The Three Factors That Determine VoIP Call Quality
VoIP call quality is determined by three network metrics: latency (delay), jitter (variation in delay), and packet loss. Unlike file downloads, where lost packets are simply retransmitted, VoIP is a real-time service. Lost or delayed audio packets cannot be recovered; they result in gaps, distortion, or robotic-sounding audio.| Latency (one-way) | Jitter | Packet loss | |
|---|---|---|---|
| Good | < 50ms | < 10ms | < 0.5% |
| Acceptable | 50-150ms | 10-30ms | 0.5-1% |
| Problematic | > 150ms | > 30ms | > 1% |
How Australian NBN Connection Types Affect Call Quality
The biggest variable in Australian VoIP quality is NBN connection type. FTTP (Fibre to the Premises) delivers the most consistent low-latency performance because the fibre runs all the way to your building. FTTN (Fibre to the Node) relies on copper from the node to your premises, and the quality of that copper run has a direct impact on latency and packet loss.During peak evening hours (6-9pm) on congested NBN infrastructure, even FTTP connections can show elevated latency. For business users who need consistent quality during business hours, NBN performance during business hours is generally more reliable than residential peak hours.How to Measure Your Connection Quality for VoIP
A standard internet speed test does not measure VoIP-relevant metrics. To assess whether your connection can support VoIP well, you need to measure latency, jitter, and packet loss. Tools for this:Ping test to your VoIP provider's SIP server (ask them for the server IP or hostname). Most routers have a built-in ping tool, or use the Windows or macOS command prompt. Run 100 pings and look at average, minimum, maximum, and any lost packets. For a more comprehensive test, use Cloudflare's speed.cloudflare.com which measures latency, download speed, and jitter. Run tests during your business hours, not late at night when the network is quieter.Codec Selection: G.711 vs G.722 vs G.729
VoIP audio is compressed using a codec (coder-decoder). The codec affects both call quality and bandwidth usage. For Australian NBN connections, the recommended choices are:| G.722 (wideband) | G.711 ulaw/alaw | G.729 | Opus | |
|---|---|---|---|---|
| Audio Quality | HD audio, excellent | Good, standard telephone quality | Compressed, lower quality | Adaptive quality, excellent |
| Bandwidth | ~80 kbps/call | ~80 kbps/call | ~24 kbps/call | ~30-80 kbps/call |
| Recommended Use | Best choice for good NBN connections | Solid default for all NBN types | Not recommended. Higher latency, degrades under packet loss | Good for variable connections, not universally supported |
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G.729 is sometimes still used by VoIP providers and phone manufacturers as a default because it uses less bandwidth. On Australian NBN connections where bandwidth is rarely the constraint, G.729 provides no benefit and its higher compression introduces more latency. If your phones or provider default to G.729, switching to G.711 or G.722 will often improve quality.
QoS: Prioritising Voice Traffic on Your Network
Quality of Service (QoS) configuration on your router ensures that VoIP packets are prioritised over other network traffic. Without QoS, a large file upload or a software update download can introduce enough network congestion to degrade active calls. For a business VoIP setup, QoS configuration is not optional for offices with more than a few staff.Most business-grade routers support QoS. The configuration approach: mark SIP traffic (UDP port 5060) and RTP audio traffic (your provider's RTP port range, typically UDP 10000-20000 or similar) with the highest priority queue. This ensures voice packets are processed ahead of less time-sensitive traffic even during periods of high network utilisation.Diagnosing Specific Call Quality Problems
| Choppy, robotic, or stuttering audio | Echo on calls (you hear yourself) | One-way audio (only one party can hear) | Calls drop after exactly 30-90 seconds | Calls not connecting at all | Good quality early in the day, poor later | Poor quality on mobile app only | |
|---|---|---|---|---|---|---|---|
| Likely Cause | Packet loss or excessive jitter | Acoustic or electrical echo in handset | Firewall blocking RTP audio ports | NAT timeout or SIP session timer mismatch | SIP registration blocked by firewall | Network congestion (shared FTTN infrastructure) | Mobile network quality issue |
| Solution | Check NBN line stats, enable QoS, check for background downloads | Check handset placement, try a different phone or headset | Open RTP port range in router firewall | Disable SIP ALG on router, check SIP session timer settings | Ensure UDP 5060 is not blocked, check SIP credentials | Schedule bandwidth-intensive tasks outside business hours, consider NBN upgrade | Test on Wi-Fi, check mobile data signal strength |
Why do my VoIP calls sound good in the morning but bad in the afternoon?
This pattern typically indicates network congestion on shared infrastructure, most commonly FTTN or HFC NBN connections. As more users in the area are active in the afternoon, the shared link from the node or pillar to the NBN exchange becomes more congested, increasing latency and packet loss. Solutions include: requesting an NBN upgrade to FTTP (where available), using QoS to maximise priority of voice traffic on your internal network, or contacting your NBN provider to report congestion.
How much bandwidth does VoIP use?
Each active VoIP call uses approximately 80-100 kbps of bandwidth (with G.711 or G.722 codecs). Ten simultaneous calls use less than 1 Mbps. Bandwidth is almost never the limiting factor for VoIP on Australian NBN connections. Even an NBN25 connection can support multiple simultaneous calls. Latency and jitter are far more important than raw bandwidth speed.
Will a better NBN plan improve my VoIP quality?
Upgrading your NBN speed tier (e.g. from NBN25 to NBN100) rarely improves VoIP quality because bandwidth is not usually the constraint. However, upgrading your NBN technology type (e.g. from FTTN to FTTP, where FTTP upgrade is available in your area) can significantly improve quality because it replaces the variable copper run with consistent fibre. Contact your NBN provider or check NBN Co's website for upgrade availability at your address.
Is my VoIP provider responsible for call quality problems?
Your VoIP provider is responsible for quality on their network from their data centre outward. They are not responsible for the quality of your NBN connection or your internal network. In practice, most call quality problems originate in the last mile (your NBN connection) or internal network configuration. Start troubleshooting at your router and NBN connection before escalating to your VoIP provider.
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