Problem
As we have learned, the cyberspace physical layer includes the geographic component and the physical network component. Focusing on the physical network components and using the OSI physical layer, taking a look at the physical layer:
SANS Institute Understanding Security Using the OSI Model
SANS - GIAC - OSI Defense in Depth to Increase Application Security (See Layer 1 (Physical Security).
What can we do to protect this layer? As shown on the GIAC training slides below, a few things to consider are power, access, and natural events disrupting the use of the physical layer.