Data Communication — NCERT Solutions

HTTP stands for: HyperText Transfer Protocol

• It is the primary protocol used to access the World Wide Web.
• It was developed by Tim Berners-Lee at CERN in 1989, in collaboration with IETF and W3C.
• HTTP is a request-response (client-server) protocol that runs over TCP.
• It defines how information is formatted and transmitted, and how web servers and browsers should respond to various commands.

HTTP (HyperText Transfer Protocol):

• Full form: HyperText Transfer Protocol.
• Purpose: It is the primary protocol used to access the World Wide Web (WWW).
• Developer: Developed by Tim Berners-Lee at CERN in 1989, in collaboration with IETF and W3C.
• Working Model: HTTP follows a request-response (client-server) model and runs over TCP.
• The client (web browser) sends an HTTP request to the server.
• The server responds with the requested web page or resource.
• Function: It defines how information (hypertext) is formatted and transmitted, and how web servers and browsers should respond to various commands.
• Hypertext refers to a document that contains images or text that can be linked to another document or text.
• Example: When you type http://www.example.com in a browser, HTTP is used to fetch and display the web page.

Bandwidth:

• Definition: Bandwidth of a channel is the range of frequencies available for transmission of data through that channel.
• Formula:

$$\text{Bandwidth} = \text{Maximum Frequency} - \text{Minimum Frequency}$$

• Unit: Measured in Hertz (Hz).
• $1 \text{ KHz} = 1000 \text{ Hz}$
• $1 \text{ MHz} = 1000 \text{ KHz} = 1,000,000 \text{ Hz}$
• Significance: Higher the bandwidth, higher the data transfer rate. It determines the capacity of a communication channel.
• Example: If a channel can carry frequencies from 500 MHz to 1 GHz, its bandwidth is:

$$1000 \text{ MHz} - 500 \text{ MHz} = 500 \text{ MHz}$$

Bluetooth:

• Definition: Bluetooth is a short-range wireless communication technology used to connect devices wirelessly over a short distance.
• Range: Typically up to 10 metres (some versions up to 100 metres).
• Frequency: Operates in the 2.4 GHz ISM (Industrial, Scientific, Medical) frequency band.
• Uses: Used to connect mobile phones, mouse, headphones, keyboards, computers, printers, speakers, etc., without physical cables.
• Standard: Based on the IEEE 802.15 standard.
• Advantages:
• No cables required.
• Low power consumption.
• Supports both voice and data transmission.
• Limitations:
• Short range.
• Lower data transfer rate compared to Wi-Fi.
• Example: Connecting wireless earphones to a smartphone via Bluetooth.

DNS (Domain Name System):

• Full form: Domain Name System.
• Purpose: DNS is a protocol/system that translates human-readable domain names (like www.google.com) into IP addresses (like 142.250.64.100) that computers use to identify each other on the network.
• Need: Computers communicate using IP addresses (numerical), but humans find it easier to remember domain names. DNS acts as a "phone book" of the Internet.
• Working:

1. A user types a domain name in the browser.
2. The DNS server looks up the corresponding IP address.
3. The browser uses the IP address to connect to the web server.

• Hierarchy: DNS follows a hierarchical structure — Root DNS servers → Top-Level Domain (TLD) servers (e.g., .com, .in) → Authoritative DNS servers.
• Importance: Without DNS, users would have to remember IP addresses of every website they visit.

Data Transfer Rate:

• Definition: Data transfer rate is the number of bits transmitted between source and destination in one second. It is also known as bit rate.
• Unit: Measured in bits per second (bps).
• Higher Units:

$$1 \text{ Kbps} = 2^{10} \text{ bps} = 1024 \text{ bps}$$
$$1 \text{ Mbps} = 2^{20} \text{ bps} = 1024 \text{ Kbps}$$
$$1 \text{ Gbps} = 2^{30} \text{ bps} = 1024 \text{ Mbps}$$
$$1 \text{ Tbps} = 2^{40} \text{ bps} = 1024 \text{ Gbps}$$

• Significance: Higher the data transfer rate, faster the data is transmitted. It depends on the bandwidth of the channel — higher bandwidth leads to higher data transfer rate.
• Example: A broadband connection with a speed of 100 Mbps can transfer 100 × 2²⁰ bits every second.

Protocol in Data Communication:

Definition: A protocol is a set of standard rules that the communicating parties — the sender, the receiver, and all other intermediate devices — must follow to ensure successful and reliable data communication.

Why Protocols are Needed:
When two devices communicate, they must agree on:

• How computers identify one another on a network (addressing).
• The form to which data should be converted for transit.
• How to decide whether data received is for that node or to be forwarded.
• Ensuring all data reaches the destination without any loss (flow control).
• How to rearrange packets and process them at the destination.

Functions of Protocols:

1. Flow Control: Manages the rate of data transmission between sender and receiver to prevent data loss.
2. Access Control: Determines which device has control over the communication channel at a given time.
3. Addressing: Ensures data is delivered to the correct destination.
4. Error Detection and Correction: Detects and corrects errors in transmitted data.

Example — HTTP (HyperText Transfer Protocol):
When a user types a URL in a web browser:

1. The browser (client) sends an HTTP request to the web server.
2. The web server processes the request and sends back an HTTP response containing the web page.
3. Both the browser and server follow the rules defined by HTTP — the format of the request, the format of the response, status codes (like 200 OK, 404 Not Found), etc.

Without this common protocol, the browser and server would not understand each other.

Other Examples of Protocols: FTP, TCP/IP, PPP, Ethernet.

Given:

• Minimum frequency $= 500 \text{ MHz}$
• Maximum frequency $= 1 \text{ GHz} = 1000 \text{ MHz}$

Formula:
$$\text{Bandwidth} = \text{Maximum Frequency} - \text{Minimum Frequency}$$

Calculation:
$$\text{Bandwidth} = 1000 \text{ MHz} - 500 \text{ MHz}$$
$$\boxed{\text{Bandwidth} = 500 \text{ MHz}}$$

Answer: The bandwidth of the composite signal is 500 MHz.