Mean Opinion Score: What SA Telecoms Providers and Resellers Need to Know

Every voice call your customers make is silently judged. Not by a person sitting in a room with a clipboard — but by the international measurement framework that underpins voice quality worldwide. The Mean Opinion Score (MOS) is the telecommunications industry’s universal metric for quantifying how a voice call actually sounds to the human ear, and in South Africa, it sits at the intersection of regulatory compliance, competitive differentiation, and customer retention. For providers operating under ICASA licensing obligations, understanding MOS is not optional — it is foundational to delivering the service quality that their licences require.

What Is a Mean Opinion Score?

The Mean Opinion Score is a numerical measure of voice quality, expressed on a scale of 1 to 5 as defined by the International Telecommunication Union’s ITU-T Recommendation P.800. The scale is straightforward: 5 means excellent quality indistinguishable from face-to-face conversation, 4 means good quality with minor imperfections that most listeners would not notice, 3 means fair quality where imperfections are noticeable but not irritating, 2 means poor quality where the listener must concentrate to understand speech, and 1 means bad quality where communication effectively breaks down.

Originally, MOS was calculated by gathering a group of listeners in a controlled environment, playing back voice samples transmitted through a telephone system, and averaging their subjective quality ratings. This process, known as subjective testing under ITU-T P.800, remains the gold standard for accuracy. However, it is expensive, time-consuming, and impractical for continuous network monitoring. That is why the industry developed objective, algorithmic alternatives that can estimate MOS scores automatically.

How Is MOS Measured Today?

Modern voice quality measurement relies on two key ITU standards that algorithmically predict what a human listener would score.

PESQ (ITU-T P.862), or Perceptual Evaluation of Speech Quality, was standardised in 2001 and became the industry workhorse for objective voice quality testing. PESQ compares a reference speech signal against the degraded version that emerges from the network, producing a MOS-like score. It was designed primarily for narrowband (300 Hz to 3.4 kHz) telephony and served the industry well for a decade, with a wideband extension added via ITU-T P.862.2.

POLQA (ITU-T P.863), or Perceptual Objective Listening Quality Analysis, succeeded PESQ in 2011. Developed by ITU-T Study Group 12 over a five-year period, POLQA handles narrowband, wideband, and super-wideband audio — making it suitable for modern VoIP, VoLTE, and HD Voice services. For any provider or reseller deploying wideband or HD Voice services in South Africa, POLQA is the relevant measurement standard today.

Both algorithms work on the same principle: inject a known reference signal, capture what arrives at the other end, compare the two, and produce a score on the MOS scale. The difference is that POLQA handles the full range of modern voice codecs and transmission technologies that PESQ was never designed for.

What MOS Scores Should Providers Be Targeting?

Not all MOS scores are created equal, and the target depends heavily on the voice codec in use and the network conditions between endpoints. Here is how the most common VoIP codecs compare under ideal conditions, based on standardised testing:

• G.711 (64 kbps, uncompressed PCM): MOS of approximately 4.1 to 4.4. This is the traditional PSTN-quality codec and remains the benchmark for toll-quality voice. It consumes the most bandwidth but delivers consistently high quality.
• G.722 (48–64 kbps, wideband): MOS of approximately 4.5. The HD Voice codec that delivers noticeably richer audio than G.711, covering a wider frequency range (50 Hz to 7 kHz).
• G.729 (8 kbps, compressed): MOS of approximately 3.9 to 4.0 after a single compression cycle. Highly bandwidth-efficient but quality degrades with each additional transcoding hop — a real concern when calls traverse multiple networks.
• Opus (6–510 kbps, adaptive): Widely regarded as the most versatile modern codec, Opus adapts dynamically to available bandwidth and is the default codec for WebRTC-based communications.

The critical threshold for business voice quality is a MOS of 4.0 or above — this is considered toll quality. In practice, most VoIP calls fall in the 3.5 to 4.2 range. Scores below 3.5 indicate audible quality problems that will generate customer complaints. Scores below 3.0 represent a service that is essentially unusable for professional communication.

What Factors Degrade MOS in South Africa?

MOS is not determined by the codec alone. Network conditions between the caller and the recipient have an enormous impact, and South Africa presents some unique challenges that providers and resellers must account for.

Latency (delay) is the time it takes for voice packets to travel from sender to receiver. For acceptable conversational quality, one-way latency should stay below 150 milliseconds. Above 300 ms, conversation becomes difficult because speakers talk over each other. South African calls that route internationally — including calls that traverse offshore data centres — add significant latency compared to locally hosted voice infrastructure.

Jitter is the variation in packet arrival times. Even if average latency is acceptable, high jitter causes packets to arrive out of order, creating choppy or robotic-sounding audio. ICASA’s quality of service monitoring has repeatedly identified jitter and packet loss as primary drivers of poor voice quality across South African networks.

Packet loss is the percentage of voice packets that never arrive. Voice communication is real-time and cannot wait for retransmissions the way a file download can. Even 1% packet loss can noticeably degrade a MOS score; above 3%, calls become unpleasant.

Load shedding remains a uniquely South African factor. When power fails, routers, fibre ONTs, and ISP network equipment go offline or restart. The minutes following power restoration often produce severe packet loss and jitter as equipment reconnects and routing tables rebuild. Providers who have not invested in UPS-backed infrastructure — or whose underlying network partners have not — will see MOS scores collapse during and immediately after load shedding events.

Contention ratios on shared fibre and wireless links mean that a connection performing well at 6 AM may deliver terrible voice quality at 2 PM when neighbours are streaming video. Business-grade SLAs with guaranteed bandwidth and priority QoS markings are essential for maintaining consistent MOS scores.

How Does ICASA Regulate Voice Quality?

South Africa’s telecommunications regulatory framework places clear obligations on licensed providers to deliver measurable service quality. Under Section 69 of the Electronic Communications Act (No. 36 of 2005), ICASA is empowered to set minimum standards for the quality of electronic communications services.

The End-User and Subscriber Service Charter Regulations, first gazetted in 2016 and amended in 2023, establish specific benchmarks that all licensed operators must meet. These include a minimum of 95% network service availability averaged over six months and a connectivity failure rate (which includes dropped calls) not exceeding 3% of all connections over the same period.

ICASA actively monitors compliance through its Quality of Service reporting programme, which measures network accessibility (can the user make a call?) and retainability (does the call stay connected without dropping?). The Authority publishes provincial QoS reports that benchmark operators against these standards.

Non-compliance carries real consequences. Violations of the End-User and Subscriber Service Charter Regulations can result in fines of up to R5 million. For broader licence condition breaches under the Electronic Communications Act, ICASA’s Complaints and Compliance Committee can impose penalties, issue compliance notices, or recommend licence suspension.

For providers, this means that voice quality is not merely a competitive differentiator — it is a regulatory obligation. And for resellers, it means that the providers you partner with must be able to demonstrate compliance with these standards. A provider operating without a valid ICASA licence, or one that consistently fails quality benchmarks, exposes both themselves and their channel partners to regulatory and reputational risk. The complete guide to ICASA licence types, requirements, and the application process explains who needs which licence and what ongoing compliance looks like.

Why MOS Matters for Reseller Confidence

When a reseller recommends a voice provider to a business customer, they are staking their own reputation on that provider’s ability to deliver consistent call quality. MOS provides an objective, vendor-neutral metric for evaluating whether a provider can deliver on that promise.

Here is what to look for when assessing a provider’s quality credentials:

Active quality monitoring. Does the provider continuously measure MOS across their network, or do they only investigate quality after a customer complains? Proactive monitoring — using tools that measure MOS on synthetic test calls or live traffic — indicates a mature operation.

Published SLAs with MOS commitments. The strongest providers commit to specific MOS thresholds in their service level agreements. A provider willing to contractually guarantee a minimum MOS of 4.0 on their network is demonstrating confidence in their infrastructure.

ICASA licence compliance. Every provider offering voice services in South Africa must hold a valid Electronic Communications Service (ECS) licence. This is not a formality — it means the provider is subject to ICASA’s quality of service monitoring framework and must meet the Charter’s minimum standards. Resellers should verify their providers’ licensing status as a baseline due diligence step.

Local infrastructure. Providers hosting voice infrastructure within South Africa — particularly at local data centres with direct peering to major ISPs — will consistently deliver lower latency and better MOS scores than those routing calls through offshore platforms. For the SA market, local hosting is a quality advantage, not just a data sovereignty consideration.

What Other Metrics Support MOS?

MOS is the most widely recognised voice quality metric, but it works best alongside supporting measurements. The R-Factor (ITU-T G.107) is a transmission planning score from 0 to 100 that accounts for codec quality, network impairments, and equipment factors — an R-Factor above 80 corresponds roughly to a MOS of 4.0. For real-time troubleshooting, the individual network KPIs that drive MOS — latency below 150 ms, jitter below 30 ms, and packet loss below 1% — are often more actionable than the composite score itself. MOS remains the best starting point for resellers because it is standardised, universally understood, and directly maps to the end user’s perception of call quality.

Frequently Asked Questions

What is a good MOS score for business VoIP?

A MOS of 4.0 or above is considered toll quality — equivalent to the traditional PSTN experience. For professional use, including contact centres and customer-facing communications, this should be the minimum target. Scores of 4.3 and above indicate excellent quality. Most modern VoIP platforms using G.711 or G.722 codecs on well-configured networks achieve MOS scores in the 4.0 to 4.4 range.

Do resellers need an ICASA licence to sell voice services?

Resellers operating under an upstream provider’s licence typically do not need their own ECS licence, provided they are genuinely reselling the licensed provider’s service rather than operating their own network infrastructure. However, the upstream provider must hold a valid licence and meet ICASA’s quality standards. The full breakdown of licence types and requirements clarifies where the boundaries fall.

How does load shedding affect MOS scores?

Load shedding causes immediate call drops when equipment loses power, and degraded MOS scores for several minutes after power returns as network equipment reboots, routing tables reconverge, and buffered traffic creates congestion. Providers with UPS-backed infrastructure and redundant power at their core network sites will maintain significantly better MOS scores through load shedding events than those without.

Find Out More

Mean Opinion Score is the bridge between technical network performance and the voice quality your customers actually experience. For South African providers, maintaining strong MOS scores is both a regulatory requirement under ICASA’s quality framework and a competitive necessity in an increasingly quality-conscious market. For resellers, understanding MOS gives you a concrete, measurable basis for evaluating providers, differentiating your offering, and having informed conversations with enterprise buyers who expect more than feature lists and pricing tables.

To understand the full ICASA licensing landscape and what compliance means for providers and their channel partners, read our comprehensive guide: Telecoms Licensing in South Africa: ICASA Licence Types, Requirements and How to Apply.

Sources

• ITU-T Recommendation P.800.1 — Mean Opinion Score (MOS) Terminology
• ITU-T P.800.1 Summary — MOS Terminology (2006)
• ITU-T Recommendation P.862 — Perceptual Evaluation of Speech Quality (PESQ)
• POLQA — The Next-Generation Voice Quality Testing Standard (ITU-T P.863)
• ICASA End-User and Subscriber Service Charter Regulations (2018)
• ICASA Charter Amendments (2023)
• ICASA Quality of Service Reports
• Electronic Communications Act No. 36 of 2005
• VoIP MOS Score Reference — VoIP Mechanic
• Measuring VoIP Quality with MOS Score — Obkio
• Understanding VoIP Jitter, Latency, and Packet Loss — United World Telecom
• Ellipsis — ICASA Service Licensing Penalties

About ICASA on Telecoms-Channel
For comprehensive coverage of ICASA licensing, regulations, and compliance requirements for South African telecoms providers, visit the ICASA page on Telecoms-Channel.

About the Author

Mechelle Gindra

Mechelle Gindra is the managing editor and lead content strategist at Telecoms-Channel, South Africa's dedicated intelligence platform for telecoms resellers, ICT distributors, and channel partners. She oversees the editorial team's AI-assisted content production pipeline, ensuring vendor news, market analysis, and regulatory updates are accurate, timely, and actionable for the SA telecoms channel community. With deep expertise in the South African telecoms reseller ecosystem, Mechelle directs coverage of vendor partner programmes, ICASA regulatory developments, wholesale market dynamics, and channel business strategy. She is responsible for maintaining Telecoms-Channel's editorial standards, fact-checking processes, and corrections policy.