210-060 · Question #98
An administrator wants to verify that a new PRI is properly connected to the PSTN status. Which Layer 2 status should be seen?
The correct answer is A. MULTIPLE_FRAME_ESTABLISHED. For a properly connected ISDN PRI at Layer 2, the expected status is MULTIPLE_FRAME_ESTABLISHED, indicating that the Q.921 LAPD data link is fully operational.
Question
An administrator wants to verify that a new PRI is properly connected to the PSTN status. Which Layer 2 status should be seen?
Options
- AMULTIPLE_FRAME_ESTABLISHED
- BTEI_ASSIGNED
- CLINK_UP
- DCONTROLLER_UP
How the community answered
(43 responses)- A88% (38)
- B2% (1)
- C7% (3)
- D2% (1)
Why each option
For a properly connected ISDN PRI at Layer 2, the expected status is MULTIPLE_FRAME_ESTABLISHED, indicating that the Q.921 LAPD data link is fully operational.
ISDN PRI uses Q.921 (LAPD) for Layer 2 signaling, and MULTIPLE_FRAME_ESTABLISHED is the state that confirms the data link layer connection between the CPE and the PSTN switch is fully up and capable of carrying Q.931 call signaling. This is the required Layer 2 state before calls can be placed.
TEI_ASSIGNED indicates a Terminal Endpoint Identifier has been assigned but the data link has not yet reached full multi-frame operation, meaning Layer 2 is not completely established.
LINK_UP is not a standard ISDN Q.921 Layer 2 state descriptor; it is more commonly associated with Ethernet or serial interface Layer 1 status.
CONTROLLER_UP refers to the Layer 1 physical controller status of the T1/E1 span, not the Layer 2 ISDN signaling link state.
Concept tested: ISDN PRI Q.921 Layer 2 status verification
Source: https://www.cisco.com/c/en/us/support/docs/wan/integrated-services-digital-network/9764-isdn-debug.html
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