Which OSI/OSI layer defines the X.24, V.35, X.21 and HSSI standard interfaces?
A. Transport layer
B. Physical layer
C. Network layer
D. Data link layer
Answer:B
Which OSI/OSI layer defines the X.24, V.35, X.21 and HSSI standard interfaces?
A. Transport layer B. Physical layer C. Network layer D. Data link layer
Explanation: The physical layer (layer 1) defines the X.24, V.35, X.21 and HSSI standard interfaces. Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 3: Telecommunications and Network Security (page 83).