IoT connectivity reference

How IoT connectivity works, in plain words, with the engineering detail a click away.

Networks and roaming

SteeringWhat steering of roaming is, the ways operators do it, and what no steering and light steering mean for an IoT device.
How a device chooses a networkThe 3GPP order a device follows to pick a network, manual mode, the forbidden lists and why a registered device doesn’t hop to a stronger signal.
Roaming and permanent roamingHome and visited networks, roaming agreements, home routing and local breakout, permanent roaming and how EU rules treat M2M devices.
Permanent roaming rules by countryWhich regulators limit or ban permanent roaming of IoT devices, what each rule says, its source and the date we last checked it.
Multi-network SIMs and multi-IMSIHow multi-network and multi-IMSI SIMs work, what makes a multi-IMSI applet switch identity, and how it differs from eUICC profiles.

eSIM, eUICC and MFF2What a UICC, an eUICC, eSIM, MFF2 and iSIM each describe, how they combine, and what the EID identifies.
eSIM standards SGP.02, SGP.22 and SGP.32How the GSMA's M2M, consumer and IoT eSIM architectures work, who controls profile changes in each, and what to check when choosing.
SIM form factorsThe standard SIM sizes from 1FF to 4FF, soldered MFF2 and integrated iSIM, their dimensions, and how to choose between removable and soldered.
SIM identifiers ICCID, IMSI, IMEI, EID and MSISDNWhat ICCID, IMSI, IMEI, EID and MSISDN identify, how each is structured, and which ones change when a SIM, profile or device changes.

LTE-MWhat LTE-M is, its real data rates and latency, coverage enhancement, handover, voice, power saving, its place in 5G and how roaming on it works.
NB-IoTWhat NB-IoT is, its categories, real data rates and latency, deep coverage, mobility limits, data and SMS over NAS, and why roaming on it is limited.
PSM and eDRXHow power saving mode and extended DRX let IoT devices sleep, the timers and limits in the standards, and what that means for reaching a device.
Choosing a radio technologyLTE-M, NB-IoT, LTE Cat-1, Cat-1 bis and 5G RedCap compared by data rate, power, mobility, voice and roaming, and why 2G and 3G aren’t options.

2G and 3G switch-offWhen operators in Europe, the Americas, Asia-Pacific, the Middle East and Africa close 2G and 3G, with sources, and what it means for IoT devices.

APNWhat an Access Point Name is, how it’s built, what gateway and IP service it selects, and why a wrong APN stops a device connecting.
CGNAT and static IPHow carrier-grade NAT, private and shared address space, and static private or public IP addresses decide whether IoT devices can be reached.
Private APN and VPNWhat a private APN is, how its traffic reaches a customer network by IPsec or interconnect, and how device-side and network-side VPNs differ.

SMS for IoT and SMS APIHow SMS works for IoT devices over LTE, NB-IoT and 5G, its size limits, why sleeping devices miss messages, and how applications send them.