Class 4: Network Security and Compliance: Basics of Network Security

Networking for Dummies:  Seven Layers of the OSI Reference Model

SANS Institute Infosec Reading Room:  Applying the OSI Seven Layer Network Model to Information Security

Natarajan Meganathan, A Tutorial on Network Security:  Attacks and Controls (Note:  there is some degree of technical detail in this paper that you can skim over, but what you should take away from it is a general understanding of the kinds of security responses that relate to different kinds of vulnerabilities, as well as familiarity with some of the network security lingo).