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Using Direct Dial In (DDI) with ISDN30 and ISDN30e | BT Business

Using Direct Dial In (DDI) with ISDN30 and ISDN30e

You can have an unlimited number of Direct Dial In (DDI) numbers, which lets customers and business contacts dial directly through to staff members without passing through a switchboard.

DDIs are normally used with a PBX, providing separate numbers for individual staff. Your PBX is programmed to route incoming calls using DDI numbers to the correct extensions.

You can order sets of DDIs but the minimum purchase is 10 numbers.

If you want to keep an existing phone number and you have:

  • ISDN30e, you can set it up as a single-number DDI.
  • ISDN30, you’ll need to contact Business Sales on 0800 800 152 to order or find out the current connection and rental costs.

DDI ranges on an ISDN30e circuit

With ISDN30e you can have up to 5 layers of DDI numbers which can either be single numbers or DDI ranges. DDI ranges are supplied in blocks of 10, but can be anything (for example 100s or 1000s). The maximum number of layers is 5. All numbers are applied consistently to all channels.

For example, 5 layers shared over all channels. On an ISDN30e setup, what applies to one channel applies to them all:

5 layers of DDI numbers

DDI ranges and numbers on an ISDN30 (DASS) circuit

With ISDN30 (DASS) each channel can individually be assigned a single number or a DDI range in multiples of 10. The maximum allowed is dependant on exchange capacity.

Similarly, a group of several channels can be assigned a single number or a DDI range.

You can stack up to 5 DDI ranges on any channel or group of channels as long as the group is the same (for example, you can’t have 1 range over 5 channels and another layer over 10 channels). Each group of channels is treated like a totally separate circuit and what you do to one channel in the group has to apply to them all.

Remember, you cannot 'stack' single numbers.

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