This Recommendation | Technical Report describes the cross layer aspects of the provision of security services in the lower layers of the OSI Reference Model (Transport, Network, Data Link and Physical layers). This Recommendation | Technical Report describes: a) architectural concepts common to the lower layers based on those defined in CCITT Rec. X.800 | ISO 7498-2; b) the basis for interactions relating to security between protocols in the lower layers; c) the basis for any interactions relating to security between the lower layers and upper layers of OSI; d) the placement of security protocols in relation to other lower layer security protocols and the relative role of such placements. There should be no conflict between the security protocols for the lower layers and the model described in this Recommendation | Technical Report. CCITT Rec. X.500 | ISO/IEC 9594-1 identifies the security services relevant to each of the lower layers of the OSI Reference Model.