Digital Subscriber System No. 1
Digital Subscriber Signaling 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 was developed by the CEPT , today the European Institute for Telecommunications Standards (ETSI) with the support of the European Community , to replace earlier national standards (such as FTZ 1 TR 6 in Germany) and thereby to break down market barriers caused by different standards in the member states of the European Community. In 1989, 26 network operators from 20 European countries decided to use this protocol.
The protocol is one of the factors responsible for the success of ISDN in Europe and especially in Germany . The protocol is also used outside of Europe - with the exception of North America and Japan .
Differences to the former national protocol FTZ 1 TR 6 are, among other things, that the terminals with basic connections are addressed via an MSN (Multiple Subscriber Number) and not via a phone number with an appended terminal selection number (EAZ) .
Layer model
The DSS1 has a reference model with three layers. The layers are structured according to the OSI model . Service elements are used for flow control between the layers .
Physical layer
The bit transmission layer is the lowest layer (layer 1) of the D-channel and is used together with the B-channels . This is where the multiplexing and the transmission of the data takes place on bit level. Layer 1 has functions for displaying defects. Selection of service elements that Layer 1 makes available to Layer 2:
| Service element | abbreviation | meaning |
|---|---|---|
| Ph-activate-request | Ph-AR | Activate layer 1 |
| Ph-data-indication (dat) | Ph-DAI | Exchange of messages |
| Ph-rds-on-indication | Ph-RDSI | Confirmation: U K0 interface activated |
| Ph-loop-2-request | Ph-L2R | Activate layer 1 and close test loop 2 in the NT |
Data link layer
The data link layer is layer 2 of the D channel and is used for the secure transmission of the layer 3 protocol data elements. For this purpose, the LAPD security protocol is used within Layer 2 . Selection of service elements provided by Layer 2 of Layer 3:
| Service element | abbreviation | meaning |
|---|---|---|
| Receive Ready | RR | Display of readiness to receive, confirmation of receipt |
| Receive Not Ready | RNR | no willingness to receive |
| Reject | REJ | Request to repeat |
| Set Asynchronous Balanced Mode Extended | SABME | Request to establish a layer 2 connection |
| Disconnect | DISC | Request to terminate the Layer 2 connection |
Layer 2 connections are addressed using the Service Access Point Identifier (SAPI) and Terminal Endpoint Identifier (TEI).
Network layer
The network layer (layer 3) provides services that are required for subscriber connections (e.g. basic connections ). The control of performance features is also carried out with layer 3 functions. Selection of service elements of layer 3:
| Service element | meaning |
|---|---|
| ALERTING | The target subscriber is called. |
| CONNECT | The called subscriber accepted the connection. |
| CONNECT ACKNOWLEDGE | Confirmation from CONNECT. |
| SET UP | Initiation of a connection establishment . |
| HOLD | "Hold" feature is requested. |
| RETRIEVE | Withdrawal of "Hold" is requested. |
| INFO / FACILITY | Transmission of additional information before or during a connection. |
| DISCONNECT | Request to disconnect. |
See also
swell
- ↑ ITU-T I.430 / 431 Basic / Primary User-Network Interface Layer 1 Specification
- ↑ ITU-T Q.921 User-Network Interface Datalink Layer Specification
- ↑ ITU-T Q.931 User-Network Interface Layer 3 Specification for Basic Call Control
literature
- Andreas Kanbach, Andreas Körber: ISDN - The Technology . Hüthig Verlag, Heidelberg 1999, ISBN 3-7785-2288-4 .