Direct Inward Dialing (DID) is a service offered by telephone companies that enables callers to dial directly into an extension on a switch without the assistance of an operator or automated call attendant.
Note:
DID is a method of routing calls that applies to both analog and digital (T1/E1) lines. However, while the method is typically referred to as DID in the analog world, it is usually called Dialed Number Identification Service (DNIS) in the digital world. Despite the difference in names, the concept is the same.
The Branch Gateways support DID central office trunk interfaces, and the digit transmission from the central office is configurable when ordering the service:
Immediate The DID signaling starts immediately after the central office seizes the analog DID trunk by closing the loop (across tip and ring). In addition, analog DID trunk lines only support inbound calls. For this reason, Customer Premise Equipment (CPE) utilizing DID trunk lines for inbound routing may utilize loop-start lines for outbound transmission.
Wink The DID signaling starts after the Branch Gateway’s analog trunk interface reverses the battery polarity and sends a wink to the central office.
Other:
An analog two-wire DID trunk line is different from a standard analog loop-start line. With analog DID trunk lines, the battery (power feed) to the line is supplied by the Branch Gateway’s analog trunk interface. With a standard loop-start line, the power is supplied by the central office, which is why damage can occur from connecting a loop-start PSTN trunk to the DID port.
The number of sent digits (3 to 4 typically) and signaling type (Pulse/DTMF) are also configurable at ordering time.
