2. Data transmission

it is broken down into packets to be transmitted

• packet header • payload • trailer

• senders IP adress • recievers IP adress • Packet number

• Data is broken down into packets • Each packet could take a different route • A router controls the route a packet takes • Packets may arrive out of order • Once the last packet has arrived, packets are reordered

serial parralel

serial transmission, a single wire is used to connect the sending device to the receiving device. Bits are transmitted one at a time. it is reliable over long distance, less likely to get lost, wont arrive in wrong order, take long time

multiple wires are used to connect the sneding device and recievig device. several bits aee sent simultaneously. each bit travels through a seperate wire. it is faster but bits may arrive rearanged and can be expensive

simplex half- duplex full duplex

only 1 device can transmit data in 1 direction only eg:files sent to be printes

data can be sent both directions but 1 at a time. eg: walkie talkies

data can be sent forward and backwards simultaneously eg: online video game

s a communication interface that has become a standard for connecting devices to their parent

serial transmission- only 1 direction

• it is univeral • can only be inserted a certain way • compatible with many devices • use other cables while using usb

involves a parity bit at the end or start of binary number and is sent along with the data. there is an even parity or add parity ( refering to th enumbers of 1s)

if the sum of bytes is less than 255- that is the checksum if not then - divide the sum of bytes by 256 - round to nearest integer multiply integer by 256 - origingal sum- product

• a method of error detection where the receiving computer sends back an exact copy of the data to the sending computer. • The sending computer then compares the data it originally sent to the data it has received back. • If there is a match between the two data sets, then the transmission took place without error. If there is an error, the sending computer resends the data, and the process starts all over again.

A check digit is an extra digit added to a number that is calculated from the existing digits in the number. It is used to check for errors during data entry. eg: ISBN, barcodes

• controls errors • when data is recieved computer sends the aknowladgement which indicates weather data was sent correctly. can be positive or negative • if negative computer will re request the data • this process is repeated until tmeout is passed

encryption scrambles data so it cant be understood without decoding it.

plaint text- regular cipher text- encrypted

shifts letter a number of positions to the right or to the left

a single key is used for encrypting messege and decrypting it. messege and key are send to reciever in seperate texts

uses 2 keys, one private and one public- 1 for encryption and other is used for decryption.