VDV Voice Systems 5 — Questions and Answers
Question 1: Which standard defines Power over Ethernet delivering up to 30 watts per port?
- IEEE 802.3af
- IEEE 802.3at (Correct answer)
- IEEE 802.3bt
- IEEE 802.11ac
Correct answer: IEEE 802.3at
IEEE 802.3at (PoE+) defines delivery of up to 30 watts per port, which supports higher-power devices like PTZ cameras and wireless access points.
Question 2: What is the purpose of Automatic Gain Control (AGC) in a telephone system?
- Automatically route calls to available agents
- Normalize audio levels so quiet and loud voices are heard equally (Correct answer)
- Generate dial tone for analog extensions
- Detect busy signals to redirect calls
Correct answer: Normalize audio levels so quiet and loud voices are heard equally
AGC automatically adjusts the gain of incoming audio signals so that voice levels remain consistent regardless of the speaker's volume.
Question 3: In a structured cabling installation, where should voice patch panels be terminated to allow easy moves, adds, and changes?
- Directly at the IP phone handset
- At the MDF/IDF on a 110 or RJ-45 patch panel (Correct answer)
- At the demarc extension block only
- At the end-user's desk jack in the wall plate
Correct answer: At the MDF/IDF on a 110 or RJ-45 patch panel
Terminating voice pairs at a centralized patch panel in the MDF/IDF allows technicians to reconfigure circuits with short patch cords without re-pulling cable.
Question 4: What happens to VoIP calls when the IP network goes down if the phones have a PSTN analog backup (POTS survivability) configured?
- All calls drop immediately
- Calls are routed over the analog PSTN lines automatically (Correct answer)
- Calls are queued until the network recovers
- Extensions send a busy signal to all callers
Correct answer: Calls are routed over the analog PSTN lines automatically
PSTN survivability allows VoIP systems to automatically fail over to analog POTS lines so that inbound and outbound calling continues during an IP network outage.
Question 5: Which SIP response code indicates that a called party is temporarily unavailable (e.g., phone is off or unregistered)?
- 180 Ringing
- 200 OK
- 404 Not Found
- 480 Temporarily Unavailable (Correct answer)
Correct answer: 480 Temporarily Unavailable
SIP response code 480 (Temporarily Unavailable) indicates the endpoint exists but cannot accept calls at this moment, often because the device is unregistered.
Question 6: What is the function of a Direct Inward Dialing (DID) number in a PBX system?
- Allow extensions to dial out directly without an operator
- Allow outside callers to reach a specific extension without going through a receptionist (Correct answer)
- Define the emergency dial plan for 911 routing
- Provide a dedicated fax line for the system
Correct answer: Allow outside callers to reach a specific extension without going through a receptionist
DID numbers map individual PSTN phone numbers to specific internal extensions, allowing external callers to reach employees directly without an operator.
Question 7: A VDV technician is installing a new IP phone and the phone cannot register with the call manager. The phone obtains an IP address but shows 'TFTP timeout.' What should be checked first?
- The physical RJ-45 crimp on the patch cable
- The DHCP option 150 or 66 pointing to the correct TFTP server address (Correct answer)
- Whether the phone is set to the correct codec
- The DNS A record for the call manager
Correct answer: The DHCP option 150 or 66 pointing to the correct TFTP server address
Cisco and many other IP phones use DHCP Option 150 (or Option 66) to discover the TFTP server address for downloading their configuration and firmware files.
VDV Voice Systems 5
Which standard defines Power over Ethernet delivering up to 30 watts per port?