How calls travel

VoIP, Wi-Fi calling, codecs and call quality, explained without jargon.

• How much data does a VoIP call use? The calculation, codec by codec

  Work out how many megabytes an internet voice call uses per hour: codec bitrate, packet headers, both directions, and why video calls are a different story.

• VoLTE and the 2G/3G switch-off: will your phone still make calls?

  What VoLTE is, why operators are switching off 2G and 3G networks, which phones are affected, and how to check whether your phone, or a relative's, will keep working.

• What is VoIP? How a phone call travels over the internet

  VoIP explained step by step: signalling with SIP, voice packets with RTP, codecs, NAT traversal and the difference between app-to-app calls and calls to real phone numbers.

• Why VoIP calls break up: latency, jitter, packet loss and how to fix them

  A practical troubleshooting guide for robotic voices, echoes, one-way audio and dropped internet calls, from Wi-Fi placement to router settings.

• Wi-Fi calling explained: how it works and how it differs from calling apps

  What carrier Wi-Fi calling (VoWiFi) is, how your phone reaches the operator over any Wi-Fi network, what it costs at home and abroad, and when an app call is the better choice.