ACA Quality of Service & Media Handling 1 — Questions and Answers
Question 1: Which DSCP value is recommended by Cisco and widely used for marking VoIP RTP media traffic to ensure priority queuing?
- EF (Expedited Forwarding, DSCP 46) (Correct answer)
- AF41 (DSCP 34)
- CS3 (DSCP 24)
- BE (DSCP 0)
Correct answer: EF (Expedited Forwarding, DSCP 46)
EF (Expedited Forwarding, DSCP 46) is the standard DSCP marking for real-time voice RTP traffic, ensuring it receives lowest latency and jitter in network queues.
Question 2: In AudioCodes Mediant, which parameter configures the DSCP value applied to outgoing RTP packets?
- Premium Service Class Media (PremiumServiceClassMedia) (Correct answer)
- Voice Quality DSCP
- RTP Type of Service
- Media Priority Tag
Correct answer: Premium Service Class Media (PremiumServiceClassMedia)
The PremiumServiceClassMedia parameter sets the DSCP/ToS value stamped on outgoing RTP media packets, enabling QoS prioritization in the network.
Question 3: What is the primary purpose of a jitter buffer in VoIP media processing?
- To absorb network delay variation and deliver audio packets to the codec at a steady rate (Correct answer)
- To compress audio samples before transmission
- To detect and suppress background noise
- To reorder out-of-sequence TCP segments
Correct answer: To absorb network delay variation and deliver audio packets to the codec at a steady rate
A jitter buffer temporarily stores arriving RTP packets to smooth out variable network delays, providing a steady stream of audio samples to the decoder.
Question 4: AudioCodes Mediant supports which type of jitter buffer that automatically adjusts its depth based on network conditions?
- Adaptive jitter buffer (Correct answer)
- Fixed jitter buffer
- Static jitter buffer
- Buffered playout jitter
Correct answer: Adaptive jitter buffer
The adaptive jitter buffer dynamically increases or decreases its depth in real time based on measured network jitter, balancing latency against packet loss concealment.
Question 5: What is Packet Loss Concealment (PLC) in AudioCodes media processing?
- An algorithm that synthesizes substitute audio when RTP packets are lost, reducing perceived quality degradation (Correct answer)
- A method to retransmit lost RTP packets
- A codec that adds FEC redundancy to each RTP packet
- A feature that mutes audio when loss exceeds a threshold
Correct answer: An algorithm that synthesizes substitute audio when RTP packets are lost, reducing perceived quality degradation
PLC generates plausible substitute audio frames when packets are missing, minimizing the audible impact of network packet loss on voice quality.
Question 6: Which MOS (Mean Opinion Score) threshold is typically considered the minimum acceptable quality for enterprise VoIP calls?
- 3.6 (Correct answer)
- 2.5
- 4.5
- 5.0
Correct answer: 3.6
A MOS score of 3.6 or above is generally considered the minimum acceptable voice quality threshold for enterprise VoIP deployments.
ACA Quality of Service & Media Handling 1
Which DSCP value is recommended by Cisco and widely used for marking VoIP RTP media traffic to ensure priority queuing?