Computer Science-Protocol Layers
Protocols
Protocols are a set of rules made for transmission of data. Each type of data has its own rules e.g. sound, text and web pages. For protocols, there are four basic layers.
The four layers
Application
Transport
Internet
Data Link
Note: An easy way to remember these layers in order could be to use the mnemonic ‘Are They In Doubt’.
1) Application
consists of programs used to exchange data with web browsers and server software and sends files to the Transport layer. Data packets are called ‘packets’ on this layer. Uses the following protocols:
HTTP: (Hypertext transfer protocol) used to load HTML documents from the web server, underpins the WWW (world-wide web). There are usually seperate servers for different types of data, such as adverts, videos, files and more. This is done through a URL request to the server, then in the Transport layer, the data is made into data packets and sent from port 80 to the destination port.
SMTP: (Simple mail transfer protocol) used only to send an email to an email server. The emails are text-based only. It is also known as a push protocol.
POP 3/4: (Post office protocol 3/4) used to receive emails from the email server, and once attained, the email is deleted from the server. It is also known as a pull protocol.
IMAP: (Internet messaging access protocol) used to receive emails from the email server, the email is copy/pasted to the destination. It like pop 3/4 is also known as a pull protocol, and HTTP supersedes both of them.
DNS: (Domain name server/system) this has a database of URLs and their corresponding IP addresses, it uses the URLs to find the IP addresses, having received a URL request.
FTP: (File transfer protocol) used to transfer files, one can have an anoymous FTP.