The SANS Institute was established in 1989 as a cooperative research and education organization. Here is one published research whitepaper in the SANS Institute Information Security Reading Room:
One Approach to Enterprise Security Architecture
This paper discusses an approach to Enterprise Security Architecture, including a security policy, security domains, trust levels, tiered networks, and most importantly the relationships among them.
The objective of enterprise security architecture is to provide the conceptual design of the network security infrastructure, related security mechanisms, and related security policies and procedures. The enterprise security architecture links the components of the security infrastructure as one cohesive unit. The goal of this cohesive unit is to protect corporate information.