Data Transmission (Cambridge (CIE) O Level Computer Science): Revision Note

What is data transmission?

• Data transmission is the process of transferring data from one device to another using a wired or wireless connection

• Wired data transmission can be completed in two ways:

  • Serial 

  • Parallel

Serial & Parallel Transmission

What is serial & parallel transmission?

• Serial and parallel are methods of transmitting data (bits) from a sender to a receiver

• Each method determines how many bits can be transmitted at once

Serial transmission

• A stream of bits is sent in sequence, one after the other, along a single wire

• USB is an example of a wired serial connection

Parallel transmission

• Multiple bits are sent simultaneously, with each bit travelling on its own separate wire

• Parallel transmission is usually synchronous, using a clock signal to keep data aligned

• However, bits can arrive at slightly different times due to skew (timing differences between wires)

• A traditional printer cable is an example of a wired parallel connection

Advantages and disadvantages of serial & parallel transmission

Simplex, Half-Duplex & Full-Duplex Transmission

What is simplex, half-duplex & full-duplex transmission?

• Simplex, half-duplex and full-duplex describe the direction in which data can be transmitted between a sender and receiver

Simplex transmission

• Data travels in only one direction

• Sending data from a computer to a monitor is an example of simplex transmission

Half-duplex transmission

• Data can travel in both directions, but only one direction at a time

• A printer cable which waits for the data to be received before sending back a ‘low ink’ message is an example of half-duplex transmission

Full-duplex transmission

• Data can travel in both directions at the same time

• Network cables can send and receive data at the same time and are examples of full-duplex data transmission

• Full-duplex is used in local and wide area networks

Advantages and disadvantages of simplex, half-duplex & full-duplex transmission

• Wires can be combinations of serial, parallel, simplex, half-duplex and full-duplex

• Serial-Simplex

  • Data is transmitted one bit at a time in one direction only on a single wire

• Serial-Half-duplex

  • Data is transmitted one bit at a time, and can flow in both directions, but not at the same time

  • This typically uses a single shared wire.

• Serial-Full-duplex

  • Data is transmitted one bit at a time in both directions simultaneously, but this requires two wires, one for each direction.

• Parallel-Simplex

  • Multiple bits are transmitted simultaneously in one direction only, using multiple wires

• Parallel-Half-duplex

  • Multiple wires send multiple bits of data in both directions, but only one direction at a time

• Parallel-Full-duplex

  • Multiple wires send multiple bits of data in both directions simultaneously