Traditionally, networks are defined in layers that allow functionality to be separated. TCP/IP combines a number of different protocols across several network layers. It is easiest to view these layers as a sequence of steps a data packet follows as it makes its way from one computer on a network to another.
Figure 2.1 TCP/IP protocol layers
Between each layer is an application programming interface (API) or convention for interpreting messages, or packets, as they pass between layers. Under Windows, you write to the Windows Sockets API (even though it is not part of the TCP/IP protocol suite). The Windows Sockets API manages all the layers beneath your application, including how TCP packets are passed through IP and then on to the network card in the link layer. Windows Sockets allows applications written to it to run over different vendors ' TCP/IP implementations .
Before you continue with the lesson, run the Chap02.exe animation located on the CD-ROM that accompanies this book. This animation explains how data moves through each of the TCP/IP layers.
NoteFor more information on networks, including details on hardware requirements, see the Microsoft course, Networking Essentials .
An application is a particular protocol built at the application layer of the TCP/IP suite. There are literally dozens of TCP/IP application protocols. In addition to the established standard protocols, you can create custom protocols. The following table lists a few of the most popular TCP/IP application protocols:
Application Protocol | Name | Description |
DNS | Domain Name System | Distributed database that allows applications to map between computer names and IP addresses. |
FTP | File Transfer Protocol | Copies files from one Internet machine to another. |
Telnet | Telecommunications Network Protocol | Remote login between hosts running potentially different operating systems. |
HTTP | Hypertext Transfer Protocol | Protocol for distributed hypertext document searching, navigation, and retrieval. This is the protocol used by the World Wide Web. |
NNTP | Network News Transport Protocol | This protocol provides access to Internet news servers. |
SMTP | Simple Mail Transfer Protocol | Protocol for exchanging e-mail across the Internet. |