Transcript No Slide Title

Introduction to Computer Networks
Training & Development Department
Agenda
Introduction.
Types of Networks.
Clients and Servers.
Network Topologies.
Internet and Intranet.
Network Hardware and Software.
Review.
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Purpose
As part of the job you may be required to use a TTC network
to perform duties such as:
• Remotely monitor a system.
• Work with data.
• Run diagnostics.
The purpose of this course is to introduce and familiarize you
with the basic aspects of computer networks and how they
relate to the TTC networks.
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Computer Networks
INTRODUCTION
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Introduction.
Networks
Two or more computers connected together in a way that
allows resource sharing.
• A network contains any combination of computers,
computer terminals, printers, display devices, cables, or
wireless connections.
• A network is a collection of computers or other hardware
devices that are connected together using special
hardware and software. This allows them to share
information and cooperate.
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Introduction.
Resources
Resources may be:
• Files.
• Folders.
• Printers.
• Memory.
• Applications.
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Introduction.
Computer networking
Advantages
Disadvantages
Communication between computer Access restrictions
processing units (CPUs)
Data sharing
Server failures
Hardware sharing
Privacy concerns
Internet access
Security threats
Data management
Redundancy
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Computer Networks
TYPES OF NETWORKS
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Types of Networks.
Network types
Computer networks vary in shape (topology) and size
depending on their application.
Some of the major types are:
• Local area networks (LANs).
• Wide area networks (WANs).
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Types of Networks.
Local area networks (wireless and wired)
• Span a small geographic area.
• Usually confined to a
building, a group of buildings,
or a vehicle, for example
a train or a streetcar.
• Data travels between network
devices via network
cables (LANs) or wireless
signals (WLANs).
• The most common types are
Ethernet and Wi-Fi.
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Types of Networks.
Wide area networks (WAN)
• A WAN is a computer network that covers a large area
(any network whose communication links across
metropolitan, regional, or national boundaries).
• A network that uses routers, modems, and public
communication links.
• The world’s largest WAN is the Internet.
• WANs are used to connect LANs and other types of
networks together, so that users and computers in one
location can communicate with users and computers in
other locations.
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Types of Networks.
WAN
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Computer Networks
CLIENTS AND SERVERS
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Clients and Servers.
Servers
• A server is a core
component of the network,
providing access to the
resources.
• The access it provides
could be to a resource
existing on the server itself
or a resource on a client
computer.
• The server assigns IP
addresses to each
resource.
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Clients and Servers.
IP addresses
• IP stands for Internet Protocol.
• IP addresses serve as the location of
websites on the Internet as well as
workstations that are connected to the
network.
• IP addresses are made up of four sets of
numbers called “octets.”
• There are two types of IP addresses:
‒ Static IP addresses.
‒ Temporary IP addresses.
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Clients and Servers.
Static IP addresses
• Located on servers and do
not change.
• Example:
The HVAC units on the
Toronto Rocket have a static
IP address on the Train
Information Network (TIN).
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Car
Number
HVAC
position
IP
address
1
1
10.0.1.5
1
2
10.0.1.26
2
1
10.0.2.5
2
2
10.0.2.22
3
1
10.0.3.5
3
2
10.0.3.22
4
1
10.0.4.5
4
2
10.0.4.22
5
1
10.0.5.5
5
2
10.0.5.22
6
1
10.0.6.5
6
2
10.0.6.26
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Clients and Servers.
Temporary IP addresses
• A device connected to the network
is assigned a new IP address each
time it is logged on.
• Assigned by an Internet Service
Provider (ISP) each time a
computer is logged on to the
network.
‒ On the TIN, the Train
Information Management
System (TIMS) assigns a
temporary IP to laptops
connected to the Ethernet.
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Clients and Servers.
Client
• Clients are computers/devices that request and receive
information over a network.
• Client computers can also depend on the central server for
processing activities.
‒ For example a laptop running diagnostics on trains.
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Clients and Servers.
Client/server networking
• A client/server network is a system where one or more
computer called a client connects to a central computer
called a server to share or use resources.
• A computer network is referred to as a client/server if, at
least, one of the computers is used to “serve” other
computers referred to as “clients.”
• Many types of devices can be part of the network; e.g.,
scanners, printers, laptops–portable test equipment (PTE),
and desktop computers.
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Clients and Servers.
Client/server networking
• In a client/server network, each computer can store
resources and files. Clients can also access resources
stored on other clients.
• Most files and resources are centralized. This means that
one computer (the server) stores them and other
computers (the clients) access them.
• The server is always on, allowing any client to access files
and resources even if the other clients (computers) are off.
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Clients and Servers.
The relationship between a client and a
server
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Computer Networks
NETWORK TOPOLOGIES
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Network Topologies.
Network topologies
Network topology refers to the shape of a network, or the
network’s layout. A network’s topology determines how
different devices in a network are connected to each other
and how they communicate.
The different network topologies are as follows:
• Bus.
• Hybrid.
• Star.
• Mesh.
• Ring.
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Network Topologies.
Network topologies
Physical topology
The physical structure of the network.
The layout of the cables and connections between the
network components.
Logical topology
Defined by the network protocols and explains how data
travels across the cables.
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Network Topologies.
Bus topology
• All devices are connected to a central cable, called a bus
or a backbone.
• The simplest physical topology–least amount of cables–but
also covers the shortest distance.
• There are terminators at each end of the bus that stop the
signals and keep them from travelling backwards.
• All computers share the same data and address path.
Messages pass through the central cable and each
computer checks to see if the message is addressed to
itself. If the address of the message matches the
computer’s address, the network adapter copies the
message to the card’s on-board memory.
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Information flow
BUS TOPOLOGY
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Network Topologies.
Ring topology
• All devices are connected to
one another in the shape of
a closed loop.
• Each device is connected
directly to two other
devices, one on either side
of it.
• An equivalent system exists
on the trains (TIN) and on
streetcars (the Streetcar
Network).
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Information flow
RING TOPOLOGY
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Ring topology on the Toronto Rocket
RING TOPOLOGY
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Network Topologies.
On the train: ring switch
• Contains the network software.
• Assigns IP addresses.
• Enables communication over
the TIN.
• Routes the signals to the TIMS
for monitoring.
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Network Topologies.
On the streetcar: ring switch
• Contains the network software.
• Assigns IP addresses.
• Enables communication
over the streetcar network.
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Network Topologies.
Star topology
• Devices are not directly connected to each other, rather
through a central hub.
• Devices communicate across the network by passing data
through the hub or switch.
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Information flow
STAR TOPOLOGY
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Network Topologies.
Mesh topology
• The simplest logical topology in terms of data flow, and
the most complex topology in terms of physical design.
• Each device is connected to every other device.
• This topology is rarely found in LANs, mainly because of
the complexity of the cabling.
• Because of its design, the physical mesh topology is very
expensive to install and maintain.
• The advantage you get from mesh topology is that it has a
high fault tolerance.
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Information flow
MESH TOPOLOGY
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Network Topologies.
Hybrid topology
A hybrid topology is produced when two, or more different
basic network topologies are connected (bus, star, ring).
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Computer Networks
INTERNET AND INTRANET
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Internet and Intranet.
Internet vs. intranet
Internet
A worldwide system of computer networks. A network of
networks in which users at any one computer, with the
necessary permissions, can get information from any other
computer.
The most commonly used protocol is TCP/IP, it stands for:
TCP/IP
Transmission Control Protocol
Internet Protocol
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Internet and Intranet.
Internet protocol
The most common network protocol in public use is the IP.
• The basic protocol that enables home computing devices
and LANs across the Internet to communicate with each
other.
• Works well for moving individual messages from one
network to another.
• TCP allows continuous transmission of data (streaming).
• The two protocols are almost always paired together and
are known as TCP/IP.
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Internet and Intranet.
Internet vs. intranet
Intranet
• A self-contained private network.
• It may consist of many interlinked local area networks and
also use leased lines in a wide area network.
• Uses TCP/IP, hypertext transfer protocol (HTTP) and other
Internet protocols.
• Companies can send messages through the public
network, using encryption/decryption and other security
safeguards to connect one part of the intranet to another.
‒ http://intranet.int.ttc.ca/Pages/default.aspx
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Internet and Intranet.
Network/communication protocols
A protocol is simply an agreed on set of rules and procedures
for transmitting data between two or more devices.
Hundreds of different protocols have been developed, each
designed for specific purposes and environments.
The protocol defines:
• How the sending device indicates it has finished sending
the message.
• How the receiving device indicates it has received the
message.
• How data is transmitted from source to destination.
• The type of error checking to be used.
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Internet and Intranet.
Network protocols
• Network protocols are
layered such that each one
relies on the protocols that
underlie it. Sometimes
referred to as the protocol
stack.
• Both TCP and IP operate
somewhere in the middle
of a network protocol
stack.
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Internet and Intranet.
The Open System Interconnection (OSI)
model
A logical representation of the path data must travel in order
to go through the network.
• Upper layers:
Represent software that implements network services like
encryption and connection management.
• Lower layers:
Implement hardware-oriented functions like routing,
addressing, and flow control.
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Internet and Intranet.
The OSI model
• Data communication
starts with the top layer of
the stack at the sending
side.
• Travels down the stack to
the sender’s lowest
(bottom) layer.
• Then traverses the
physical network
connection to the bottom
layer on the receiving
side, and up its OSI model
stack.
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Internet and Intranet.
The OSI model – Data flow
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Computer Networks
NETWORK HARDWARE AND
SOFTWARE
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Network Hardware and Software.
Network hardware and software
Aside from clients and servers, computer networks may also
contain the following components:
• Network interface
card (NIC).
• Hub.
• Bridge.
• Router.
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•
•
•
•
•
Modem.
Gateway.
Switch.
Firewall.
Operating System.
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Network Hardware and Software.
Network interface card (NIC)
• Provides the physical interface between computer and
cabling.
• In the computer, data moves along buses in parallel, as on
a four-lane highway. But on a network cable, data travels
in a single stream as on a one lane highway.
‒ The NIC’s job is to translate the data from the
computer into signals that can flow easily along the
cable. It does this by converting digital signals into
analog signals.
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Network Hardware and Software.
Network interface card (NIC)
Ethernet
port
Coaxial
port
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Network
port on the
Toronto Rocket
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Network Hardware and Software.
Hub
Hubs are devices used to link several computers together.
• A hub repeats any signal that comes in on one device and
copies it to all other devices connected to the hub.
There are two types of hubs:
• Passive hubs (not powered): connect all devices together.
• Active hubs (powered): use electronics to amplify and
clean up the signal before it is broadcast to the other
devices.
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Network Hardware and Software.
Hub
HUB
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Network Hardware and Software.
Bridge
Joins similar topologies and is used to divide LANs into
segments.
• If a bridge knows the destination address, it is able to
forward packets to that address, otherwise a bridge will
forward the packets to all devices.
• Filters out noise.
• The main disadvantage of bridges is that they can’t
connect dissimilar network types or perform intelligent
path selection. For that function you require a router.
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Network Hardware and Software.
Bridge: an example
With 200 clients on one
Ethernet segment, the
performance will be slower
because of the design of the
Ethernet and the number of
workstations that are fighting
to transmit information.
By dividing the 200 clients into
two segments of 100 clients
each, the traffic will be much
lower on either side, and
speed will increase.
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Network Hardware and Software.
Router
• Routers are important devices that let messages flow
between networks, rather than within networks.
• Home networks use a wireless or wired Internet Protocol
router. An IP router, such as a digital subscriber line (DSL)
or a cable modem broadband router, joins the home’s LAN
to the WAN of the Internet.
• Broadband routers combine the functions of a router with
those of a network switch and a firewall in a single unit.
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Network Hardware and Software.
Router
When you connect to a website through an ISP and
exchange information, there is no fixed connection between
your computer and the Web server computer hosting the
website. Routers find the best possible path, these paths
avoid slow links and favour fast ones.
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Network Hardware and Software.
Modem
• Stands for MODulatorDEModulator.
• Modern modems, such as
cable TV and DSL modems,
no longer modulate and
demodulate the signals.
• Routers provide access to a
LAN, however, in order for
the router to connect to
the Internet, it must be
connected to a modem.
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Network Hardware and Software.
Gateway
• Gateways are routers that rout between networks,
however, they also perform protocol conversions so that
different networks can work together.
• A gateway is an essential feature of most routers. A
gateway may contain devices such as protocol translator,
impedance matching devices, rate converters, fault
isolators, or signal translators as necessary to provide
system interoperability.
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Network Hardware and Software.
On the train: gateway example
On the TIN there is a Mobile Communications Gateway
(MCG), which provides wireless communication between a
train and the yard maintenance system.
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WLAN communication via the MCGs
TIN DIAGRAM
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Network Hardware and Software.
Switch
• A switch is a computer network device that connects
network segments.
• Network switches are capable of inspecting data packets
as they are received, determining the source and
destination device of that packet, and forwarding it
appropriately.
• By delivering each message only to the connected device it
was intended for, a network switch conserves network
bandwidth allowing for better system performance.
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Network Hardware and Software.
Switch
Computers 1 and 5 transmit first and then 2 and 3.
SWITCH
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Network Hardware and Software.
Ethernet protocol
Ethernet uses a protocol called CSMA/CD, this stands for:
CSMA/CD
Carrier Sense
Multiple Access
with Collision Detection
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Network Hardware and Software.
Ethernet protocol
Carrier Sense
When a device connected to an Ethernet network wants to
send data, it first checks to make sure it has a carrier on
which to send its data (usually copper cable connected to a
hub).
Multiple Access
All machines on the network are free to use the network.
Collision Detection
Ensures that if two computers transmit data simultaneously,
data re-transmissions are generated at differing time
intervals.
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Network Hardware and Software.
Ethernet
The basic bus topology:
• The computers are daisy chained together.
• Each packet of data contains the destination address, the
sender’s address and the data.
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Network Hardware and Software.
Ethernet
• Computer 2 wants to send a message to computer 4.
• Computer 2 checks to make sure the network is not in
use. If all clear, it will transmit the data onto the network.
• Signal is sent to every computer on the network but only
addressed to computer 4, the other computers ignore it.
• Computer 4 sends a message back to computer 2
acknowledging receipt of data.
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Network Hardware and Software.
Ethernet
What happens if two computers try to transmit at the same
time?
A COLLISION occurs and each computer has to back off for
a random period of time before retrying.
• On small networks, this goes unnoticed. On larger
networks, the more collisions you have, the slower the
network functions.
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Network Hardware and Software.
Hub vs. switch
An Ethernet hub changes the
topology from a bus to a star
network.
Collisions are still possible,
however, hubs have
centralized wiring, and can
automatically bypass any
ports that are disconnected
or have cabling faults.
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Network Hardware and Software.
Hub vs. switch
• Switches are used to overcome the problem of collisions.
• With a switch, computers can transmit simultaneously.
• Switches read the destination address and switch the
signal directly to the recipient without broadcasting to all
the computers on the network.
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Network Hardware and Software.
Hub vs. switch
• A vital difference between a hub and a switch is that all
the devices connected to a hub share the bandwidth
among themselves, while a device connected to a switch
has the full bandwidth to itself.
• Example:
If 10 devices are communicating using a hub on a 10
Megabits per second (Mbps) network, then each device
may only get a portion of the 10 Mbps if other devices on
the hub want to communicate as well. With a switch, each
device can communicate at the full 10 Mbps.
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Network Hardware and Software.
Firewall
• Firewall is a software loaded onto a network that serves as
a barrier to keep destructive forces away from a network
of computers.
• Firewall can block information from entering a network or
from getting out of a network, they can permit different
users to perform different kinds of operations, according to
the user’s permissions.
• Packets of data are analyzed against a set of standards
called filters. Filters block certain designated IP addresses.
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Filtering signals before allowing them to
access the network
FIREWALL
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Computer Networks
REVIEW
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Review.
Identify the type of network
Local
Wide area network
LAN
WAN
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Review.
Name the network components
Server
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Client
Resource
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Review.
Name the network components that
control the data transmission
Hub
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Switch
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Review.
Which of the following network
topologies require terminators?
Star
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Bus
Mesh
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?
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End
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