Why Does My VoIP Call Keep Cutting Out?

VoIP calls usually cut out because of packet loss, jitter, or bandwidth saturation on the internet connection, most often caused by network congestion, poor Wi-Fi, or incorrect router configuration, rather than a fault with the VoIP service itself. Most call quality issues can be resolved by improving the local network or internet connection.
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What Are the Common Causes?
Insufficient Bandwidth
VoIP calls need a stable, sufficient amount of both upload and download bandwidth to carry audio smoothly. As a rule of thumb, each concurrent call uses roughly 85 to 100 kbps in each direction, so ten simultaneous calls need around 1 Mbps up and down set aside just for voice. If multiple people in the office are on calls at the same time, streaming video, backing up files, or uploading large attachments, the shared connection can become overloaded, causing choppy audio or calls dropping altogether.l
Lack of Quality of Service (QoS)
Without QoS configured on the router, voice traffic competes equally with every other type of data on the network. During busy periods, a large file download, a video call in another room, a software update running in the background, voice packets can be delayed or dropped, causing jitter, gaps, robotic-sounding audio, or full disconnects.
Wi-Fi Instability
VoIP calls carried over Wi-Fi are more prone to interruption than those over a wired connection, especially in offices with weak signal in certain areas, thick walls, or interference from other wireless devices like microwaves or neighbouring networks.
Router or Firewall Configuration
Some routers and firewalls aren't configured correctly to handle VoIP traffic, particularly around Session Initiation Protocol (SIP) and the ports VoIP uses. This can cause one-way audio (where one person can hear the other but not vice versa), jitter, or calls dropping shortly after connecting.
ISP-Level Problems
Occasionally, the issue sits upstream of the office network entirely, such as packet loss, an unstable connection, or congestion at the internet service provider's end, which no amount of internal network configuration can fully resolve.
Outdated Hardware or Firmware
Older routers, switches, or VoIP handsets running outdated firmware can also struggle to handle VoIP traffic reliably, particularly as call volumes or the number of connected devices increase over time.
How Can It Be Fixed?
In the call-quality issues we investigate for customers, the most common root cause is Wi-Fi rather than the VoIP service itself, and moving the handset to a wired connection resolves a large share of them on its own.

- Enable QoS on the router to prioritise voice traffic over other types of data
- Use a wired (Ethernet) connection for VoIP devices where possible, rather than relying on Wi-Fi
- Upgrade to a business-grade internet plan with sufficient bandwidth for the number of simultaneous calls expected
- Separate VoIP traffic onto its own network or VLAN, so it isn't competing directly with general office internet use
- Check firewall and router settings to ensure SIP traffic and VoIP ports aren't being blocked or throttled
- Keep router, switch, and handset firmware up to date
- Ask the provider to run network diagnostics if problems persist despite the above changes
When Should a Business Get Outside Help?
If dropped calls continue after checking the basics, particularly if they happen at predictable times of day, or only on certain devices, it's usually worth asking the VoIP provider to run a proper network assessment. This can identify whether the bottleneck is internal (office network, router, Wi-Fi) or external (the internet connection or ISP itself), which then determines the right fix.
Does the Time of Day Matter?
It can. Calls that cut out mainly during peak business hours often point to bandwidth being shared across too many users or devices at once, rather than a fault with the VoIP system itself. If problems appear at a similar time each day, for example, when a scheduled backup or large download runs, that pattern is usually a strong clue pointing to the underlying cause.
Looking for a More Reliable VoIP Setup?
The VoIP Shop can help assess network requirements and configure VoIP systems for stable, reliable call quality. Book a free consultation and we will run a network assessment to find what is causing your calls to drop.
Written By | About the Author
Kully has over 15 years of experience in the VoIP and telecoms industry. Drawing on a background in telecoms sales and leadership, he provides expert, impartial advice on VoIP and cloud telephony solutions. As a lead author for The VoIP Shop, Kully helps businesses understand and adopt modern communication technologies
