Direct Inward Dialing is a calls routing feature that provides an employee with a standard ten digits personal phone number (besides his extension or internal PBX phone number) without his company having to invest in dedicated physical lines.
DID provides multiple phone numbers as an economical choice for a company and makes it easier and faster for its clients to contact employees directly without having to navigate the company's phone menu.
Without DID, employees can still be contacted separately on their PBX phone lines or extensions, but clients have to navigate the dial-by-extension or dial-by-name options. With DID they simply dial a standard phone number to reach an employee.
In a traditional phone system, a separate physical line is needed for every phone number. With DID, all desired numbers must be reserved, but only one physical line is required.
Calls arriving at this line are routed to the correct PBX line or extension based on a list of reistered SIP user accounts. The caller ID of the caller is carried over in the routing process and presented to the employee or agent for a more productive cal experience.