VDV Voice Systems 3 — Questions and Answers
Question 1: What is the primary purpose of a dial plan in a PBX or IP-PBX system?
- Define which phones get Power over Ethernet
- Specify rules for routing calls based on dialed digits (Correct answer)
- Assign IP addresses to VoIP endpoints
- Configure voicemail box sizes
Correct answer: Specify rules for routing calls based on dialed digits
A dial plan defines the rules that a PBX uses to interpret dialed digit strings and route calls to the appropriate destination.
Question 2: Which type of VoIP gateway converts calls between the analog PSTN and a SIP-based IP network?
- Media gateway (Correct answer)
- Session border controller
- VPN concentrator
- ATA only
Correct answer: Media gateway
A media gateway performs the conversion between circuit-switched PSTN signals and packet-switched VoIP protocols such as SIP.
Question 3: What does QoS DSCP marking AF41 indicate for VoIP traffic?
- Best effort delivery
- Assured Forwarding class 4, drop probability 1 — high priority multimedia (Correct answer)
- Expedited Forwarding — voice bearer
- Network control traffic
Correct answer: Assured Forwarding class 4, drop probability 1 — high priority multimedia
DSCP AF41 (Assured Forwarding 41) indicates Class 4, low drop precedence, typically used for interactive video and high-priority multimedia traffic.
Question 4: A hunt group is configured with a 'linear' (top-down) hunting method. Which phone rings first?
- The phone that has been idle the longest
- The first phone in the list, every time (Correct answer)
- A randomly selected phone
- The last phone that answered a call
Correct answer: The first phone in the list, every time
In linear hunting, the system always starts at the first agent in the list and works down, meaning the first phone rings on every new call if it is available.
Question 5: Which cable category is the minimum recommended for deploying PoE-powered IP phones to avoid excessive heat buildup?
- Cat 3
- Cat 5
- Cat 5e
- Cat 6 (Correct answer)
Correct answer: Cat 6
Cat 6 cable is recommended for PoE applications because its larger conductors produce less resistance and less heat under the current loads used by PoE devices.
Question 6: What is the function of a Session Border Controller (SBC) in a VoIP network?
- Convert analog signals to digital
- Control and secure signaling and media at the network border (Correct answer)
- Provide DHCP addresses to IP phones
- Amplify VoIP signals over long distances
Correct answer: Control and secure signaling and media at the network border
An SBC sits at the edge of a VoIP network to enforce security policies, perform NAT traversal, and control signaling and media flows between networks.
Question 7: When testing an analog voice line with a butt set, the technician places it in 'monitor' mode. What does this allow?
- Seize the line and place a test call
- Listen to the line without interrupting an active call (Correct answer)
- Send a tone down the pair for tracing
- Measure the DC loop current
Correct answer: Listen to the line without interrupting an active call
Monitor mode on a butt set allows the technician to bridge across the line and listen in on an active call without interrupting it.
VDV Voice Systems 3
What is the primary purpose of a dial plan in a PBX or IP-PBX system?