CS CH2: Data Transmission

What are the three main factors to consider in data transmission?

Direction, Method of Transmission, and Timing (synchronization)

What is simplex transmission?

A one-way transmission where data only flows from sender to receiver (e.g. keyboard to CPU)

What is half-duplex transmission?

A two-way communication system where data flows in both directions but only one direction at a time (e.g. walkie-talkies)

What is full-duplex transmission?

A two-way communication system where data flows in both directions simultaneously (e.g. phone call)

What is serial transmission?

Data is sent one bit at a time over a single wire/channel, making it slower but reliable over long distances with less interference.

What is parallel transmission?

Multiple bits are sent simultaneously over multiple wires; it's faster but prone to timing errors (skew) over long distances.

Why is serial transmission preferred for long-distance communication?

It uses fewer wires, is less expensive, and avoids skew/timing issues that occur in parallel transmission.

What is USB and what type of transmission does it use?

USB (Universal Serial Bus) is a standard interface that uses serial transmission for data transfer and power supply.

List two advantages of USB.

Automatic device detection; plug-and-play functionality with fast data transfer.

List two disadvantages of USB.

Limited cable length (usually ~5 meters); older devices may not be supported by newer ports.

What is a data packet?

A small chunk of data with a header (source/destination IP, packet number), payload (actual data), and trailer (error check like CRC).

What is packet switching?

A method where data is split into packets, each taking independent routes through the network and reassembled at the destination.

State one advantage and one disadvantage of packet switching.

Advantage: Efficient use of bandwidth and avoids congestion; Disadvantage: Packets may arrive out of order or be delayed/lost.

What is a parity check?

An error detection method where a parity bit (even or odd) is added to ensure the total number of 1s is correct.

What is a transposition error and why can it go undetected with a parity check?

It’s when two adjacent bits are swapped (e.g. 1101 becomes 1011); overall parity may still appear correct, so the error is not detected.

What is a parity block?

A 2D grid of bits using row and column parity bits; allows both detection and location of a single-bit error within the block.

What is a checksum?

A numeric value generated by adding all bytes in the data, taking the two’s complement, and sending it with the data; the receiver recalculates the sum, adds the checksum, and expects a result of 0 (or predefined value) to confirm no error.

What is echo check?

A method where the receiver sends the received data back to the sender, who compares it to the original data to detect any mismatch.

What is a check digit?

A digit calculated from the other digits in a number (like ISBN); it is used to verify data entry or transmission errors through mathematical rules (e.g. Mod-11 or ISBN-13).

What is ARQ (Automatic Repeat reQuest)?

An error-control protocol where the sender waits for an acknowledgment (ACK); if none is received within a timeout, it resends the data; can use positive/negative ACKs.

What is symmetric encryption?

A method of encryption where the same secret key is used for both encryption and decryption; key must be securely shared beforehand.

What is the main weakness of symmetric encryption?

If the key is intercepted during transmission, the entire communication becomes insecure since the same key decrypts all messages.

What is asymmetric encryption?

A form of encryption using a pair of keys: a public key to encrypt and a private key to decrypt; only the private key holder can read the message.

How does asymmetric encryption work between two users?

User A wants to send a message to User B. A encrypts the message using B’s public key; only B can decrypt it using their private key, ensuring confidentiality.

What is plaintext and ciphertext?

Plaintext is the original readable message; ciphertext is the scrambled, encrypted version that appears unreadable without the correct decryption key.

Why is encryption used in data transmission

A digit calculated from the other digits in a number (like ISBN)