The Caller ID technology, which replaced the traditional Soviet-era AON system in the mid-2000s, remains the standard for identifying incoming calls on analog landline phones. Unlike the older AON, Caller ID does not require picking up the receiver to request the number, preventing accidental charges for unanswered calls.
Data transmission in Caller ID occurs between rings using two primary methods: DTMF, which is sensitive to interference, and FSK. The FSK standard, commonly operating at 1200 baud, transmits the caller's number, date, time, and name, utilizing a checksum to ensure data integrity.
The author demonstrated the implementation of Caller ID using a legacy Cisco 1751 router equipped with voice interface cards (VIC-2FXO-M2 and VIC-2FXS). The setup requires a Packet Voice/Digital Signal Processor Module (PVDM) to handle voice traffic processing and offload the main processor.
Configuration of the router involves accessing the command-line interface via a console cable and setting the 'caller-id enable' parameter for specific voice ports. The author noted that this hardware configuration successfully supported a rotary phone, which failed to function with standard VoIP gateways like the Linksys SPA2102.
