Short definitions of the terms that come up when you buy and set up 4G data SIMs and routers. Each links to the guide with more detail where there is one.
- APN
- Access Point Name. The setting that tells the network which gateway to connect a device to, and so which service it gets. See APN settings.
- Band
- A block of radio frequencies used by a network, such as band 20 (800MHz). See UK 4G bands.
- Carrier aggregation
- Using two or more bands at once to increase speed. Needs a Cat 6 or higher modem.
- CGNAT
- Carrier-grade NAT. The network shares public addresses between many users, which blocks inbound connections. See CGNAT and remote access.
- eSIM
- A SIM profile stored on a chip in the device rather than a plastic card, which can be changed remotely.
- eUICC
- The chip that holds one or more eSIM profiles.
- Failover
- Switching automatically to a backup connection when the main one fails. See 4G backup broadband.
- Fixed IP
- A public IP address that stays the same every time a device connects. See fixed IP SIMs.
- ICCID
- The serial number of a SIM card, usually printed on it.
- IMEI
- The unique identity of a mobile device or modem. Some SIMs are locked to one IMEI.
- IMSI
- The subscriber identity stored on the SIM, which the network uses to recognise it.
- LTE
- Long Term Evolution, the technology behind 4G.
- LTE category
- A rating of a modem’s maximum speed, such as Cat 4 or Cat 6. See LTE categories.
- LTE-M
- A low-power version of LTE for devices that send small amounts of data and run on batteries.
- M2M
- Machine to machine. The older term for what is now usually called IoT.
- MIMO
- Multiple input, multiple output. Using two or more antennas at once for better speed and reliability. See 4G antennas.
- Multi-network SIM
- A SIM that can use more than one network and switches if it loses one. See IoT and multi-network SIMs.
- MVNO
- Mobile virtual network operator. A brand that sells SIMs on another company’s network.
- NB-IoT
- Narrowband IoT. A very low data, low-power technology for static sensors and meters.
- Pooled data
- One shared data allowance across many SIMs on the same account.
- Private APN
- An APN that connects SIMs into a private network rather than the public internet.
- RSRP
- Reference Signal Received Power. 4G signal strength in dBm. See signal strength.
- RSRQ
- Reference Signal Received Quality. How clean and uncongested the 4G signal is, in dB.
- SINR
- Signal to Interference plus Noise Ratio. The best single predictor of 4G speed.
- VoLTE
- Voice over LTE. Making calls over 4G, needed once 2G and 3G are gone. See switch-off guide.
NANick Appleby
Nick Appleby has worked in UK telecoms since 1998, starting at BT, and has spent most of that time on cellular routers, data SIMs and the antennas that connect them for business and industrial sites. He writes 4G SIM to explain how the networks and the kit actually behave, in plain English.