Internet Protocol Definition

Internet protocol (IP), one of the two main protocols in the TCP/IP (transmission control protocol/Internet protocol) suite of communications protocols, is a simple, connectionless protocol for delivering packet-based data across the Internet and other TCP/IP networks.

IP provides features for dividing messages into packets, addressing the packets, specifying the type of service, reassembling messages from packets at the destination and security. It is connectionless in the sense that no setup of a route to the destination is needed prior to a transmission. It is also an unreliable (but best effort) service because it makes almost no guarantees that individual packets will arrive undamaged, arrive out of sequence, be duplicated, or be lost.

If an application program requires a high level of reliability, it can be provided by using higher level protocols on top of IP. Thus, most networks combine IP with TCP, which establishes virtual connections between a destination and a source and provides a reliable service with guarantees of delivery.

IP can be compared to the postal system. The latter allows a sender to address a letter or package and drop it into a postal box for delivery without any prearranged link between the sender and intended recipient. That is, the sender does not need to inform the recipient that it is sending the item, and the recipient does not inform the sender that it is able and willing to accept it. The sender by default receives no acknowledgment of delivery to the correct recipient; however, it can if it pays extra for a return receipt, which is analogous to a using a higher level protocol on top of IP.

IP is a data delivery method in which each host (i.e., computer connected to the network) is allocated a unique address (i.e., an IP address), analogous to the addresses of buildings used by the postal system. IP forwards each packet based on its destination IP address, and thus each packet is routed individually; consequently, the various packets comprising a message can (and frequently do) travel across different routes to reach a common final destination.

IP operates at the network layer, which is the third layer from the bottom in the OSI (open systems interconnect) seven-layer model. This is the layer just below the transport layer, at which TCP and UDP (user datagram protocol) operate.

The current version of IP is IPv4. A new version, called IPv6, which features a vast increase in the number of IP addresses as well as a variety of other improvements, is scheduled to gradually replace IPv4 over the next ten or 15 years.

Created October 24, 2005. Updated June 26, 2006.
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