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What do I get with ISDN30 (DASS)? | BT Business

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 ISDN30e superseded ISDN30 with its ETSI or Q931 signalling which is the standard ISDN protocol used throughout Europe.

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.

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.

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.

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).


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.

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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