TCP/IP ( Transmission Control Protocol/ Internet Protocol)

Computer with the same network communicate with each other using their physical addresses, which are hard coded on the Network Interface Card (NIC) of a computer ( The NIC is a device that is attached to each of the workstations and the server, and helps the workstation establish the all important connection with the network). But these physical addresses can not be used across multiple networks. Different networks have different addresses lengths as well addressing formats. As we know, Internet is a network of many heterogeneous computer networks. This means that physical addressing would not work on the internet. Therefore, the concept of logical addresses is used in the internet to make it a virtual network. This logical address is the 32 bit IP address. However, at the lowest level, computers must still use physical addresses to communicate with computers on the same networks. Therefore we need a mechanism to convert a logical IP address to a physical address before the actual transmission can take place over a local network.

The TCP/IP  suite of communication protocols makes the internet a worldwide network of computers networks. Since TCP/IP  software is always the same across all computers connected to the internet, we can connect different computers running different operating systems, or better yet, different networks themselves.

TCP/IP  is a layered set of protocols. In order to understand what this means, it is useful to took at an example. A typical situation is sending mail, first, there is a protocol for mail. This defines a set of commands which one machine sends to another,  e.g., commands to specify who the sender of message is, whom iti s being sent to, and then the text of the message. However, this protocol assumes that there is a way to communicate reliably between the two computers. Mail, like other application protocols, simply defines a set of commands and messages to be sent. It is designed to be used together with TCP and IP . TCP is responsible for making sure that the commands get through to the other end. It keeps track of what sent, and retransmits anything that did not get through. Generally, TCP/IP applications use 4 layers :

1. An application protocol such as mail.
2. A protocol such as TCP that provides services needed by many applications
3. IP, which provides the basic service of getting datagrams (a datagram is a collection of the data that is sent as a single message) to their destination.
4. The protocols needed to manage a specific physical medium.