paper 1 - laws and protocols

a set of rules for how devices communicate and how data is transmitted across a network

how communication between two devices should start and end, how the data should be organised, and what the devices should do if data goes missing

• header - contains control information - like the envelope of a letter - includes packet’s destination address (where it’s going), the source address (where it’s come from) and the packet number • payload - the letter inside the envelope - the thing the person is likely to read, and the reason it was sent in the first place. might be part of an email, document, web page of streamed video. • likely to include a checksum number - a form of validation used to check that the payload data hasn’t been corrupted during transit. the sending and receiving devices both calculate a checksum value by performing a function on the payload data. if the values match then the data has been received correctlly

dictate how data is sent between networks

Transmission control protocol (TCP) and Internet Protocol (IP)

set the rules for how devices connect on the network. It’s in charge of splitting the data into packets and reassembling the packets back into the original data once they reach the receiving device. It’s also responsible for checking the data is correctly sent and delivered

packet switching

used by web browsers to access websites and communicate with web servers

a more secure version of HTTP. encrypts all information sent and received

used to access, edit and move files between devices on a network e.g. to access the files on a server from a client computer

Post Office Protocol - version 3

used to retrieve emails from a server. The server holds the email until you download it at which point it is deleted from the server

Internet Message Access Protocol

used to retrieve emails from a server. The server holds the email until you delete it - you only download a copy. Used by most web-based email clients

simple mail transfer protocol

used to send emails. Also used to transfer emails between servers

a group of protocols which have similar functions

application layer

turns data into websites and other applications and vice versa

transport layer

controls data flow - e.g. splitting data into packets and checking packets are correctly sent and delivered

network layer

makes connections between networks, directs data packets and handles traffic. used by routers

data link layer