ACA Quality of Service & Media Handling 2 — Questions and Answers
Question 1: What does the G.729 codec offer compared to G.711 in VoIP deployments?
- Lower bandwidth usage (8 kbps vs 64 kbps) at the cost of slightly reduced audio quality (Correct answer)
- Higher audio quality with no compression
- Lossless audio compression with the same bandwidth
- Built-in encryption for voice streams
Correct answer: Lower bandwidth usage (8 kbps vs 64 kbps) at the cost of slightly reduced audio quality
G.729 uses 8 kbps versus G.711's 64 kbps by applying compression algorithms, reducing WAN bandwidth requirements with a minor, usually acceptable, quality trade-off.
Question 2: In AudioCodes Mediant, 'Voice Activity Detection (VAD)' when enabled will:
- Suppress RTP transmission during silence to conserve bandwidth using comfort noise generation (Correct answer)
- Amplify quiet speech to improve intelligibility
- Detect caller ID tones from the PSTN
- Monitor for echo and trigger echo cancellation
Correct answer: Suppress RTP transmission during silence to conserve bandwidth using comfort noise generation
VAD detects silence periods and suspends RTP transmission, replacing it with Comfort Noise Generation (CNG) signals, reducing bandwidth usage during pauses in speech.
Question 3: What is echo cancellation in AudioCodes gateway media processing designed to eliminate?
- Acoustic or hybrid echo caused by signal reflection on PSTN lines coupling into the receive path (Correct answer)
- Background noise picked up by the microphone
- Sidetone in handset earpieces
- Reverb in conference room environments
Correct answer: Acoustic or hybrid echo caused by signal reflection on PSTN lines coupling into the receive path
Echo cancellation removes the echo artifact caused by electrical or acoustic coupling of the far-end signal back into the return audio path, which is common on PSTN connections.
Question 4: Which RTP header field is used by AudioCodes and VoIP devices to detect out-of-order or duplicate packets?
- Sequence Number (Correct answer)
- SSRC
- Timestamp
- Payload Type
Correct answer: Sequence Number
The RTP Sequence Number increments by one for each packet sent, allowing receivers to detect missing, out-of-order, or duplicate packets.
Question 5: AudioCodes RTCP (Real-Time Control Protocol) is used alongside RTP to provide:
- QoS statistics including packet loss, jitter, and round-trip delay for active media streams (Correct answer)
- Call setup and teardown signaling
- Encryption key exchange for SRTP
- DTMF relay in-band signaling
Correct answer: QoS statistics including packet loss, jitter, and round-trip delay for active media streams
RTCP carries sender/receiver reports with statistics on packet loss, interarrival jitter, and round-trip time, enabling real-time monitoring of RTP stream quality.
Question 6: What AudioCodes feature measures voice quality metrics (MOS, delay, jitter) per call and can send alerts when thresholds are breached?
- Voice Quality Monitoring (VQM) (Correct answer)
- SNMP Trap Engine
- CDR Quality Tags
- SIP Session Timer
Correct answer: Voice Quality Monitoring (VQM)
Voice Quality Monitoring (VQM) on AudioCodes devices computes MOS estimates and measures delay and jitter per call, generating alerts when configured thresholds are exceeded.
ACA Quality of Service & Media Handling 2
What does the G.729 codec offer compared to G.711 in VoIP deployments?