1/7     Some literatures say the OSI is 7 layers while some say it's
        4 layers. What accounts the difference?
        \_ OSI is 7 layers, the older view networking was only 4
           layers: physical, mac, transport (tcp/ip), application.
           \- and then there is implementation reality/practice ...
              \_ yermom doesn't mind 3 layers, and accepts all out-of-band
                 traffic.