Chapter 2 - Data transmission

Data packets

Data sent over long distances is usually broken up into data packets.

Packet structure

A typical packet is split up into a packet header, payload, and trailer.

Packet switching

A method of data transmission where a message is broken into packets and sent independently from start point to end point.

Hopping

A method where a hop number is added to the header of each packet, and this number is reduced by 1 every time it leaves a router.

Simplex data transmission

Data can be sent in ONE DIRECTION ONLY.

Half-duplex data transmission

Data can be sent in BOTH DIRECTIONS but NOT AT THE SAME TIME.

Full-duplex data transmission

Data can be sent in BOTH DIRECTIONS AT THE SAME TIME.

Serial data transmission

Data is sent ONE BIT AT A TIME over a SINGLE WIRE/CHANNEL.

Parallel data transmission

SEVERAL BITS OF DATA (usually one byte) are sent down SEVERAL CHANNELS/WIRES at the same time.

Universal serial bus (USB)

A form of serial data transmission and the most common type of input/output port found on computers.

Parity checks

Used to check whether data has been changed or corrupted following data transmission based on the number of 1-bits in a byte of data.

Checksum

Used to check if data has been changed or corrupted following data transmission by sending an additional value called the checksum at the end of the block of data.

Echo check

When data is sent to another device, this data is sent back again to the sender to check if any errors occurred during the transmission process.

Check digits

The final digit included in a code, calculated from all the other digits in the code, used to identify errors in data entry caused by mis-typing or mis-scanning a barcode.

Automatic Repeat Requests (ARQs)

Used to check data following data transmission by using positive and negative acknowledgements and timeout to ensure data integrity.