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1. Which of these error detection techniques would be the most likely to detect data that has been tampered with by changing the order of the bytes?

a) Checksum
b) CRC
c) Biased Checksum
d) Longitudinal Parity
e) Lateral Parity

2. Given G(x) = X^7 + X^3 + X^2 + 1, what is the hexadecimal value of the divisor?

a) $CB
b) $8D
c) $1E
d) $5A
e) None of these

3. A group of data sent together is called a/an:

a) Block check character
b) Frame
c) Block
d) (B) or (C)
e) None of these

4. 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

5. 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

6. 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

7. 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

8. You're troubleshooting an IBM 3270 network that seems to be locked - no communications is occuring and host has locked out all the remote terminal units. On the host modem you notice that the DCD light is steadily lit. What is likely wrong?

a) The host modem is defective and unable to receive any signal from the network
b) The host modem is stuck in transmit mode and unable to receive any signals
c) One of the remote units is stuck in transmit mode
d) None of these

9. 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

10. Where is the address contained within a 3270 message?

a) After the STX character within the message
b) Within the header
c) After the BCC
d) None of these

11. 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

12. If a terminal doesn't respond to a host poll or select command in a 3270 network, what will likely happen next?

a) The host will exclude the device on subsequent rounds; the terminal is locked out
b) The host will try communicating with the device for about 150 seconds before giving up
c) The host will skip the device and try it again on the next loop
d) None of these

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

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