Data Transmission

Header - IP of sender and receiver - size of packet - number sequence of packet Payload - where the message is stored Trailer - checks message if its the right one by identifying the end of the packet (uses CRC)

When each packet of a message takes a different path to increase efficiency, but they can arrive to the destination in the wrong order and therefore need to be ordered

Data can be sent in one direction only E.g printer

Data can be sent in both directions, but not at the same time E.g walkie-talkie

Data can be sent in both directions at the time of E.g using broadband internet connection

Data is sent one bit at a time down a single channel/wire E.g USB connection

Several bits of data are sent down several wires/channels at the same time - each wire/channel transmits each bit E.g using the internal circuits of a computer

Universal serial bus Computer automatically detects the device

• can be odd or even • counts number of 1’s to see if message is corrupted or not • if number is correct then add 0 as the parity bit but if it’s wrong add 1

• criss cross • parity blocks

• data block is about to be transmitted - check sum is calculated • calculation is done by an agreed algorithm - agreed by sender and receiver • checksum is sent with the data block • receiving computer calculates checksum and compares • if incorrect is sent request is made for resend

• data is sent • data is returned • data is compared and re-sent if any errors are found

The final digit included in a code, its calculated from all the other digits in the code - ISBN 13 and Modulo 11

1 - add all odd numbered digits 2 - add all even numbered digits and do result ×3 3 - add results together and divide by 10 4 - minus remainder from 10, if remainder is 0 that’s the check digit

1 - each digit is given a number starting from 2, right to left 2 - digit is multiplied by it’s number and all digits are added together 3 - result is divided by 11 4 - remainder is subtracted from 11, if remainder is 10 check digit is 1 or X

Automatic repeat requests - uses positive and negative acknowledgements - uses timeout - time interval allowed to pass before an acknowledgment is received