A downlink between a communications dispatch console and a digitally trunked radio repeater system site controller efficiently transfers message data between the site controller and the console over a standard 9.2 kilobit per second landline. A downlink trunking card identical in structure to trunking...http://www.google.de/patents/US4835731?utm_source=gb-gplus-sharePatent US4835731 - Processor-to-processor communications protocol for a public service trunking system
