The new cellular modems transmit Ethernet and I/O data over the mobile phone network. The system can send digital or analog data as SMS text messages for remote alarming. An integrated firewall and VPN ensure reliable protection from manipulation and data theft. The DSL modem transmits data up to 30 Mbps and distances reaching 10 km (six miles). The modems can communicate serial, Profibus or Ethernet data over existing copper cables. Using current infrastructure will reduce installation cost and start-up time. The modem integrates remote external stations and substations into a private network.