The internet protocol suite, or TCP/IP protocol suite, refers to the set of communications protocols that form the basis for transmitting and routing packets of data on the internet. Its name comes from two of its most important protocols - the Transmission Control Protocol (TCP) and the Internet Protocol (IP).  These protocols were developed by DARPA to allow communication between various types of computers and computer networks. The TCP/IP is one thing that all internet sites have in common.

  

The entire TCP/IP protocol suite may be viewed as consisting of 5 layers: 1) the Physical Layer, which includes specifications and protocols for physical devices such as modems, USB, RS-232, Wi-Fi, ISDN, Bluetooth, and the Ethernet; 2) the Data Link Layer, which includes protocols for linking devices belonging to a local network, i.e., protocols for local area networking;  3) the Network Layer, which includes protocols for interconnected networks, or 'internetworks', (the IP is in the Network Layer); 4) the Transport Layer, which covers the routing protocols that mediate between the Network Layer and the Application Layer (the TCP is in the Transport Layer); and 5) the Application Layer, which includes protocols for actual internet applications such as file transfer, email, web browsing, and terminal emulation applications - the FTP, HTTP, POP3, SMTP, DNS, TELNET, etc.

   

Each layer in the protocol suite addresses a specific set of problems for successful data transmission, but may also provide a designated service to an upper layer protocol.  In general, the higher the layer, the closer its service is to the end-user, and the more abstract the data that it handles.

   

As mentioned, the IP and the TCP are the most important components of the internet protocol. The IP is a connectionless protocol while TCP is connection-oriented, i.e., it establishes connection and maintains it until the required data exchanges have been completed.

   

The TCP

   

The connection-oriented transport protocol TCP enables two hosts to establish a reliable connection and exchange data, guaranteeing not only delivery of the data, but their delivery in the same order as they were sent as well.  It transmits data as an unstructured stream of bytes.

       

The TCP employs sequence numbers and acknowledgement messages to provide the sending node with information about the delivery of the data packets transmitted to the destination node.  If data is lost during transmission, the TCP can retransmit the data until they are successfully delivered, or until a time-out condition is reached.  The TCP can also slow down the rate of flow of data transfer if the sending computer is too fast for the receiving computer. Delivery information can also be relayed by the TCP to upper-layer protocols and other applications.

        

The TCP, which is in the Transport Layer, runs on top of the internet protocol (IP), which is in the Network Layer. 

             

The IP

   

The IP is considered to be the 'heart' of the internet protocol suite. It is in the third layer of the TCP/IP layer structure.  Its primary function is routing of data between interconnected networks, but it also provides error reporting as well as fragmentation and reassembly of data units for inter-network transmission.  IP networks all over the world communicate with each other through globally unique IP addresses, each of which consists of 3 parts.

   

The first part of the IP address is the network address, the second part is the subnet address, and the third part is the host address.