The Internet Protocol (IP) is the most widely used implementation of a hierarchical network-addressing scheme. IP is a connectionless, unreliable, best-effort delivery protocol. The term connectionless means that no dedicated circuit connection is established prior to transmission as there is when placing a telephone call. IP determines the most efficient route for data based on the routing protocol. The terms unreliable and best-effort do not imply that the system is unreliable and does not work well, but that IP does not verify that the data reached its destination. This function is handled by the upper layer protocols.

As information flows down the layers of the OSI model, the data is processed at each layer. At the network layer, the data is encapsulated into packets, also known as datagrams. IP determines the contents of the IP packet header, which includes addressing and other control information, but is not concerned with the actual data. IP accepts whatever data is passed down to it from the upper layers.

Web Links Understanding Routing Protocols http://www.oreillynet.com/pub/a/network/ 2001/05/22/net_2nd_ lang.html