Digital Subscriber System No. 1

Digital Subscriber Signalling System No.. 1 (DSS1) is a signaling protocol for the D channel of the ISDN. It is also known as Euro -ISDN or E -DSS1.

DSS1 today European Telecommunications Standards Institute (ETSI ) has been prepared by CEPT, developed with support from the European Community to former national standards (such as FTZ 1 TR 6 in Germany ) to replace and thereby reduce market barriers by different standards in the Member States of the European Community. In 1989 it was decided by 26 operators from 20 European States to use this protocol.

The protocol is one of the factors that are responsible for the success of ISDN in Europe, especially in Germany. Outside Europe - except North America and Japan - is the protocol in use.

Differences from the former national protocol FTZ 1 TR 6 are that the devices are addressed at base terminals via an MSN (Multiple Subscriber Number), among others, and do not have a phone number with an attached terminal selection digit ( EAZ ).

Layer model

The DSS1 has a reference model with three layers. The layers are divided according to the OSI model. For flow control between the layers service elements are used.

Physical layer

The physical layer is the lowest layer (layer 1) of the D- channel, and is shared with the B- channels. Here, the multiplexing and transfer of data at the bit level. Layer 1 has functions for displaying defects. Selection of primitives, layer 1 layer 2 makes available:

Link layer

The data link layer, layer 2 of the D channel and is used to secure transmission of the layer 3 protocol data elements. To this end, the backup log LAPD is used within the layer 2. Variety of service elements, the layer 2 layer 3 makes available:

Layer 2 connections are addressed by the Service Access Point Identifier ( SAPI ) and Terminal Endpoint Identifier ( TEI).

Network layer

The network layer (layer 3) provides services (eg bases ) are required to subscriber lines ready. And the control of features is carried out with layer 3 functions. Variety of service elements of the layer 3: