The illustration has three areas bordered by dotted lines and arranged side-by-side. From left to right, they are labelled "Client Tier", "Middle Tier", and "Database Tier". A box labelled "Internet" extends from the Client Tier to the Middle Tier. Inside the Internet box and completely inside the Client Tier is a box labelled "Browser". In the Middle Tier area, the Internet box is connected to a box labelled "Firewall" by a double-headed arrow labelled "z1". The Firewall box is connected to a box labelled "DMZ" by a double-headed arrow labelled "z2". Completely inside the DMZ box are two more boxes labelled "Webcache" and "Non-sensitive Application server". Still in the Middle Tier area, the Firewall box is connected to a box labelled "Intranet" by a double-headed arrow labelled "z3". The Intranet box extends from the Middle Tier area to the Database Tier area. Inside the Intranet box and completely inside the Middle Tier is a box labelled "Sensitive Application server". In the Database Tier area are three more boxes, labelled "SQL*NET", "Database machine 1", and "Database machine 2". Unlabelled double-headed arrows connect the SQL*NET box to each database box and to the Sensitive Application server box.