DNS—The Internet’s Directory Service

The Domain Name System (DNS) is a hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates more readily memorized domain names to the numerical IP addresses needed…

Simple Mail Transfer Protocol

Simple Mail Transfer Protocol (SMTP) is the principal application-layer protocol for Internet electronic mail. It uses the reliable data transfer service of TCP to transfer mail from the sender’s mail server to the recipient’s mail server. Simple Mail Transfer Protocol As with most application-layer protocols, SMTP has two sides: a client side, which executes on…

File Transfer Protocol

The File Transfer Protocol (FTP) is a standard network protocol used for the transfer of computer files between a client and server on a computer network. File Transfer Protocol   As shown in Figure, the user interacts with FTP through an FTP user agent. The user first provides the hostname of the remote host, causing…

Hyper Text Transfer Protocol

The HyperText Transfer Protocol (HTTP), the Web’s application-layer protocol, is at the heart of the Web. HTTP defines how Web clients request Web pages from Web servers and how servers transfer Web pages to clients. When a user requests a Web page (for example, clicks on a hyperlink), the browser sends HTTP request messages for…