How it works
The voice is digitised, compressed with a codec (for example G.711 or Opus) and sent in packets over the network. The SIP protocol sets up and ends calls. To keep calls from breaking up, the network has to give voice packets priority (QoS).
A business phone system
A modern phone system (PBX) is a program running on a server or in the cloud. It can:
- forward a call to your mobile when you are away from your desk,
- play a voice menu (“press 1 for…”),
- handle call queues, recording and statistics,
- connect to your CRM and calendar.
Gateways for old lines
If a company has an analogue line or old phones, they can be connected through gateways: FXO connects the operator's analogue line to an IP phone system, while FXS does the opposite and connects an analogue phone to the IP network. The company keeps its numbers and can move to a modern system step by step. I deploy this kind of setup as part of my Business phones and PBX service.