Voice Systems Flashcards

Which protocol does SIP use for transporting voice media (audio packets) between endpoints?

Answer: RTP over UDP

SIP uses RTP (Real-Time Protocol) carried over UDP to transport the actual voice media between endpoints due to UDP's low latency characteristics.

What is the acceptable maximum one-way voice delay recommended by ITU-T G.114 for toll-quality calls?

Answer: 150 ms

ITU-T G.114 recommends a maximum one-way delay of 150 ms for toll-quality voice to prevent noticeable conversational degradation.

A technician measures 24 VDC on a tip and ring pair at a 66-block. What does this indicate?

Answer: The line is on-hook and active

A standard on-hook analog POTS line carries approximately 48 VDC (–48V); reading 24 VDC suggests the line is active but at half battery, which may indicate a high-resistance fault.

What is the purpose of a Music on Hold (MOH) server in a PBX system?

Answer: Stream audio to callers placed on hold

An MOH server streams audio content — music, announcements, or promotional messages — to callers who have been placed on hold.

Which feature in a VoIP system allows an extension to be answered from a different phone without transferring?

Answer: Call pickup

Call pickup allows a user at one extension to answer a call ringing at a different extension by dialing a pickup code.

What is the role of LLDP-MED in a VoIP deployment?

Answer: Allow IP phones to discover VLAN and QoS configuration from the switch

LLDP-MED (Media Endpoint Discovery) allows IP phones to automatically receive voice VLAN IDs, QoS policies, and network policy information from the connected switch.

A customer reports that callers hear echo during calls. Which device is most likely causing the echo if it is near-end echo?

Answer: The hybrid circuit at the CO or gateway where 2-wire meets 4-wire

Near-end echo is typically caused by impedance mismatch in the hybrid circuit that converts between 2-wire analog and 4-wire circuits at the gateway or CO.