350-801 CLCOR: Implementing and Operating Cisco Collaboration Core TechnologiesDemo

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QuestionQ386

Media and QoS

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Refer to the exhibit. Given this debug isdn q921 output, what problem is present with the PRI?

  • A Layer 1 is down on the controller.
  • B PRI does not have an IP address configured on the interface.
  • C Nothing, the PRI is sending keepalives.
  • D Layer 2 is down on the controller.
Explanation

Q.921 SABME frames initiate establishment of the ISDN Layer 2 data link and must be acknowledged with a UA response. Repeated transmitted SABME frames without a received UA show that the PRI controller's Layer 2 link is down. Cisco documents debug isdn q921 as displaying Layer 2 D-channel procedures and states that SABME is retransmitted until confirmed by UA.

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