Digital Modulation Method for Caller ID on Cisco FXS Ports

C.

Link:-http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/vcr1/vcr1-cr-book/vcr-c4.html.

The correct answer to this question is C. FSK (Frequency Shift Keying).

FSK is a type of digital modulation method in which the frequency of the carrier wave is varied in accordance with the digital signal being transmitted. In the case of caller ID information on analog FXS (Foreign Exchange Station) ports on Cisco IOS routers, the caller ID information is transmitted as a digital signal using FSK modulation.

Analog FXS ports on Cisco IOS routers are typically used to connect analog telephones or fax machines to a digital telephone system. When a call is made from an analog phone connected to an FXS port, the caller ID information is transmitted in a digital format using FSK modulation. The FSK signal is sent at a frequency of 1200 Hz for a logic 0 and 2200 Hz for a logic 1.

DTMF (Dual-Tone Multi-Frequency) is another type of digital modulation method used for transmitting signals over analog telephone lines. However, DTMF is primarily used for transmitting dialing signals, such as the numbers dialed by a caller, and not for transmitting caller ID information.

PSK (Phase Shift Keying) is a type of digital modulation method used for transmitting digital signals over radio waves, and is not typically used for transmitting signals over analog telephone lines.

MF (Multi-Frequency) and pulse dialing are both legacy methods of transmitting dialing signals over analog telephone lines, and are not used for transmitting caller ID information.