Prowid course material: https://kurslar.prowid.com/en/index.php?id=lesson&m=3120
The PSTN Telephone Network: Subscriber Line, DTMF, Exchange, CAS · DTMF: tone dialing
The DTMF matrix: every key is two tones
🔒 This is the beginning of the lesson. The full lesson is available with a subscription.
