What is DID - Direct Inward Dialing?

DID stands for - Direct Inward Dialing (otherwise called DDI, Direct Dialing Inward in Europe). It is a service offered by telephone companies for use with their customers' PBX system. The telephone company (telco) allocates a range of telephone numbers associated with one or more phone lines. DID allows a company to assign a personal number to each employee, without requiring a separate physical phone line for each, to connect to the PBX. By setting up these virtual numbers, inbound calls can be routed directly to the desired extension. This way, telephony traffic can be split up and managed more easily.

DID setup - a practical example

DID Diagram

If an organization has 25 employees and each employee has a separate telephone number, or extension, within its physical location, the organization can rent 10 physical trunk lines from the telephone company. This will allow 10 phone calls to take place simultaneously. Others would have to wait for an available line. Anyone dialing into the system while all 10 lines are in use would get either a busy signal or be directed to a voice mail system. A DID system can also be used for fax and voice transmissions.

DID works similarly for VoIP communications. To allow PSTN users to directly reach VoIP users, DID numbers are assigned to a gateway. The VoIP gateway connects the PSTN (public switched telephone network) to the VoIP network, routing and translating calls between the two networks for the VoIP user. Calls from the PSTN will be directed to the VoIP user who holds the corresponding DID number.

What is Direct Outward Dialing (DOD)?

In contrast to Direct Inward Dialing, Direct Outward Dialing (DOD) is a local exchange carrier service that allows team members within the PBX system to make outbound calls directly. DOD bypasses having to press a number before connecting to the operator, or dial other numbers first.

How do I get a direct dial-in?

DID requires that you purchase an ISDN or SIP trunk and ask the telephone company to assign a range of numbers. You will then need DID-capable equipment at your premises which consists of BRI, E1 or T1 cards, or a SIP trunk enabled PBX.

Benefits of direct inward dial

The benefits of DID apply to every sized business today, including:

  • Save on costs - Reduce the number of trunk lines required to connect your business. You can also save on long-distance and overseas call costs by using DIDs with a VoIP system.

  • Save on time - Route incoming calls directly to the individual user instead of having to go through the receptionist / switchboard operator.

  • Improve customer experience - Keep customers happy with a direct line to their favorite agent.

  • Connect to the team - Easily connect to remote workers through their dedicated extensions.

  • Work remotely - Forward calls from your direct dial number onto your mobile app without the need to give out personal mobile numbers.

Further reading