The internet protocol is responsible for addressing hosts and for routing datagrams(packets) from a source host to a destination host across one or more IP networks Functions of IP protocols are -
i) Addressing :
In order to perform the job of delivering datagrams, IP must know where to deliver them. For this, reason, IP includes a mechanism for host addressing.
ii) Data encapsulation and formatting/packaging :
IP accepts data from the transport layer protocols UDP and TCP. It then encapsulates this data into an IP datagram using a special format prior to transmission.
iii) Fragmentation & Reassembly :
IP includes the ability to fragment IP datagrams into pices so they can each be carried on the local network. The receiving device uses the reassembly fucntion to recreate the whole IP datagram again.
iv) Routing/Indirect delivery :
However, in many the final destination is on a distant network not directly attached to the source. In this situation the datagram must be delivered. This is accomplished by routing the datagram through intermediate devices.