Web (Internet) Protocols

The standard network protocol of the Internet, TCP/IP, stands for Transmission Control Protocol/Internet Protocol. The Internet Protocol part of the standard refers to the addressing of data message packets. Additional protocols that operate within the TCP/IP framework include UDP, HTTP and FTP. Each has different functions and purposes that ultimately work together to provide assorted capabilities through what's currently known as the World Wide Web.

What is a domain name?

A domain name is a string of text that maps to a numeric IP address, used to access a website from client software. In plain English, a domain name is the text that a user types into a browser window to reach a particular website. For instance, the domain name for Google is ‘mobilinfoworld.com’.

What is a Sub domain ?

A subdomain name is a piece of additional information added to the beginning of a website’s domain name. It allows websites to separate and organize content for a specific function — such as a blog or an online store — from the rest of your website.

A domain name typically has two parts: The top-level domain (TLD) is the extension, such as .com or .org, and the second-level domain (SLD) is the unique part of the domain name, often a business or brand name. In the monileinfoworld.com example, com is the TLD and monileinfoworld is the SLD.
http://mobileinfoworld.com/web-structure-protocol-domain/