Class 12 Computer Network Transmission Control Protocol

TCP(Transmission Control Protocol)

It ensures reliable communication to deliver the packets. It also fragments and reassembles messages using a sequencing function so that they can be reassembles in correct order.

Network Congestion and retransmission in TCP

Network congestion is a specific condition in a network when more data packets are coming to network devices than they can handle and process at a time. Network congestion is analogous to the congestion on roads and can be handled similarly. To control the road’s congestion problem, often a technique called metering is used that controls the incoming traffic( number of vehicles entering a road) on roads by employing measures like traffic-signals or rerouting the traffic.

The metering technique is used to control network congestion in the following way :-

(i) It ensures that sender does not overflow the network and it is one by controlling the flow of data packets.
(ii) It ensures the routers along the path work as per their capacity to handle network traffic and do not become overloaded by rerouting the data packets or delaying the transmission or informaing the senders about the network congestion.

Cellular/ Wireless connectivity Protocols

2G( the second Generation)

2G was introduced in 1992 and is fully digital technology. It allowed some data along the calls in the form of text messages. IT improved security by allowing voice and control signals to be encrypted. It enables new services such as text messages, MMS, caller ID and also introduced SIM(Subscriber Identity Module) It can handle data speed of up to 64 kbps. 2G system was based on the technology called GSM(Global system for mobile communication)and its technological backbone is TDMA(Time Division Multiple Access). But TDMA has some diaadvantages like low network range and slow data rates. T overcome these problems two new networks were introduced – CDMA(Code Division Multiple Access) and EDGE

3G(the third generation)

3G was introduced in 2000 to cater to increasing demands for data by consumers. 3G has intitially offered speed of 500 Kbps to 2 Mbps. It is now as high as 20 Mbps. It can handle data in the form of text messages and multimedia such as audio/video messages along with voice calls. Web browsing, email, video downloading, picture sharing and other smart phone technologies were introduced in the third generation. The 3G utilizes a new technology called UTMS(Universal Mobile Telecommunications System) and its technological backbone is wideband version of CDMA(WCDMA). The main features of 3G are
• Devices are called smartphones
• Fast communication, data speed between 144 kbps and 2mbps
• High quality voice transmission
• Supported multimedia
• Mobile TV, mobile internet

4G (the fourth generation)

It was introduces in 2013. It offers data aped upto 50 Mbps and even high depending upon the technology. The salient features of 4G are
• Wireless broadband
• Based on LTE(Long Term Evolution)-Advanced is a series of upgrades to existing UMTS technology
• Significantly faster speed(100 Mbps-1Gbps)and reduced network congestion.
• High voice quality(as if voice is just next to you)


Wi-Fi( Wireless Fidelity) protocol governs the rules to connect to the internet without a direct line from your PC to the ISP. Devices that can use Wi-Fi technology include PCs, video game consoles, smartphones, digital cameras, smart TVs, digital audio players and modern printers. These devices can connect to the internet via a WLAN and wireless access point(hotspot). This hotspot had a range of about 20 meters indoors and greater range outdoors.

Various protocols used in networks

HTTP(Hypertext Transfer Protocol)

HTTP means HyperText Transfer Protocol. HTTP is the underlying protocol used by the World Wide Web and this protocol defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.

FTP(File Transfer Protocol)

The File Transfer Protocol (FTP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a web page file to a Web server). FTP is a client-server protocol that relies on two communications channels between client and server: a command channel for controlling the conversation and a data channel for transmitting file content. Clients initiate conversations with servers by requesting to download a file. Using FTP, a client can upload, download, delete, rename, move and copy files on a server.

POP(Post Office Protocol)

Post Office Protocol version 3 (POP3) is a standard mail protocol used to receive emails from a remote server to a local email client. POP3 allows you to download email messages on your local computer and read them even when you are offline. Note, that when you use POP3 to connect to your email account, messages are downloaded locally and removed from the email server. By default, the POP3 protocol works on two ports:
Port 110 – this is the default POP3 non-encrypted port
Port 995 – this is the port you need to use if you want to connect using POP3 securely

IMAP(Internet Message Access Protocol)

The Internet Message Access Protocol (IMAP) is a mail protocol used for accessing email on a remote web server from a local client. IMAP and POP3 are the two most commonly used Internet mail protocols for retrieving emails. Both protocols are supported by all modern email clients and web servers. While the POP3 protocol assumes that your email is being accessed only from one application, IMAP allows simultaneous access by multiple clients. By default, the IMAP protocol works on two ports:
Port 143 – this is the default IMAP non-encrypted port
Port 993 – this is the port you need to use if you want to connect using IMAP securely

SMTP(Simple Mail Transfer Protocol)

Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending emails across the Internet.By default, the SMTP protocol works on these ports:
Port 25 – this is the default SMTP non-encrypted port
Port 465 – this is the port used if you want to send messages using SMTP securely.

VoIP(Voice over Internet Protocol)

Voice over Internet Protocol (VoIP), is a technology that allowing you to make voice calls over a broadband Internet connection instead of a analog (regular) phone line. Some VoIP services allow you to call people using the same service, but others may allow you to call anyone. Voice are converted into a digital signal by VoIP services that travel over the Internet. If regular phone number is called, the signal is converted to a regular telephone signal i.e. an analog signal before it reaches the destination. VoIP can allow you to make a call directly from a computer having a special VoIP phone, or a traditional phone connected to a special adapter. Wireless hot spots in locations such as airports, hospitals, cafes etc allow you to connect to the Internet and can enable you to use VoIP service wirelessly.

NFC(Near Field Communication)

NFC is a short-range high frequency wireless communication technology that enables the exchange of data between devices over about a 10 cm distance.

How HTTP Works–A Basic Idea

For web Communications, the request message (HTTP request) is sent to an HTTP server in the form of URLs by the HTTP client. The HTTP server receives the request, fetches the information as per the request and sends it to the HTTP client. This is called the response message from HTTP server. The HTTP client( the browser) receives the response message, interpret the message and displays the contents of the message on the browser’s window.