Podcast Ep. 6: VoIP MOS Score: What It Means and How to Fix Bad Call Quality

Episode 6 of ViciStack Call Center Tech — the VoIP call quality episode for people who are tired of agents saying “the phones sound bad.”

MOS scores, jitter, packet loss, latency — these terms get thrown around a lot, but most call center operators don’t know what they actually mean or how to fix them. This episode translates the ITU standards into plain-English troubleshooting for Asterisk and VICIdial environments.

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Duration: 6:03

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Timestamps

• 0:00 — Intro: Why agents complain about call quality and what MOS means
• 0:45 — The MOS scale: 1.0 to 5.0 and what each range sounds like
• 1:35 — ITU-T P.800 methodology and how measurement actually works
• 2:25 — Measuring VoIP quality: RTCP stats, Asterisk CLI, network tools
• 3:15 — Jitter, packet loss, and latency thresholds for call centers
• 4:10 — Codec selection: G.711 vs G.729 and impact on MOS
• 4:55 — QoS configuration for VICIdial networks
• 5:30 — Quick wins for improving call quality today
• 5:55 — Outro

Key Takeaways

1. MOS 4.0+ is the target for call centers. Below 3.5, calls sound noticeably degraded. Below 3.0, agents and prospects both have trouble understanding each other. Aim for 4.0-4.3 on every trunk.
2. Jitter kills call quality faster than latency. 150ms of consistent latency is workable. 30ms of jitter is not. Jitter buffers help, but only if you configure them — Asterisk defaults are often too small for high-volume environments.
3. G.711 gives better quality but uses more bandwidth. For local trunks and LAN agents, always use G.711 (ulaw/alaw). G.729 saves bandwidth for remote/WAN connections but drops your MOS ceiling by 0.3-0.5 points.
4. QoS tagging is pointless without end-to-end enforcement. DSCP marking on your VICIdial server does nothing if your ISP or the carrier’s network ignores it. Verify QoS is honored at every hop.
5. The fastest fix is usually the network, not the software. Dedicated VLAN for voice traffic, wired (not Wi-Fi) connections for agents, and a separate ISP circuit for SIP trunks solve 80% of call quality complaints.

Read the Full Article

The full written guide includes Asterisk CLI commands, network diagnostic tools, and QoS configuration examples:

VoIP MOS Score: The Complete Guide

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