Transcript Document

Chapter 1:
Introduction to Local Area Networks
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What is a LAN?
A type of network where nodes are connected
at high speed in a confined geographical area.
Network: A connection between two or more computers
to exchange data or provide shared access to resources
Node: Any device that can send or receive data via a
network
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Why use a LAN?
LANs provide the ability to share resources to
other nodes on the network.
Resources include:
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Shared files
Shared printers
Shared Internet
connection
Shared applications
such as database and
e-mail servers
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The First LAN
• Was built at the Xerox Palo Alto Research Center
(PARC) in 1973.
• Xerox PARC was also responsible for the
invention of:
o The first personal computer (the Alto)
o The first laser printer
o The first Graphic User Interface
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• Although Xerox PARC pioneered many of these
technologies, other companies, such as Apple,
Microsoft, 3Com and Cisco would make them
famous.
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Other Types of Networks
Campus area network (CAN): Spans a group of buildings,
generally within walking distance of each other that belong
to the same organization.
Metropolitan area network (MAN): Medium speed network
that connects sites over distances up to 50 miles. Generally
used by organizations that have several locations over the same
city. Most MANs can also be described as WANs
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Other Types of Networks
Wide area network (WAN):
WANs are made up of LANs connected by
lower speed long distance links. WANs usually
cover a significant geographical area.
WANs use slightly different transmission methods & media and often use
a greater variety of technologies than LANs.
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LAN vs. WAN
• Geography – small / large
• Ownership – self owned / leased
• Management – self admin / contract leased
• Speed – faster / slower
• Cost – hundreds / thousands or millions
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Authentication
• The process by which a user is identified
on the network.
• Most frequently accomplished
by means of a logon account
and a password.
• Each user must have a valid logon account on the
computer or network to be authenticated. Sometimes
authentication is centralized and sometimes each
resource requires individual authentication.
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Client/Server Network
• Server provides specific services for a specific purpose.
• Users connected to the LAN through client computers
can access resources on any server on the network.
• Centralized database illustrate the concept:
Client
Serverrequests
responds
Information.
to request.
• Servers tend to have faster processors, more RAM,
and more hard disk space. They perform the
processing for many clients. A slow server slows
all clients that use it.
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Peer-to-Peer (P2P) Network
• Decentralized. There are no dedicated servers and no
single set of resources that all clients access.
• Each host on a P2P network can act as a client, a
server or both.
• Each host performs authentication
for other hosts that request its
resources.
Advantage: Loss of a single computer doesn’t mean that
all data is lost.
Disadvantages: Can be difficult to find a resource, and
a user must remember many different passwords.
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Individual
P2P clientsP2P
request
servers
grant/deny
authentication.
access.
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Centralized Networks
Rather than having to authenticate against each computer,
a user authenticates once and then can access all resources
on a LAN.
Assuming that their account has permissions of course!
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Centralized Networks
Advantages of Centralized Networks:
• Files can be stored and backed up centrally.
• Servers can be located centrally for easy access.
• Centralized administration
Fewer support personnel required.
Disadvantages of Centralized Networks:
• Fewer points of failure
If a central resource like a file share goes offline,
many more users are inconvenienced.
• Security
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If you get a users password, you can access all
resources on the network, not just on one computer.
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Centralized Network Administration
Centralized networks allow an administrator to:
• Deploy an application to a thousand desktop
computers at the same time rather than visit each
computer with the installation CD-ROM.
• Standardize of modify the look and feel of all client
computers or make configuration changes centrally.
• Have security updates automatically deployed to all
computers as they become available rather than having to
visit each computer, check which updates are installed,
and then finally install relevant updates.
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The OSI Reference Model
• The OSI Reference Model is a complete conceptual
model for describing functions performed by network
hardware and software.
• Each layer of the OSI model describes a particular
aspect of the network communication process.
• Services provided at each layer interact directly with
those provided by the layers immediately above and/or
below.
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Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
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Layer 7
Initiates communication to
Layer 6
use the network, such as
Translates data into formats
Layer a5file transfer or
starting
such as text, graphics, audio
EstablishesaaWeb
displaying
logical
page.
Layer
4 Also
and
video.
includes data
communication channel for
Breaks
compression
data
and encryption.
into
Layer
3 message
data transfer
between hosts.
transmittable
Identifies the segments
location ofand
ensures
accurate
and reliable
source
hosts
Layerand
2 destination
transmission
ofbest
datapathway
packets
and
routes
thedata
Ensures
that
transmitted
Layer
1 sequence
in
the proper
between.
on
the
transmission
media
Transmitshosts.
data across
the
between
has
a
destination
on
the
local
physical media as a stream
of
network.
binary numbers in the form
of electrical signals, light
pulses of radio waves.
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Summary
• A LAN is a type of network where two or more hosts are
connected at high speed.
• LANs are used to share a small number of resources with
a large number of hosts.
• P2P networks allow hosts to act as both client and server.
• Client/server networks have resources centralized on
servers which clients access.
• The benefits of LANs is that they allow centralized
administration, centralized applications and centralized
file storage and backup.
• The OSI Reference Model has seven layers, which can
conceptually be used to represent how software and 16
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hardware interact with one another on a network.
Discussion Questions
 What is the difference between a LAN and a WAN?
 What are the differences between a client and a server?
 What are the advantages of a client/server network
model over a peer-to-peer network model?
 What are the benefits of centralized administration of
computers on a LAN?
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