What do I get with ISDN30 (DASS)?


What is DASS?

DASS stands for Digital Access Signalling System. BT’s original ISDN30 offering used this as a signalling standard. ISDN30e superseded ISDN30 with its ETSI or Q931 signalling which is the standard ISDN protocol used throughout Europe.

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What does ISDN30 (DASS) terminate on?

At a customer premise ISDN30 (DASS) terminates on a BNC socket, also known as coaxial. It cannot be terminated in any other way.

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Is my ISDN30 (DASS) service Balanced or Unbalanced? My switch engineer has asked me to find out.

ISDN30 (DASS) is referred to as G703, 75 Ohms, Unbalanced.

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How many DDI ranges and numbers can I have 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 (i.e. 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.

Please note: You cannot 'stack' single numbers.

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Could you provide some examples of valid numbering?

On 60 channels:

  • Single number over a group of channels, single number assigned to 1 channel, then 2 single numbers assigned to 2 more groups of channels (see illustration below).
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On 30 channels:

  • single number for each

  • 5 DDI layers over 20 channels and a single number applied to the other 10 channels

  • 3 DDI layers on 15 channels, 4 DDI layers on 10 channels, and a single number on the remaining 5 channels.
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Can I divert single number DDI?

No, not on ISDN30 (DASS), except through performing a trunk-to-trunk diversion on suitable equipment. The equipment accepts the call and diverts it off again and requires 2 channels to be busy.

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