i hate it in communication systems when they ask you to explain how 'the message is split into packets and sent and then resassebmled at the destination' for 3 marks. I have no idea how to write that without making my answer last 3 pages...
I remember that question. Think of it this way
Application Level
File is created by source
File goes through the process of packet assembly being encapsulated in a header and a trailer, establishing necessary transmission protocols (HTTP, SSL) and error detection methods
Sent to the modem through the communication control and addressing level
Communication, Control and Addressing level
In this level the communication with the receiver is established and maintained, through the protocol of TCP/IP
TCP Performs the process of handshaking, agreeing on transmission protocols and error detection methods whilst deciding on how long the transmission with remain open and closing the transmission when necessary.
IP determines the address of the receiver and routes of necessary packets, in hand with managing the actual routing of data to the receiver
Transmission Level
Packets are modulated from digital to analogue data to be send over a wired or wireless transmission medium such as a copper coaxial cable or satellite microwave medium. The modem additionally determining the size and speed of packets
The analogue data packets will be sent through the switching and routing stage in which they will be switched and routed to the receiver as necessary
Packets are demodulated by the receiver modem, through the process of demodulation, turning the analogue signals back into digital signals to be interpreted by the destination
Communication, Control and Addressing Level
TCP/IP Acknowledges that the data has been sent and closes the connection. Process of decryption occurs in this stage if necessary
Destination
Process of packet reassembly occurs in which packets are reorganized into the original data block, error checking methods undertaken in order to determine the successful transfer of the message.