Direct Inward Dialing Number (Also known as DID/DDI)

DID (DDI) Background

Most businesses have several incoming telephone numbers used for specific purposes. For example customer service, sales, etc. Some have an individual telephone number for each user in the system. In a home setting, on the other hand, each telephone number comes in on a different pair of wires typically. This is not practical in a business environment that has many telephone numbers.

Why was DID actually Created?

So DID (“direct inward dialing”) was invented as a way to re-use a limited number of physical phone lines to handle calls to different published numbers. In a business with DID, the phone company uses DID signaling to identify the number they are about to connect to the business’s PBX. Historically, this was done by pulsing the last 3 or 4 digits of the number being dialed before connecting the number. The PBX would use these DID digits to switch the call to the right recipient.

In modern PBX’s, typically, digital methods (example: PRI) are used to do the same thing, ie. supply the “called party” information. But many businesses still have old PBX’s which use the analog signaling I mentioned before. The type of telephone lines used for analog DID are different than regular home telephone lines. Usually, battery voltage is supplied by the business PBX instead of the telco. Also, the telco signals a new call by bridging the line instead of ringing the line. The receiving PBX signals back that it’s ready to take the call by momentarily reversing the polarity of the voltage on the line (this is called “winking” the line)

Old Fashion Way: (PSTN WORLD)

Direct Inward Dialing is used when your PBX telco connection allows direct dialing to extensions within a PBX, using physical lines (or channels on a PRI) on a shared basis. DID service consists of identifying the “called party” by using DTMF or by digital means, before connecting each call. The service can be sent over an E&M Wink T-1 as DTMF and also as D-Channel information on a PRI.

On a PRI connection, the telco can send only the digits that differ between the group number and the extension (often four digits) or the whole number – it depends on the connection to the telco.

DID (DDI) in the new VOIP World

Let’s say you buy a phone line from Vonage or some other phone service provider who offers phone service over broadband. The number that they provide to you, in technical terms is a DID number. This is the number that they have assigned to you to connect you to the old PSTN Networks around the world. Any service provider who wants to offer phone service over IP address needs to buy DID numbers from his CLEC or any other large service provider like Level 3 in the United States or go to a consortium (company that will take large blocks from many providers and hand them out one at a time)

If you are using an IP PBX like Asterisk, and you want to connect yourself to PSTN so people can call your office, you can either

1. Buy an Analog or E1/T1 card from Digium, Openvox, Rhino Equipment Corp or Sangoma
2. Buy DID number from DID Service Providers

DID Service Providers, convert the analog to digital and provide these DID numbers over the Internet, with SIP or IAX2.

Service providers such as
BuyDIDNumber, DIDForSale, DIDLogic, DIDNumbers.com, DIDWW, DIDx, DivertMyCalls, HyperCube, Magic Telecom, VirtualPhoneLine, VoIP Innovations, and Buy Local Numbers do this.

You buy the number, and send it straight to your sip address, and you are good to go.

The call will then come to your IPPBX as a real phone line. Then you can use as your phone number, and route it to your IVR or direct extension.

Video and audio files that explain what DID (direct inward dialing) is:

What is DID? by Suzanne

Get a DID for your Asterisk: DID Service Providers

Also See

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• Ukraine mobile DIDs | Virtual mobile cell multi-channel numbers Ukraine.
• 1Pipe Telecom | OnePipe is a licensed carrier providing Hosted PBX and SIP Trunking in over 50 countries. We have regional network facilities spread across the globe. Wholesale DID’s available.
• Wholesale DID Numbers with SMS HyperCube SMS Enabled DIDs. Covering 2400 Rate centers.
• Wholesale DID Numbers Provider Wholesale platform for buying and selling DIDs.
• Asterisk tips did
• CFMS – Call Forwarding and Management System for DID Number Billing
• Cheapest ATAs and Service – Lists all DID per country (including free & pay ones)
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• DIDWW The Source for DIDs and Toll-Free Numbers Worldwide
• DID Origination Service Provider – Lists all DID within the USA (includes only pay ones)
• DOD: Direct outward dialing
• DIDforSale Wholesale DID Origination and Termination provider with the largest coverage in Canada, UK, and USA.
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• Cheapest Virtual Number Provider Asterisk Supported
• Wholesale, Retail DID Numbers Asterisk, Fax, Multi Chanel Number, Toll-Free Number Available.
• Pseudo DID
• What is a DID Number (by DIDx.net)
• Virtual PRI
• DivertMyCalls Unlimited Channels, Toll-Free Numbers Available, Cheapest Rates. Forwarding to Google Talk, Skype, Any VoIP allowed.
• FlyNumber.com : International DID / Virtual Phone number Provider
• MyVNumber DID local access numbers, virtual numbers for more than 60 countries. Flexible forwarding Options
• VoIP Innovations: Wholesale VoIP DID Numbers, Worldwide Coverage for ITSPs & Resellers
• Switch2Voip: Free USA and Canada DID, Virtual Phone Numbers from more than 30 countries, USA, Canada and United Kingdom Toll-Free Numbers.
• Yuboto Telephony Greek DIDs from 56 Cities
• Sticky Number Free UK DID Numbers and Paid DID’s in 1220 Cities over 60 Countries.
• DID2CALL Virtual Numbers over 70 Countries.
• Magic Telecom – Geographic, Non-Geographic, and Toll-Free DIDs with worldwide coverage.