Chapter 2 Lesson Reviewer

​DATA TRANSMISSION

By Casielyn Capistrano

DATA TRANSMISSION

• Data transmission is the movement of data from one device or computer system to another, typically over a communication medium such as cables, wireless signals, or optical fiber.

• The process of sending data from one computer or device to another, using defined directions, methods, and modes.

​Data transmission is the transfer of data from one digital device to another

DATA PACKETS

- A data packet is a small, formatted unit of data carried across a network. When information like a file, email, or video stream is transmitted over a digital network, it is broken down into packets to make transmission more efficient and reliable.
- Data packets are the fundamental units of communication for devices connected to the internet.
- Data packets are individual information organized into one packet sent through a network path.

- Packets are small 'chunks' of data that make up a larger piece of data that has been broken down by the TCP protocol so that it can be transmitted over the internet.
- TCP stands for Transmission Control Protocol and is used for organising data transmission over networks

- Small 'chunks' of data are easier and quicker to route over the internet than big 'chunks' of data
* Routing involves finding the most optimal path over a network

- Data can include anything from text, images, audio, video, animations, etc, or any combination of these

​When data is sent over the internet, it is broken into packets. Each packet follows a journey through different stages before reaching its destination.
1. The user creates or requests data e.g., sending an email or loading a webpage.
2. The data is divided into smaller packets, each containing part of the message along with addressing information.
3. The packets are processed and prepared for transmission using the Transmission Control Protocol (TCP)
4. The packets are assigned an IP address to identify the sender and receiver.
5. The packets are sent to the user’s Internet Service Provider (ISP).

When data is sent over the internet it is first broken down into packets. Each packet is given a destination IP address and other control information. The packets are sent to the sender’s local ISP (Internet Service Provider), where they are passed through routers using TCP/IP. The packets may travel across many different networks, through long-haul providers and exchanges, using the best available route chosen by routing protocols such as BGP. Once they reach the destination ISP, the packets are delivered to the receiver’s router and modem. The packets are then reassembled in the correct order and passed to the receiving application.

6. The packets travel across several networks, through:

- The local ISP of the destination

- Long-haul providers

- Additional network exchanges

- Border Gateway Protocol (BGP) routers that direct packets along the best available path
7. The packets arrive at the ISP serving the destination device.
8. The packets are passed through the modem and router, ready for delivery.
9. The packets are reassembled in the correct order to recreate the original data.
10. The receiving application e.g., a web browser or email client uses the data.

Fill in the Blank

When data is sent over the internet it is first broken down into __________.
Each packet is given a destination __________ address and other control information.
The packets are sent to the sender’s local __________, where they are passed through routers using __________.

/

Fill in the Blank

The packets may travel across many different networks, through long-haul providers and exchanges, using the best available route chosen by routing protocols such as border Gateway Protocol (BGP).
Once they reach the __________ ISP, the packets are delivered to the receiver’s __________ and modem.
The packets are then __________ in the correct order and passed to the receiving application.

Multiple Choice

Why is data split into packets before being transmitted?

• To prevent viruses spreading across the network

• To remove the need for error checking

• To allow multiple users to share the same communication line efficiently

• To make transmission slower but more reliable

HEADER - Sender's IP address, Receiver's IP address, Protocol, Packet Number
PAYLOAD - Data
TRAILER - Data to show end of packet, error correction

PACKETS STRUCTURE

What do packets contain?

To transmit the message “This is a message :)”over the internet, TCP might break the message down into 4 packets.
- Each packet contains a:

• source IP address

• destination IP address

• payload (the data)

• a packet number/sequence number (critical for reliability, ordering, and integrity of communication over networks where packets may arrive late, out of order, duplicated, or lost)

- Error checks make sure that when a packet is received there is minimal or no corruption of the data

- Corruption is where packet data is changed or lost in some way, or data is gained that originally was not in the packet

Multiple Choice

Which of the following is found in the payload of a data packet?

• Destination address

• The actual data being sent

• Error detection code

• Sequence number

Multiple Choice

What is included in the header of a data packet?

• The data only

• The IP address of the destination and source

• The speed of the network

• The username of the sender

Multiple Choice

Which of the following correctly describes the three main parts of a packet?

• Bit, byte, frame

• Source, destination, data

• Address, error code, checksum

• Header, payload, trailer

Multiple Choice

What is the main purpose of the trailer in a data packet?

• To identify the type of network used

• To store the password of the sender

• To check for errors in transmission

• To indicate the size of the packet

Multiple Choice

What happens if a packet is lost during transmission?

• Only the missing packet is requested again

• The sender is disconnected from the network

• The entire message must be resent

• The receiver ignores it and completes the message

Multiple Choice

A packet trailer contains error detection information. What is its purpose?

• To check whether data has been corrupted

• To recover lost packets

• To store the destination IP address

• To encrypt the data

Multiple Choice

Why is a sequence number included in the structure of a packet?

• To identify the start and end of a file

• To prevent data from being corrupted during transmission

• To ensure packets can be reassembled in the correct order

• To encrypt the packet for security

Multiple Choice

Which of the following statements best describes the structure of a data packet?

• A packet contains a header, payload, and trailer, each with a specific role.

• A packet is a continuous stream of binary digits with no divisions.

• A packet is a single unit of storage used to hold data inside the CPU.

• A packet consists only of the message data being transmitted.

Open Ended

Explain the structure of a data packet.

Multiple Choice

Why might packets from the same message arrive in the wrong order?

• Packets are corrupted in transit

• The receiving computer requests them out of order

• The sender’s computer sends them randomly

• Packets may take different routes through the network

PACKET SWITCHING

Packet Switching is like sending letters or the internet today, think of it like sending DMs or snaps., sending 100 TikTok clips via Wi-Fi, they take different routes but still reach your friend’s phone because data split into small pieces, each may take different paths, then reassembled while Circuit Switching is like a phone call or an old-school phone calls. Think of it like being on a private FaceTime call where a lane is reserved just for you, staying on a Discord voice call, one private “line” is locked for you two the whole time, circuit switching is a fixed path is reserved for the whole communication.

​In other words, in packets switching data split into small pieces, travel separately or in different path then reassembled Circuit switching used a fixed path and reserved for the whole communication..

When data is transmitted across a network, it is often broken down into packets. These packets may travel through different routes in the network before reaching their destination. Certain devices are responsible for deciding the path that each packet should take.

Switch- is a device that controls where packets go inside a LAN”
Router is device that controls which path a packet takes between networks

Devices that control Data Packets

• Devices use routing algorithms and tables:

  • Static routing, predefined fixed path.

  • Dynamic routing, path chosen depending on network traffic, failures, or congestion.

• Factors include:

  • Distance (number of hops).

  • Network congestion.

  • Reliability of the route.

How the Path is Decided?

Devices that control Data Packets

Multiple Choice

Packet switching is used to transmit data packets across the network.

Identify the device that controls which path is taken by each data packet.

• Switch

• Hub

• Gateway

• Router

Multiple Choice

In packet switching, what happens if a network link is busy or unavailable?

• The router chooses an alternative path

• The switch retransmits the packet

• The router stores the packet until the link is free.

• The hub delays the packet until the network is clear

Multiple Choice

Which device controls the path taken by each data packet?

• Router

• Switch

• Hub

• Bridge

Multiple Choice

Which device controls the path taken by each data packet?

• Router

• Switch

• Hub

• Bridge

DIRECTION OF TRANSMISSION

DIRECTION OF TRANSMISSION

- Direction of transmission refers to the way data flows between two devices during data transmission.

- The direction of transmission describes whether data is sent in one direction or both directions between two devices.

It can be:

1. Simplex
- data flows in one direction only e.g., keyboard to computer.

2. Half-duplex
- data flows in both directions, but only one at a time e.g., walkie-talkie.

3. Full-duplex

- data flows in both directions simultaneously e.g., phone call.

MODE OF TRANSMISSION

Mode of transmission refers to the how data is sent. This refers to how bits are transmitted between devices.

A. Serial Transmission

- Bits are sent one at a time over a single channel.

- Slower for short distances but more reliable over long distances (less interference).

- Example: USB, Ethernet.

B. Parallel Transmission

- Multiple bits sent simultaneously across multiple channels.

- Faster for short distances but prone to interference and timing issues (skew).

- Example: Inside CPU to memory bus, older printers.

Serial is for long distance, reliable

Parallel is for short distance, faster but error-prone

Synchronous & Asynchronous Transmissions

When data is transmitted, the sender and receiver must agree on how and when the bits are sent. This agreement is handled by synchronization methods:
Synchronous Transmission

-Data is sent one byte or character at a time.
- Each unit of data is wrapped with control bits: Start bit (alerts the receiver that data is coming, Data bits (the actual byte), Stop bit(s) (signal the end of transmission.
- Timing between characters is not important, as the start bit re-synchronizes the devices each time.

Asynchronous Transmission

- Data is sent in a continuous stream of bits, grouped into blocks or frames, without start/stop bits for each byte.
-Sender and receiver share a common clock signal to stay synchronized.

More efficient because less overhead is required.

REMEMBER ME!

Mode (Serial vs Parallel) is concerns the number of data lines used and how the bits travel. Think of it like Are we sending one bit at a time or many at once?
Serial like one lane road, bits one by one, long distance, slower but reliable while Parallel like multi-lane highway, many bits at once, short distance, faster but costly.
- Serial = Simple wire, Parallel = Plenty of wires.

Direction (Simplex, Half, Full) is concerns who can send/receive and whether it’s simultaneous or not. Think of it like Who gets to talk, and when?
Simplex is like only one talks, the other only listens. (TV broadcast).

Half-Duplex is like both can talk, but one at a time. (Walkie-talkie).

Full-Duplex is like both can talk at the same time. (Telephone).
- Simplex = Single-way, Half = Half the time, Full = Free both ways.

Timing (Synchronous vs Asynchronous) is concerns the synchronization methof between sender and receiver during data transmission like how the sender and receiver stay coordinated in time when exchanging data. Think of it like How do we stay in sync while talking?
Synchronous is like shared clock, continuous flow, efficient while Asynchronous is like start/stop bits, slower but simple.

Sync = Same clock, Async = Alone (start/stop help).

Open Ended

Why is synchronous transmission faster?

Open Ended

Give an example of asynchronous transmission.

Multiple Choice

Which type of transmission sends data in both directions but only one way at a time?

• Simplex

• Half-duplex

• Full-duplex

• Multoplex

Multiple Choice

Which type of data transmission sends bits one at a time over a single wire?

• serial

• parallel

• duplex

• packet

Multiple Choice

Which data transmission method is described below?
“Data is transmitted down a single wire, one bit at a time, in one direction only.”

• Serial Simplex

• Parallel Simplex

• Serial Half-Duplex

• Parallel Full-Duplex

Multiple Choice

Which data transmission method is described below?
“Data is transmitted down a single wire, one bit at a time, in both directions at the same time.”

• Parallel Half-Duplex

• Serial Simplex

• Serial Full Duplex

• Parallel Duplex

Multiple Choice

Which data transmission method is described below?
“Data is transmitted down multiple wires, multiple bits at a time, in one direction only.”

• serial simplex

• parallel half-duplex

• serial full-duplex

• parallel simplex

Multiple Choice

Which data transmission method is described below?
“Data is transmitted down multiple wires, multiple bits at a time, in both directions, but only one direction at a time.”

• Parallel Half-Duplex

• Serial, Full-Duplex

• Serial, Half-Duplex

• Serial, Half-Duplex

Multiple Select

Which improvements would be made if parallel transmission is used instead of serial transmission? Choose possible answer.

• More than one bit is transmitted at the same time, making transmission faster over short distances.

• The data may be transmitted faster. 

• The cost of the transmission medium is reduced.

• Data can travel longer distances without errors.

• Data can only be sent in one direction at a time.

Multiple Select

A school has introduced a smart attendance system. Students tap their ID cards on a scanner when they arrive. The data is transmitted across the school network to the main server that stores attendance records. The data is sent using serial full-duplex data transmission.

Give two reasons why serial full-duplex is a suitable data transmission method for the attendance data. Choose all possible answer.

• It uses fewer wires, making it cheaper to install and more reliable over longer distances.

• Data can travel in both directions at the same time, allowing confirmation messages to be sent while data is transmitted.

• It is always faster than parallel transmission because it sends multiple bits at once.

• Serial is suitable as there is less chance of error and Full-duplex is suitable as data data needs to go in both directions.

• Serial has sufficient transmission speed as not much data being sent. Full-duplex as so notification

  of errors can be sent back to customer .

Open Ended

Define serial transmission and give one advantage of using it.

Open Ended

Explain the difference between synchronous and asynchronous data transmission.

Open Ended

State two reasons why parallel transmission is not commonly used over long distances.

Open Ended

A student is streaming a video online.

Explain why packet switching is used instead of circuit switching.

Open Ended

Data can be transmitted in parallel or serial. Describe each method, compare their advantages/disadvantages, and explain which is better for long-distance communication.

FACTORS AFFECTING DATA TRANSMISSION

Baud Rate: Number of signal changes per second.

Bit Rate: Number of bits transmitted per second.

Bit Rate = Baud Rate × Number of bits per signal

Bandwidth: Range of frequencies available for transmission.

Latency: Time delay in transmission.

Error rate: How many bits get corrupted.

DATA TRANSMISSION ERRORS

Data Transmission Errors

A data transmission error occurs when the data received does not match the data that was originally sent. This happens when bits are changed, lost, or corrupted during transmission due to problems in the communication medium.

Causes of Data Transmission Errors

• Noise or interference happens when unwanted electrical signals disturb the data being transmitted.

  • Example: A Wi-Fi connection becoming unstable because a nearby microwave oven or cordless phone is emitting signals on a similar frequency.

• Attenuation refers to the weakening of a signal’s strength as it travels over long distances.

  • Example: An Ethernet cable that runs for more than 100 metres without a repeater may deliver a much weaker signal at the other end.

• Synchronization issues occur when the sender and receiver clocks are out of step, causing data misalignment.

  • Example: If two computers using synchronous transmission do not share an accurate clock signal, bits may be read at the wrong time, leading to corrupted data.

Causes of Data Transmission Errors

• Hardware faults may result from faulty cables, connectors, or devices that corrupt the data.

  • Example: A damaged USB cable or a loose connector on a router can cause files to transfer with missing or corrupted parts.

• Crosstalk occurs when signals from one channel interfere with signals in another channel.

  • Example: In telephone lines or poorly shielded network cables, one conversation or data stream may “leak” into another, creating noise and errors.

ERROR DETECTION METHODS

ERROR DETECTION AND CORRECTION METHODS

An extra parity bit is added to the data so that the total number of 1s is either even (even parity) or odd (odd parity).

Data = 1010 (two 1s, even). With even parity, parity bit = 0. Transmitted data = 10100.

It is simple and fast but if two bits change, the error may not be detected.

Parity Check

Error Detection and Correction Methods

​The table below shows 6 bytes that are transmitted using odd parity. Each byte already includes its parity bit. Complete the parity byte for the entire block of data.

PARITY CHECK

PARITY CHECK

​The table below shows 6 bytes that are transmitted using odd parity. Each byte already includes its parity bit. Complete the parity byte for the entire block of data.

Each column (parity bit, bit 6 … bit 1) must have an odd number of 1s.

If the count of 1s in a column is already odd THEN parity byte = 0.

If the count is even THEN parity byte = 1 to make it odd.

PARITY CHECK

​The table below shows 4 bytes that are transmitted using even parity. Each byte already includes its parity bit. Complete the parity byte for the entire block of data.

Each column (parity bit, bit 7 … bit 1) must have an even number of 1s.

If the count of 1s in a column is already even THEN parity byte = 0.

If the count is odd THEN parity byte = 1 to make it odd.

CHECKSUM

The data is split into blocks. The values of the blocks are added together. The sum (checksum) is transmitted along with the data. The receiver recalculates the checksum and compares.

Data blocks = 1010 (decimal 10) and 1100 (decimal 12). Sum = 22. Checksum = 22. Receiver adds blocks; if the result is not 22, error detected.

Detects more errors than parity however it cannot correct errors, only detects them.

​A system uses the checksum method for error detection. The data to be transmitted is divided into three 8-bit blocks:

Block 1: 10101100

Block 2: 11110000

Block 3: 00011110

Calculate the checksum value that will be transmitted with the data.
(At the receiver side, the data blocks received are:
Block 1: 10101100

Block 2: 11110000

Block 3: 00011111

CHECKSUM

CHECKSUM

​A system uses the checksum method for error detection. The data to be transmitted is divided into three 8-bit blocks:

Block 1: 10101100

Block 2: 11110000

Block 3: 00011110

Calculate the checksum value that will be transmitted with the data.
(At the receiver side, the data blocks received are:
Block 1: 10101100

Block 2: 11110000

Block 3: 00011111

Solution:
Sender side:

1. Convert each block to denary:
- Block 1 = 172
- Block 2 = 240
- Block 3 = 30

2. Add them together:
172 + 240 + 30 = 442
3. Convert the sum into binary let’s use 8 bits, so we only take the lower 8 bits if it overflows:

442 in binary = 110111010

Take lower 8 bits = 10111010 (denary 186)
4. Checksum = 10111010

CHECKSUM

​A system uses the checksum method for error detection. The data to be transmitted is divided into three 8-bit blocks:

Block 1: 10101100

Block 2: 11110000

Block 3: 00011110

Calculate the checksum value that will be transmitted with the data.
(At the receiver side, the data blocks received are:
Block 1: 10101100

Block 2: 11110000

Block 3: 00011111

Solution:
Sender side:

1. Convert each block to denary:
Block 1 = 172

Block 2 = 240

Block 3 = 31

2. Add them together:
172 + 240 + 31 = 443
3. Compare with checksum (denary 186).

Expected total (with checksum) = 442

Actual total (with checksum) = 443

Take lower 8 bits = 10111010 (denary 186)
Since they are different, an error occurred during transmission.

Echo Check

Echo check is an error detection method used during data transmission. The idea is simple:

The sender transmits the data to the receiver.

The receiver immediately returns the same data back to the sender (an “echo”).

The sender compares the returned data with the original data it sent.

If the two sets of data match THEN transmission is considered correct.

If they don’t match THEN an error has occurred.

Echo Check

Step-by-Step Example

• Sender transmits the binary sequence: 1011001

• Receiver gets it and immediately sends back: 1011001

• Sender compares:

  • If returned = original then data accepted.

  • If returned ≠ original (e.g., 1011101) then error detected.

Echo Check

A company is transmitting employee records to a remote server. The system uses an Echo Check to verify the accuracy of data transmission.

(a) Describe how an echo check works.

(b) State one advantage and one limitation of using an echo check.

Echo Check

A company is transmitting employee records to a remote server. The system uses an Echo Check to verify the accuracy of data transmission.

(a) Describe how an echo check works.
The data is sent from the sender to the receiver.

The receiver immediately returns the same data back to the sender.

The sender compares the returned data with the original to check for errors.

(b) State one advantage and one limitation of using an echo check.
Advantage: Easy/simple to implement.

Limitation: Requires two-way communication, doubles transmission time, or only detects but does not correct errors.

CHECK DIGITS

Worked Example (ISBN-13)

Number (first 12 digits): 7 9 8 1 3 1 6 4 0 6 1 5

• Multiply alternately by 1 and 3:
  7×1 + 9×3 + 8×1 + 1×3 + 3×1 + 1×3 + 6×1 + 4×3 + 0×1 + 6×3 + 1×1 + 5×3
  = 7 + 27 + 8 + 3 + 3 + 3 + 6 + 12 + 0 + 18 + 1 + 15 = 103

• 103 mod 10 = 3 → check digit = 10 − 3 = 7

Final ISBN-13: 798131640615 7

CHECK DIGITS

Worked Example (ISBN-10)

Number (first 9 digits): 0 3 0 6 4 0 6 1 5

• Multiply each digit by descending weights 10 to 2:
  (0×10) + (3×9) + (0×8) + (6×7) + (4×6) + (0×5) + (6×4) + (1×3) + (5×2)
  = 0 + 27 + 0 + 42 + 24 + 0 + 24 + 3 + 10 = 130

• 130 mod 11 = 9 → check digit = 11 − 9 = 2

Final ISBN-10: 0 3 0 6 4 0 6 1 5 2

CHECK DIGITS

A formula is applied to the main digits (weights, sums, or modulus calculations).

The result is turned into the check digit.

The number is stored or transmitted with this extra digit.

When the number is received or entered, the same calculation is repeated:

If the check digit matches then data accepted.

If not then error detected.

CHECK DIGITS

A check digit is an extra digit added to the end of a number (like ISBN, credit card, or barcode) to detect errors during data entry or transmission.

It is calculated from the other digits using a specific algorithm.

If the check digit does not match when the number is re-calculated, an error has occurred.
it use to detect common errors such as mistyping a digit e.g., typing 6 instead of 8 and swapping digits e.g., typing 27 instead of 72. Also, to reduce incorrect data being accepted into systems.

Examples of Systems Using Check Digits

• ISBN-10 and ISBN-13 for books.

• Bank account numbers and credit cards (Luhn algorithm).

• Barcodes on products in supermarkets.

​A company librarian is entering new books into the computerized library system. Each book has a unique International Standard Book Number (ISBN). To check for transmission errors, the librarian uses ISBN check digit algorithms. (a) Using the ISBN-10 algorithm, calculate the check digit for: 1 5 1 0 4 5 7 5 9
b) Using the ISBN-13 algorithm, calculate the check digit for:
7 7 9 1 5 1 1 4 5 7 6 9

You will compute or find the check digit here

​A company librarian is entering new books into the computerized library system. Each book has a unique International Standard Book Number (ISBN). To check for transmission errors, the librarian uses ISBN check digit algorithms. (a) Using the ISBN-10 algorithm, calculate the check digit for: 1 5 1 0 4 5 7 5 9
Rule:

Multiply the first 9 digits by weights 10 down to 2, sum the products.

Choose check digit d₁₀ so that total sum + d₁₀ is divisible by 11.

If the check digit is 10, write X.

(a) Using the ISBN-10 algorithm, calculate the check digit for: 1 5 1 0 4 5 7 5 9
Rule:

Multiply the first 9 digits by weights 10 down to 2, sum the products.

Choose check digit d₁₀ so that total sum + d₁₀ is divisible by 11.

If the check digit is 10, write X.
Sum of products = 173

173 mod 11 = 8

Check digit d₁₀ = 11 − 8 = 3

ISBN-10: 1 5 1 0 4 5 7 5 9 3

Answer is 3

​A company librarian is entering new books into the computerized library system. Each book has a unique International Standard Book Number (ISBN). To check for transmission errors, the librarian uses ISBN check digit algorithms. b) Using the ISBN-13 algorithm, calculate the check digit for:
7 7 9 1 5 1 1 4 5 7 6 1

Rule:

1. Multiply the first 12 digits alternately by 1 and 3 (starting with 1), sum the products.

2. Check digit d₁₃ = the number that makes the total a multiple of 10.

3. Equivalently: d₁₃ = (10 − (sum mod 10)) mod 10.

​Sum = 7 + 21 + 9 + 3 + 5 + 3 + 1 + 12 + 5 + 21 + 6 + 3 = 96

Rule:

1. Multiply the first 12 digits alternately by 1 and 3 (starting with 1), sum the products.

2. Check digit d₁₃ = the number that makes the total a multiple of 10.

3. Equivalently: d₁₃ = (10 − (sum mod 10)) mod 10.
Find remainder (mod 10) 96 mod 10 = 6
Calculate check digit

d₁₃=(10−(summod10)) mod 10
= (10 − (96-10)
= 4


or = 10 - remainder
= 10-6
=4
Check digit is 4

The ISBN-13 check digit is 4.

So the complete ISBN-13 is:

7 7 9 1 5 1 1 4 5 7 6 1 4

​Automatic Repeat reQuest (ARQ)

Automatic Repeat reQuest (ARQ) is an error detection and correction method used in data transmission. It ensures that the data received is exactly the same as the data sent by using acknowledgments (ACKs), negative acknowledgments (NACKs), and timeouts. It combines: Error detection (using methods like parity check, checksum). Error correction (by retransmitting incorrect data).

Example:

Imagine a student downloading a file.
The file is divided into packets, and each packet is sent and checked by the receiver.
If a packet arrives correctly, the receiver sends back an acknowledgment (ACK).
If a packet is corrupted or missing, the receiver either sends a negative acknowledgment (NACK) or the sender detects a timeout, and the packet is retransmitted.

This process continues until the entire file is received correctly.

Types of ARQ

Positive ARQ

• Receiver only sends back an ACK when the data is correct.

• If the sender does not receive an ACK within the timeout, it resends the data.

Negative ARQ

• Receiver sends a NACK if an error is detected.

• Sender immediately retransmits the data.

​Automatic Repeat reQuest (ARQ) Definition

How ARQ Works:

Sender transmits data in packets.

Receiver checks the data using an error-detection method (parity, checksum, etc.).

If correct:

• The receiver sends back an ACK (acknowledgment).

If incorrect:

• The receiver sends a NACK (negative acknowledgment), or

• If the sender does not receive an ACK within a certain timeout period, it assumes the packet was lost or corrupted.

Sender retransmits the packet until it is received correctly.

This guarantees that no corrupted data is accepted.

Encryption

Encryption is the process of converting plaintext (readable data) into ciphertext (unreadable code) using a mathematical algorithm and a key.

It protects data during storage or transmission so that only authorized users can read it.

Decryption is the reverse process: converting ciphertext back into plaintext using a key.

Multiple Choice

Which error detection method uses a mathematical calculation on the data?

• Check digit

• ARQ

• Parity check

• Checksum

Fill in the Blank

Plain text is encrypted into ______ text.

Fill in the Blank

Plain text is encrypted into cipher text
using a ______ key

Fill in the Blank

The encrypted data is then transmitted from the

sender to the receiver. The encrypted data is then decrypted using a _______ key

Multiple Select

Which improvements would be made if parallel transmission is used instead of serial transmission? Choose possible answer.

• More than one bit is transmitted at the same time, making transmission faster over short distances.

• The data may be transmitted faster. 

• The cost of the transmission medium is reduced.

• Data can travel longer distances without errors.

• Data can only be sent in one direction at a time.

Multiple Select

Which of the following describe the checksum process? Select ALL possible answer.

• The data is divided into blocks or packets before transmission.

• The receiver recalculates the checksum value from the received data.

• Each block of data is added together using a formula to produce a value called the checksum.

• If the calculated checksum matches the transmitted checksum, the data is assumed to be error-free.

• The checksum value is appended to the end of the data before transmission.

Multiple Choice

Describe how positive automatic repeat requests (ARQs) operate to check for errors.
Which of the following BEST describes the process?

• The receiver sends an acknowledgment (ACK) back to the sender when data is received correctly; if no acknowledgment is received, the sender retransmits the data.

• The receiver automatically fixes errors in the received data and continues without informing the sender.

• The sender adds extra parity bits to every packet so the receiver can always detect and correct errors without feedback.

Multiple Choice

A byte of data is transmitted using odd parity. The byte 1011001 is sent with an extra parity bit. What should the parity bit be?

• 0

• 1

• Cannot be determined

• No parity bit needed

Multiple Choice

Which of the following is an error detection method used in data transmission?

• Parity Check, CheckSum, Echo Check

• Parity Check, CheckSum, Echo Check, ARQ

• Parity Check, CheckSum, Echo Check, ARQ, ISBN, Compression, Encryption, Decryption

• Parity Check, CheckSum, Echo Check, ARQ,, ISBN

Multiple Choice

Which error detection method works by the receiver sending the received data back to the sender for comparison?

• Parity check

• Checksum

• Echo check

• Automatic Repeat reQuest (ARQ)

Multiple Choice

Which error detection method involves adding up all the data values and sending the total with the data?

• Parity check

• Cipher key

• Checksum

• Echo check

Multiple Choice

Which of the following is the main limitation of a parity check?

• It cannot detect when an even number of bits have changed.

• It requires too much processing power.

• It increases data size by one extra byte.

• It cannot detect a single-bit error.

Multiple Choice

Which of the following error detection methods can also be combined with ARQ Automatic Repeat reQuest to request retransmission of corrupted data?

• Parity check

• Checksum

• Both A and B

• Neither A nor B

Multiple Choice

In Positive ARQ, what happens if the sender does not receive an acknowledgment (ACK) within a set time?

• The sender retransmits the data.

• The receiver automatically fixes the error.

• The sender stops sending any further data.

• The sender assumes the data was received correctly.

Open Ended

Explain how Automatic Repeat Request (ARQ) ensures error-free data transmission.

Open Ended

A student is downloading a file from the internet. Describe how ARQ is used to make sure the file is received without errors.

Multiple Choice

Which of the following describes how ARQ works?

• The data is sent twice and compared.

• The receiver checks the data and requests retransmission if errors are found.

• An extra parity bit is added to make the number of 1s even.

• The checksum is calculated and compared at the sender only.

Open Ended

State the difference between positive ARQ and negative ARQ.

Multiple Choice

During a video call of Sunoo, one packet is corrupted. The receiver detects the error and does not send an acknowledgment. After a timeout, the sender transmits the packet again.

• Parity check

• Checksum

• ARQ

• Echo check

Multiple Choice

Which of the following best describes symmetric encryption?

• Uses one key for encryption and decryption

• Uses two different keys for encryption and decryption

• No keys are required

• Uses only a public key

Multiple Choice

Why is asymmetric encryption slower than symmetric encryption?

• It can only encrypt small files

• It always requires digital signatures

• It requires data to be transmitted twice

• It uses longer keys and more complex algorithms