1.3.7 Network Protocols

A communication protocol is a set of rules for transferring data between devices. Protocols ensure that devices agree on how data should be sent, received and interpreted. Different protocols are designed for different purposes, so several protocols may be involved in the same network communication.

Common communication protocols include TCP/IP, HTTP, HTTPS, FTP, POP, IMAP, and SMTP.

TCP and IP are two protocols that commonly work together when data is transmitted across networks.

TCP (Transmission Control Protocol) splits data into smaller units called packets before transmission. A packet contains part of the original data together with additional information needed to help transmit and reassemble it correctly. TCP includes information that helps the receiving device check the packets and place them back into the correct order so that the original data can be reconstructed.

IP (Internet Protocol) is responsible for addressing and directing packets between networks. Source and destination IP addresses allow routers to determine where packets need to be sent.

Together, TCP and IP allow data to be divided into manageable packets and directed towards the correct destination across interconnected networks.

HTTP and HTTPS are protocols used when a web browser communicates with a web server. Both are used to request and transfer web resources such as webpages, images and other files, but HTTPS adds security by encrypting the communication.

HTTP (HyperText Transfer Protocol)

HTTP (Hypertext Transfer Protocol) is used for communication between web browsers and web servers. It defines how browsers request web resources and how web servers respond.

HTTP does not encrypt the data being transferred, so information sent using HTTP can potentially be read if the communication is intercepted.

HTTPS (HyperText Transfer Protocol Secure)

HTTPS (Hypertext Transfer Protocol Secure) is the secure version of HTTP. It uses TLS (Transport Layer Security), historically known as SSL (Secure Sockets Layer), to encrypt communication between the client and web server. A digital certificate is also used to help verify the identity of the website or server.

Encryption means that if the transmitted data is intercepted, it should not be readable without the information needed to decrypt it. This makes HTTPS suitable for transmitting sensitive information such as login details or payment information.

FTP (File Transfer Protocol) is used to transfer files between a client and a server, allowing files to be uploaded to or downloaded from the server.

Email communication uses different protocols for sending and receiving messages. SMTP is used to send email, while POP and IMAP are used to access email that has arrived at a mail server. POP and IMAP perform similar roles but handle stored messages differently.

POP (Post Office Protocol)

POP (Post Office Protocol) is used to retrieve emails from a mail server by downloading them to a device. Depending on the configuration, downloaded messages may then be removed from the mail server.

IMAP (Internet Message Access Protocol)

IMAP (Internet Message Access Protocol) is used to access emails while keeping them stored on the mail server. This allows the same mailbox to remain synchronised across multiple devices.

SMTP (Simple Mail Transfer Protocol)

SMTP (Simple Mail Transfer Protocol) is used to send emails from a client to a mail server and to transfer emails between mail servers.

The email protocols perform different roles when a message is sent and received. As shown in Figure 5, SMTP is first used to send the email from the sender's device to the sender's mail server. SMTP is then used again to transfer the email between the sender's mail server and the recipient's mail server.

Once the email has reached the recipient's mail server, the recipient can access it using either IMAP or POP. With IMAP, the email remains stored on the mail server and the mailbox can stay synchronised across multiple devices. With POP, the email is downloaded to the recipient's device and, depending on the configuration, may then be removed from the server.