“Our internet is fast, so why do our VoIP calls sound terrible?” It’s one of the most common support questions, and the answer surprises people: call quality has very little to do with raw speed. A single voice call uses around 100kbps — a fraction of even a modest fibre line. What voice traffic actually needs is consistency.
The three numbers that matter
Latency is the time it takes a packet to travel from you to the other party. Above roughly 150ms one-way, conversations start to feel awkward — people talk over each other because the delay disrupts natural turn-taking.
Jitter is variation in latency. Voice packets need to arrive in a steady stream; if they arrive in bursts, the audio stutters or sounds robotic. Jitter above 30ms is where problems typically start.
Packet loss is exactly what it sounds like — packets that never arrive. Voice codecs can conceal a little loss, but beyond about 1% you’ll hear dropped syllables and gaps.
Common culprits
- Congested uplink. The classic scenario: someone starts a large upload (cloud backup, file sync) and saturates the connection’s upload channel. Voice packets queue behind bulk traffic and arrive late or not at all.
- Wi-Fi handsets and softphones. Wi-Fi introduces its own jitter, especially in congested spectrum. Wherever possible, desk phones should be cabled.
- Cheap or misconfigured routers. Consumer routers with no Quality of Service (QoS) treat a voice packet the same as a Netflix packet. Under load, voice loses.
- Double NAT and SIP ALG. A router “helpfully” rewriting SIP traffic is a leading cause of one-way audio and dropped registrations. SIP ALG should almost always be disabled.
- Wireless last-mile links. LTE and congested wireless connections have inherently higher and more variable latency than fibre.
How to fix it
1. Prioritise voice with QoS. Configure your router to give voice traffic priority over everything else. This single change resolves the majority of quality complaints.
2. Put phones on fibre, cabled. Fibre plus ethernet gives you single-digit jitter and near-zero loss — the conditions voice was designed for.
3. Disable SIP ALG. Check your router; most have it on by default.
4. Separate voice from bulk traffic. On busier networks, a dedicated VLAN for voice keeps phones isolated from backup jobs and guest Wi-Fi.
5. Monitor, don’t guess. Intermittent problems need data. Your provider should be able to pull call statistics (MOS scores, jitter, loss per call) to pinpoint whether the issue is your LAN, your internet link, or upstream.
The takeaway
Great VoIP quality isn’t luck — it’s a properly configured network on a stable connection. If your calls are suffering, the fix is usually straightforward once the actual cause is measured rather than guessed.
Struggling with call quality? We deploy and support business VoIP end-to-end, including router QoS configuration and network diagnostics. Talk to us.