The IP (Internet Protocol) is a protocol which uses datagrams to communicate over a packet-switched network. The IP protocol operates at the network layer protocol of the OSI reference model and is a part of a suite of protocols originally developed by the US Department of Defense (DoD).
The Internetwork Protocol (IP) provides a best effort network layer service for connecting computers to form a computer network. Each computer is identified by one or more globally unique IP addresses. The network layer PDUs are known as either "packets" or "datagrams". Each packet carries the IP address of the sending computer and also the address of the intended recipient or recipients of the packet. Other management information is also carried.
The IP network service transmits datagrams between intermediate nodes using IP routers. The routers themselves are simple, since no information is stored concerning the datagrams which are forwarded on a link. The most complex part of an IP router is concerned with determining the optimum link to use to reach each destination in a network. This process is known as "routing". Although this process is computationally intensive, it is only performed at periodic intervals.
An IP network normally uses a dynamic routing protocol to find alternate routes whenever a link becomes unavailable. This provides considerable robustness from the failure of either links or routers, but does not guarantee reliable delivery. Some applications are happy with this basic service and use a simple transport protocol known as the Universal Datagram protocol (UDP) to access this best effort service.
Most Internet users need additional functions such as end-to-end error and sequence control to give a reliable service (equivalent to that provided by virtual circuits). This reliability is provided by the Transmission Control Protocol (TCP) which is used end-to-end across the Internet.
In a LAN environment, the protocol is normally carried by Ethernet, but for long distance links, a serial data link protocol is usually used.
Other protocols associated with the IP network layer are the Internet Control Message Protocol (ICMP) and the Address Resolution Protocol (arp).
http://www.erg.abdn.ac.uk/users/gorry Date: 10/11/1995 Revised: 7/10/2003