Framework X.800 - http://www.uio.no/studier/emner/matnat/ifi/INF3510/v10/learningdocs/X0800E.pdf
Network Security Essentials Applications and Standards 4th ed -  http://fit.hcmup.edu.vn/~hienlth/COMP1049/References/3.%20Network-security-essentials-4th-edition-william-stallings.pdf