Air Interface: The cellular air interface is the radio connection between a handset and a base station. There are many cellular network types each with its own air interface standards which as a total set are extremely flexible and primarily communicate with base stations. Note: A number of general threats to the cellular air interface are listed, yet when there's a threat that is specific to a particular cellular protocol (e.g., GSM, CDMA, LTE) that is explicitly listed.
Consumer grade small cell: Small cells are often used to extend cellular network coverage into homes, offices, and other locations lacking service.
Carrier-grade Messaging Services: Messaging services (i.e., SMS, MMS, RCS) allow text, photos, and more to be sent from one device to another. Although third-party messaging services exist, carrier-grade messaging services are pre-installed with nearly ubiquitous supported "out of the box" on nearly every mobile phone, and interoperable with most MNO's networks.
USSD: A method for establishing a real-time session with a service or application to quickly share short messages. Although USSD messages may travel over SMS, the protocol itself is distinct.
Carrier Infrastructure: This category includes threats to the base stations, backhaul and core cellular network.
Carrier Interoperability: This subcategory is primarily reserved for signaling threats associated with the Signaling System No. 7 (SS7) network.
VoLTE: The packet switched network application used for making voice calls within LTE. Although not supported in every MNO's network, large-scale rollouts are underway throughout the world.