Every ordinary phone call on 4G or 5G is now internet telephony
Internet calling once meant a headset plugged into a desktop computer. Today, if you ring someone on a 4G or 5G phone, your voice is chopped into data packets and sent over an internet-style network, because those mobile systems carry voice no other way. The old dedicated telephone circuit has quietly disappeared from most calls.
Voice over IP works much like earlier digital telephony at the start: the call is signalled and set up, and the speaker's analog voice is digitised and encoded. The difference is what happens next. Rather than reserving a continuous circuit between two phones, the system slices the audio into packets and sends them across a shared packet-switched network, where they are reassembled at the far end. Even an old landline handset can join in through an analog telephone adapter, which turns its signal into packets.
Much depends on the codec, the scheme that compresses speech. Most rely on two methods, linear predictive coding and the modified discrete cosine transform. FaceTime uses AAC-LD, WhatsApp uses Opus and Skype used SILK, while a lean standard called G.729 needs just 8 kilobits per second in each direction. Some codecs squeeze narrowband speech hard; others deliver high-fidelity stereo.
The business side evolved in stages. Early providers simply copied the structure of the traditional phone network. A second wave, led by Skype, built closed networks with free calls between members but charged to reach ordinary phones, and locked users into their own software. A third generation, including Google Talk, embraced federation, letting users on different internet domains call each other directly.
Mobile operators then absorbed the technology into their own networks. Voice over LTE arrived with 4G, bringing high-definition audio and faster call setup, and Voice over 5G builds on it with lower delay and more capacity. Unlike standalone calling apps, these services connect directly to the global numbering system and include emergency calling and guaranteed call quality.
Source: Voice over IP
