21. If the ASCII character G is sent and the character D is received, what type of error is this?
A. single-bit
B. multiple-bit
C. burst
D. recoverable
22. Which layer of OSI determines the interface of the system with the user?
A. Network
B. Application
C. Data-link
D. Session
E. None of the above
23. The transfer of data from a CPU to peripheral devices of a computer is achieved through
A. modems
B. computer ports
C. interfaces
D. buffer memory
E. None of the above
24. What is the number of separate protocol layers at the serial interface gateway specified by the X.25 standard?
A. 4
B. 2
C. 6
D. 3
E. None of the above
25. Many data communication networks have been established which provide a wealth of on-demand information services to people at home. What is the name of the system which provides an interactive, graphics-rich service that permits user to select what they want?
A. Teletex system
B. Fax system
C. Videotex system
D. Microwave system
E. None of the above