Source 4G Modem convert serial RS485 Modbus RTU to modbus tcp on m.alibaba.com
MODBUS GATEWAY - Programmable industrial converter Modbus TCP to Modbus RTU / MQTT / SNMP, up to 6x RS-232/485, up to 2x Ethernet TCP, up to 2x GPRS/3G/4G/LTE modem
Amazon.com: USR-G771-E RS232/RS485 to LTE CAT 1 Cellular Modem Support LTE and GSM TCP UDP Transparent Transmission with SIM Card Support HTTP, MQTT, SMS (Modbus RTU to TCP Version NO Adapter) :