At the Network layer the data from the higher layers (after the data is encapsulated with headers and trailers at each higher layer) is again encapsulated with the IP header and Trailer. At this stage the data is called a Datagram. If the size of the datagram is too large it is segmented into smaller size datagrams.These are called packets.On the other hand octets are nothing but a group of 8 bits.(1 octet = 8 bits).
