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Networking Overview
Frank Schneemann
This short PowerPoint Presentation is designed to
give you a general overview of how networks are,
most likely, set-up in your school.
Network Theory
Learning networks in one lesson is a daunting task. Still, it is important for
administrators to have at least a basic understanding of how networks work. After
you study the online tutorial on networks, the PowerPoints and notes below, you
should have a basic understanding of how networks work and how they can be
used in the educational environment.
Any time you connect at least two computers together, you have a computer
network. Computer networks allow you to share information and devices. A
classroom of the 21st century is no longer a classroom bounded by 4 walls.
Networks enable the teacher to expand their classroom to include the class next
door, the entire school, the entire district or even the world. The Internet is a
network of networks around the world that is built on the same basic principles as
the small computer network in your class.
Without communications, there is no education and computer networks enhance
our communication. Suppose you are teaching a unit in basic Spanish. How much
more rewarding is it to include students from another class at your school in the
dialogue between students? Why not dialogue with students from Spain or Mexico
City? Networks make that possible.
Types of Networks
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•
•
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Computer networks that cover a small geographic area, like a classroom or
building, are called LAN's (Local Area Networks).
Networks that cover a large geographic area are called WAN's (Wide Area
Networks)
Networks that cover a city are sometimes called MAN's (Metropolitan Area
Networks)
Networks that are interconnected with other networks all over the world are
called the Internet.
The key device that allows us to connect networks is the router. We will discuss
routers in more detail in a later lesson.
Networks allow us to share devices as well. Suppose you have one printer and ten
computers. You can attach the printer to one of the computers and share it with
all other computers. In fact you can use any printer in the school district to print
as long as that printer is shared. There are many other things that you can
share. You can share CD ROM's, documents, programs, faxes, connections to
the internet, scanners, hard drives, floppy drives, Zip drives; and the list goes
on.
.
Network Interface Card NIC
But before you can connect two or more computers together to form a network, you
must install an important piece of equipment, in each computer, called a Network
Interface Card (NIC)
Each NIC has a unique number installed on a memory chip at the factory when the
card is manufactured. No two network cards have the same number. This number
becomes the address of your computer on the network. We call this number the
MAC address or Media Access Control address.
Having an address on the network allows other users to find you on the network and
communicate with you.
ARP Table
Not only does your network card have it's own address but it is constantly
broadcasting that address to all of the other computers on the LAN. In turn, each
computer on the LAN maintains a table that lists the names and MAC addresses of
each computer on the local area network. The table is called an ARP table
(Address Resolution Protocol)..
When computer X wants to send information to computer Y it simply looks in its
ARP table for the address
Peer to Peer Networks
The basic difference between a peer to peer network and a server based network is
control. In a peer to peer network each computer is equal. Each computer keeps its
own programs and no one computer has control over other computers. You can
share information, printers and other devices in a peer to peer network but
otherwise all computers are equal
Server Based Network
In a server based network the server exercises some control. A server can control
who has access to the network and what things each user on the network can do.
A server can also hold programs that it can share with other users. You could
install one copy of Microsoft Word on a server and everyone on the network could
share it. You could also set up a mail system on a server so everyone can have an
email account
A server can be any computer on the network that is running server software such
as Microsoft Windows 2000 server. There is also a version of Windows 2000 called,
"2000 Professional" that is used as a workstation operating system
School Infratructures
The following graphics show how networks on most K12 schools are organized. The
following definitions might be helpful in understanding the graphics
Router
Used to connect
different
networks
together
Hubs and Switches
Used to connect
individual classroom
computers to the
backbone cabling
.
POP (Point of Presence)
Where the internet or outside
networks like district offices come into
the school
MDF (Main Distribution Facility)
The main wire facility or closet where
the main network devices are kept.
Most of the time the POP is located
here. May be a separate room or just
a rack on the library or main office
IDF (Intermediate Distribution
Facility)
Every building in the school should
have an IDF. It is a room or may be
just a rack in some room in the
building. The IDF’s are connected to
the MDF with “backbone” cabling or
wiring. The IDF sends wires out to
each classroom, called drops, where
a hub or switch is connected. The
individual classroom computers
connect into the hubs or switches.
Wireless LAN’s
Today many schools are using wireless LAN’s (Local Area Networks). The graphic
below shows how wireless LAN’s are most likely set up in a classroom or in your
home
The wireless
access point is
connected to the
rest of the school
with wires. But,
once inside the
classroom it be
becomes
wireless.
Computers
communicate with
the access point
with radio waves
Network Addressing
Every computer on a network has two addresses
Physical Address
IP Address
• The first address is called the MAC
address (Media Access Control)
• The second address is called
an IP address.
• The MAC address is on the network
card and is burned on at the factory
that made the NIC.
• The IP Address is a logical
address assigned by the
network administrator.
• No two MAC address can be the
same.
• It is entered into the computer
when you set the computer up
for the network.
Two Addresses for each computer on this small network
• Below are the logical IP addresses and physical MAC addresses of
each computer on the network
• The physical MAC address is a 24 bit hexadecimal number
• The logical IP address is a 4 byte number (32 bits long).
192.168.2.1
192.168.2.2
192.168.2.3
00 03 0a 00 3e 71
32 92 62 02 9e 69
22 7f a7 f2 4d 72
How the network keeps track of IP
addresses and MAC addresses
Every computer on the network has an ARP table in the memory of its
network card to keep track of the physical MAC address and IP address
Below is an actual ARP table from my computer. My IP address is
192.168.2.2
It contains the IP Address on the left and the physical (MAC) address on
the right of every computer on the network
Checking your own ARP Table
To check your own ARP table follow the steps below
• Click the Start Button on the bottom of the screen
• Click the Run button
• Type the word, Command, and a box will open up
• Type arp –a (arp space -a)
• Your ARP table should show
Every time you try to communicate with another computer on the network,
the address is added to your ARP table
Static vs Dynamic Addressing
There are two ways to assign an IP address to a computer.
1. Static Addressing - You can enter them by hand into each computer.
This is not the preferred method because it is tedious and open to many
errors in entering the numbers and keeping track of addresses.
2. Dynamic Addressing - Allow a server, called a DHCP server to enter them
for you.
How DHCP Servers Work
•
You install the server and
give it a bank of available IP
addresses
•
Every time a computer
comes on line it is assigned
a new address by the DHCP
server
Three Basic Types of Network Topology
(topology means the layout)
• Bus
• Star
• Token Ring
BUS ETHERNET NETWORK
Computers connected in a row using coaxial cable
BUS ETHERNET
In the illustration above, computer E sends a packet of
information to computer B.
In a BUS Network every computer on the network
receives the information but only computer B accepts it
because it has the right address.
This type of network is called ETHERNET.
STAR ETHERNET NETWORK
A STAR
network
performs the
same as a
BUS network
except the
computers
are
connected to
a central
port, such as
a hub or
switch
STAR ETHERNET
In a STAR ETHERNET network, every computer gets each
packet sent on the network but only the destination
computer accepts the packet
Hubs and Switches can be connected together in a
“Distributed Star Network”
STAR Ethernet NETWORK
Token Ring Networks
Only the
destination
computer gets
the packet
In a TOKEN RING network, a token circles around the
network and you have to wait grab the token before you can
transmit.
TOKEN RING HUB
T
A TOKEN RING
HUB looks like a
physical star but
inside the hub
the token circles
from computer
to computer and
you must grab
the token to
send a
message..
Network Cables
Coaxial Cable
Twisted Pair (Cat 5)
Fiber Optic
BUS ETHERNET NETWORK USING COAX
Computers connected in a row using coaxial cable
CAT5
CABLE
CAT 5 is the
most popular
type of
network cable
RJ45
Connector
FIBER OPTIC CABLE
How computers think and communicate.
Computers do not use words or letters to communicate and
think. Computers are like calculators, they only understand
numbers.
When a computer wants to process information the
information is converted into numbers. Computers use the
BINARY NUMBER SYSTEM
Binary Numbers
• The decimal number system has 10 numbers 0 1 2 3 4 5 6 7 8 9
• The binary number system has only 2 numbers 0 and 1
• Computers do not understand decimal numbers, they only understand
binary 1’s and 0’s
• An individual binary number (1 or 0) is called a bit
• A group of 8 bits are called a byte.
• Every character on your keyboard has a binary number associated
with it consisting of 8 bits or 1 byte.
• Any number that can be expressed in decimal can also be expressed
in binary.
• In binary the value of a number (1or 0) depends on its position in the
byte.
• Example: to the computer a capital A is the number
• 65 decimal or
• 01000001 binary
• Every other character on your keyboard has some number assiciated
with it
Try This!
•
Open MS Word
•
In MS Word, hold down the ALT key and press 65 on the number
keypad
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What happens?
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Try ALT and other numbers on the keypad.
•
These are the decimal equivalents of the binary numbers
associated with each key.
•
Each number you press on the keypad is equal to 1 byte
•
There is a table called, ASCII, which shows which byte represents
which keyboard character.
•
Click here for web ASCII code pages
Turning letters into pulses of electricity on
the network wire
When you sit at your computer writing an email, you are
typing letters that must be turned into 1’s and 0’s. The 1’s
and 0’s are called bits. These bits are turned into pulses
of electricity on the wires of the network. One way is for a
3 volt bit = 1 and 0 volt bit = 0
It is important that these bits have some order and
structure, otherwise the bits of your email will just blend
with the bits from other emails and you will have network
confusion on the wires. Where does your message end
and another message start ???
Your questions are welcome
[email protected]