The Internet Protocol is part of a suite of communication protocols of which TCP and IP (Transfer Control Protocol and Internet Protocol) are the two best known. Internet protocols were first introduced in the 1970's, when the Defense Advanced Research Projects Agency (DARPA) had an interest in implementing a packet-switched network that would be able to communicate between different computer systems at research institutions. The Internet protocols policies are now documented in technical reports called Request For Comments (RFCs). The Internet Protocol is addressed in RFC 0791 (1, 475).
The Internet Protocol operates in Layer 3 of the OSI model, the network layer. IP is a connectionless protocol. There is no guarantee of delivery or acknowledgement of receipt, and it operates on a best-effort delivery of datagrams through an internetwork. The Internet Protocol has two functions, addressing and fragmentation. IP uses the addresses located in the internet header to deliver datagrams to their destination, and provides fragmentation and reassembly of datagrams to support data links with different maximum transmission unit sizes (2, 1.4).
IP uses a packet method because it is a connectionless protocol. An IP packet is comprised of fourteen different fields, illustrated in diagram 1.1. Version (VERS) indicates the version of the IP currently used. The header length (Hlen) indicates the datagram header length in 32-bit words. The total length, a 16-bit field, specifies the length, in bytes, of the entire IP packet, including the data and the header. Identification, which is used to piece together datagram fragments, contains an integer that identifies the current datagram and is 16 bits long. Flags are a 3-bit field in which the first bit specifies whether a packet can be fragmented, the middle bit specifies whether the packet is the last fragment in a series of fragmented packets, and the third bit is not used.
