Direct Dial In (DDI) with ISDN30/30e


What are DDIs?

DDIs are ‘Direct Dial In’ numbers. These are additional numbers that can be associated with the main number of your ISDN circuit. This allows each telephone extension to have an individual number. As long as your equipment supports it, when a call comes through on a specific DDI number it is routed through to the required extension. DDIs are compatible with ISDN lines that operate in point-to-point configuration (sometimes referred to as ‘system access’ or ‘T reference point-configured’ lines).

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I want to present a DDI number on my outgoing CLI. How do I do this?

This can be done through your PBX or switch, provided that it supports this function. By default, BT lines use the main billing number, or directory number, as their outgoing CLI (Caller Line Identity). You can configure your PBX or switch to override this and present a DDI number.

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Where can I purchase additional DDIs?

DDIs can be ordered in blocks of 10 or as single numbers from ISDN30/30e Business Sales.

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I just had a new ISDN30/30e line installed and my PBX maintainer needs only 4 digits sent. How can I change this?

By default, 6 digits are sent from the exchange down the ISDN line to your equipment. To change this to 4 digits, contact the PSTC if you are an ISDN30e (ETSI) customer, or ISDN Business Sales if you are an ISDN30 (DASS) customer.

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How do I use Direct Dial In (DDI) numbers with ISDN30/30e?

Direct Dial In numbers (DDIs) are additional numbers that allow calls to bypass the operator and be directed straight to the required extension. They 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 (minimum purchase is 10 numbers). If an existing phone number is important to your organisation and you have ISDN30e, you may be able to set it up as a single-number DDI. This is not possible with ISDN30. To order, or find out the current connection and rental costs, contact Business Sales on 0800 800 152.

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