Telecommunications - Layer 2 Exam

1 - A protocol tester is to be used to investigate a link level fault where would it be tee'd into the circuit ?

2 - What is the main job of the link layer.

  1. routing.
  2. error correction.
  3. end-to-end flow control
  4. speed changing


4 - What is transmitted to line when no information is

available for transmission.

  1. flags
  2. permanent 1s
  3. permenant 0s
  4. idles


5 - By monitoring an X.25 line how can you tell if the link is in the down state ?

a) the network polls with SABMs

b) the network polls with DISCs

c) the customer polls with SABMs

d) the customer polls with DISCs


6 - If a computer calls another computer through Public Network and sends a frame with a sequence number N(S) of 5, what sequence number will be received by the distant end computer ?

a) N(S) = 4

b) N(S) = 5

c) N(S) = 6

d) not enough information here to tell


7 - What is the P bit used for ?

a) to indicate a sequence number error

b) to indicate PAD data is being transmitted

c) to demand an immediate response from the other end.

d) to indicate a FCS error


8 - what are the 9 types of frame ?

what is each one used for ?


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