TCP/IP Model

The TCP/IP Model is similar to the OSI model. It's older, and serves as the basis for real-world networking. The TCP/IP model consists of four layers: Application, Transport, Internet and Network Interface. Between the for layers they cover the same range of functions as the seven layers of the OSI model.

• Application

• Transport

• Internet

• Network Interface

The common question is why bother with the OSI model if it's not actually used for anything in the real-world. But simply put, the OSI model ( due to being less condenses and more rigid than the TCP/IP model ) tends to be easier for learning the initial theory of networking.

The two models match up like:

OSI	TCP/IP
Application Presentation Session	Application
Transport	Transport
Network	Internet
Data Link Physical	Network Interface

The process of encapsulation and de-encapsulation work in exactly the same way with the TCP/IP model as they do with the OSI model. At each layer of the TCP/IP model a header is added during encapsulation, and removed during de-encapsulation.

Practical

When we mention TCP/IP, it's great to think about a table with four layers, but we're actually talking about a suite of protocols -- sets of rules that define how an action is to be carried out. TCP/IP takes its name from the two most important of these: The Transmission Control Protocol that controls the flow of data, and the Internet P

TCP is a connection-based protocol. In other works, before you send any data via TCP, you must form a stable connection between the two computers. The process of forming this connection is called the three-way handshake.

When you attempt to make a connection, your computer first sends a special request to the remote server indicating that it wants to initialize a connection. The request contains something called a SYN ( short for synchronize ) bit, which essentially makes first contact in starting the connection process. The server will then respond with a packet containing the SYN bit, as well as another "acknowledgment" bit, called ACK. Finally, your computer will send a packet that contains the ACK bit by itself, confirming that the connection has been setup successfully. With the three-way handshake successfully completed, data can be reliably transmitted between the two computers. Any data that is lost or corrupted on transmission is re-sent, thus leading to a connection which appears to be lossless.

History

The TCP/IP and OSI models were originally created to form a level of standardization. Prior to these models ther was none -- different manufacturers would follow their own methodologies, and consequently systems made by different manufacturers were completely incompatible when it came to networking. The TCP/IP models were introduced by the american DoD in 1982 to provide a standard -- something for all manufacturers to follow. This sorted out the inconsistency problems. Later the OSI model was also introduced by the International Organization for Standardization ( ISO ); however, it's mainly used as a more comprehensive guide for learning, as the TCP/IP model is still the standard upon which modern networking is based.rotocol, which controls how packets are addressed and sent. There are many more protocols that make up this suite, but this is the initial one we'll discuss.