Transcript An Introduction to Local Area Networks

An Introduction to
Local Area Networks
An Overview of Peer-to-Peer
and Server-Based Models
The simplest form of networking
occurs when two computers are
connected together with a cable
to share data. The far-reaching
networks that we use today were
born from this simple but
revolutionary idea.
Before the advent of networks:
• Each computer had to have its own
software and hardware installed,
greatly increasing the total cost of
ownership.
• Information was shared between
computers by “sneaker net”, where
the users would carry a floppy disk
from one computer to another.
Stand-alone computer systems are
both expensive and hard to manage
because each system must have its
own resources:
•
•
•
•
•
•
Floppy disks
Hard disks
CD-ROM drives
Printers
Modems and Faxes
Software
When computer systems are
networked, they can share:
•
•
•
•
•
•
•
Software
Data
Printers
Storage systems
Faxes and Modems
Backup systems
Other hardware resources
Although networks such as the
Internet connect computers
throughout the world, most
networks are local area
networks (LANs). These are
networks that are installed by
organizations to share
resources at one location of
the organization.
Local area networks generally consist of
these resources:
• Servers - computers that provide resources
to the network
• Client computers - computers that access
resources from the network
• Media - the cabling that connects the
network
• Shared software applications
• Shared data
• Shared peripherals - printers, storage
devices, communications devices, and other
resources
There are only two basic
types of computer networks.
All computer networks are a
variation or a combination of
these two types:
• Peer-to-Peer
• Server-based
The choice of which network model
to deploy is based on many factors:
• The number of computers which
must be networked
• The level of security necessary
• The amount of network traffic
• The needs of the users
• The support staff available
• The budget allocated for the
network
In the peer-to-peer model, each
user acts as the administrator for
their own workstation. They grant
the use of resources to other users
by adding the other users to their
local database of users and giving
the other users permission to use
files and hardware resources
located on their computer.
A peer-to-peer network is
typically implemented when:
• There are 10 or less users of the
network
• Security is not an important issue
• All of the users are located in the
same area
• The networking needs of the
organization are not expected to grow
• There is a limited budget for network
support personnel
The peer-to-peer model has
some advantages:
• Low cost – networking is built in to the
operating system of the computers
• Easy to implement – cabling is generally
inexpensive, simple and visible
• No stand-alone server to install and
configure
• Low system administration costs – each
user acts as the administrator of their
workstation
There are also disadvantages to
the peer-to-peer model:
• Low level of security
• Users must be created and permissions
must be granted on each computer on the
network
• Each user must be trained in the
administration of their workstation
• Low levels of performance – each computer
acts as both a workstation and a server
• Data is spread out over many different
computers making it harder to administer
and back up
The server-based model is
generally used when there are
more than 10 users on the
network and is always employed
for mission-critical applications.
In the server-based model, the
network has one or more
dedicated server computers.
Network server computers:
• Serve files and applications
• Provide hardware resources such
as printers, plotters, faxes and
modems
• Provide centralized storage of
programs and applications
• Allow for secure, centralized
management of user accounts and
files
There are many types of specialized servers.
A typical LAN may be constructed of:
• File servers – servers that provide applications
and data to the client computers
• Applications servers - servers that run
applications such as databases – the information
is processed on the server and the results are
sent to the client
• Mail servers – servers that provide electronic
mail access and storage
• Fax servers – servers that manage multiple fax
boards to provide fax capabilities to each user
• Communications servers – servers which provide
communications with external networks such as
the Internet
The server-based model has many
advantages:
• Security – policies may be set by the system
administrator and applied to all users of the system.
File permissions may be applied to individual files
• Sharing resources – hardware and software
resources may be shared by all users – management
of these resources is centralized on the server
• Backup – centralized data storage allows for easier
backup of important files
• Redundancy – programs and data may be stored on
backup servers so that they are available even if
the main server fails
• Support for a large number of users – may support
thousands of users
Disadvantages of the server-based
model:
• More expensive – requires at least
one dedicated server and a network
operating system
• Administration costs - continuing
costs for employees to manage the
network
• Installation – the wiring of the
network is more complex using
switches, routers, and hubs
The peer-to-peer model should
be chosen when:
• Network security is not an important
issue
• There are 10 or less users of the network
• The budget for the network is limited
• The users are all in one small area
• The company and the network are unlikely
to expand
• There is limited technical support
available
The server-based model should
be chosen when:
•
•
•
•
•
The network is mission-critical
Network security is a primary consideration
Data redundancy and backup are important
Many types of services are required
There are more than 10 users of the
network
• The company and the network is likely to
expand
• The budget is available to provide network
support personnel
An Introduction to
Local Area Networks
© Stephen M. May
1998