What is IP

The Internet Protocol (IP) is the most widely used method for transporting data within and between communications networks. IP provides the function of linking between physical networks, creating communication paths between nodes on different networks. IP provides a connectionless, unreliable, best effort packet delivery system. IP is called connectionless because it resembles a Postal Service more than a telephone system: When a node using IP wishes to send a message, it simply sends an IP packet, properly addressed, similar to sending a letter or a telegram. Every packet is treated independently. The telephone system on the other hand, creates a connection between two users which is maintained throughout the information exchange. Connection oriented operation can be performed over IP using higher level protocols. Unreliable delivery means that packets may be lost or delayed and delivered not in order. Reliable connection can also be created using higher level protocols. TCP (Transmission Control Protocol) is the most common example for these two characteristics. Best effort delivery means that packets will not be discarded without any good cause, such as lack of resources or physical link failure.

As we have already mentioned, in order to create more complex services, higher level protocols are used over IP. The two main protocols are UDP (user datagram protocol) and TCP (transmission control protocol). UDP is also unreliable and connectionless but it introduces the concept of ports. An application is identified by a port number (e.g. port number 80 is identified with HTTP protocol on the Internet). TCP also uses the port method, but provides in addition a reliable connection between entities using packet numbering and tracking to ensure delivery of all messages. The vast majority of traffic using IP in the Internet is transfered today through TCP.