Digital Access Signalling System

For the Depression, Anxiety and Stress Scale (DASS), see DASS (psychology).

For the Defensive Aid Sub-System of an aircraft, see Defensive Aids System.

The Digital Access Signalling System (DASS) is the United Kingdom proprietary standard created by British Telecom to provide ISDN services in the United Kingdom. The first incarnation DASS1 is now obsolete and has been replaced by DASS II. This itself will become obsolete over the coming years as Q.931, a European standard becomes widely adopted in the EU.

DASS II is purely a protocol used to control data flow across the ISDN doing a similar job to the protocols used with modems when sending the data over the analogue PSTN. It is more highly specified and controlled and operates at higher speeds.