Download Intro to Networks - Drexel University

Chapter One
An Introduction
to Networking
Networks and Standalone
Computers
Network


Group of computers and other devices
connected by some type of transmission
media
Networks enable users to share devices and
data, collectively called a network’s
resources
Standalone computer

Uses programs and data only from its local
disks and is not connected to a network
Standalone Computers
Method of sharing data by copying it to a disk
and carrying the disk from computer to computer
Figure 1-1: Data sharing before the advent of networks
Network
A Network is an Any-to-Any
Communication System
 Can connect any station to any other
Network
Advantages of a Network in an Office Setting
 Recourse Sharing
- All office members can share computer files
- Laser printers can be shared
-Software applications are more easily shared and upgraded
 Electronic mail can be implemented
 Office computers can be backed up over the network
 Working groups can share information within the each group
Saving money :- In a distributed network computers have a
better price/performance ratio as compared to large ones.
E.g. Mainframes are 10 times faster than personal computers, but
they cost 1000 times more.
Basic Components of Network
 Workstations
 Network Operating System
 Cabling
Basic Network Components
Workstation
File Server with NT
Server Operating System
Cabling
Workstation
Workstation
Workstation
Networking Basics
Workstation

Computer that typically runs a desktop operating
system and connects to a network
Client/server architecture

Networking model in which clients use central
server to share applications, devices, and data
Network operating system

Special software designed to manage data and
other resources on a server for a number of clients
Terminal-Host Systems
(Mainframe Architecture)



Central host computer does all the processing
Terminal is dumb--only a remote screen and
keyboard
Host are mainframes
Terminals
Host
Distributed Networks
(Client/Server Architecture)
The Most Common Platform in Organizations


Based on Client/Server Architecture
Allows PCs to share resources
Client
PC
PC File Server
Network
PC E-mail Server
Client
PC
Client / Server
Networked Computers
Client

User (PC, Workstation, Laptop) Requires
Data, Application, Communications It Does
Not Have
Server

Component (Computer) Having Desired Data,
Application, Communications
Client/Server Processing
Cooperation Through Message Exchange


Client program sends Request message, such as
a database retrieval request
Server program sends a Response message to
deliver the requested information or an
explanation for failure
Server
Program
Client Program
Request
Response
Client Machine
Server
PC Network Components
File Servers



Store files (data files and programs)
The most common type of server in PC
networks
Almost all file servers are themselves PCs
File Server
File Server Program Access
File Server Program Access is the Most Common Way to
Execute Programs in PC Networks
 Program files are stored on the file server
 But downloaded (copied) to client PC for execution
 Executed on client PC, not on file server
Executed
on
Client PC
Stored
on the
File
Server
Download
Client PC
File Server
LANs – WANs - MANs
Networks Have Different Geographical
Scopes
Local Area Networks (LANs)



Small Office
Office Building
University Campus
Wide Area Networks (WANs)

Connect Customer and Supplier across various
building within a city.
Metropolitan Area Network (MAN)

Connect corporate sites across cities
Local Area Network (LAN)
Network of computers and other devices
confined to relatively small space
LANs involving many computers are
usually server-based

On a server-based network, special
computers (known as servers) process data
for and facilitate communication between
other computers on the network (known as
clients)
Figure 1-3:
LAN with a file
server
Small Peer-Peer PC Network
No dedicated (fulltime) server
User PCs supply
services to each
other
So user PCs act
both as clients and
as servers
Small Peer-Peer PC Network
File Sharing



Each PC can make
certain disk drives or
directories available
to to other user PCs
Can allow others
read-only or full
access to files there
Can require
password for access
Small Peer-Peer PC Network
Printer Sharing



Each PC can make
one or more printers
attached to it
available to others
Windows 95 can be
used as for Peer – to
– peer network.
Windows NT can
also be used but it is
designed to work in a
centralized
networking model
Small Peer-Peer PC Network
Advantage

No dedicated
server to
purchase and
maintain
Small Peer-Peer PC Network
Disadvantages

If someone turns
off their PC or
crashes it, people
using its files or
printer are cut out
Small Peer-Peer PC Network
Disadvantages (Cont.)



Users often set up
security poorly giving
access to unauthorized
people
Special problem if home
network is connected to
the Internet
Experience slow
response if heavily
loaded.
Small Peer-Peer PC Network
Overall


Beyond about 5
users, problems
become
pronounced
Beyond about 10
users, very bad
idea
MANs and WANs
Metropolitan area network (MAN)

Network connecting clients and servers in
multiple buildings within limited geographic
area
Wide area network (WAN)


Network that spans large distance and
connects two or more LANs
The Internet is an example of a very
intricate and extensive WAN that spans the
globe
WAN
Figure 1-5:
A simple
WAN
Elements Common to All
Server-Based Networks
Client

In addition to referring to a computer on the network,
may also refers to human user of client workstation
Server – It runs the NOS ( Eg. UNIX, NT4.0)
Cabling
Network interface card (NIC)

Enables workstation to connect to the network and
communicate with other computers
Elements Common to All
Server-Based Networks
Figure 1-6:
A network
interface
card (NIC)
Servers

Provide services to client PCs

Usually PCs themselves

Most PC nets have multiple servers

Require a NIC


Require a server operating
system (SOS)
Require application software
Server Operating System (SOS)


Servers need operating systems more reliable
than client PC operating systems
Windows NT/2000 Server, Novell NetWare, UNIX,
LINUX
Application Software

Provides the services offered by the servers

E-mail, word processing, file sharing, etc.

More expensive than the SOS
Novell NetWare SOS

Once dominant, but market share has
shrunk

Excellent file and print service

Excellent directory service (later)

Until recently, was not sufficiently robust
and scalable for servers other than file
servers
Microsoft Windows Server Operating System

More robust than desktop Windows (Win 95, Win
98, Win 2000 Professional, etc.)

All 32-bit code

Microsoft Windows NT Server before 2000

Newer Microsoft Windows 2000 Server
New
Versions in order of increasing functionality: Windows
2000 Server, Advanced Server, DataCenter Server
Microsoft Windows Server Operating
System


Easy to install, learn, and use because
resembles desktop Windows
Becoming dominant for small business and
small department servers
UNIX

Powerful workstation servers run UNIX

Extremely reliable

Workstation servers running UNIX
dominate the enterprise server market
UNIX

Expensive to buy

Must retrain staff or hire UNIX staff

Many versions of UNIX exist
Most run the same application software
However, have different management utilities,
etc., requiring training for each version used

Not for Small PC Networks
Server Application Software
File Service Allows File Sharing



File server stores program and data files
Shared file be accessed by any user with
access rights
Built into most SOSs
Access Rights
File
Server
No Access Rights
Server Application Software
File Service


For sharing application program files also
No need to install applications on each PC
Greatly reduces installation labor
File
Server
Server Application Software
File Server Program Access

Program is STORED on the file server
File
Server
Server Application Software
File Server Program Access


But program is EXECUTED on the client PC
Limited by power of client PCs, which do not
get very large
File
Server
Server Application Software
Print Service




Also built into SOSs
Print jobs go to shared printers
But they first go to the file server
Not directly to the print server!
Print Server
File Server
Client PC
Shared
Printer
Server Application Software
Print Service


File server stores print job in a print queue until print
server is ready to print it
File server sends the print job to the print server
Print Server
File Server
Shared
Printer
Server Application Software
Print Server



Print server feeds the print job to the printer
Print servers are simple and inexpensive because the
file server does most of the work
Low print server cost allows shared printers can be
scattered throughout the office
Print Server
File Server
Server Application Software
Typical Application Software


Word processing, e-mail, etc.
Must buy multiuser versions, not just a single
copy from a retail store

License will limit the number of users

Will cost more than the SOS
Server Application Software
Remote Access Service (RAS)




User dials into a remote access server
Server authenticates the user (user must prove
identity)
If authenticated, user may use internal servers
RAS
Client PC needs RAS software
Internal
Server
LAN
RAS
Client
Software
Dial-Up
Telephone
Line
Dial-In
Client
Server Application Software
Directory Servers


Problem: Most networks have many
servers
To use a resource, must know the server
To send e-mail, address is user@server
Files must be accessed on particular servers
Server Application Software
Directory Servers



Directory server knows all resources on all
servers
Can send mail to user (without @server)
Can search for a specific
file across
Directory
servers
Server
Server Application Software
Directory Servers
 Know user access rights on all servers
 Single login to directory server
 After that, get access to all other servers
where user has access rights
Directory
Server
Single
Login
Elements Common to All
Server-Based Networks
Topology

Physical
layout of
computer
network
Figure 1-7: Commonly used network topologies
An Ethernet Bus Network
Laser
Printer
Desktop
Computer
File Sever
Laptop
Computer
File Sever
Pen
computer
Desktop
Computer
Terminator
The Ring Topology
Workstation
File Server
Ring
Workstation
Workstation
Ethernet Star Topology with a Concentrator
File Server
Concentrator
UTP
Cabling
Workstation
Workstation
Elements Common to All
Server-Based Networks
Protocol

Rules network uses to transfer data
 NetBEUI (native to NT Server)
 TCP/IP (important for networks with UNIX, Internet
communications)
 IPX/SPX (for communications on networks with Novell
Netware)
Data Packets

The distinct units of data transmitted from one
computer to another on a network
Elements Common to All
Server-Based Networks
Addressing


Scheme for assigning unique identifying
number to every workstation on network
The number that uniquely identifies each
workstation and device on a network is its
address
Elements Common to All
Server-Based Networks
Transmission
media

Means
through
which data
are
transmitted
and received
Figure 1-8: Examples of network transmission media
How Networks Are Used
Services

Features provided by a network
File and print services
Communications services
Mail services
Internet services
Management services
Network Services
File services


Refers to capability of a server to share data
files, applications, and disk storage space
Server that provides file services is called a
file server
Print services

Allows printers to be shared by several users
on a network
Network Services
Communications services

Allow remote users to connect to a network
Remote user


Person working on a computer in a different geographical
location from the LAN’s server
Communications server
Server that runs communications services
Also referred to as access servers and remote
access servers
Network Services
Mail services

Coordinate storage and transfer of e-mail
between users on a network
Gateway

Combination of software and hardware enabling two
different kinds of networks to exchange data
Internet services

Enable networks to communicate with the
Internet
Network Services
Management services


Centrally administer and simplify complicated
management tasks on the network
Numerous services fall under category of
network management