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1. What is the meaning of the control signal NAK in an ARQ system?

a) Bad data detected; resend the data again
b) Receiver unreachable; no connection was possible
c) Too many retries in transmitting the data; abort
d) None of these

2. When a Hamming data receiver half-adds (exclusive-ORs) the received checkbits with the regenerated checkbits, what is the meaning of the result?

a) The count of bits in the word that were in error
b) The checksum of the all the data in the block
c) The address of the bit in error
d) None of these

3. In a Hamming encoder for 4-bit data, the checkbits would be in what positions?

a) C1, C2, C3
b) C2, C3, C4
c) C2, C4, C5
d) C1, C2, C4
e) None of these

4. When would a FEC system most likely be utilized?

a) When there are very large amounts of data being sent in each data block
b) When parity is being used to check the contents of each data block
c) When the receiver is expected to request the retransmission of any damaged blocks
d) None of these

5. What is the purpose of a block check character in data communications?

a) It contains redundant information for check the accuracy of the data
b) It contains a duplicate of all the information within the data block
c) It holds the address of the sender and receiver units
d) None of these

6. Which BCC value below is the correct EVEN longitudinal parity for the data block {$02, $03}? The values are in hexadecimal.

a) $af
b) $01
c) $04
d) None of these

7. Which BCC value below is the correct 8-bit checksum for the data block {$42, $C3}? The values are in hexadecimal.

a) $27
b) $FF
c) $05
d) None of these

8. Which of these gives the correct order of operations for a 3270 point-to-point network?

a) Bid, communicate, release
b) Communicate, release, poll
c) Poll, communicate, Bid
d) Select, communicate, release
e) None of these

9. When IBM3270 is running in multidrop mode, what response does a terminal provide to a poll when it has no data for the host?

a) EOT
b) ACK0
c) ACK1
d) WACK
e) None of these

10. What is the correct response to the 5th valid data block in an IBM3270 "conversation?"

a) ACK0
b) WACK
c) ACK1
d) NAK
e) None of these

11. Why is an alternating acknowledge system used in the IBM 3270 protocol?

a) To increase the speed of communications on the network
b) To detect lost message packets
c) To improve error detection quality on individual packets
d) None of these

12. If a terminal is busy or has a full memory buffer when it is selected by a host, how might it respond to a select command in the IBM 3270 protocol?

a) ACK0
b) ACK1
c) WACK
d) RVI
e) None of these

13. When is it permissible for a terminal to transmit on a 3270 multidrop network?

a) Whenever the terminal's data buffer is full
b) Only in response to host commands
c) Whenever another terminal needs data from the unit
d) None of tnese

14. When a terminal unit is selected in IBM 3270 protocol (and is ready for data), what is its normal response?

a) WACK
b) ACK1
c) NAK
d) None of these

15. The NR/NS acknowledgment system of HDLC could be classified as functioning in what OSI model layer?

a) 1 - Physical
b) 2 - Data Link
c) 3 - Network
d) 4 - Transport
e) 5 - Session
f) 6 - Presentation
g) 7 - Application

16. What is a "piggybacked acknowledge?"

a) An acknowledge that is sent within an information frame
b) An acknowledge that confirms reception of several consecutive frames
c) An acknowledge that confirms that at least 50% of the data in a frame is correct
d) None of these

17. In the HDLC protocol, what pattern marks the beginning and end of data frames?

a) FLAG
b) BCC
c) FCS
d) LRC
e) None of these

18. The following HDLC exchange occured on a network:

RR A=7E P/F=1 NR=07

                    I A=7E P/F=0 NR=06 NS=07
                    I A=7E P/F=1 NR=06 NS=00

What will the host respond with if all the frames have been correctly received (assuming that the host doesn't have any data to send to unit $7E.)

a) RR A=7E P/F = 1 NR=02
b) RNR A=7E P/F = 1 NR=07
c) RR A=7E P/F = 0 NR=01
d) None of these

19. A primary unit sends the following frame. What will probably happen next on the network?

RR A=02 P/F=1 NR=03

a) Secondary unit 03 will stop responding to any further host requests
b) All units on the network will get ready to receive the subsequent broadcast data frame(s)
c) Secondary unit 02 will respond with a frame for the host
d) None of the above

20. The following HDLC exchange occured on a network:

RR A=43 P/F=1 NR=07

                    I A=43 P/F=0 NR=06 NS=07
                    I A=43 P/F=0 NR=06 NS=00
                    I A=43 P/F=0 NR=06 NS=01
                    I A=43 P/F=1 NR=06 NS=02
RR A=43 P/F=1 NR=00

What will happen next on the network?

a) The primary unit will service the next terminal in the poll list
b) Secondary unit 43 will transmit frames 0,1,2
c) Secondary unit 43 will transmit only frame 0
d) The host will lock secondary unit 43 off the network, no longer polling it

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