Integrated Services Digital Network is a technology of telecommunication networks designed to use PSTN infrastructure for providing digital services directly to end users (without the mediation of analogue devices) (End-to-end circuit-switched digital services). ISDN connections among to the group dial-up connections.
ISDN was standardized by ITU-T and ETSI organizations. European standards have been introduced to the system as a group of Polish Standards ICS 33.080 - Network Integrated Services Digital. There are two types of access to ISDN:
In Central Europe countries, in the context of access original 30 data channels (mainly data call) with 64 kbps capacity each (the so-called B channel), one signalling channel (D channel) with 64 kbps capacity and channel for synchronization stream E1 (also 64 kbps) are used
For the purpose of the data channel B, the DSS1 signalling protocol is used and it is transmitted in the signalling channel D. Data channels are used for voice and data. Signalling channel is used for call setup and management. When the connection is created then bi-directional synchronous data transmission channel between users is established. It is closed at the end to the call. It is possibility to combine as many connections as there are data channels. The various channels can open connections to the same or different destinations. The data channels can be used for transmission of the digitally-encoded voice (called a PCM code. Pulse Code Modulated voice calls) which gives an access to traditional voice telephony. This information can be transferred between networks to the end user during call setup.