DID (Direct Inward Dial), Pilot Numbers and Extentions in Skype for Business Enterprise Voice

Pilot Number = single phone number, e.g. caught by a hunt-group
A pilot number is the address, extension, or location of the hunt group inside the PBX or IP PBX. It’s generally a blank extension number or one extension number from a hunt group of extension numbers that doesn't have a person or telephone associated with it. For example, you might configure a hunt group on a PBX or IP PBX to contain extension numbers 4100, 4101, 4102, 4103, 4104, and 4105. The pilot number for the hunt group is configured as extension 4100. When a call is received on extension number 4100, the PBX or IP PBX looks for the next available extension number to determine where to deliver the call. In this example, the PBX or IP PBX will use its programmed search algorithm to look at extension numbers 4101, 4102, 4103, 4104, and 4105.

PILOT NUMBER: e.g +49 89 1234 0
Next we talk about the DID/DDI, this is the range assigned to the callee.

DID or DDI = Direct Inward Dialing number
The telco configures how many digits of the telephone number dialled by the caller is sent down to your PBX. Some connections, PRI or BRI, send all digits and some only the part that distincts the number from others, like the four last digits.
Any PSTN subscriber can contact an enterprise user inside or outside the corporate firewall by dialing a Direct Inward Dialing (DID) number associated with that enterprise user.
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.
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.

PILOT NUMBER: e.g +49 89 1234 0
with a range of 1234-0000 until 1234-9999 possible.
A caller can now DIRECTLY dial to a target user, e.g +49 89 1234 1111

Extension = numbers extension behind the central number
Not like a phone number (like DID), more like an internal identifiy....
also used for internal dialing and AutoAttendants (e.g. Exchange AA)

If we work with extensions, we need for callees an INTERNAL number. The internal number in Skype for Business/ Lync should be in E.164 from, but can be also a shorter number, even a extension.
In PBX, the Auto Attendant can receive an external call, and proxy this call to the internal extension.

Important is, not to be confused with DIAL PLAN and EXTENSIONs!

If we have our Skype for Business real work scenario:
Exchange and Skype for Business is required. Exchange handles the Auto Attendant and will be used for the INTERNAL EXTENSION. Therefore the user needs to be UM enabled. Only than a external Pilotnumber can be assigned to Exchange Auto Attendant and the user can be called from external without a DID.

Difference between, EURO ISDN and NA ISDN
;ext=123 (EU)
x123 (NA)

E.164 maximum length is 15-digits

Recommended link for Lync normaizations between EU and NA formats and how to handle the AD assigend phonnumbers (not the Lync assigned! ones)


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