Answer: Voice Services.
Explanation:
In the legacy cellular technologies, starting with analog AMPS and following with 2G / 3G technologies, voice services were transmitted in a similar way to wired digital telephony, setting up a dedicated circuit between the endpoints of the link.
This guaranteed a reliable connection, only subject to impairments like noise and distortion.
The LTE standard uses packet switching for all services, including voice, which is called VoLTE (voice over LTE, similar to VoIP service), and uses IP protocol, which as a best-effort protocol, can't guarantee neither that the packets arrive to destination nor that they arrive in the right order, which obviously affects the perceived quality of the conversation.
