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Lecture 09
Networking & Telecommunications
CSCS100 - Fall 2009 – Forman Christian College
Asher Imtiaz
*Several of these slides have been adapted and modified from LUMS CS101
course (Dr Tariq Jadoon), VU CS101 slides (Dr. Altaf A. Khan) and Peter Norton’s
supplementary material.
Today’s Goals
• What is Network and role of networks
in computing
• We will look at several different types
of networks
• We will familiarize ourselves with
networking topologies and protocols
• Warriors on the Net (Movie)
The Basic communication problem
• Sender
• Channel (Medium)
• Message
• Protocol
• Receiver
All of you have used
computer networks.
What is a
computer network?
Computer Network
Multiple computers that are connected
together to share information and other
resources
• Set of technologies that connects
computers
• Allows communication and collaboration
between users
Examples of Computer Network Usage
• I can send an eMail message to a remote
computer using the SMTP protocol
• I can browse documents residing on a
remote computer using the HTTP protocol
• I can download or upload files to a remote
computer using the FTP protocol
• I can run a program on a remote computer
using the TELNET protocol
Examples of Computer Network
Computer
A
Computer
E
Computer
D
Switch
Computer
C
Computer
B
The Uses of a Network
• Simultaneous access to data
• Data files are shared
• Access can be limited
• Shared files stored on a server
• Software can be shared
• Site licenses
• Network versions
• Application servers
The Uses of a Network
• Shared peripheral device
• Printers and faxes are common shares
• Reduces the cost per user
• Devices can be connected to the network
• Print servers control network printing
• Manage the print queue
• Easier data backup
• Backup copies data to removable media
• Server data backed up in one step
Sharing Data
File server contains documents
used by other computers.
The Uses of a Network
• Personal communication
• Email
• Instantaneous communication
• Conferencing
• Tele conferencing
• Videoconferencing
• Audio-conferencing
• Data-conferencing
• Voice over IP
• Phone communication over network wires
Components of Conventional CN
1. Computers
2. Network Interface Cards (NIC)
•
•
I/O device that plugs into the computer
Enables it to communicate over a network
3. Switch
•
The network traffic controller (usually Hub)
4. Cables
•
•
Are either electrical or optical
Not required at all for wireless networks
5. Protocol
•
Rules governing communications over the network
How Does a Conventional Network Work?
1. Suppose computer A wants to send a
message to D
2. Computer A sends the message to its NIC
3. The NIC translates the message into
electrical pulses suitable for the computer
network in use & transmits it to the switch
through the cable
How Does a Conventional Network Work?
4. The switch receives them and forwards
them to all computers connected to the
it
5. The NICs of all computers connected to
the switch receive the forwarded
electrical pulses
6. The NIC of computer D decides that the
message is for it, & translates the pulses
back to a form suitable for the computer
Switch
• A device that is used to connect several
computers to form a network
• A switch has several ports. The number generally
is 8, 12, 16, 24, 32, or 48
• Each computer in a network is connected to one
of those ports through a cable
• A computer wanting to send a message to one
of the others in the network sends a message to
the switch, which, in turn, broadcasts the
message to all others connected to it
Types of Computer Networks
according to the network access policy
• Private
• Public
Private Networks
• Organizations having many computers usually
connect them in the form of private networks
• Access to these network is restricted to authorized
computers only
• This allows computers from within the organization
to exchange info, but keeps the info private and
protected from outsiders
• All equipment on a private network is generally
for the exclusive use of that organization
Public Networks
• All networks that are not private, are …
public
• Example: PSTN, Internet
• Communication equipment used in these
networks is generally being used by users
belonging to several (possibly thousands of)
organizations as well as those belonging to
no organization
Types of Computer Networks
according to the distance between nodes
• LAN: Local Area Network
• WAN: Wide Area Network
Common Network Types
• Local Area Network (LAN)
• A network of computers located in the same
building or a handful of nearby buildings
• Contains printers, servers and computers
• Systems are close to each other
• Contained in one office or building
• Organizations often have several LANS
• Examples:
• Computer network of a University campus
Common Network Types
• Wide Area Networks (WAN)
• Two or more LANs connected
• Over a large geographic area (typically across
cities or even continents)
• Typically use public or leased lines
• Phone lines
• Satellite
• Example:
• The network connecting the ATM of a bank
located in various cities
• The Internet is a WAN
Hybrid Network Types
• Personal Area Network (PAN)
• Very small scale network
• Range is usually few meters
• Cell phones, PDAs, MP3 players
• Example
• Network created with Bluetooth
Connecting LANs to other Networks
Special-purpose devices are used to link
LANs to other networks
They may belong to one of the following
categories:
• Routers
• Gateways
• Modems
Router
• A special-purpose computer that directs data
traffic when several paths are available
• A router examines the destination info in each
arriving packet and then routes it through the
most efficient path available
• The router either delivers the packet to the
destination computer across a local network or
forwards the packet to another router that is
closer to the final destination
Gateway
• A special-purpose computer that connects
and translates between networks that use
different communications protocols
• LAN’s may use a gateway (or router) to
connect to the Internet
Modem
• I/O device used for connecting two
computers over telephone lines
• modem = modulator + demodulator
• Modulator converts computer messages to
electrical pulses that are suitable for
transmission over the telephone lines
• Demodulator converts electrical pulses
received over telephone lines into messages
that are comprehensible for computers
Computer Networks
=
Computers
+
Communications
Types of Communication Channels
1. Wire
2. Wireless
A key characteristic of these channels is
bandwidth
Bandwidth
• Capacity of a communication channel for
carrying data
• Measured in bits/s (bps), kb/s, Mb/s, Gb/s, Tb/s
• Optical fiber channels have the highest (1 Tb/s)
• Telephone lines the lowest (56 kb/s)
Types of Communication Channels
Wireless
– Line-of-sight
Wire
– Copper
• Twisted-pair
• Coaxial cable
– Optical fiber
• Microwave
• Optical
– Non-line-of-sight
• Satellite
• Radio
• Cellular
Wireless (Radio) LANs Are Becoming Popular
Key benefits:
• Set-up time
• Set-up cost
• Maintenance cost
• Cost
Key challenges:
– Security & privacy
– Quality of service
How Networks Are Structured
• Server based network
• Node is any network device
• Servers control what the node accesses
• Users gain access by logging in
• Server is the most important computer
How Networks Are Structured
• Client/Server network
• Nodes and servers share data roles
• Nodes are called clients
• Servers are used to control access
• Database software
• Access to data controlled by server
• Server is the most important computer
How Networks Are Structured
• Peer to peer networks (P2PN)
• All nodes are equal
• Nodes access resources on other nodes
• Each node controls its own resources
• Most modern OS allow P2PN
• Distributing computing is a form
• Kazaa
Wireless Media
• Data transmitted through the air
• LANs use radio waves
• WANs use microwave signals
• Easy to setup
• Difficult to secure
Wireless Usage Scenario
• Want to instantly connect notebook to another
notebook to transfer a file.
• Application Category:
• Wireless Standard:
WPAN
Bluetooth
• Want to always be connected to corporate LAN
while moving about in office building or campus.
• Application Category:
• Wireless Standard:
WLAN
WiFi
• Want access to e-mail and web resources while
traveling away from the home/office.
• Application Category:
• Wireless Standard:
WWAN
Cellular Technologies (GSM)
http://www.tutorial-reports.com/wireless/wlanwifi/index.php
Wireless Networks
• Benefits
• No cable to pull
• Mobile devices access network resources
• Mobility and flexibility for office workers