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TCP/IP – The Entire Net
Runs On A Set of Rules

The entire Net runs on a set of rules. Rules defining a technology are known as protocols. They serve as a guiding factor for the technology to build upon. The Internet runs on the TCP/IP  protocol. So to know the working of the Net, we must learn the basics first. So let's start.

What Is TCP/IP?

TCP/IP refers to two network protocols (or methods of data transport) used on the Internet. They are Transmission Control Protocol and Internet Protocol, respectively. These network protocols belong to a larger collection of protocols, or a protocol suite. These are collectively referred to as the TCP/IP suite. Protocols within the TCP/IP suite work together to provide data transport on the Internet. In other words, these protocols provide nearly all services available to today's Net surfer. Some of those services include

• Transmission of electronic mail.

• File transfers.

• Usenet news delivery.

• Access to the World Wide Web.

There are two classes of protocol within the TCP/IP suite. Those two classes are

• The network-level protocol.

• The application-level protocol.

Network-Level Protocols

Network-level protocols manage the discrete mechanics of data transfer. These protocols are typically invisible to the user and operate deep beneath the surface of the system. For example, the IP protocol provides packet delivery of the information sent between the user and remote machines. It does this based on a variety of information, most notably the IP address of the two machines. Based on this and other information, IP guarantees that the information will be routed to its intended destination. Throughout this process, IP interacts with other network-level protocols engaged in data transport. Short of using network utilities (perhaps a sniffer or other device that reads IP datagrams), the user will never see IP's work on the system.

Application-Level Protocols

Conversely, application-level protocols are visible to the user in some measure. For example, File Transfer Protocol (FTP) is visible to the user. The user requests a connection to another machine to transfer a file, the connection is established, and the transfer begins. During the transfer, a portion of the exchange between the user's machine and the remote machine is visible (primarily error messages and status reports on the transfer itself, for example, how many bytes of the file have been transferred at any given moment). For the moment, this explanation will suffice: TCP/IP refers to a collection of protocols that facilitate communication between machines over the Internet (or other networks running TCP/IP).

How Does TCP/IP Work?

TCP/IP operates through the use of a protocol stack. This stack is the sum total of all protocols necessary to complete a single transfer of data between two machines. (It is also the path that data takes to get out of one machine and into another.) The stack is broken into layers, five of which are of concern here. To grasp this layer concept, examine the figure.

The TCP/IP stack. After data has passed through the process illustrated in figure, it travels to its destination on another machine or network. There, the process is executed in reverse (the data first meets the physical layer and subsequently travels its way up the stack). Throughout this process, a complex system of error checking is employed both on the originating and destination machine. Each layer of the stack can send data to and receive data from its adjoining layer. Each layer is also associated with multiple protocols. At each tier of the stack, these protocols are hard at work, providing the user with various services.

Study of TCP/IP is a vast topic and naturally is impossible to cover in one lecture. So I will cover in depth in parts. Knowledge of TCP/IP is necessary to understand the concept of ports, sniffers, scanners and herein lies the fundamental concepts of Internet security. So follow the concepts clearly. Will see you next time.      

– Mayur Kamat
January 25, 2000

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