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What affects VoIP call quality and how to improve it
For many organisations, phone calls remain key to their operations and are the first point of contact with customers, users or patients.
Ensuring the quality of all VoIP components, including call routing and sound quality, virtual receptionists, and even hold music, is therefore paramount, as nobody wants to sell less or lose clients over a bad line.
This guide explains the factors that affect VoIP call quality and the best practices to ensure VoIP system quality remains high.
Contents:
- Signs of low VoIP call quality
- How to measure VoIP call quality
- What causes low VoIP call quality
- How to identify the cause of VoIP call quality issues
- How to improve VoIP call quality
What is VoIP call quality?
VoIP call quality refers to how clear, stable, and natural a voice call sounds when it is delivered over an internet connection.
High call quality means the voice is heard clearly, without interruption, delay, or distortion. In contrast, low call quality presents as audio delays, choppy or robotic sound, echo, distorted or muffled audio, and call drops.
VoIP call quality is determined by how reliably voice data packets are captured, transmitted across the network in real time, and reconstructed at the receiving end.
When issues occur, it is necessary to monitor key call quality and network metrics, such as latency, jitter, packet loss, and available bandwidth, at different points in the network to identify where performance is breaking down.
Signs of low VoIP call quality
Low VoIP call quality presents as issues that disrupt conversation or make speech difficult to understand:
- Audio delay: Noticeable lag between speaking and hearing a response, leading to talk-over
- Choppy or robotic sound: Inconsistent audio caused by uneven delivery
- Dropped words or silence: Parts of speech missing or cut out entirely
- Echo: Hearing your own voice repeated back with a delay
- Distortion or muffled audio: Unclear or degraded sound quality
- Dropped calls: Calls disconnecting unexpectedly
These symptoms indicate that voice data is not being transmitted or reconstructed reliably in real time, and show that there is something wrong with the setup or the underlying network.
How to measure VoIP call quality
To understand and diagnose VoIP call quality issues, it is necessary to measure how voice data is being transmitted across the network. The three primary metrics used are:
- Latency: The time it takes for voice data to travel from sender to receiver. Higher latency introduces noticeable delay in conversation.
- Jitter: The variation in the timing of packet arrival. High jitter results in uneven or distorted audio.
- Packet loss: The percentage of voice data packets that fail to reach their destination. This leads to missing words or audio dropouts.
These metrics do not cause VoIP call quality issues but describe how well or poorly the network delivers voice data in real time. By measuring these at different points in the call path, it becomes possible to identify where performance degradation occurs.
What causes low VoIP call quality
Low VoIP call quality is caused by issues in the underlying network, infrastructure, and system configuration that affect how reliably voice data is transmitted.
These can occur across components of the end-to-end journey of a call, which are four groups:
- Broadband connection quality: Connection type (e.g. copper, cable, fibre, mobile, satellite, radio waves), contention ratios (e.g. fully dedicated 1:1 to highly contended 1:50), and provider routing in that area all influence latency, reliability, and consistency.
- LAN configuration: Poorly configured local networks, lack of Quality of Service (QoS), overloaded switches, or reliance on WiFi (especially older generation, or badly designed access point placement) instead of wired Ethernet can introduce congestion and instability.
- WAN and routing paths: The distance and number of network hops between endpoints affect delay, while inefficient routing (e.g. a lack of SD-WAN optimisation, an MPLS backbone, or Business Ethernet) introduces variability in packet delivery.
- VoIP hardware and software: Headset quality, device performance, codec selection, and platform configuration all influence how clearly voice is captured, processed, and reproduced.
In practice, these factors affect how consistently voice data can be delivered, which is then reflected in latency, jitter, and packet loss measurements.
How to identify the cause of VoIP call quality issues
Identifying the root cause of VoIP call quality issues involves measuring performance across the call path and isolating the points of degradation.
Where to measure network and call performance
These are the key areas to measure separately to pinpoint where the issues are occurring:
- Within the local area network (LAN): Between user devices, switches, and routers, where bottlenecks may be forming due to a lack of capacity or misconfiguration.
- At the network edge: As traffic leaves the local network via the broadband connection, it may be insufficient or under stress due to shared network congestion.
- Across the wide area network (WAN)/internet: Between your local network and the VoIP provider, where routing may be sub-optimal or simply impaired due to issues with your business broadband providers.
- At the provider level: Within the VoIP platform and its infrastructure. They may be suffering from DDoS attacks or having issues at their local Points of Presence.
The most common issues are along the network edge or with the business VoIP provider.
What to look for when measuring performance
When measuring performance, these are the telltale signs that something is failing:
- Spikes or consistently high latency
- Variability in packet delivery (visible jitter)
- Packet loss, especially during peak usage
- Reduced or inconsistent available bandwidth
- Record call quality empirically through your staff, noting issue persistence and the time that they occur.
Focus on patterns over time rather than single measurements, as these can tell if issues are momentary or persistent.
How to isolate the VoIP call quality issue
Once enough data is available, VoIP system owners:
- Compare results across different network segments, and during peak and off-peak hours
- Switch between WiFi and wired connections
- Use VoIP testing and network monitoring tools to simulate calls
This process helps determine whether the issue originates in the local network, the internet path, the provider, or the endpoint devices.
Usually, issues are identified quickly, without significant analysis and with limited monitoring data.
How to improve VoIP call quality
Improving VoIP call quality involves addressing the underlying infrastructure, configuration, and device issues identified during the monitoring phase that are actively affecting the transmission of voice data.
Here we map the issues that cause poor VoIP call quality with solutions:
| Issue | Solution |
|---|---|
| High latency from the broadband connection | - Upgrade to higher bandwidth and lower contention broadband. - Install dedicated business leased line broadband where possible |
| Dropped calls due to unstable broadband | - Add a secondary broadband connection for redundancy - Configure automatic network load balancing between connections - Avoid unstable wireless connections, such as business wireless broadband or 5G business broadband |
| WiFi-related instability (jitter, packet loss) | - Use wired Ethernet connections for VoIP devices - Reduce interference and optimise WiFi channels if wireless is required - Upgrade to WiFi 7 and redesign the supporting mesh network. |
| Poor LAN performance (internal network bottlenecks) | - Upgrade firewalls, network switches and routers if overloaded or outdated. - Enable QoS (VoIP data priorisation) across internal network devices - Segment VoIP traffic from general data traffic using a VLAN |
| Inefficient routing across the WAN | - Use VoIP providers with optimised routing paths - Extend QoS (VoIP data priorisation) across the wide area network through SD-WAN or dedicated Ethernet. - For site-to-site communications, implement a point-to-point leased line for optimal performance. |
| Poor audio quality from devices | - Use high-quality headsets and VoIP phones - Ensure devices meet performance requirements - Avoid using low-quality built-in microphones or speakers |
| Misconfigured VoIP system or codecs | - Optimise codec selection for your network conditions - Ensure correct SIP and platform configuration - Enable features such as jitter buffers where appropriate |
| VoIP provider performance issues (external platform) | - Choose providers with strong SLAs covering uptime, latency, and call quality - Review provider routing quality and geographic coverage - Use providers with redundant infrastructure and failover capabilities - Escalate persistent issues through provider support and monitoring tools |
VoIP call quality – FAQs
Our business VoIP experts answer frequently asked questions regarding the quality of VoIP calls:
How does call quality compare between VoIP and traditional phone lines?
A business VoIP phone system can match or exceed the quality of traditional phone lines when properly configured, as it supports higher-quality codecs and more flexible routing. However, unlike traditional PSTN lines, VoIP depends on network performance, so poor connectivity or misconfiguration can degrade call quality.
How to set up Quality of Service (QoS) for VoIP
QoS is configured on business broadband routers and switches to prioritise VoIP traffic over other data traffic. This typically involves identifying VoIP packets (via SIP or RTP), assigning them higher priority, and ensuring sufficient bandwidth is reserved so calls are not affected by congestion.
How can a business ensure consistently high VoIP call quality?
Ensure high call quality by using reliable, fully dedicated broadband, prioritising VoIP traffic across local and wide area networks with QoS, using wired connections instead of WiFi, selecting high-quality devices, and continuously monitoring latency, jitter, and packet loss to detect issues early.
Does VoIP call quality depend on the provider?
Yes. VoIP providers influence call quality through their routing infrastructure, geographic coverage, and platform reliability. Providers with strong SLAs, optimised routing, and backup systems are more likely to deliver consistent call performance.
Why is there a delay or lag in VoIP calls?
Delay is caused by high latency, which occurs when voice data takes too long to travel between endpoints. This is often due to long routing paths, network congestion, or inefficient provider routing.
Why do VoIP calls drop or cut out?
Calls typically drop due to network instability or packet loss. This can result from unstable broadband connections, WiFi interference, overloaded networks, or provider-side issues.
How much internet speed do I need for good VoIP call quality?
VoIP does not require high bandwidth per call (typically around 100 kbps for voice only), but it does require consistent availability. The key factor is not just business broadband speed, but ensuring sufficient uncontended bandwidth to handle simultaneous calls without congestion.
What is the fastest way to improve VoIP call quality?
The quickest improvements usually come from switching to wired Ethernet, enabling QoS to prioritise VoIP traffic, and reducing competing network usage during calls.
Do I need a leased line for good VoIP quality?
Not always. Standard business broadband can support good VoIP quality if it is stable and not heavily contested. However, leased line providers guarantee bandwidth and low latency, making them ideal for businesses with high call volumes or strict reliability requirements.
Can VoIP quality be improved without upgrading the internet speed?
Yes. Many issues can be resolved by improving network configuration, such as enabling QoS, reducing congestion, optimising routing, or upgrading internal network equipment and devices. Internet speed (bandwidth) is only one part of the equation.
Why does VoIP quality drop when uploading or downloading files?
Large uploads or downloads consume available bandwidth and introduce congestion, which increases latency, jitter, and packet loss. Without QoS, VoIP traffic competes with other data and suffers as a result.
What network setup gives the best VoIP call quality?
The best setup includes a stable, low-contention broadband connection (i.e. leased lines, wireless leased lines and full fibre business broadband), wired Ethernet for VoIP devices, properly configured QoS, optimised routing, and high-quality hardware.
Where required, dedicated connectivity such as Ethernet WAN, MPLS, or SD-WAN solutions can further improve performance.
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