What is Direct Inward Dialing? What are the benefits when used with SIP or IAX?

Traditional speaking, Direct Inward Dialing(DID) is a service of a local phone company (or local exchange carrier) that provides a block of telephone numbers for calling into a company’s private branch exchange (PBX) system. Using DID, a company can offer its customers individual phone numbers, one for each person or workstation within in the company. Even early on, some local phone companies began to provide multiple numbers on one single telephone line. This very concept started to gain momentum when even CLECs began to provide these numbers by routing them on a SIP server. SIP (Session Initiation Protocol) is a protocol used in VoIP communications which enables users to make/receive Voice and Video calls over the Internet instead of through traditional telephone lines.

When DID(Direct inward dialling) is transferred via SIP, it becomes boundary-less. This means, for example, if your USA number you have purchased for your communications service customer is routed on SIP, it provides the possibility to ring on any device that is linked to the Internet anywhere in the world. This is where SIP gives the big boost to DID numbers. When a call routes on a SIP server, it can be handled in any way and transferred in many ways. It can even be controlled programmatically. The voice can be transcribed, digitized, recorded and replied back to by using Text to Speech software, for example. So that is just one example. There are numerous, exciting use cases for this technology.

IAX is also a protocol created to save bandwidth. It lets multiple SIP servers connect together. SIP is very famous and has received more attention than IAX. Even people who do not have much technical education dropped the acronym VoIP and began talking more about SIP. IAX is a very good protocol for connecting servers to servers. That does not mean IAX cannot be used on the client side, but commonly SIP is more famous for connecting with clients.

Note: In Europe, DID is referred as DDI(Direct Dial in). There is also a growing number of people who define the acronym “DID” as direct inbound dialing.

By Kamal Panhwar, CTO and Lead Developer at DIDX

Communications companies in any nation that want to sell direct inward dialing phone numbers to the 25,000 DIDX commmunications service provider customers or who want to buy direct inward dialing phone numbers and resell to their clients, sign up today at http://www.didx.net.