Why is the type of "beep" sometimes different?

Question

Telephony

Hello, dear site users!
Perhaps, many have noticed that the type of beep when establishing a connection is different, depending on the calling and called subscriber of the telephone network. For example: if you call from a "landline" phone to a mobile phone, then KPV (Ringback Control or RBT) has the form of two short signals, and if you dial from a "city phone", then the signal looks like a signal of the form "long beep" usual for the Russian PSTN "duty cycle equal to 5 sec. Does this feature correlate with the difference between PBXs of cellular networks and PBXs of wired telephones. In general, if there are people who, according to the specifics of their kind of activity, are connected with the equipment of the automatic telephone exchange and their principles of operation, and also if there are simply knowledgeable people, then could you enlighten me on that interesting issue. I will accept recommendations for reading literature.