Packet communication splits the data to be sent into small units called packets and moves them across the network individually. Every packet carries its destination, so even when packets travel by different routes the receiving end puts them back in the right order. All traffic on the internet works this way.
Circuit switching holds one path for the duration of a call, whereas packet communication lets many users share the same line. Nothing flows while a speaker is silent, so there is no need to keep bandwidth reserved and idle. Japan's fixed-line network was itself moved onto IP in stages from January 2024, and the migration finished by January 2025. IP-based services such as VoIP and video calling rest on this efficiency.
When a mobile plan advertises a data allowance in gigabytes, that figure counts the data carried as packets. Charging was once metered by the packet, and the fear of a bill that grew with every use is what gave the Japanese market its phrase for flat-rate packet plans. Now that flat rates and monthly data allowances are the norm, the unit subscribers actually watch has shifted from packets to gigabytes.
The weak point of packet communication is congestion: packets arrive late or out of order. On a voice call that shows up as speech breaking apart. Delay compensation at the protocol level and jitter buffers have brought VoIP, as of 2026, to a quality that everyday use does not stumble over. The underlying behavior has not changed, though, so quality still slips on a thin connection or at busy times; when a call turns unstable, look first at signal strength and at whatever else is using the connection. VoIP basics covers more ground.