Well, after numerous meetings and talks about DIDs and definitely a lot of illustrations and use cases, it would have seemed that I knew what DIDs were, but I didn't. Suddenly, I was given the task to follow up on some providers and the time to really understand what DIDs were had come.
DID is a feature offered by telephone companies for use with their customers' private branch exchange (PBX) systems. In a DID service, the telephone company provides one or more trunk lines to the customer for connection to the customer's PBX and allocates a range of telephone numbers to this line (or group of lines) and forwards all calls to such numbers via the trunk. As calls are presented to the PBX, the dialed destination number (DNIS) is transmitted, usually partially (e.g., last four digits), so that the PBX can route the call directly to the desired telephone extension within the organization without the need for an operator or attendant. The service allows direct inward call routing to each extension while maintaining only a limited number of subscriber lines to satisfy the average concurrent usage of the customer.
Direct Inward Dialing service has similar relevance for Voice over Internet Protocol (VoIP) communications. To reach users with VoIP phones, DID numbers are assigned to a communications gateway connected by a trunk to the PSTN network and the VoIP network. The gateway routes and translates calls between the two networks for the VoIP user. Calls originating in the VoIP network will appear to users on the PSTN as originating from one of the assigned DID numbers.
