Download Slide 1

Information and Communication
Technology Fundamentals
Credits Hours: 2+1
Instructor: Ayesha Bint Saleem
HIGHLIGHTS OF LAST LECTURE
3 aspects of a network
• Software
• Hardware
• Medium
Software
• Application
• Protocols
• Packet
• Payload (Data part)
• Header (Control information part)
Hardware
• Modem
• ISDN
• DSL
• LAN Card
• Wireless LAN Card
• ATM
• Wimax
Medium
• Wired
• Twisted pair cable
• Co-axial cable
• Fiber optic cable
• Wireless
Network Topologies
• Point 2 Point
• Bus
• Ring
• Mesh
• Star
Network Linking Devices
• Hub
• Bridge
• Switch
• Router
• Gateway
Classification of Networks according to
geographical scope
• Wide Area Networks
• Metropolitan Area Networks
• Campus Area Networks
• Local Area Networks
• Home Area Networks
• Personal Area Networks
NETWORKS - II
Presentation Credits
• “Data Communications and Networking”,
Behrouz A. Forouzan
• “Computer Networks”, Tanenbaum
• Dr Junaid, EE Dept, SEECS
Types of communication
• According to data direction
• Simplex
• One-way communication (only send or only receive)
• Half-Duplex
• Two-way communication (send/receive) but one at
a time
• Full Duplex
• Two-way communication (send/receive) at the
same time
Types of communication
• According to intended recipients
• Unicast
• Sending data to only one recipient
• Multicast
• Sending data to multiple recipients
• Possibly at different locations
• Broadcast
• Sending data to everybody
• You open a browser e.g. Internet Explorer
• Type address on the browser’s address bar
NETWORKING SOFTWARE
Address
Bar
Example
application
http://www.niit.edu.pk
This is an example of a browser (Internet
Explorer)
Other browsers include Firefox, Opera.
Browser acts as:
1 a client of webserver
2 fetches and displays user requested
documents
• The SEECS page is displayed in front of you
after some time
• A lot of things are happening from your
typing the address to getting to see the
SEECS home page
• Inside your computer
AND
• On the network
• Like
• Locating where the SEECS server is located
which is hosting the SEECS website
• Establishing a connection with the SEECS server
• Requesting server to send you the webpage
• Receiving data from server in the form of
packets
• Ensuring packets arriving are free of error
• Arranging packets in order to re-create the
original webpage
• Who is dealing-with/enabling all this?
• Network software on your computer
• Network software on the NIIT server
• Network software on many other devices that
you are not aware of
• DNS Server
• Router
• Possibly many others
• Network software follows different procedures to
have the web-page displayed to you
• These procedures are called protocols
• Variety of protocols are running on your
computer
• Each responsible to perform a different task
• To reduce design complexity, the functions that a
network software provides are organized as a
stack of levels or layers
• Each layer uses the services of the layer below it
• Each layer offers some services to the layer
above it
• The concept of layering is used in daily life
Two friends communicating through postal mail
Letter is written, put in an
envelope, and dropped
in mailbox
The letter is carried from
the mailbox to a post
office
The letter is delivered to
a carrier by the post
office
Higher Layers
Letter is picked up
removed from the
envelope and read
Middle Layers
The letter is carried from
the post office to the
mailbox
Lower Layers
The letter is delivered to
from the carrier to the
post office
Parcel is carried from the source to destination
Internet Model
• The layering structure that internet uses
• Consists of five layers
Internet TCP/IP Model
Application Layer
Transport Layer
TCP
Network Layer
IP
Data Link Layer
Physical Layer
• Physical Layer:
• Responsible for transmitting raw bits over a
communication medium (channel)
• Data Link Layer
• Source DLL gives a packet to the physical layer in the
form of bits
• Destination DLL receives bits of the packet from the
physical layer
• Node to node delivery of a packet
• Error control
• Use of Acknowledgements
• Network Layer
• End –to-end delivery of a packet
• Transport Layer
• Process to process delivery of a packet
• May include error control
• Application layer
• Enable use of network
• Provides Interface
Addressing in the Internet
• Each station must be addressable
• Two kinds of addresses:
• 1) Physical addressing (MAC addresses)
• 2) Logical addressing (IP addresses)
Addressing in the Internet
• The communicating applications (source/
destination applications) must also be
identifiable
• Identified through TCP ports
•
• A socket (IP address + TCP port)
identifies both an application and the
machine it’s on.
Physical Addressing: MAC
MAC Address: 48 bits
(Ethernet)
Flat addressing
Usually non-configurable
Logical Addressing: IP
IP Version 4; Address: 32 bits 4,294,967,296
possible addresses = 2
IP Version 6; Address: 128 bits
32
Hierarchical addressing
2 parts: a network part and a host part.
Machines in a LAN have the same
network part; they differ in host parts
Logical Addressing: IP
How is the network part of an IP address
defined
Subnet mask
IP (Internet Protocol)
IP Address
192.168.15.2 (decimal)
11000000 10101000
00001111 00000010
(binary)
Subnet Mask:
255.255.255.0 (decimal)
11111111 11111111
11111111 00000000
(binary)
Network part Host part
Applications Identification
How to identify source/ destination
application communicating
The source/ destination applications are
identified through TCP ports
Common TCP Ports:
HTTP: 80; SMTP:25; DNS: 53
Naming
Machine addresses are difficult to memorize
Solution: Provide recognizable names to
numerically addressed Internet resources.
Examples:
google.com; stanford.edu; niit.edu.pk
Naming
How to manage address to name
1) A hosts file onmapping?
each machine
Unix/ Linux: /etc/hosts file
Windows:
%SystemRoot%\system32\drivers\etc
2) A decentralized domain name server
system
Scalable solution
The name to IP mapping is available at a
DNS server
Example application
D
N
S
W
W
W
(contd.)
DNS Client/Server Exchange
D
N
S
Reques
t
Tell me the IP
address of
www.niit.edu.pk?
W
W
W
DNS Client/Server Exchange
D
N
S
Reply
W
W
W
The IP address of
www.niit.edu.pk is
202.125.157.196
ARP Client/Server Exchange
D
N
S
Request
Any one knows the
MAC (physical) address
of 202.125.157.196 ?
W
W
W
ARP Client/Server Exchange
D
N
S
Reply
W
W
W
The MAC address of
202.125.157.196 is
12:34:aa:bb:cc:dd
HTTP Client/Server Exchange
D
N
S
Request
Send me the index.html page
for the host www.niit.edu.pk
using HTTP version 1.1
W
W
W