Digital Access Signalling System 2 (DASS2) is an obsolescent protocol defined by British Telecom for digital links to PSTN based on ISDN. Although still available on request, it has been superseded by ETS 300 102 ("EuroISDN").
DASS2 is an improved version over DASS1, based on experiences with DPNSS.
In the UK, the ISDN concept was first introduced to customers by BT with their
DASS2 connections. DASS2 (Digital Access Signalling System) is a BT-designed
signalling standard, and was introduced before the Q.931 standard was finalised
by the international community. British Telecom used the term ISDN when
describing their DASS2 lines.
DASS2 lines are provided to customers on a 2Mbit/s link and can handle 30 simultaneous calls (64kbit/s each). DASS2 is still offered by BT and other UK carriers. Q.931 is the name of the CCITT document that describes the agreed signalling format for International ISDN. CCITT had previously been known as International Telegraph and Telephone Consultative C