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Choppy VoIP calls? The first things to check

· 2 min read · By the Comdeal team

In short

Robotic voices and dropouts usually come from the network, not the phone. These checks quickly narrow down where the problem is.

Describe the symptom first

The symptom tells you where to look.

  • Choppy or robotic audio both ways: usually network quality, meaning delay, jitter or packet loss.
  • One-way audio or silence: usually a firewall or NAT problem. The call set up, but the audio is being blocked.
  • Calls that drop after about 30 seconds, or phones that lose registration: often a firewall timeout or a router feature called SIP ALG.

Narrow down the scope

Before changing anything, answer these:

  1. Is it one phone or all of them?
  2. Does it happen between two extensions in the same office? If so, look at your local network. If only external calls suffer, look at your internet connection or provider.
  3. Is it worse at certain times of day?

The usual suspects

  1. A saturated upload link. Cloud backups, file syncing, video meetings and software updates all use upload bandwidth, and voice needs a steady share of it. Check your router's traffic graph while the problem is happening.
  2. Wi-Fi. Wireless handsets and softphones on a busy channel struggle. Test the same phone on a cable.
  3. SIP ALG. A router feature meant to help SIP that often breaks it. Turning it off is a standard early test.
  4. No QoS. Without prioritisation, a large upload can crowd voice out. Voice audio is normally marked DSCP EF (46) and should be prioritised on both your network and your router.
  5. Cabling and switches. A worn patch lead, an overloaded cheap switch or an exhausted PoE budget can all cause drops.

A quick network test

From a computer on the same network as the phones, run a ping to your phone system or provider and look at the loss and the spread of times:

ping -n 50 your-pbx-address

On macOS or Linux, use -c 50 instead of -n 50. As a rough guide, healthy voice paths have one-way delay under about 150 ms, jitter under about 30 ms and packet loss under 1%.

Change one thing at a time

Write down what you change and what happened. If you change three things at once, you will not know which one fixed it, or which one broke something else.

When to call an engineer

If the problem survives the cable test and the SIP ALG change, if it comes and goes at set times, or if several sites are affected, it is time for proper monitoring and traces rather than guesswork.

Want to know whether your link is big enough for your calls? Use the VoIP bandwidth calculator.

Still stuck, or want it done properly?

Tell us what you are seeing and an engineer will come back to you.

Talk to an engineer

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