Transcript Introduction to computer networks and network topologies

Introduction to Computer Networks
Chapter 2
INTRODUCTION TO COMPUTER
NETWORKS
Learning outcomes
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The difference between networks and internets
The difference between logical and physical
addresses
What is a protocol in the context of computer
networking
How protocols are used on remote computers to
communicate easily
Explain the concept of layering
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OSI ,
TCP/IP and
hybrid models
Reading
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Joe Casad, Teach Yourself TCP/IP, Chs 1-2
William Buchana, Mastering the Internet, Ch. 3
Neil Briscoe, Understanding the 7-layer OSI model, July 2000.
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http://pcnetworkadvisor.com
Julian Moss, Understanding TCP/IP (first part September 1997)
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http://pcnetworkadvisor.com
What is a network?
A network consists of two or more computers
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connected by network media
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.i.e cables, telephone lines, radio waves
share the same resources such as database, printer
Exchange files
Exchange electronic message between each others
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Email
Example of a simple network
How are they linked?
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Computers on a
network may be linked
through:
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cables,
telephone lines,
radio waves, satellites or
wireless technologies
An example of a network
Router
Hub
Bridge
Hub
Internet
Segment
Node
Introduction to Computer Networks
Applications of Networks
Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files, databases)
Search Capability (WWW)
Communication
Email
Message broadcast
Remote computing
Distributed processing (GRID Computing)
Categories of networks
Local Area Network
• A LAN is a network that is used for communicating among
computer devices, usually within an office building or
home
• LAN’s enable the sharing of resources such as files or
hardware devices that may be needed by multiple users
• Is limited in size, typically spanning a few hundred
meters, and no more than a mile
• Is very fast, with speeds from 10 Mbps to 10 Gbps
• Requires very little wiring, typically a single cable
connecting to each device
• Has lower cost compared to MAN’s or WAN’s
LAN
LAN (Continued)
Metropolitan-Area Networks (MAN)
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MAN is designed extended over an entire city.
• May be wholly owned and operated by a private company, or it
may be a service provided by a public company, such as a local
telephone company.
Wide-Area Networks (WAN)
•Provides long-distance transmission of data, voice, image, and video
information over large geographic areas
WAN (Continued)
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WANs connect larger
areas, such as whole
states, or even the world.
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Transoceanic cables and
satellites are used to
connect WANs
Topology
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The physical topology of a network refers to the
configuration of cables, computers and other
peripherals.
The main types of network topologies are:
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Linear Bus
Star
Ring
Tree or Hybrid
Linear Bus topology
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A linear bus topology consists of a main run of cable
with a terminator at each end. All servers workstations
and peripherals are connected to the linear cable
Star topology
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A star network is
designed with each
node (file server,
workstation,
peripheral) connected
directly to a central
network hub or server
Ring topology
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A ring network is one
where all workstations
and other devices are
connected in a
continuous loop. There
is no central server
Tree or hybrid topology
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A tree or hybrid
topology combines
characteristics of linear
bus and star and/or
ring topologies.
It consists of groups of
star-configured
workstations connected
to a linear bus
backbone cable
Network Operating Software
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Network operating systems coordinate the activities of
multiple computers across a
network
The two major types of
network OS are:
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Peer-to-peer
Client/server
Peer to peer network OS
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In peer to peer network OS, there is no
file server or central management source;
all computers are considered equal
Peer to peer networks are design
primarily for small to medium LANS
AppleShare and Windows for
Workgroups are examples of programs
that can function as peer to peer
Client/Server network OS
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Client/server network OS
centralise functions and
applications in one or more
dedicated file servers.
The file server provides access to
resources and provides security
Novel Netware and Windows NT
Server are examples of
client/server network operating
systems
Network Hardware and Physical
Media
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Network hardware
includes:
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Computers
Peripherals
Interface cards and
Other equipment needed
to perform data
processing and
communications within
the network
File servers
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A very fast computer
with a large amount of
RAM and storage space
along with a fast
network interface card
The network operating
system software resides
on this computer
Workstations
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All computers
connected to the file
server on a network are
called workstations
Network interface cards
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The network interface card
(NIC) provides the physical
connection between the network
and the computer workstation.
Most NICs are internal with the
card fitting into an expansion
slot in the computer.
Three common network
interface connections are
Ethernet cards, Local Talk
connectors and Token Ring
cards
Ethernet cards
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The most common
Network Interface
Cards are Ethernet
cards
They contain
connections for either
coaxial or twisted pair
cables, or both
Co-axial
cable
Twisted
pair cable
Concentrators / Hubs
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A concentrator is a
device that provides a
central connection point
for cables from
workstations, servers
and peripherals
Hubs are multi-slot
concentrators
Switches
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hubs provide an easy way to
scale up and shorten the
distance that the packets must
travel to get from one node to
another
they do not break up the actual
network into discrete segments.
That is where switches come in.
Switches (continued)
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A vital difference between a hub and a switch is
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all the nodes connected to a hub share the bandwidth among themselves.
while a device connected to a switch port has the full bandwidth all to itself.
Think of a switch as a ‘clever’ hub
Repeaters
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A signal loses strength as it passes along a
cable, so it is often necessary to boost the
signal with a device called a repeater
A repeater might be a separate device, or
might be part of a concentrator
Bridges
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A bridge is a device that allows you to
segment a large network into two
smaller, more efficient networks
An example of a network with a bridge
Router
Hub
Bridge
Hub
Internet
Segment
Node
Routers
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A router translates information from one network to
another
The router directs traffic to prevent “head-on”
collisions
If you have a LAN that you want to connect to the
Internet, you will need a router to serve as the
translator between information on your LAN and the
Internet
Routers (continued)
Physical Media
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Physical media provide the connections
between network devices that make
networking possible
There are four main types of physical media
in widespread use today:
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Coaxial Cable
Twisted Pair
Fiber Optic Cable
Wireless Media
LAN Technologies
Ethernet
Physical Media :10 Base5
10 Base2
10 BaseT
10 BaseFL
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Thick Co-axial Cable with Bus Topology
Thin Co-axial Cable with Bus Topology
UTP Cat 3/5 with Tree Topology
Multimode/Singlemode Fiber with Tree
Topology
Maximum Segment Length
10 Base5
10 Base2
10 BaseT
- 500 m with at most 4 repeaters (Use Bridge to extend
the network)
- 185 m with at most 4 repeaters (Use Bridge to extend
the network)
- 100 m with at most 4 hubs (Use Switch to extend the
network)
Thick Coaxial Cable
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Used in the first Ethernet networks
Type RG-11 / 10Base5
Usually orange/black
Thickness of a small garden hose
Very expensive and heavy cable
Two strands along the axis
Conductor down the center
Insulator surrounds conductor
Shielded mesh serves as outside
Thin Coaxial Cable
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Alternative to Thick Ethernet Cable
Type RG-58 / 10Base2 / “Cheapnet”
Usually black
Thickness of a pencil
More flexible than thick Ethernet
Reduced the cost of the cabling
Flexible
Coaxial cable connectors
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The most common type of connector used
with coaxial cables is the BNC connector
Twisted Pair Cable
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Phone Systems
Twisted Pair Cable consists of two copper
wires, usually twisted around each other to
cancel out any noise in the circuit
Two main type of Twisted Pair Cabling
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Shielded Twisted Pair (STP)
Unshielded Twisted Pair (UTP)
Shielded Twisted Pair (STP)
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STP is the original media used for token ring networks
STP can be used for high-speed networks, such as FDDI or ATM,
where shielding is important.
RJ-45
Unshielded Twisted Pair (UTP)
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UTP has four pairs of wires inside the jacket
Each pair is twisted with a different number of twists per
inch to help eliminate interference from adjacent pairs
UTP (Continued)
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Most commonly used twisted pair cable
Uses common telephone wire
UTP was standardized by the IEEE 802.3
committee in October of 1990
UTP for LANs is now classified as:
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Category 3 - used for LANs up to 10 Mbps
Category 4 - used for LANs up to 16 Mbps
Category 5 - used for LANs up to 100 Mbps
Fiber Optic Cable
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Fiber optic cabling consists of a center glass core
surrounded by several layers of protective materials
It transmits light rather than electronic signals
It is the standard for connecting networks between
buildings, due to its immunity to the effects of moisture
and light
Fiber Optic (continued)
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Fiber optic cable has the ability to transmit signals over
much longer distances than coaxial or twisted pair
It can also carry information at vastly greater speeds
Fiber optic cable is more difficult to install than other
cabling
Wireless LANS
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Wireless networks use high frequency radio signals to
communicate between the workstations and the fileserver or
hubs.
Disadvantages of wireless networks are:
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they are expensive (relatively),
provide poor security,
are susceptible to interference and
are slower than cabled networks
Introduction network Protocol
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A protocol is a set of rules that
governs the communications
between computers on a
network
These rules include guidelines
that regulate:
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the method of access,
types of cabling and
speed of size data transfer
PROTOCOL =
SET OF RULES
ABOUT
COMMUNICATIONS
BETWEEN
NETWORKS!
The most common protocols are:
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Ethernet
Local Talk
Token Ring
FDDI
ATM
Protocol = a formal
description of a set of
rules and conventions
that govern how
devices on a network
exchange information
Did you ever wonder what HTTP in web addresses was about? It stands
HyperText Transfer Protocol
Ethernet
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Most widely used
Uses an access method
called CSMA/CD (Carrier
Sense Multiple
Access/Collision Detection
What does that mean?
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Each computer in the network ‘listens’ to the cable
before sending anything through the network. If the
network is clear, the computer will transmit.
If another computer is already transmitting on the
cable, the computer will wait and try again when the
line is clear
A bit like waiting for some one to get
off the telephone
Ethernet (continued)
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A collision happens if two computers attempt to transmit at the
same time.
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Each computer then backs off and waits a random amount of time
before attempting to retransmit
.It is normal to have collisions using this method,
but the delays caused by collisions and transmissions is small, and
does not effect speed of transmission on the network
CSMA/CD =Carrier
Sense Multiple
Access /Collision
Detection
Ethernet (continued)
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Ethernet protocol
allows for data to be
transmitted over twisted
pair, coaxial or fiber
optic cable at a speed
of 10 Mbps
(more on that later)
Fast Ethernet
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To allow for faster transmission, the Ethernet
protocol has developed a new standard that
supports 100 Mbps
Fast Ethernet requires the use of more expensive
equipment and network cards
Gigabit Ethernet
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The Ethernet protocol has also developed a
new standard that allows transmission of 1
Gbps (gigabit per second)
One gigabit per
second = one
thousand
megabits per
second
Local Talk
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Local Talk is a network protocol that was developed
by Apple for Macintosh computers
Local Talk uses the CSMA/CA
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Carrier Sense Multiple Access with Collision Avoidance
It works in a similar way to CSMA/CD
It is a lot slower than Ethernet (only 230 Kbps)
Token Ring
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Token ring protocol
involves ‘tokenpassing’.
It is not as popular
as Ethernet protocol
A single electronic ‘token’
moves around the ring from
one computer to the next. If a
computer wishes to transit
and receives an empty token,
it attaches data to the token
which then proceeds around
the ring until it comes to the
computer the data is meant
for.
FDDI
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Stands for Fiber
Distributed Data
Interface
Is used mainly to
connect two or more
LANs, often over large
distances
Can operate over fiber
optic cable at 100 Mbps
ATM- Asynchronous Transfer Mode
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Transmit data at a speed of 155 Mbps and higher
Works by transmitting all data in small packets of
fixed size (other protocols transfer variable size
packets)
Like FDDI , is most often used to connect two or
more LANs
Where does TCP/IP fit into all this?
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TCP/IP is the protocol that is used for the
transmission of information over the Internet
IP (Internet Protocol) - the main delivery system for
information over the Internet
TCP (Transport Control Protocol) - used to break
apart and rebuild information that travels over the
Internet
In Chapter 3 We will look into this protocol in details.