Computer Networks

Evolution of Network

Introduction to Computer Network

Two or more computing devices connected to one another in order to exchange information or share resources , form a computer network.

Advantages of networks :

• Share resources – For example we can share one printer with a many computers which are connected to each other. because it would be expensive to buy printer for each computer.
• Share storage –  We can access files from any computer on the network.
• Share software – We can install software on a centralized main system, rather than installing it on  every computer.

Disadvantages of networks :

• Networking is a complex setup. We may need to hire a network specialist.
• File security becomes more important because many users can access same file.
• If files and resources are saved central main system, and if the that computer fail, then every computer in the network becomes idle.

Evolution

The original aim was to create a network that would allow users, of a research computer at one university to “talk to” research computers at other universities.

• JCR Licklider of MIT in august 1962 – discussed interconnected computer concept
• Oct 1962 – licklider headed computer research program at DARPA ( Defence Advanced Research Project Agency )
• Initially 3 computers in California and 1 in Utah was connected

ARPANET: The network, developed in the late 1960s. It connected universities and research centers, enabling communication and resource sharing. Developed key Internet technologies like TCP/IP, ARPANET was the foundation for the modern Internet. It was decommissioned in 1990.

NSFNET: Launched in 1985 by the National Science Foundation, it connected universities and research institutions, replacing ARPANET. NSFNET became a major Internet backbone, promoting academic and research networking. It was privatized and decommissioned in 1995, paving the way for commercial Internet growth.

Internet : The Internet, sometimes called simply “the Net,” is a worldwide system of computer networks. A network of networks in which users at any one computer can, if they have permission, get information from any other computer.

Data Communication Terminologies

Concept of Communication

• Communication means to exchange information between two or many users in anyways like speaking, texting, or any other modes of the medium.
• So, data communication is simply the exchange of data between two or many users through the transmission media like twisted pair cable, coaxial cable, optical fibers, radio wave, satellite, microwave, etc.
• The user or device that sends the data is the source and the user that receives the data is a receiver.
• For data interchange to take place, the communicating devices must be a part of a system comprising of a combination of hardware and software.

Components of data communication

There are mainly five components of a data communication system :

• Message
• Sender
• Receiver
• Transmission Medium
• Set of rules (Protocol)

• Message : Data or piece of information which is to be communicated. It may be in form of a text file, an audio file, a video file, etc.
• Sender : Sender is a source / device that sends data message. Computer, mobile, telephone, laptop, video camera etc.
• Receiver : It is destination where message sent by source has arrived. It is a device that receives message. computer, telephone, mobile etc
• Transmission Medium : It is path by which data or message travels from sender to receiver. Transmission medium could be guided (with wires) or unguided (without wires), for example, twisted pair cable, fiber optic cable, radio waves, microwaves, etc.
• Set of rules (Protocol) : To govern data communications, various sets of rules had been already designed by the designers of the communication systems.

Measuring Capacity of Communication Media

Data Transfer Rate : It defines the number of data elements (bits) sent in 1 second. Kbps (Kilo bits per second) , Mbps (Mega bits per second) , Gbps (Giga bits per second) , Tbps ( Tera bits per second )

Bandwidth : Data transfer rates that can be supported by a network is called its bandwidth.

Switching Techniques

• In large network, there might be multiple path ( wired/wireless ) linking the sender and receiver.
• Switching is the technique by which nodes control or switch data to transmit it between specific points on a network
• So We can say Switching techniques are used for transferring data across different computers in a network.
• When data/file is sent in a network to any computer , file is divided into smaller data files called packets.

Two types of Switching Techniques : Circuit switching & Packet switching

Circuit switching

• All packets use same path
• In circuit switching there are 3 phases: 
  i) Connection Establishment. 
  ii) Data Transfer. 
  iii) Connection Released.
• In circuit switching, each data unit know the entire path address which is provided by the source.
• Circuit switching is more reliable.

Packet Switching

• In Packet switching directly data transfer takes place.
• In Packet switching, each data unit just know the final destination address intermediate path is decided by the routers.

IP ADDRESS

·      Every machine on the internet has unique IP address.

·      216.45.34.135 etc… 4 octets

·      Ip address is designed by IETF.

·      Ip address is made of 32 bits number.

Ex 76.240. 249.145 into 1001100. 11110000. 11111001. 10010001

An IP address has two main parts:

1. Network Address (Network ID): Identifies the network.
2. Host Address (Host ID): Identifies a device on that network.

Here’s an example:

• IP Address: 192.168.1.100
• Network Address: 192.168.1 (identifies the network)
• Host Address: 100 (identifies the device on the network).

Network devices/hardware

Hosts/nodes – means computers which are connected to the network.

Server –a server is just a powerful computer with more processing power and more memory. it is the main computer in a network. It has the files or resources which are requested by client computer.

Clients – client is   a computer that that requests for file or services from a server.

Modem – Modem is short for “Modulator-Demodulator.“

1. It is a hardware component that allows a computer or another device,such as a router or switch,to connect to the Internet.
2. As we know phone lines work on analog signal while computer works on digital signal,So the role of Modem is to convert Digital signal to Analog so that it can be carried by telephone lines and other side it again convert analog signal to digital form.

RJ45 Connector – The “RJ” in RJ45 stands for “registered jack”.

• Registered Jack 45 (RJ45) is a standard type of physical connector for network cables.
• RJ45 connectors are most commonly seen with Ethernet cables and networks.Modern Ethernet cables feature small plastic plugs on each end that are inserted into the RJ45 jacks of Ethernet devices.

Ethernet Card or Nic ( network interface card ) – it is a network card , it is present in every computer.

• A computer need NIC to connect with a network it is like a gateway of computer to network.
• NIC is also called terminal access point(TAP) or
• network interface unit (NIU).
• different manufacturers give it different names.

Each nic has MAC ADDRESS (media access control )

Mac address – mac address is also called physical address. It is assigned during manufacturing of card.

• It is a 6byte address ex.(19:b7:e5:6t:g6:d4).

• First three bytes (19:b7:e5) are manufacturer id and last three bytes (6t:g6:d4) are nic card number.

• Every mac address is unique for each card.

• Mac address is used to  identify a device in a network.
• Wifi card – it is a adapter with built in wireless radio and antenna. Most common wifi cards are pci express wifi cards .it if fit into motherboard.

It allow us to connect to a network wirelessly.

• Hub (concentrator)-  it is a hardware device used to connect several computer together.

Hub sends data to all nodes in the network , specified node accept data and other ignore it. it is of two types .

active hubs – it electrically amplify signal as data/signal moves from one connected computer to another.

passive hubs – allow the data or signal to pass from one computer to another without any changes.

• Switch – it is a device that is used to divide network into sub-networks (subnet) to prevent traffic overloading.

How a switch works :

It does not  send data to all nodes like hub ,instead a switch create a temporary connection between the source and the destination and terminate the connection once the conversation is done.

(LANs which are segmented through switch are called  switched LANs)

• Bridge – this device is used to link two separate network together.

This device is smart enough to know that which computer is in which network.

Bridges can only handle networks that follow same protocols.

Bridge use physical means mac address.

• Router – a router is responsible for forwarding data from one network to ta different network. router works like a bridge but can handle different protocols.a router uses logical address means ip address.

1. Gateway – a gateway is a device that connects dissimilar networks.

In enterprises a gateway often acts as a proxy server and a firewall

Proxy server –   a machine that is not actually a server but appears as a server

Firewall –  a system designed to prevent unauthorized access to or from a private network

1. Access point  (wireless access point )- WAP is a hardware device that establishes connection (by broadcasting wireless signals ) of computing devices on wireless LAN with a fixed wire network.

ACCESS POINT device has approx 150 feet range (home based APs).

• Wifi routers can function as access points but not all access points can work as routers.

Hosts/nodes – means computers which are connected to the network.

Server – a server is just a powerful computer with more processing power and more memory. it is the main computer in a network. It has the files or resources which are requested by client computer.

Clients – client is a computer that that requests for file or services from a server.

1. Modem – Modem is short for “Modulator-Demodulator.“
2. Allows a computer connect to the Internet.
3. As we know phone lines work on analog signal while computer works on digital signal,So the role of Modem is to convert Digital signal to Analog so that it can be carried by telephone lines and other side it again convert analog signal to digital form.

• RJ45 Connector – The “RJ” in RJ45 stands for “registered jack”.
• Registered Jack 45 (RJ45) is a standard type of physical connector for network cables.
• RJ45 connectors are most commonly seen with Ethernet cables and networks.
• Modern Ethernet cables feature small plastic plugs on each end that are inserted into the RJ45 jacks of Ethernet devices.

• Ethernet Card or Nic ( network interface card ) – it is a network card , it is present in every computer.
• A computer need NIC to connect with a network it is like a gateway of computer to network.
• NIC is also called terminal access point(TAP) or
• network interface unit (NIU).
• different manufacturers give it different names.

• A Repeater is an electronic device in a communication channel that increases the power of a signal and retransmits it, allowing it to travel further.

• Wifi card – it is a adapter with built in wireless radio and antenna. Most common wifi cards are pci express wifi cards .it if fit into motherboard.

It allow us to connect to a network wirelessly.

• Hub (concentrator)-  it is a hardware device used to connect several computer together.

Hub sends data to all nodes in the network , specified node accept data and other ignore it. it is of two types .

Active hubs – it electrically amplify signal as data/signal moves from one connected computer to another.

Passive hubs – allow the data or signal to pass from one computer to another without any changes.

• Switch – How a switch works :

It does not  send data to all nodes like hub ,instead a switch create a temporary connection between the source and the destination and terminate the connection once the conversation is done.

• Router – a router is responsible for forwarding data from one network to a different network.A router uses logical address means ip address.

• Gateway – a gateway is a device that connects dissimilar networks.

In enterprises a gateway often acts as a proxy server and a firewall

Proxy server –   a machine that is not actually a server but appears as a server Firewall –  a system designed to prevent unauthorized access to or from a private network

Network Topologies

The way in which the computers/devices are physically interconnected to form a network is called a Topology.

It can be defined as the arrangement or structure of network.

Types of Topologies Are :

1. Bus Topology – In bus topology all the nodes are connected to a main cable called backbone.
2. If any node has to send some information to any other node, it sends the signal to the backbone. The signal travels through the entire length of the backbone and is received by the node for which it is intended.
3. A small device called terminator is attached at each end of the backbone.

When the signal reaches the end of backbone, it is absorbed by the terminator and the backbone gets free to carry another signal.

• Star Topology – In star topology each node is directly connected to a hub/switch.

• If any node has to send some information to any other node, it sends the signal to the hub/switch. This signal is then broadcast (in case of a hub) to all the nodes but is accepted by the intended node(s).

• Tree Topology – Tree topology is a combination of bus and star topologies.

• It is used to combine multiple star topology networks.
• All the stars are connected together like a bus.

Types of network

Types of networks based on geographical spread.

1. Lan ( local area network ) – this network is limited to local area .

(eg office , building or a factory or approx 1km area)

Hardware resources as well as software are shared among users.

• Wan ( wide area network ) – these networks can spread across  countries.

It can be group of LAN networks connected with each other forming a wan network.

Largest wan network is INTERNET.

• Pan ( Personal Area network ) – It is a computer network for interconnecting electronic devices centered on an individual person’s workspace.

A PAN provides data transmission among devices such as computers, smartphones, tablets and personal digital assistants.

MAN (Metropolitan Area Network) : Covers a city or town, connecting multiple LANs. Provides high-speed connectivity for businesses, universities, and government institutions. Typically uses fiber-optic cables, Wi-Fi, or other wireless technologies to link locations within a metropolitan area, enabling fast data transfer 🌟.

Network Protocols

A protocol is a set of rules.

These protocols are followed by nodes/servers etc for communication purposes.

TCP/IP is a collection of protocols that includes transmission control protocol , internet protocol , user datagram protocol and many others.

TCP – connection oriented protocol bcoz connection between two nodes is built CALLED handshake process.

Uses ports to ensure delivery of packets.

tcp fragments and reassembles messages/DATA in correct order using sequencing function.

IP – connectionless protocol, it is responsible for providing address of each computer and performing routing.

http : HTTP is designed for transferring a hypertext among two or more systems.

HTML tags are used for creating links.

These links may be in any form like text or images.

HTTP is designed on Client-server principles.

Client Server Architecture : which allow a client system for establishing a connection with the server machine for making a request. The server acknowledges the request initiated by the client and responds accordingly.

2. ftp : FTP transfers file from one one host to another.Efficient for sending & receiving larger files.

Advantages of ftp : used for transfer files from one network in organization to another. Allow geographically dispersed group to co-operate on a project.

Ftp also works as a client server process.Ex.

site:ftp.studytoppers.org login:mcalore pass:h4x0r4lyfe port:21

we can issue more commands , process will respond appropriately.

3. pop3 (post office protocol 3 ) :  this protocol is used by email clients to retrieve email messages from mail servers over TCP/IP network.

Pop3 deletes emails on the server after downloading then on our local email client.

POP3 supports only one mail server for each mailbox

Pop3 works on 2 ports :

port 110 – default, non encrypted port, used for unsecured email communications

port 995 –  encrypted port, used for secure email communications

port – In computer networking, a port is a communication endpoint. Physical as well as wireless connections are terminated at ports of hardware devices. At the software level, within an operating system, a port is a logical construct that identifies a specific process or a type of network service. Ports are identified for each protocol and address combination by 16-bit unsigned numbers, commonly known as the port number

• PPP (Point-to-Point Protocol): Establishes direct network connections between two devices. Used for dial-up, VPNs, and router connections. Provides authentication, compression, and encryption. Widely used for secure remote access. Simple, efficient, and reliable.
• Telnet: Allows remote access to devices over a network. Uses plain text, making it insecure for sensitive data. Common for device management, but SSH is preferred for security. Easy to use, but vulnerable to attacks.
• VoIP (Voice over Internet Protocol): Transmits voice calls over IP networks, like the internet. Enables internet phone calls, video conferencing, and messaging. Cost-effective, scalable, and feature-rich. Popular for business and personal use.

Introduction to Web Services

World Wide Web ( WWW )

WWW is a collection of hypermedia documents , standards and protocols governing the way in which these documents are created and displayed on the internet.

English scientist Tim Berners-Lee invented the World Wide Web in 1989 while employed at CERN.

European Organization for Nuclear Research ( CERN ) – Conducts Physics Research

HTTP – Hyper Text Transfer Protocol

HTTP stands for Hypertext transfer protocol.

 It is used to manage communications between web browsers and servers.

It retrieve interlinked text documents ( hypertext documents )

Domain name and address

• Every machine on the internet has unique IP address.
• 216.45.34.135 etc… 4 octets
• Ip address is designed by IETF.
• Ip address is made of 32 bits number.

 Ex 76.240. 249.145 into 1001100. 11110000. 11111001. 10010001

 Ip address has two parts : 1. Network Address    2. Local/Host Address

 Commonly used worldwide domain types :

.com – commercial purposes    /    .edu – education purposes  /  .gov – government sites   / .net – tech purpuses   /   .org – ngo

 Abbreviations used as country suffix are :

.in – india   /   .uk – united kingdom   /   .au – Australia   Etc…

Domain Name Service

• Domain name convention is introduced for user’s convenience.

·      We cannot remember all the IP address of websites we use.

• So domain name service is an electronic directory/server which control the mechanism of translation of domain names and ip address.

Uniform resource locator

Ex. https://www.india.gov.in/my-government/indian-parliament

https://www.mentorwish.com

URL is Used to identify a webpage or website .

It has several parts : protocol , host , domain name & type

Web server

• Web server is a computer where the web content is stored. Basically web server is used to host the web sites
• Web server respond to the client request by Sending the file to the client associated with the requested URL.
• A client is a end user which request some information on the internet.

Web browser

A web browser (commonly referred to as a browser) is a software application for accessing information on the World Wide Web. When a user requests a particular website, the web browser retrieves the necessary content from a web server and then displays the resulting web page on the user’s device.

Ex. chrome , mozilla etc

Incognito mode – It is a private browsing feature.

Website

A website (also written as web site) is a collection of web pages that is identified by a common domain name and published on at least one web server. Domain names Examples are topperg.com , wikipedia.org, google.com, and amazon.com.

HTML – Stands for Hypertext Markup Language

• Hypertext Markup Language is the standard markup language for documents designed to be displayed in a web browser.
• It is generally assisted by other technologies like CSS, JavaScript,AJAX etc.
• It is tag based code, where tags are predefined. Tags are the instruction how web page will appear on browsers.
• It is not case sensitive.

HTML files are stored with extension .HTM or .HTML

Few tags are:<HTML>,<TITLE>,<A>,<IMG> etc.

Xml – Extensible Markup language

• Extensible Markup Language is a markup language that defines a set of rules for encoding data in a format that is both human-readable and machine-readable.
• It allows us to exchange data between heterogeneous computer systems.
• XML stores information in a plain text format so it is not blocked by any firewall.
• Tags are not predefined i.e. we can create our own tag .It is case sensitive.

Web Hosting

It is a service which allows individual or organization to make their website accessible through world wide web.

Website is hosted on Web servers.       

• Web Hosting provides various services like – FTP upload, Email  account, website building tool, databases etc.