What are the common network protocols and their purposes?

Common network protocols include HTTP for web browsing, SMTP for email, FTP for file transfer, and TCP/IP for internet communication.

HTTP, or Hypertext Transfer Protocol, is used for transmitting hypertext over the internet. It forms the foundation of any data exchange on the web and is a protocol used for transmitting web pages. When you enter a URL in your web browser, this actually sends an HTTP command to the web server directing it to fetch and transmit the requested web page.

SMTP, or Simple Mail Transfer Protocol, is used for sending and receiving email. It is an internet standard for email transmission across IP networks. SMTP is typically used to send messages from a mail client to a mail server and then from that server to another mail server.

FTP, or File Transfer Protocol, is used for transferring files from one host to another over a network, like the internet. It is a standard network protocol used for the transfer of computer files between a client and server on a computer network. FTP is built on a client-server model architecture using separate control and data connections between the client and the server.

TCP/IP, or Transmission Control Protocol/Internet Protocol, is the suite of communications protocols used to connect hosts on the internet. TCP/IP uses several protocols, the two main ones being TCP and IP. TCP/IP is not just a protocol, but a protocol suite. It encompasses many protocols, such as HTTP, FTP, SMTP, and more. It is named after two of its most important protocols, but there are other protocols as well within the suite.

Another common protocol is UDP, or User Datagram Protocol. It is used for tasks requiring low latency, where you'd want the information to be delivered as quickly as possible. Unlike TCP, it doesn't provide the reliability of checking whether the data reached its destination or not.

Lastly, there's the Internet Control Message Protocol (ICMP), used by network devices to send error messages and operational information. For example, if a requested service is not available, or a host or router could not be reached, ICMP will report this back to the sender.