The Internetwork (IP) layer is responsible for the delivery of the packets to the computer whose address they contain. It does this by talking to its IP layer counterparts on every computer that the data passes through on the way. The addressing scheme in the form 188.8.131.52 tells each computer what computer to send the data to next. At each hop along the way, the IP layer has to decide whether the packet was intended for this computer. If not, it has to decide which other computer that it is directly connected to will provide the best route to the packet's final destination.
The packet is broken into datagrams, which are a kind of minipacket. Each datagram contains part of the packet. When all the datagrams for one packet arrive at the destination computer, they are reassembled into a packet and handed to the transport layer.
A datagram is a string of characters that is made up of a header, the data, and a trailer. The header contains the IP addresses of both the source and the destination along with some security information. The trailer normally contains a checksum that is used to verify that accidental corruption has not occurred.
This layer has no concept of a session. To the IP layer, a datagram is forgotten once it is sent. If a broken datagram arrives, it is discarded and the packet that it belongs to will be broken, too. The Transport layer will notice the broken packet and request a resend.