U 2 Data transmission 

Types and Methods of Data Transmission

Data transmission is the process of sending information between devices, whether they’re in the same room or across the globe. This involves breaking data into manageable pieces, choosing how to send it, and ensuring it arrives correctly. Let’s explore the key concepts in simple terms.

1. Data Packets

When you send large files (like photos or videos), the data isn’t sent as one big chunk. Instead, it’s split into smaller pieces called data packets.

Why Use Packets?

• Control: Smaller packets are easier to manage than a continuous stream.

• Flexibility: Packets can take different routes to avoid busy or broken paths.

• Efficiency: If one packet gets lost, only that part needs resending, not the whole file.

Structure of a Packet

Each packet has three parts:

1. Header:

   • Contains the sender’s and receiver’s IP addresses.

   • Includes a sequence number (to reassemble packets in order).

   • Lists the total number of packets (e.g., “Packet 3 of 10”).

2. Payload:

   • The actual data being sent (e.g., part of a photo).

   • Typically around 64 KiB in size.

3. Trailer:

   • Marks the end of the packet.

   • Includes error-checking methods like Cyclic Redundancy Check (CRC):

     • The sender counts all the 1-bits in the payload and converts the total to a hex value.

     • The receiver repeats this check. If the values match, the packet is error-free.

Example:
Imagine mailing a book page by page. Each page (packet) has an address (header), the text (payload), and a seal (trailer) to ensure it wasn’t tampered with.

2. Packet Switching

This is the method used to send packets over networks like the internet.

How It Works

1. A file (e.g., a photo) is split into packets.

2. Each packet travels independently through routers (devices that direct traffic).

3. Routers choose the fastest available path for each packet.

4. At the destination, packets are reassembled in order using their sequence numbers.

Example:
Suppose you send a photo split into 5 packets from New York to London:

• Packet 1 → Route A (via Canada)

• Packet 2 → Route B (via undersea cable)

• Packet 3 → Route C (via satellite)
  Even if packets arrive out of order (e.g., 3, 1, 5, 2, 4), the sequence numbers let the receiver rebuild the photo correctly.

Pros and Cons

• Pros:

  • No single route gets overloaded.

  • Works around broken connections.

  • Fast transmission rates.

• Cons:

  • Packets can be delayed or lost.

  • Reordering causes delays (bad for live streams like Zoom calls).

  • “Hopping” prevents endless lost packets: Each packet has a “hop count” (e.g., 10). Every router reduces this count by 1. If it hits 0, the packet is deleted.

3. Data Transmission Methods

How data is sent depends on distance, speed, and direction.

A. Serial vs. Parallel Transmission

Serial

Parallel

Sends 1 bit at a time over a single wire.

Sends multiple bits (e.g., 8 bits) at once using multiple wires.

Example: USB cables, internet cables.

Example: Internal computer circuits (e.g., CPU to RAM).

Pros: Works well over long distances; no data skewing.

Pros: Faster for short distances.

Cons: Slower than parallel.

Cons: Bits can arrive out of sync over long distances (skewing).

Skewing Example:
Imagine 8 runners (bits) starting a race together. Over a long track, some runners slow down, causing them to finish in the wrong order.

B. Simplex, Half-Duplex, Full-Duplex

Mode

Description

Example

Simplex

Data flows one way only.

Printer (computer sends data; printer doesn’t reply).

Half-Duplex

Data flows both ways, but not at the same time.

Walkie-talkies (you press “talk” to speak, then release to listen).

Full-Duplex

Data flows both ways simultaneously.

Phone calls (both people can talk and listen at once).

4. Universal Serial Bus (USB)

USB is the most common way to connect devices (e.g., keyboards, phones) to computers.

How USB Works

• A USB cable has 4 wires:

  • 2 for power (+5V and ground).

  • 2 for data (send and receive).

• Automatic Detection: When plugged in, the computer detects the device and loads drivers.

• Transmission Modes:

  • Half-duplex: Data goes one way at a time (e.g., older USB 2.0).

  • Full-duplex: Data flows both ways (e.g., USB 3.0+).

USB-C

• A newer, reversible connector (no “wrong way” to plug in).

• Supports faster speeds (10 Gbps) and higher power (100W for charging laptops).

• Backward compatible with older USB versions using adapters.

Pros and Cons

• Pros:

  • Easy to use (plug-and-play).

  • Supplies power to devices (no extra cables).

  • Error detection and retransmission.

• Cons:

  • Limited cable length (5 meters max without hubs).

  • Slower than Ethernet for large data transfers.

Real-World Examples

1. Video Conference (Packet Switching Issues):

   • Problem: Delayed packets cause frozen screens or garbled audio.

   • Cause: Network congestion or lost packets needing retransmission.

2. Printing a Document (Simplex Mode):

   • The computer sends data to the printer, which doesn’t send anything back.

3. Charging Your Phone (USB):

   • USB-C cables transfer data while charging your device at high speed.

Summary

Data transmission involves breaking information into packets, choosing efficient routes (packet switching), and selecting the right method (serial/parallel, simplex/duplex). USB simplifies connecting devices, while error checks like CRC ensure accuracy. Understanding these basics helps explain how emails, videos, and files move seamlessly across the globe!

Methods of Error Detection

When data is transmitted over a network, errors can occur due to interference, hardware malfunctions, or transmission noise. Various techniques have been developed to detect and correct errors to ensure reliable communication. Below, we explore some of the key methods of error detection, along with examples to illustrate their applications.

1. Data Collision and Conflict Detection

One of the most common types of errors in a network is data collision. This happens when two or more devices send data simultaneously on the same channel, causing data to mix and become unreadable. Ethernet networks use a method called Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to manage collisions.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

• This technique listens to the channel before transmitting data.

• If a collision is detected (identified by voltage changes in the Ethernet cable), the transmission is stopped.

• A "jam" signal is sent to notify all devices.

• The device waits for a random time before attempting to resend the data.

Example:

Imagine two computers on a local network trying to send an email simultaneously. Without collision detection, the emails might become garbled. CSMA/CD ensures that one computer waits while the other transmits, preventing errors​.

2. Parity Checking

Parity checking is a simple error detection method used in digital communications. It involves adding an extra bit (parity bit) to data to indicate whether the number of 1s in the data is even or odd.

Types of Parity Checking:

1. Even Parity: The parity bit ensures the total number of 1s in the data (including the parity bit) is even.

2. Odd Parity: The parity bit ensures the total number of 1s is odd.

Example:

If the binary data 1011001 (which has four 1s) is transmitted with even parity, the parity bit will be 0 to maintain evenness. If an error occurs and a bit flips, making it 1011101 (five 1s), the receiver detects the error because the parity is incorrect.

3. Checksum Method

The checksum method is commonly used in network protocols such as TCP/IP. It works by summing up all the data bytes in a transmission and sending the total sum along with the data. The receiver calculates its own sum and compares it with the transmitted checksum.

Example:

• If a data packet contains the bytes 101, 110, and 011, the sum (in decimal) is 322.

• The sender includes 322 as the checksum.

• The receiver performs the same calculation; if the result matches, the data is correct. If not, an error has occurred.

This method is widely used in financial transactions and file transfers.

4. Cyclic Redundancy Check (CRC)

The Cyclic Redundancy Check (CRC) is a more powerful error detection technique used in network communications and storage devices. It uses polynomial division to detect changes in transmitted data.

How CRC Works:

• A mathematical algorithm generates a CRC value (checksum) based on the data.

• The CRC value is appended to the transmitted data.

• The receiver applies the same algorithm; if the calculated CRC matches the received one, the data is correct.

Example:

CRC is used in Wi-Fi and Bluetooth data packets to ensure error-free communication. If a bit in the transmission changes due to interference, the receiver detects it and requests a retransmission​.

5. Hamming Code (Error Correction)

Unlike other methods that only detect errors, Hamming Code allows both detection and correction of single-bit errors.

How Hamming Code Works:

• Redundant bits are added to the data at specific positions.

• These bits help in identifying and correcting errors.

• If a single-bit error is found, the incorrect bit is flipped to restore the correct data.

Example:

Suppose we want to send the data 1011. Using Hamming Code, we add extra bits:

Data:               1    0 1 1

Hamming bits: P1 P2 1 P3 0 1 1

If an error is detected in P2, the receiver can correct it without retransmission.

6. Automatic Repeat Request (ARQ)

ARQ is an error detection and correction method where the receiver requests retransmission of data if an error is detected.

Types of ARQ:

1. Stop-and-Wait ARQ: The sender waits for an acknowledgment before sending the next packet.

2. Go-Back-N ARQ: If an error occurs, all subsequent packets are retransmitted.

3. Selective Repeat ARQ: Only the erroneous packets are retransmitted.

Example:

If a mobile phone user is downloading a file and a data packet gets corrupted, the ARQ mechanism ensures only the faulty packet is resent, rather than the entire file.

7. Bit Streaming and Buffering

When streaming videos or music online, bit streaming and buffering help manage transmission errors.

How Buffering Works:

• Data is preloaded into a buffer before being played.

• If there’s a temporary drop in network speed, the buffered data prevents interruptions.

• The media player ensures smooth playback by keeping data within a set range.

Example:

Watching a YouTube video without buffering could lead to pauses due to network fluctuations. Buffering ensures a seamless experience by preloading some of the video​.

Conclusion

Error detection methods are essential in networking and digital communication to ensure accurate data transmission. While simple techniques like parity checking and checksums detect errors, advanced methods like CRC and Hamming Code allow for both detection and correction. These techniques are widely used in internet communication, streaming, and file transfers, ensuring reliable and error-free data transmission in our digital world.

1. What is Encryption?

Encryption is a method of encoding data so that only authorized users can access it. The original data, known as plaintext, is transformed into an unreadable format called ciphertext using an encryption algorithm and a key. Only those with the correct key can decrypt the data back into its original form.

Example:

Imagine you want to send a secret message to a friend. Instead of writing it in plain text, you use a code that only your friend knows. Even if someone intercepts the message, they won’t be able to understand it without the code.

2. Types of Encryption

There are two main types of encryption:

a) Symmetric Encryption

• Uses a single key for both encryption and decryption.

• Faster than asymmetric encryption.

• Commonly used for securing data at rest (e.g., stored files, databases).

Example:

The Advanced Encryption Standard (AES) is a widely used symmetric encryption method for protecting sensitive data, such as credit card transactions.

b) Asymmetric Encryption

• Uses a pair of keys: a public key (for encryption) and a private key (for decryption).

• More secure but slower than symmetric encryption.

• Commonly used in secure email communication and digital signatures.

Example:

RSA encryption is a popular asymmetric encryption method used in secure online transactions, such as online banking.

3. How Encryption Works

Encryption follows a process where:

1. The sender encrypts the message using an encryption algorithm and a key.

2. The encrypted data (ciphertext) is transmitted or stored.

3. The recipient decrypts the ciphertext using the correct key to retrieve the original message.

Illustration:

Plaintext → Encryption Algorithm + Key → Ciphertext → Transmission → Decryption Algorithm + Key → Plaintext

4. Applications of Encryption

Encryption is used in various areas to protect sensitive information:

a) Online Banking and E-Commerce

• Secure Socket Layer (SSL) and Transport Layer Security (TLS) encrypt financial transactions to protect credit card details and personal data.

b) Email Security

• Encryption tools like PGP (Pretty Good Privacy) ensure that only the intended recipient can read an email.

c) Cloud Storage Security

• Services like Google Drive and Dropbox use encryption to secure stored files.

d) Wireless Network Security

• Wi-Fi encryption protocols such as WPA2 (Wi-Fi Protected Access) prevent unauthorized access to wireless networks.

5. Importance of Encryption

Encryption is essential for:

• Data Privacy: Preventing unauthorized access to personal information.

• Data Integrity: Ensuring that data is not altered during transmission.

• Authentication: Verifying the identity of users and devices.

• Compliance: Meeting legal and industry standards for data protection.

6. Encryption Challenges

While encryption is crucial for security, it has some challenges:

• Key Management: Losing an encryption key can make data inaccessible.

• Performance Issues: Strong encryption can slow down data processing.

• Quantum Computing Threats: Future quantum computers may break current encryption methods.

7. Future of Encryption

With advancements in technology, encryption methods continue to evolve. Post-quantum cryptography is being developed to resist future quantum attacks, ensuring long-term data security.

Conclusion

Encryption is a vital tool for securing digital information. By understanding how it works and where it is applied, individuals and organizations can better protect their data from cyber threats. As technology advances, encryption will remain a key defense against data breaches and unauthorized access.