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Direct Inward Dialing Number (Also known as DID or 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 signalling 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
business's still have old PBX's which use the analog signalling we 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 by ringing the line. The receiving PBX signals back
that it's ready to take the call by momentarily reversing 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 dialling 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. ISDN connections are delivered in
two variants, PRI - Primary Rate Interface
and BRI - Basic Rate Interface.
DID (DDI) in the new VOIP World
EX4U Telecom offers phone service
over broadband. The number that we provide to you, in technical terms is a DID
number. This is the number that we have assigned to you to connect you to the
old PSTN Networks around the world.
If you are using an IP PBX, and
you want to connect yourself to PSTN so people can call your office, you only need to purchase a DID number from us.
We convert the analog to digital and provide these
DID numbers over the internet, with SIP or H323.
You buy
the number from us, and we send it straight to your sip address, and you are good to go.
The call will then come to your IP PBX or IP phone & softphone as a real phone line. Then you can
use the DID as your phone number or direct extension. We offer as well VoIP extension service, please contact us for further details.
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Feature Overview is here...
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