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 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 application Other browsers include Firefox, Opera. Browser acts as: a client of webserver fetches and displays user requested documents 1 2 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: MAC MAC Address: 48 bits (Ethernet) Flat addressing Usually non-configurable

Logical Addressing: IP IP Version 4; Address: 32 bits IP Version 6; Address: 128 bits 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 4,294,967,296 possible addresses = 2 32

Logical Addressing: IP How is the network part of an IP address defined Subnet mask

IP (Internet Protocol) IP Address (decimal) (binary) Subnet Mask: (decimal) (binary) IP Address (decimal) (binary) Subnet Mask: (decimal) (binary) Network partHost 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. google.com; stanford.edu; niit.edu.pk Examples :

Naming How to manage address to name mapping? 1)A hosts file on 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

WWWWWW DNSDNS Example application (contd.)

DNS Client/Server Exchange WWWWWW DNSDNS Reques t Tell me the IP address of

WWWWWW DNSDNS Reply The IP address of is DNS Client/Server Exchange The IP address of is

ARP Client/Server Exchange WWWWWW DNSDNS Request Any one knows the MAC (physical) address of ? Request

WWWWWW DNSDNS Reply The MAC address of is 12:34:aa:bb:cc:dd ARP Client/Server Exchange The MAC address of is 12:34:aa:bb:cc:dd

HTTP Client/Server Exchange WWWWWW DNSDNS Send me the index.html page for the host using HTTP version 1.1www.niit.edu.pk Request Send me the index.html page for the host using HTTP version 1.1www.niit.edu.pk