A cellular modem is a device that provides a connection to a mobile network, typically without the routing, VPN, firewall, and LAN-side features of a full cellular router. Where a router manages a local network and provides services like DHCP and NAT, a modem provides a single point-to-point link from a host device to the cellular network.

In short: Industrial cellular modems are used where the host device already provides its own networking intelligence: a PLC with its own IP stack, an industrial PC running its own routing logic, or specialist equipment that simply needs raw cellular connectivity. Examples include Teltonika's TRB series (TRB142, TRB245) and embedded cellular modules used inside OEM products. Modems typically present a USB, Ethernet, or serial interface to the host, and are configured either via the host or via a simple onboard interface.

Choosing between a modem and a router depends on what the host expects. A standalone Modbus PLC that needs cellular backhaul to a SCADA system is typically better served by a router, which can handle the VPN, MQTT translation, and SIM management without needing the PLC to know it is on cellular. An industrial PC running its own VPN client and managing its own network stack may need only a modem, with the cellular connection presented as a standard network interface.

For OEM integration, embedded cellular modules (typically based on chipsets from Quectel, Telit Cinterion, Sierra Wireless, or Fibocom) are used inside finished products like vending machines, payment terminals, EV chargers, and digital signage players. These modules implement the cellular stack on the product's own PCB rather than as a separate boxed device.