NCERT Solutions for Class 12 Computer Science Chapter 11: Data Communication

Full-duplex communication mode allows communication in both directions simultaneously.

LAN (Local Area Network) offers the highest speed and WAN (Wide Area Network) covers the largest area.

Optical Fiber transmission media carries signals in the form of light.

The range of frequency for radio waves is between 3 KHz to 1 GHz.

HTTP stands for Hyper Text Transfer Protocol.

Data communication refers to the exchange of data between two or more networked or connected devices. The main components of data communication are sender, receiver, communication medium, the message to be communicated, and certain rules called protocols to be followed during communication.

The three categories of wired media are as follows :

1. Twisted Pair Cable — A twisted-pair cable consists of two copper wires twisted like a DNA helical structure. Both the copper wires are insulated with plastic covers. Usually, a number of such pairs are combined together and covered with a protective outer wrapping. Each of the twisted pairs act as a single communication link. The use of twisted configuration minimizes the effect of electrical interference from similar pairs close by. Twisted pairs are less expensive and most commonly used in telephone lines and LANs. These cables are of two types: Unshielded twisted-pair (UTP) and Shielded twisted-pair (STP).

2. Co-axial Cable — Coaxial cable has a copper wire at the core of the cable which is surrounded with insulating material. The insulator is further surrounded with an outer conductor (usually a copper mesh). This outer conductor is wrapped in a plastic cover. The key to success of coaxial cable is its shielded design that allows the cable's copper core to transmit data quickly, without interference of environmental factors. These types of cables are used to carry signals of higher frequencies to a longer distance.

3. Fiber-Optic Cable — The optical fiber cable carries data as light, which travels inside a thin fiber of glass. Optic fiber uses refraction to direct the light through the media. A thin transparent strand of glass at the centre is covered with a layer of less dense glass called cladding. This whole arrangement is covered with an outer jacket made of PVC or Teflon. Such types of cables are usually used in backbone networks. These cables are of light weight and have higher bandwidth which means higher data transfer rate. Signals can travel longer distances and electromagnetic noise cannot affect the cable. However, optic fibers are expensive and unidirectional. Two cables are required for full duplex communication.

The advantages of optical fiber cable are as follows :

1. It is immune to electrical and magnetic interference.

2. It is highly suitable for harsh industrial environment.

3. It guarantees secure transmission and has a very high transmission capacity.

4. Fiber optic cables can be used for broadband transmission.

The disadvantages of optical fiber cable are as follows :

1. Connecting either two fibers together or a light source to a fiber is a difficult process.

2. In order to incept the signal, the fiber must be cut and a detector inserted.

3. Light can reach the receiver out of phase.

4. Connection losses are common problems.

5. Fiber optics cables are more difficult to solder.

6. They are the most expensive of all the cables.

1 Gbps is equal to 1000000000 bits per second. Therefore, to convert 18 Gbps to bits per second:

18 Gbps = 18 * 1000000000 = 18000000000 bits per second

So, 18 Gbps is equal to 18,000,000,000 bits per second.

(a) HTTP — HTTP stands for HyperText Transfer Protocol, which is the primary protocol used to access the World Wide Web. It is a request-response protocol (also called client-server) that runs over TCP. HTTP facilitates access to hypertext from the World Wide Web by defining how information is formatted and transmitted, and how web servers and browsers should respond to various commands.

For example, whenever we enter the URL http://www.ncert.nic.in in a browser, it sends an HTTP request to the web server where ncert.nic.in is hosted. The HTTP response from the web server fetches and sends the requested web page, which is then displayed on the browser.

(b) Bandwidth — Bandwidth of a channel is the range of frequencies available for the transmission of data through that channel. The higher the bandwidth, the higher the data transfer rate. Bandwidth is calculated as the difference between the maximum and minimum frequencies contained in the composite signals, and it is measured in Hertz (Hz).

(c) Bluetooth — Bluetooth is a short-range wireless technology used to connect devices like mobile phones, mouse, headphones, keyboards, and computers wirelessly over short distances. It enables tasks such as printing documents with Bluetooth-enabled printers without the need for physical connections. These devices utilize a low-cost transceiver chip that operates within the unlicensed frequency band of 2.4 GHz for data transmission and reception. Bluetooth devices can communicate within a range of 10 meters, achieving speeds of 1-2 Mbps. The technology allows up to 255 devices to form a network, with 8 devices capable of simultaneous communication while others remain inactive until prompted by the master device.

(d) DNS — DNS, known as the Domain Name System, serves as the phonebook of the Internet. It provides a character-based naming system for servers, allowing users to access websites using easy-to-remember domain names like google.com instead of numeric IP addresses such as 8.8.8.8. DNS is essential for internet navigation as it translates domain names into IP addresses, enabling seamless communication and resource access across the web.

(e) Data transfer rate — Data transfer rate is the number of bits transmitted between source and destination in one second. It is also known as bit rate. It is measured in terms of bits per second (bps). The higher units for data transfer rates are:
1 Kbps = 210 bps = 1024 bps
1 Mbps = 220 bps = 1024 Kbps
1 Gbps = 230 bps = 1024 Mbps
1 Tbps = 240 bps = 1024 Gbps

In data communication, protocol is a set of standard rules that the communicating parties — the sender, the receiver, and all other intermediate devices need to follow in order to have successful and reliable data communication.

For example, let's consider the Transmission Control Protocol/Internet Protocol (TCP/IP) suite, which is widely used for communication over the Internet. TCP/IP defines a set of protocols that govern how data is transmitted over networks. TCP (Transmission Control Protocol) ensures reliable, ordered, and error-checked delivery of data packets between devices. IP (Internet Protocol), on the other hand, handles the routing and addressing of data packets across networks.

When a user sends an email using a client like Outlook or Gmail, TCP/IP protocols come into play. TCP breaks the email message into packets, adds sequence numbers for reassembly, and ensures each packet arrives without errors. IP handles the routing of these packets over the Internet to reach the recipient's email server, where the packets are reassembled and the email is delivered to the recipient. This entire process relies on adherence to the TCP/IP protocol suite, demonstrating the role of protocols in data communication.

Bandwidth is the difference of maximum and minimum frequency contained in the composite signals.

Bandwidth = Maximum Frequency - Minimum Frequency
Bandwidth = 1000000000 Hz - 500000000 Hz
Bandwidth = 500000000 Hz

Therefore, the bandwidth of the composite signal is 500 MHz.