Information and Communication Technology FundamentalsCredits 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

Decreasing Scope

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

Example applicationExample applicationhttp://www.niit.edu.pk

Other browsers include Firefox, Opera.

Browser acts as:

a client of webserver

fetches and displays user requested documents

11

22

This is an example of a browser (Internet Explorer)

Address Bar

• 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

Letter is picked up removed from the envelope and read

The letter is carried from the post office to

the mailbox

The letter is delivered to from the carrier to

the post office

Parcel is carried from the source to destination

Higher Layers

Middle Layers

Lower Layers

Internet Model

• The layering structure that internet uses

• Consists of five layers

Internet TCP/IP Model

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Application Layer

TCP

IP

• 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: MACPhysical Addressing: MAC

MAC Address: 48 bits (Ethernet)Flat addressing

Usually non-configurable

Logical Addressing: IPLogical Addressing: IP

IP Version 4; Address: 32 bitsIP Version 6; Address: 128 bits

Hierarchical addressing2 parts: a network part and a host part.

Machines in a LAN have the same network part; they differ in host parts

4,294,967,296

possible addresses = 232

Logical Addressing: IPLogical Addressing: IP

How is the network part of an IP address defined

Subnet mask

IP (Internet Protocol)IP (Internet Protocol)

IP Address192.168.15.2 (decimal)

11000000   10101000  00001111   00000010 (binary)

Subnet Mask:255.255.255.0 (decimal)

11111111   11111111  11111111   00000000 (binary)

IP Address192.168.15.2 (decimal)

11000000   10101000  00001111   00000010 (binary)

Subnet Mask:255.255.255.0 (decimal)

11111111   11111111  11111111   00000000 (binary)

Network part Host part

Applications IdentificationApplications 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

NamingNaming

Machine addresses are difficult to memorize

Solution: Provide recognizable names to numerically addressed Internet resources.

google.com; stanford.edu; niit.edu.pkgoogle.com; stanford.edu; niit.edu.pkExamples:

NamingNamingHow to manage address to

name mapping?1)A hosts file on each machineUnix/ Linux: /etc/hosts fileWindows: %SystemRoot%\system32\drivers\etc

2)A decentralized domain name server systemScalable solutionThe name to IP mapping is available at a DNS server

WWW

DNS

Example application Example application (contd.)(contd.)

DNS Client/Server ExchangeDNS Client/Server Exchange

WWW

DNS

Request

Tell me the IP address of

www.niit.edu.pk?

WWW

DNSReply

The IP address of www.niit.edu.pk is 202.125.157.196

DNS Client/Server ExchangeDNS Client/Server Exchange

The IP address of www.niit.edu.pk is 202.125.157.196

ARP Client/Server ExchangeARP Client/Server Exchange

WWW

DNS

Request

Any one knows the MAC (physical) address

of 202.125.157.196

?

Request

WWW

DNS

Reply

The MAC address of 202.125.157.196

is 12:34:aa:bb:cc:dd

ARP Client/Server ExchangeARP Client/Server Exchange

The MAC address of 202.125.157.196

is 12:34:aa:bb:cc:dd

HTTP Client/Server ExchangeHTTP Client/Server Exchange

WWW

DNS

Send me the index.html page for the host www.niit.edu.pk

using HTTP version 1.1

Request

Send me the index.html page for the host www.niit.edu.pk

using HTTP version 1.1