Distinctive ring is a feature on a telephone or fax line. It allows for multiple phone numbers on the same line. When the line ring, each feature has a different tone.
With distinctive ring, there are multiple phone or fax numbers for the same phone line. Each phone number has a different ring to identify the number being called when the line rings.
Distinctive ring is different from a “party line” although very similar.
Distinctive ring is intended to be used within the same building or organization. It most often used to have an extra service on a line (such as a fax machine) without having to maintain the cost (and infrastructure) of an entire extra phone line.
A party line is intended to be used across multiple buildings and organizations to share a phone line. It is most often used in rural areas where phone line infrastructure is limited.
Distinctive ring is commonly used to have multiple phone numbers on the same phone line.
Common usage is to have a separate number for a fax machine, especially when there is voicemail on the primary line. Fax machines and vociemail have trouble working together (although a fax machine and a physical answering machine is possible on the same phone line).
Many fax machines have DRPD (distinctive ring pattern detection) which can answer the phone line when one tone is rung, but not the other.
Other usage of the technology is to have different phone numbers for business and personal use, or for two roomates who want their own phone number.