VoIP Call Quality: What Affects It and How to Fix It

Poor VoIP call quality is rarely the fault of VoIP itself. In most offices the cause sits closer to home: a congested Wi-Fi network, a broadband line with no headroom, an old router, or a network that treats voice like any other traffic. Fix those and a hosted phone system sounds as good as, or better than, the landline it replaced.

This guide explains how call quality is measured, what the numbers mean, and the fixes that work in a real small or mid-sized office, in the order we would try them.

TL;DR

• Call quality is judged on three network measures: latency, jitter and packet loss. A MOS score is a summary of them, not a separate fault.
• Most problems come from the local environment: Wi-Fi, an overloaded connection or poor configuration. Ofcom’s guidance points the same way.
• The quickest wins are wiring desk phones with Ethernet, giving voice priority on the router, and putting enough bandwidth behind your calls.
• Digital phones need power. Plan a battery backup or a 4G/5G failover before the UK’s landline switch-off, not after an outage.
• Test before you blame the provider: run a call over a quiet connection and compare.

Table of Contents

• How VoIP call quality is actually measured
• Why the problem is usually in your building
• A practical fix list, in the order to try it
• Power cuts and the landline switch-off
• Security affects quality too
• Our view: fix the network, then judge the phone system
• Getting help with VoIP call quality in Essex and London
• FAQ
• Sources

How VoIP call quality is actually measured

A VoIP call chops your voice into small packets of data, sends them across the internet and reassembles them at the other end. Anything that delays, scrambles or drops those packets is audible.

UK regulators use the same yardsticks. In its quality of service methodology, Ofcom describes network quality for latency-sensitive applications such as VoIP in terms of three measures:

These three interact. A line with a modest average delay can still sound terrible if the delay swings from one packet to the next, because the phone has to wait for late packets or discard them.

What is a good MOS score?

MOS (Mean Opinion Score) rates call quality on a scale of 1 to 5. Originally it came from panels of human listeners; most business phone dashboards now estimate it from latency, jitter and packet loss. A score around 4 or above is generally treated as good business-call quality, and scores drifting towards 3 usually mean callers are noticing problems.

Treat MOS as a smoke alarm. It tells you something is wrong, not what. When the number falls, open the underlying latency, jitter and loss figures for the same period, because those point to the cause.

Acceptable latency for VoIP

The ITU-T G.114 recommendation is the reference most providers quote: one-way delay up to roughly 150 milliseconds still feels like a natural conversation, and many engineers aim well below that for a local office. Jitter and loss should be as close to zero as you can get. Your own targets matter less than the trend: if a line that was clean last month now shows spikes at 9am and 2pm, something on your network has changed.

Why the problem is usually in your building

It is tempting to blame the phone provider. Ofcom’s research suggests the reality is more nuanced: service degradation, unlike a total outage, is often linked to factors on the user side, such as device placement or local network usage, rather than a fault in the wider network.

That is good news. It means the fix is usually within your control. The usual suspects, roughly in order of how often we see them:

1. Wi-Fi carrying voice. Wireless is shared and affected by walls, microwaves, neighbours’ networks and the number of devices connected. Ofcom notes that the wireless link can become the bottleneck even when the broadband connection itself is fast.
2. A connection with no headroom. Cloud backups, video meetings and software updates all compete with calls. Upload speed is the one most often forgotten, and voice needs it in both directions.
3. No traffic prioritisation. Without Quality of Service (QoS) rules, a large file upload and a phone call are treated as equals.
4. Old or cheap network kit. Consumer-grade routers and unmanaged switches struggle with many simultaneous voice streams.
5. Poor cabling. Damaged, overlong or low-grade cable can cause errors that show up as packet loss.
6. Misconfigured settings. Aggressive firewall inspection of voice traffic, mismatched codecs, or a feature such as SIP ALG on the router can garble calls.

A practical fix list, in the order to try it

1. Test before you change anything

Note when the problem happens. Is it every call, or only when the office is busy? One person, or everyone? Is it only on a particular handset, or only on the softphone app on a laptop?

• One user only: suspect their device, headset or Wi-Fi signal.
• Everyone, at busy times: suspect bandwidth or a lack of prioritisation.
• Everyone, all day: suspect the line itself, the router or a configuration fault.
• Only external calls to one network: raise it with your provider, as the fault may be elsewhere in the route.

If your phone system has a call quality report, export a week of data. A provider can often diagnose a lot remotely from it.

2. Take desk phones off Wi-Fi

This is the single most effective change for most offices. Ofcom’s background material and our own experience agree: for critical desk phones, prioritise a wired Ethernet connection to bypass Wi-Fi instability. Wireless is fine for laptops and mobiles, but a reception phone that drops words costs you customers.

If you do not have enough points near each desk, that is a cabling job, not a reason to fall back on wireless. Our network cabling installation service covers this, and a tidy structured cable run also future-proofs the office for faster equipment.

3. Fix the Wi-Fi you cannot avoid

Some handsets, tablets and softphones will always be wireless. For those, the answer is design, not another extender. A proper survey measures signal strength, interference and channel overlap room by room, then places access points where they are needed. Our Wifi survey and design service does this, and it is worth doing before any office move or refit rather than after complaints begin.

4. Give voice priority

QoS tells your router and switches to move voice packets to the front of the queue. Set it on the router at the edge of your network and on any managed switches. Be wary of leaving it to defaults: many routers ship with QoS switched off.

Also check for SIP ALG, a router feature intended to help with voice traffic that often causes one-way audio and dropped calls. Your provider or installer will normally tell you whether to disable it for your setup.

5. Size your bandwidth for the real day

A single call uses little data, but offices rarely have only calls. Count concurrent calls at your busiest time, add the video meetings and cloud tools running alongside, and leave a margin. Remember that upload matters as much as download.

The broadband options we offer, with published monthly prices:

See the business broadband page for what each tier includes. For offices where voice, video and cloud systems all run at once, or where every minute of downtime matters, a dedicated leased line removes the contention that shared connections suffer from. We do not publish a price for leased lines, as they are specified to the site.

6. Replace the weakest kit

A router that is several years old, a consumer switch hidden under a desk, or a patch lead that has been trodden on for a decade can all undermine an otherwise good line. Replace the router first, then look at switches and cabling. Wired headsets with noise-cancelling microphones also help where the complaint is background noise rather than network faults.

7. Add a failover connection

If your main line fails, so do your phones. A 4G or 5G backup router keeps calls running while the fault is fixed, and it also gives you a clean comparison when you are trying to work out whether the main line is the problem. Our 5G and 4G routers start from £20 per month.

Power cuts and the landline switch-off

This is call quality in its most extreme form: no call at all. Digital phone services depend on power at your premises. The government’s guidance says the industry plans to retire the analogue phone network, and that digital landlines will not work in a power cut without a battery backup or other power source. The same guidance says providers must keep access to 999 and 112 working for at least an hour during an outage for customers who rely solely on a landline, usually through a battery backup unit supplied on request.

The timing is close. A House of Commons Library briefing states that landline services in the UK are due to move fully to the digital network by January 2027, with calls carried over broadband.

For a business, the practical steps are:

• Put your router, switches and any phone base stations on a small uninterruptible power supply (UPS).
• Give your mobile signal and failover router a route that does not depend on the same power.
• List the devices that use a phone line: alarms, payment terminals, lift phones and door entry systems. The government guidance says these may need adaptors or replacement when you move off analogue lines.

Security affects quality too

A phone system under attack sounds bad. Toll fraud, floods of bogus registration attempts and compromised handsets all consume capacity and can run up large bills. The National Cyber Security Centre’s PBX best practice guidance recommends locking traffic down to the trusted IP addresses of your VoIP provider and keeping equipment patched. It describes security as a shared responsibility between provider and business.

The same guidance says to make sure your provider supports TLS for signalling and SRTP for the voice stream itself. Encryption adds a little processing overhead, but on modern equipment it is not something callers will notice, and it stops eavesdropping on the line. If you have in-house developers or an unusual integration, such as linking calls to a bespoke CRM, specialist system engineering and integration support can help you build that securely rather than bolting it on.

Our view: fix the network, then judge the phone system

We install and support phone systems across Essex, London and the South East, and the pattern is consistent. A business switches to VoIP, calls sound rough, and the phone provider takes the blame. Then someone looks at the network and finds voice phones on a crowded Wi-Fi, a router from a previous decade, or one connection doing everything.

Our advice is to treat the phone system, the line and the local network as one design. Look at them together before you sign anything. That is why we are vendor independent, offer our telecoms without long-term contracts, and put a survey and a cabling plan ahead of the sales pitch where the site calls for it. If your voice quality is poor, we would rather find the cause with you than sell you a new system that inherits the same problem.

There is one more thing: do not buy on headline speed alone. For voice, a steady 80 Mbps beats a line that sometimes touches 500 and sometimes stalls.

— Paul

Getting help with VoIP call quality in Essex and London

If you have worked through the list and the problem persists, bring in someone who can see the whole picture. We provide VoIP and SIP hosted telephony, business broadband, leased lines, cabling and Wi-Fi design, with UK-based support, so a call-quality fault does not bounce between three suppliers. If you want modern call handling on top, our AI-powered business phone systems handle reception and routing, and they too depend on a clean, low-delay connection. Get in touch through our website to arrange a conversation about your setup.

FAQ

Does Wi-Fi calling improve call quality?

Not by itself. Wi-Fi calling lets a mobile place calls over a wireless network, so quality depends on the same Wi-Fi and broadband that cause problems for desk phones. In a well-designed office with good coverage it works well, but in a congested one it can sound worse than the mobile signal.

Is poor call quality just part of using VoIP?

No. Ofcom’s guidance says poor quality is often traced to the local environment, such as Wi-Fi performance, bandwidth or equipment set-up, rather than to VoIP technology. These are generally things a business can fix with better design and wired connections.

How can I check my VoIP call quality?

Start with your phone system’s call report, which usually shows latency, jitter, packet loss and an estimated MOS for each call. Compare busy and quiet periods, and test one wired phone against one on Wi-Fi. If the numbers are bad on every call, ask your installer to test the line and router.

Will my phones work in a power cut?

Not without backup. Digital phone services rely on power at your premises, according to GOV.UK guidance. A UPS on your router and a 4G or 5G failover connection keep calls available during short outages.

Sources

• Ofcom: quality of service methodology (Connected Nations 2022)
• Ofcom: Wi-fi performance testing
• Ofcom: automatic compensation call for inputs
• GOV.UK: UK transition from analogue to digital landlines
• House of Commons Library: digital landline switch-over briefing
• NCSC: Private Branch Exchange (PBX) best practice

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