On the 4th floor the message is analyzes to see if it can be combined with some other small messages that need to go to the US Embassy, also if the message was very large, it might be broken into several smaller packages so other secretaries can take it and have it reassembled on the other end. The 3rd floor personnel check the address on the message, determine who the addressee is and advise Maria of the fastest route to the Embassy. On the 2nd floor the message is put into a special courier pouch (packet). It contains the message, sender and destination ID, and warns the recipient if other pieces are coming.
Maria then proceeds to the 1st floor where Mr. Boss has leased a limo for the trip. Maria departs for the US Embassy with the secret packet in hand. On the other end at the US Embassy the process is reversed. Maria proceeds from floor to floor where the message is decoded. The US Ambassador is very grateful, saying “Maria, please tell Mr. Boss I’ll be glad to meet him for dinner tonight”. Of course there are many ways this could be displayed but as long as the steps outlined are maintained in this order the OSI layers are explained very clearly.