There are a number of BT Digital Calling Features (formerly known as Digital Select Services). These include Call Forwarding, Call Barring and Calling Line Identity (CLI).

ISDN30 uses the BT signalling system DASS2, while ISDN30e uses the Q931 signalling system which conforms to the worldwide ITU-T standard. The range of Digital Calling Features available on these systems is slightly different, as shown in the table below.

Most BT Digital Calling Features are controlled by your equipment. They do not use pre-set codes such as 1471.

Calling Line Identity Presentation (CLIP)YesYes
Presentation NumberYesYes
Calling Line Identity Restriction (CLIR)YesYes
Connected line Identity Presentation (COLP)NoYes
Connected Line Identity Restriction (COLR) YesYes
Administration provided Basic Diversion – voice onlyYesNo
Administration provided Diversion on Busy or failure of BT bearer – voice onlyYes No
Administration provided set up Call Forwarding for all calls – voice onlyNo Yes
Administration set up Call Forwarding on Busy – voice and dataNo Yes
Administration set up Call Forwarding on No Reply – voice and dataNo Yes
Administration provided permanent Outoing Call Barring (OCB)YesYes
Customer controlled Services*
Diversions – not available across DDI (Basic, Busy/failure, Ringtone No Reply)YesNo
Channel BusyingYes No
Call BarringYesNo
Customer controlled Call ForwardingNoYes

Administration provided Selective Outgoing Call Barring on:

All callsInternational Calls and Premium Rate Services (PRS)National, International calls and PRSOperator callsInternational, Operator calls and PRS.
Call Charge IndicationYesNo
Sub AddressesYes
(6 octet)
(20 octet)
Call DeflectionNoYes

*For customer-controlled service features, your switch/PBX must be able to activate the service. Consult your supplier for more information.


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