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Digital Access Signaling 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 Although still available on request, it has been superseded by ETS 300 ("EuroISDN").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. It 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 the customer on a 2Mb/s link and can handle 30 simultaneous calls (64Kb/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 signaling format for International ISDN. Customers will normally choose the desired signalling system, as this will be dictated by their CPE equipment, usually a PABX. (CPE- Customer Premises equipment).
Other protocols and interfaces