Transcript IT 141: Information Systems I - Tonga Institute of Higher Education

Tonga Institute of Higher Education
IT 141: Information Systems
Lecture 9:
The Internet and
Networking
The network
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The network has enabled computers to
enter a new realm of effectiveness and
usability
It evolves rapidly and new terms are
always being introduced
In this chapter we will learn about:
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Networking Basics
Internet basics
Internet access
LANs – Local Area Networks
Sending Data
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People realized early on how useful
computers could be if they could
send data to other computers.
In 1948, Claude Shannon made a
model of communications which we
still use today
Communications model
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In this model of communication:
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Data starts from its source
It is encoded
Transmitted over some sort of network
Received by its recipient
Decoded
There may also be “noise” which means the data
might be changed while being sent.
It is important to make sure all the data sent is
the right data. Most "protocols" (ways of sending
data) have ways that check for errors.
Encoding and Decoding
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The data has to be encoded before
being sent.
For computers, this means they
must be encoded into binary.
We have already seen one type of
encoding, it is called ASCII.
Characters are encoded into binary
in ASCII
How is data sent through a network
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When data is transmitted (sent) it is
usually sent by electromagnetic signals
This means the data will take different
forms depending on the transmitter and
receiver. For example, electronic voltages,
radio waves, light waves or phone tones.
To get the Internet in Tonga, think about
all the different connections.
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Ethernet cables, satellites, underwater cables,
phone lines
Network Links
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A “communications channel” is the
way data will travel through a
network.
Computers use many different types
of methods (channels) to send data
to the correct destination.
Types of Links
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Twisted Pair cable – 4 copper wires twisted
around each other. These are what are
used for phone lines and Ethernet cables.
They will end in a RJ-45 plug for Ethernet,
or RJ-11 for a phone line
Coax Cable – one wire that is surrounded
by insulators to reduce data loss. Used for
cable television and modems sometimes
Fiber optic – A bundle of extremely small
glass tubes. They do not use electric
signals like the other cables, but use lasers
instead. They are very fast and expensive
Cable-less Types of Links
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Radio – Uses what is called RF signals (radio
waves). Sent and received with a transceiver (a
transmitter and receiver combined)
Microwaves – These can carry a lot of data, but
need a direct line of sight to work well
Because radio and micro waves cannot bend to go
around the curve of the earth, satellites are used
in space to transmit signals around the globe
Infrared light – uses light waves to transmit data.
Only good for very short distances with clear line
of sight
Bandwidth
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Bandwidth the word describe how much
data can be transmitted over a network
link over a certain amount of time
If the network is slow your "bandwidth" is
small. To get a faster speed you may
need to purchase a higher speed to obtain
more bandwidth.
If something has a lot of bandwidth it is
called broadband (Ethernet networks,
cable TV)
If it has little bandwidth, it is called
narrowband (phone lines, infrared)
Network topology
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Network topology is how the computers
connected together.
1) Star topology 2) Bus topology 3) Ring
topology
Ethernet networks use the Star Topology
because there is a hub/switch that connects the
devices together
Ethernet vs. Token Ring
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Ethernet is the name for the way most
networks are configured today.
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Packets are broadcasted over the whole
network.
If two packets run into each other, the
Ethernet will allow them to resend them again
Token Ring – older network configuration.
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It is slower.
To prevent collisions of data, it uses a “token.”
If a packet has the token, then it has priority
to send itself. Then another packet uses that
token to send data.
Network Organization
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Workgroup (Peer-to-Peer)
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A workgroup is a group of computer connected
by a LAN, but not sharing similar information,
like usernames and passwords.
This is commonly used in networks with less
than five computers where each user has their
own computer
Domain (Client-Server)
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A domain allows all computers to be a part of a
group that shares usernames, passwords and
various settings.
This allows a user to log into any computer on
a network with the same password, as well as
using the same settings
Things in a network
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A node – A single device connected to a network is
called a node
Modem – uses phone lines to transmit data over a
network
Network Interface Card – a peripheral to connect to a
local area network with Ethernet cable.
Servers – a computer that provides services for other
computers on a network
Hub/Switch – a device that connects nodes on a
network together (hub slow, switch fast)
Router – connects two different networks together
(like a local network and the internet)
Repeater – amplifies signals on a network so that
they don’t lose data to noise
Routers
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Routers are similar to
hubs in that they connect
networks together, but
routers are used to
connect different
networks together.
Most of the time, you will
use a router to connect
your network to the
Internet.
It is a special device that
determines where the
data should go on your
network. Either to the
internet (or another
network) or stay inside
your LAN
ROUTER
HUB
Network Addresses
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Every node on a network has at
least one address so that other
nodes know how to send data to it.
A node may have other addresses
depending on the protocols it uses.
Address:
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Physical Address (network address,
MAC address)
Logical Address (IP address)
Domain Name
Physical Addresses
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A physical address is built into the
hardware of a network interface
card (NIC). This address may also
be called the MAC address.
Every NIC has a unique physical
address. No other device will share
the same address.
The Logical Address - IP Addresses
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Besides the physical address, a computer needs a
logical address that is used by the operating
system and software in order to connect to other
computers.
IP addresses are the way that computers know
where to send data. Every computer on a network
has a different IP address
The IP address is a series of numbers like
192.168.0.2
Each number can range from 0-255, which means
each part is 8 bits (2^8 = 256). Since there are 4
parts, each IP address uses 32 bits.
How many IP addresses can be used on the
internet? Just over 4 billion.
Dynamic and Static IPs
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If your IP address does not ever change,
it is static.
Usually servers and websites will have
static IP addresses because other
computers always need to know where to
find them
A dynamic IP address will change every
time you connect to the internet. Usually,
if you connect to the internet through a
modem, you will have a dynamic IP
If you have a dynamic IP, you can’t have
a server on your computer
Domain Names
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Computers may be able to remember and
use IP addresses easily, but people have
trouble remembering long numbers
Domain names were invented so people
have an easier time remembering the
location of a server
A domain name will “map” an IP address
to a name
Our domain name is tihe.org and our IP
address is 209.58.72.33.
Domain names will end in an extension
that indicates something called the ‘toplevel’ domain.
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Example: .org, .to., .net
Communications Protocol
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Protocol – a set of rules for
communicating (talking). Commonly used
to describe how computers send data
over a network link
Protocols for computers decide important
things like
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Starting and ending transmissions
Transmission errors
The speed of data transmission
How to format data
TCP/IP and Network Protocols
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The most popular communications protocol is
called TCP/IP (transmission control protocol /
Internet protocol)
It is used for transferring websites and email
because it is able to safely send data without error.
All computers that use TCP/IP know how to
communicate with each other, even if they use
different operating systems or are located in
different countries.
All modern networks use TCP/IP to transmit most
data.
Other protocols commonly used are
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UDP – for sending data quickly without checking for
errors
ICMP – for checking connections between computers
Packets
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Most communication protocols will
divide data into small pieces, called
packets, when sending over a
network link
Packets contain the actual data, the
destination address, and the
address of the sender
The receiver will wait until all the
packets are received and then
process the data
Why packets?
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Why break up data into small parts?
When people designed networks, they
realized if data pieces were smaller it
would be easier to manage. If one packet
was lost it could be easily resent.
If a big file was sent all at once and there
was an error in the data, you’d have to
send the whole big data file again
With packets you just send small little
pieces of data
Internet Words
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The Internet – the global, public network that
handles web sites, email and other data
transmission
LAN – Local area network – a small network in
one location
VPN (virtual private network) – allows access to a
LAN from the internet with a password.
WAN – wide area network – a network that covers
a lot of space. The biggest WAN is the Internet
Root Servers – a group of very powerful
computers that know where to send all data on
the Internet
The Internet
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Started in 1969 as a U.S. government program to
link computers together.
At first, only a few people, mostly scientists and
professors, had access to the internet.
They knew the addresses of the computers that
they wanted to connect to.
There were no search engines and websites. The
Internet only provided a way to connect to
different computers separated by a great
distance.
By 1990, the Internet was becoming more userfriendly.
Now there are at least 100 million computers on
the Internet and there are popular protocols for
sending email, accessing websites and
transferring data
ISPs – Internet Service Providers
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To connect to the internet, you need an ISP.
Typically you can connect through a phone line,
satellite, TV cable or a special direct line
The ISP will have equipment like email servers,
modems to connect users and a router to connect to
the rest of the internet.
NSPs
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ISPs then connect to Network
Service Providers (NSPs).
These are big telecommunications
companies that provide access to
the fast fiber optic cables that make
up the "backbone" of the Internet.
They might also connect through
satellites, phone lines, TV cable
lines, along with fiber optic lines
How is data transferred
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Your computer connects to your ISP's LAN
through a phone line. When that happens your
computer is able to use their network resources
This means you can use their router to connect to
the NSP. The NSP will forward your data to the
correct place and you will receive a reply
Your data can be sent using one of many types of
protocols for transferring data.
One of the most popular is TCP/IP which breaks
the data into packets and formats it in a certain
way.
TCP/IP is used whenever a connection must be
established between two places. For example, to
make sure email is correctly sent both computers
must connect and talk to each other successively
before the email can be transferred.
Other Protocols
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TCP/IP is the foundation of most other protocols. It is
responsible for breaking data and sending it over long
distances.
There are other protocols (see below) that work to help
communication between different services.
For example, a web browser and a web server use HTTP in
order to discuss how to retrieve web pages. The information
they use to communicate is then broken up according to the
TCP/IP protocol and then sent
Domain Name Servers
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The Internet would not be popular without easy to remember
names.
Every computer on the Internet needs an IP address, but
numbers are hard to remember, so Domain Name Servers
(DNS) provide a way for you to turn a name into an IP
address or an IP address into a name.
With this service, you can type in a name, your computer
than asks a DNS server for the IP, gets an IP, then sends the
data to that IP address
Connecting to the Internet - Modems
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The most common way to get on the
internet is through a modem
A modem will dial an ISP over a regular
phone line. The ISP will have a
computer pick up the phone call.
The ISP will then send your data
through its network service provider
Modem Speeds
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Modem speed is measured in
“baud” rate, or the number of bits it
can send per second over the phone
line.
There is a maximum baud rate of
56 Kbps, but the speed also relies
on the quality of the phone lines
and the connection
Most of the time, you will not be
able to go faster than 44Kbps for
downloads
Direct Connections (DSL,ISDN,T1,T3)
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Your internet session will last only until
you disconnect with a modem.
Newer technology lets your computer
always be connected to the internet.
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ISDN – direct connection using special phone
lines
DSL – digital subscriber line – carries your
data over existing phone lines, but much faster
T1/T3 – Very expensive, very fast. You have to
lease cable lines from the phone company for
this connection.
LAN Security
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If your network or computer is always connected
to the internet, your computer might be vulnerable
to hackers (someone who tries to take over control
of your computer)
One way to protect your network is with a
"firewall"
A firewall is a device (or computer) that examines
all data coming into a network link and decides
whether to allow it to pass through or deny it.
Hackers need to send data to computers in order
to take over. If it cannot send data, it cannot take
over the computer
Setting up a simple LAN
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Setting up a LAN is not difficult.
First you must connect each computer
with an Ethernet cable to a hub/switch.
When you make a successful connection
(and your cable is good) you will see a
light appear on the hub.
You must do this for the other computers
as well
After physically connecting, you must
change the network configuration on each
computer to the accurate information so
each computer can connect
Changing network properties
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After you log onto
the Windows XP
computer, go to
Start -> Control
Panel -> Network
Connections
This will allow you
to view and
change network
configuration
information
Changing Network Settings
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With network
connections open,
you will see a
picture that
represents your
Ethernet Card.
It will give the
name of your
Ethernet Card and
tell if it is
connected properly
or not.
When you doubleclick on this you
can change
important settings
Changing Network Settings
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You can view your
network settings
by looking at the
support option.
This will tell you
things like IP
address, gateway
and netmask.
If you look at
“Details,” you can
see even more
information about
your settings.
Changing Network
Settings
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When you
are ready to
change the
settings, go
to Properties
and then
look at
“Internet
Protocol
(TCP/IP)”
What numbers should I put in?
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Click on “Use the following IP address”
This allows you to enter the IP address
Because you will be making a private LAN, you
should use the following form: “192.168.0.x”
This is a set of numbers that is reserved just for
LANs
Usually the server on a network has the first
number (192.168.0.1) and other computers come
after. You are free to use any numbers between 1254. If you use 0 or 255, there could be problems
For the first computer, use 192.168.0.1 and the
second, 192.168.0.2
What numbers should I put in?
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For the netmask, you should use 255.255.255.0.
You will almost always use this number for all
networks.
It is not necessary to have a gateway
You only need a gateway if you will be connecting your
LAN to the Internet. The gateway is another word for
your router, and the gateway number is the IP address
of your router.
This router IP address is used when data will not travel
to another computer on your LAN. Your computer will
determine that the data must be sent to another
network and it will then use the router
The same goes for DNS. You can leave both blank
unless you are using the Internet. If you are using the
Internet you will get these IP numbers from your
Internet provider (ISP).
Static and Dynamic IP addresses
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Why is there a button that says, “Obtain IP address
automatically” and “Use the following IP address”
If you obtain an IP address automatically, it means that
you are using a Dynamic IP address.
This means that your IP address will change every time
the computer starts
Where does it get the IP from?
A server will give computers IP address. This service is
called “DHCP” and it means that when a computer
starts, it will ask a server for an IP address
Then the server will give it one.
When you put the numbers in yourself, it means that
you are using a Static IP address (because it will not
change)
Checking Networks
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After we enter the numbers and press “OK” how do we
know if the network is working?
The first thing to check is that the IP was set correctly
and the computer accepts it.
We can use a program from the command line called
“ipconfig” to check the IP settings
Checking Networks
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We also want to check to see if the network is working.
How can we tell if computers are talking to each other?
There is a program called “ping” that we use to check
a network connection
It sends a little piece of data to another computer. If
the computer gets it, the computer will respond.
This will show you if the network is correctly set up
Summary
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Network physical structure and
communications protocol
How the internet works
TCP/IP and domain names
Connection devices
LANs