12 computer science networks, types, topology, LAN, WAN, hub switch

Computer Networks

Syllabus of computer Network

● Evolution of networking: introduction to computer networks, evolution of networking (ARPANET, NSFNET, INTERNET)

● Data communication terminologies: concept of communication, components of data communication (sender, receiver, message, communication media, protocols), measuring capacity of communication
media (bandwidth, data transfer rate), IP address, switching techniques (Circuit switching, Packet switching)

● Transmission media: Wired communication media (Twisted pair cable, Co-axial cable, Fiber-optic cable), Wireless media (Radio waves, Micro waves, Infrared waves

● Network devices (Modem, Ethernet card, RJ45, Repeater, Hub, Switch, Router, Gateway, WIFI card)

● Network topologies and Network types: types of networks (PAN, LAN, MAN, WAN), networking topologies (Bus, Star, Tree)

● Network protocol: HTTP, FTP, PPP, SMTP, TCP/IP, POP3, HTTPS, TELNET, VoIP

● Introduction to web services: WWW, Hyper Text Markup Language (HTML), Extensible Markup Language (XML), domain names, URL, website, web browser, web servers, web hosting

Computer Network

A computer network is a collection of interconnected autonomous computers and other devices to share data and other resources.

Advantages of computer Network:

(i) File Sharing Networking of computer helps the user to share data files.

(ii) Hardware Sharing Users can share devices such as printers, scanners, CD-ROM drives, hard drives, etc. in a computer network.

(iii) Application Sharing Applications can be shared over the network and this allows implementation of client/server applications.

(iv) User Communication This allows users to communicate using E-mail, newsgroups, video conferencing within the network.

(v) Access to Remote Database This allows users to access remote database, e.g. airline reservation database may be accessed for ticket booking.

(vi) Central Storage of Data –
Files can be stored on a central node (the file server) that can be shared and made available to each and every user in an organization.

(vii) Improved Communication:

A computer network enables fast, reliable and secure communication between users. It saves our time and offers easy communication methods.

Ex. Sending e-mail, SMS and MMS etc.

(viii)Reduced Communication cost:

Sharing resources also reduces its communication cost. Using today’s public network we can send a large quantity of data at very low cost. Internet and Mobile network playing very important role in sending and receiving text, image, audio and video data at low cost.

Structure of a Network

Sender:

A device or a computer that sends the data.

Receiver:

A device or a computer that receives the data.

Message:

Message is the information to be communicated. It may be text, images, audio or video.

Medium:

A transmission medium is a physical path through which the data flows from sender to receiver. A cable or wire or radio waves can be the medium.

Protocol:

A set of rules that governs data transmission. It represents the communication methods which to be followed by the sending and receiving devices.

ARPANET

The Advanced Research Projects Agency NETwork (ARPANET) was the world’s first operational packet switching network.

The U.S department of defense sponsored a project named ARPANET, whose goal was to connect computers at different universities and U.S defence. In 1969, the University of California at Los Angeles, the University of California and the University of Utah were connected as the beginning of the ARPANET using 50 Kbits circuits.

In mid 80’s, the National Science Foundation created a new network called NSFnet, which was more capable than ARPANET.

WWW

The World Wide Web (WWW) is a system of interlinked hypertext documents accessed via Internet. With a web browser, one can view web pages that may contain text, images, videos and other
multimedia and can navigate between them via hyperlinks

Internet:

In the 1990’s, internet, which is a network of networks, came into existence. The internet has evolved from ARPANET. The computers are connected through World Wide Web that comprises a large network and shares a common communication protocol (Transmission Control Protocol-Internet Protocol, TCP/IP). It allows computers of different types to exchange information and is known as internet. Millions of domestic, business and government networks are connected with each other for the purpose of sharing files, data, email, etc. Most of the computers are not connected directly to the internet.
Instead, they are connected to smaller networks which are further connected to a backbone network through gateways.

Interspace:

Interspace is a software that allows multiple users in a client-server environment to communicate with each other by sending and receiving data of various types such as data files, video, audio and textual data in a 3-D environment. It facilitates online real-time exchange of data. Interspace is the most advanced term of communication available on the internet today.

Intranet

An intranet is a network that connects the computers and networks with in an organization that is based on Internet technology. It uses the TCP/IP protocols, server and browser software used for the Internet. With an intranet, the basic services of the Internet like E-mail, FTP, etc. are used.

Switching Techniques

Switching techniques are used for transmitting data across networks. Different types of switching techniques are employed to provide communication between two computers. These are as follows

Circuit Switching:

Circuit switching provides end-to-end connection between two computers. It is established usually in a telephone network where one person is making a call and another is receiving a call. In a telephone system, the communication must be established between the two participants, i.e., the sender and the receiver. The circuit is established between these two participants before the transfer of data takes place.

The following actions take place during circuit switching:

A request signal is sent by the sender to set up the connection with the receiver.
It establishes a physical connection between the two participants.
All intermediate nodes are identified. These nodes are also called switching nodes.
If the destination node is available, it sends back the acknowledgement of receiving a signal. Hence, data transmission begins.
When the data transmission is complete, the call can be terminated.

Packet switching:

In packet switching technique, the entire data is divided into small fragments called packets. Each packet is of a fixed size, usually 128 bytes or 512 bytes.
Packet switching is similar to post office operation. Each packet has a source address as well as destination address (IP address) for being transmitted, in the same way as a postman delivers a letter to a specific destination address. As there is no direct connection established between the sender and the receiver, each packet follows different routes and, therefore, the packets are delivered in a random order at the destination address. It is the TCP protocol which then arranges all received packets in a sequential order. During the transfer of packets, each packet has to pass through several intermediate nodes, so each intermediate node checks for destination IP address. If the packet matches with the node address, it is received; otherwise, it is passed on to the next node until it reaches the destination IP address.

Comparison between the various switching techniques

Criteria Circuit Switching Path Packet Switching Path

established in advance Yes No

Store and forward technique No Yes

Message follows multiple routes No Yes

DATA COMMUNICATION TERMINOLOGIES:

Channel:

A channel is a communication path through which the data is transmitted from the sender device to the receiver device.

Data :

Data are entities that are stored in the form of 0’s and 1’s, which convey some special meaning to the computer system.

Signals :

Signals are the electric or electromagnetic encoding of data and are used to transmit data.

Baud:

The number of changes in a signal per second is known as baud. It is a measure of the number of symbols (signals) transferred or line changes every second. It may represent more than one binary bit. Each symbol can represent or convey one (binary encoded signal) or several bits of data. For a binary signal of 20 Hz, this is equivalent to 20 baud (there are 20 changes per second).

Data Transfer Rate:

It is the amount of data transferred in one direction over a link divided by the time taken to transfer it in bits per second (bps). The various measuring units are bits per second (bps) and bytes per second (Bps) or baud (kbps), (mbps),( gbps), (tbps.)

Bandwidth

It is the frequency range of a channel, measured as the difference between the highest and lowest frequencies that the channel supports. The maximum transmission speed is dependent upon the available bandwidth. The larger the bandwidth, the higher the transmission speed.

Point-to-Point Protocol (PPP)

It is a Data link layer (layer 2) communications protocol between two routers directly without any host or any other networking in between.

HTTP

It stands for HyperText Transfer Protocol. It is a protocol used to access the data on the World Wide Web (www). The HTTP protocol can be used to transfer the data in the form of plain text, hypertext, audio, video, and so on.

MAC (Media Access Control ) Address

A Computer or node on a network needs a Network Interface Card (NIC) or LAN card. Each LAN card has its own unique 6-Byte Physical address assigned by the manufacturer, called (MAC) Address for its identification purpose.

MAC addresses are 48-bit (6 Byte) hexadecimal numbers like – MM:MM:MM:SS:SS:SS

where first half (MM) shows Manufacturer ID and second half (SS) shows unique serial number of the card.

In a networks, the MAC address uniquely identifies each node on network segment and allows frames to be marked for specific hosts.

o MAC address is a permanent physical address and does never change.

o Example of MAC Address – 00:A0:C9:12:C5:32

Domain Name System (DNS):

It translates network address (such as IP addresses) into terms understood by humans (such as domain names) and vice versa.

Domain Host Configuration Protocol (DHCP):

It automatically assigns internet addresses to computers and users.

IRC (Internet Relay Chat)

IRC is an application layer protocol that allows users to share text messages. It uses client server model where the clients install IRC client program on their system so that they can communicate with IRC chat server to transfer messages to other clients.

PROTOCOL FOR VoIP

VoIP stands for Voice over Internet Protocol. For transferring of voice, voice over internet protocol is used. The voice calls are first digitized, compressed and then fragmented into small packets, which are then relayed by Internet Protocol (IP) cross network.
Voice-over-IP (VoIP) implementation enables users to carry voice traffic (For example, telephone calls and faxes) over an IP network.

There are 3 main causes for the evolution of the voice-over IP market:

1. Low-cost phone calls

2. Add-on services and unified messaging

3. Merging of data/voice infrastructures

IP Address

All the computers on the Network follow the some set of rules (Protocol) for Communication to each other. One of the most common protocol is TCP/IP.

Each machine in TCP/IP network needs to have a unique 32 bit (4 Byte) address called IP address.

The IP address may be static (permanent )or dynamic (temporary) depending on the network or service provider.

IPv4 addresses are usually represented in dot-decimal notation (four numbers, each ranging from 0 to 255, separated by dots). Example- 208.77.188.166.

TCP/IP (Transmission Control Protocol/Internet Protocol)

TCP enables two hosts to establish a connection and exchange streams of data.

TCP works with the Internet Protocol (IP), which defines how computers send packets of data to each other. The packets are delivered not in a sequential order; instead, they are
delivered randomly. Now, TCP at the receiver side collects all packets and arranges them in a sequential order. TCP is a reliable stream delivery service that guarantees that all bytes received will be identical with bytes sent and in the correct order.

POP3 (Post Office Protocol 3)

The POP (Post Office Protocol 3) is a simple and standard method to access mailbox and download messages to the local computers. The user can receive messages with the help of POP protocol. The advantage is that once the messages are downloaded, an internet connection is no longer needed to read the mail. A user can read all emails offline as these are saved on the computer’s hard disk.

TELNET :

Telnet is a remote login that helps a user to log on to another user’s terminal without being its original user. A user who is logging in to their own system can also get access to log on to another user system and perform various functions such as accessing files or sharing files to/from the remote system. With TELNET, a user logs in as a regular user with whatever privileges that may have been granted to the specific application and data on that computer

GSM stands for Global System for Mobile communication.

It provides its subscribers with roaming facility so that they can use their mobile phones all over the world to communicate with each other. GSM provides digital signalling as well as digital call facility and is so considered as a second generation (2G) mobile phone system. It provides consumers with better voice quality and low-cost alternatives to making calls such as short message service (SMS). It has an ability to carry 64 kbps to 120 mbps of data rates.

CDMA (Code Division Multiple Access)

CDMA stands for Code Division Multiple Access. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. It is a channel access method used by various radio communication technologies. It allows the division of transmission medium into different channels so that transmission from different stations is separated from each other. It employs spread spectrum digital technology where the data is fragmented into small chunks over a number of different frequencies available for use. Analog to digital conversion takes place where audio input is first digitized into binary elements. The CDMA system works directly on 64 kbit/sec.

GPRS (General Packet Radio Services)

GPRS or General Packet Radio Services provides various features over 2G phones with respect to high speed data transfer. A user can send and receive data at the same time and thus uses the same bandwidth for both purposes. Using GPRS technology, a user can make a call and at the same time receive a message without disconnecting the call. However, GPRS usage is charged for the amount of data sent or received. GPRS can provide data rates up to 32kbps to 48kbps.

Wireless in Local Loop (WLL)

Wireless Local Loop (wireless in local loop) technology, the subscriber is connected to the nearest exchange through a radio link instead of copper wires. Wireless in local loop is cheaper and quicker than copper wire connectivity. As the
cost of copper along with the cost of digging increases over time, this method proves cheaper than using copper wires. It is used in remote areas where digging for copper wires is not possible.

ELECTRONIC MAIL (EMAIL)

Email is a method of exchanging digital messages from a sender to one or more recipients.
Some common email protocols are:

• Internet Message Access Protocol (IMAP): A protocol for receiving email messages on the internet.

• Post Office Protocol Version 3 (POP3): A protocol used by email clients to retrieve messages from remote servers.

• Simple Mail Transfer Protocol (SMTP): A protocol used for sending email messages on the internet.

• GOPHER: Another tool of the internet is Gopher, a menu-based program that enables us to browse for information without knowing where the material is located. It lets us search a list of resources and then sends the material to us

VIDEO CONFERENCING

Video conferencing is a communications technology that integrates video and audio to connect users anywhere in the world as if they were in the same room. This term usually refers to communication between three or more users who are in at least two locations, rather than one-on-one communication and it often includes multiple people at each location. Each user or group of users who is participating in a video conference typically must have a computer, a camera, a microphone, a video screen and a sound system.

Basically, this is a system that allows us to conduct meetings or trainings in different places simultaneously. So, this technology is especially popular in the field of business because it allows meetings or conferences to be held without the need for all the participants to travel to a single location, so it saves time and money.

The most popular software used for video conferencing is:

(a) Zoom

(b) Skype