Internet Protocol(IP)

Internet Protocol (IP) – RFC 791

Internet protocol (IP) essentially is the layer. It is designed for use in interconnected systems of packet-switched computer communication networks. IP holds the big picture and that is aware of all the interconnected networks. It can do this because all the machines on the network have software, or logical, address called an IP address. IP looks at each packet’s address. Then using a routing table, it decides where a packet is to be sent next, choosing the best path. The protocols of the Network access layer at the bottom of the DoD model do not possess IP’s enlightened scope of the network; they deal only with physical links (local networks).
IP receives segments from the Host to Host layer and fragments them into datagram (packets) if necessary. IP then reassembles datagram back into segments on the receiving side. Each datagram is assigned the IP address of the sender and of the recipient. Each router that receives a datagram makes routing decisions based on the packet’s destination IP address.
The internet protocol is specifically limited in scope to provide the functions necessary to deliver a package of bits (an internet datagram) from a source to a destination over an interconnected system of networks.
The internet protocol implements two basic functions: addressing and fragmentation.
The internet protocol uses four key mechanisms in providing its service: Type of Service, Time to Live, Options, and Header Checksum. The Type of Service is used to indicate the quality of the service desired. The Time to Live is an indication of an upper bound on the lifetime of an internet datagram. The Options provide for control functions needed or useful in some situations but unnecessary for the most common communications. Header Checksum provides a verification that the information used in processing internet datagram has been transmitted correctly.
The internet protocol does not provide a reliable communication facility. There are no acknowledgments either end-to-end or
Hop-by-hop. There is no error control for data, only a header checksum. There are no retransmissions. There is no flow control. Errors detected may be reported via the Internet Control Message Protocol (ICMP).

Reference:
Information science Institute. (1981). Internet Protocol. Retrieved August 22, 2009, from http://www.ietf.org/rfc/rfc0791.txt?number=791