continued
Network Interface Card The Network Interface Card
(NIC) is used to connect a computer to a
particular type of network. An Ethernet NIC will
not run on a Token Ring network, and vice
versa. The wiring of the network is connected to
the NIC. Bridge A bridge is a means to connect
two similar networks. If a message is destined
for a computer on another network that is also
connected to bridge, the bridge will forward the
message onto the second network Gateway A
gateway is used to connect two dissimilar
networks. Some form of protocol conversion may
take place. Router A router is very much like a
bridge, and can even incorporate gateway
functions. However, it is more complex in that
it looks for ways to send traffic through a
network of networks, and find the best route for
the message.
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Introduction to Networking, continued
Sample network This is a diagram of the various
components of the network
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Introduction to Networking, continued
Protocols A protocol is a set of rules by which
communications are controlled. If a set of
computers use the same protocol, then they will
be able to communicate with each other. If the
protocol is standardized internationally, then
regardless of the computer system, and provided
the protocol was properly implemented then the
computer system will be able to communicate with
any other computer system that implements the
same protocol. The protocol for the Internet is
TCP/IP (Transmission Control Protocol / Internet
Protocol). Some other protocols are IPX/SPX,
NetBios, IEEE802.2, DECnet, AppleTalk
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Introduction to Networking, continued

• Protocols, continued
• There are protocols that allow for the TCP/IP
  protocol to be used over a serial connection (a
  modem). Two are mentioned here
• SLIP
• PPP
• SLIP
• Is an acronym for Serial Line Interface Protocol.
  This is an older protocol that supports TCP/IP
  only. The IP address of the PC as well as the IP
  address of the server that you are dialling into
  must be known. (more on IP Addresses later).
• PPP
• Is an acronym for Point-to-Point Protocol. This
  newer protocol supports TCP/IP as well as other
  protocols. Furthermore, multiple protocols can
  be running simultaneously through PPP (the term
  protocol stack refers to the protocols that are
  available/running on a machine). PPP will
  automatically configure itself during the
  connection to determine what IP address to use
  for the PC as well as the server.

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Introduction to Networking, continued

• TCP/IP Applications
• There are two TCP/IP applications that are
  commonly used. It is important to note that
  these applications are specific to TCP/IP
  networks. They are not defined for other
  protocols.
• The applications are
• telnet
• ftp
• Telnet
• Telnet is a terminal emulation package. This
  utility will be used in our labs when connecting
  to the RS/6000 (UNIX). Telnet will be configured
  to emulate a VT100 terminal.
• FTP
• FTP is an acronym for File Transfer Protocol.
  This application will also be used in our labs to
  transfer data between the PC and the RS/6000.

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Introduction to Networking, continued
IP Addresses In order to determine where a packet
needs to be sent, or where to send a response,
addresses are used. A TCP/IP address is normally
displayed in 'dotted-decimal' notation. The
address consists of 4 numbers (each between 1 and
254) separated by a period. For example
142.204.57.135 (the 0 and 255 values have
special meaning that will not be discussed
here) The following is an Instructor-led
in-class exercise to see these addresses in
action
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Introduction to Networking, continued

• IP Addresses, continued
• Determine what the IP address of your PC is
• Send a 'test' message to the Instructor's PC
• Send a 'test' message to 142.204.57.135
• Determine the route that your message took going
  to the Instructor's PC
• Determine the route that your message took going
  to 142.204.57.135

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Introduction to Networking, continued
The Internet This is a diagram of the Internet
(www.lumeta.com), colour coded by IP address
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Browsers and the Internet
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Browsers and the Internet
Background A browser is an application that
facilitates the displaying of information
retrieved from the Internet. Although many
people have surfed the web, not everybody has
learned some of the basic definitions used in the
web. This will be a general discussion of
terminology and structure of browsers, as well as
a brief look at search engines. I am making an
assumption that everybody is familiar with a GUI
interface, and know how to use scroll bars,
pull-down menus and buttons.
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Browsers and the Internet, continued
Browsers This is a diagram of a browser with the
parts labelled
Welcome Banner
Pull-down menus
Browser control panel
Buttons
Address window
Browser display window
Status line
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Browsers and the Internet, continued

• Browsers, continued
• There are terms used in the Internet, usually in
  conjunction with browsers.
• URL
• Frames
• Plug-ins
• Java
• Search engine
• These terms will be defined in the next few pages.

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Browsers and the Internet, continued
URL URL is an acronym for Uniform Resource
Locator. It is the name given to a particular
site or page within a site. The URL is composed
of The domain is structured as a
hierarchy of nodes, like a company's
organizational chart. At the top of the Internet
is the root node (symbol is '.', but nobody uses
it). The next level is the top-level domains
such as .com .ca .net. The last levels are used
to identify the company or name and then the
server or partition.
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Browsers and the Internet, continued
URL, continued The most common top level domains
are The following slides show the
progression from a file, to the top level domain
of ilearn.senecac.on.ca/homepage/Travis.Mander/i
ndex.html (this is representative only)
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Browsers and the Internet, continued
URL, continued ilearn.senecac.on.ca/homepage/Travi
s.Mander/index.html
www
ilearn
senecac
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Browsers and the Internet, continued
Frames Frames are means to subdivide the browser
display window into multiple, independently
control windows. In this example, there are five
frames in the browser display window.
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Browsers and the Internet, continued
Plug-ins Plug-ins are additional software modules
that can be hooked into the browser to enhance
its functionality. Some common plugins are
RealPlayer, Adobe Acrobat Reader,
Quicktime. To find out what plugins are
installed in a browser enter the following
command in the address window aboutplugins
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Browsers and the Internet, continued
Java Java is a programming language developed by
Sun Microsystems. It is very popular on the
Internet because it is platform
independent. Platform independent When a program
is written, it is usually targeted to run on a
specific operating system. For example if you
take an application that was written for the Mac
and try to run it on a Windows95 PC, it will not
run. Java is different, in that the Java code
can run on any machine IF it has a Java Virtual
Machine installed. The JVM is written for a
specific operating system. The Java code is
written to run on the JVM. Therefore any Java
programs can run any operating system.
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Browsers and the Internet, continued
Search engines The Internet is a vast landscape
(cyberscape?) of computers with useful and
useless data / information / misinformation,
etc. To try and find anything on the Internet is
an impossible task without some means to sift
through the sites and categorize the data. A
search engine provides this functionality
(assuming that you can find a site for a search
engine). Knowing how some of the search engines
behave will help you make intelligent decisions
as to which engine to use for which
purpose. Some engines try to catalogue all the
words it finds on the sites, others are research
based where people sift though the sites and
catalogue the sites using predefined criteria.
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Browsers and the Internet, continued

• Search engine types
• In general there are three classes of 'Search
  Engines'
• Directory
• Human researchers organize sites by content
  categories
• Search engine
• Software that resides at a site and uses a set of
  rules to automatically catalogue internet sites
• Metasearch site
• Software that searches 'search engines'

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Browsers and the Internet, continued
Search engines - Directories
Well-organized categories let user switch from
browsing to searching in a certain area. Finds
only keywords (not any word on any site).
NetGuide
Reviews entries before including, links to
articles written for NetGuide
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Browsers and the Internet, continued
Search engines - Search Engines
Very fast. Indexes every word of every page of
every site.
Good returns for simple searches. Provides
related hints and an array of extra content.
Provides directory as well.
Results ranked by algorithm based on number of
links from other pages
Fast. Unique search options let you restrict
searches. Very comprehensive. Excels at finding
current news
Searches newsgroups, FAQs and e-mail addresses.
Extras such as foreign language searches, and
searches by geographic regions
Numerous search options. Comprehensive
directory. Good returns on simple searches
Powerful and well organized. Groups results by
subject, type, source and language
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Browsers and the Internet, continued
Search engines - Metasearch Engines
Accepts search terms and submits to several
popular search engines eliminates duplicates and
ranks by relevancy
Well-designed, easy-to-use interface
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OSI Reference Model FOR INTEREST ONLY
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OSI Reference Model
Background The OSI Reference Model (Open Systems
Interconnection) was developed by the
International Standards Organization
(ISO). Protocols can be defined using this
model. There are 7 layers to the model. Each
layer solves a small portion of the problem of
getting data from one location to another,
independent of what technology exists at each end
of the communications link 7 - Application
Layer 6 - Presentation Layer 5 - Session Layer 4
- Transport Layer 3 - Network Layer 2 - Data Link
Layer 1 - Physical Layer It is not carved in
stone, it is a model to work towards when
creating a protocol. For example, TCP/IP has
only 4 layers. Some of the OSI layers are
combined into one TCP/IP layer (12 and 567).
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OSI Reference Model, continued
Application Layer Users interact with the
application layer. Presentation Layer Syntax and
representation of data is handled here (ASCII,
EBCDIC), encryption/decryption,
compression/decompression of data. Session
Layer Control mechanisms to establish, maintain
and synchronize communication. Control of Full
Duplex / Half Duplex sessions is an
example. Transport Layer Provides end-to-end
accountability through use of sequence numbers
and acknowledgements
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OSI Reference Model, continued
Network Layer Addresses are managed at this
layer, as well as routing and congestion
control. Data Link Layer Data packets are
encoded/decoded into bits. The bits are
transmitted in groups of bits called
frames. Physical Layer This layer maintains the
physical circuits between two devices. It
provides the means to send/receive data on a
carrier.