B-ISDN provides the needs (High speed and large data handling) of the next generation technology. B-ISDN is a digital service with speed above 1.544 Mbps. The original ISDN is called narrow band ISDN (N-ISDN). B-ISDN uses fiber at all levels of telecommunications. B-ISDN provides two types of services. They are interactive (conversational or messaging or retrieval). The interactive service is bidirectional. The distributive services are unidirectional (with user control or without user control).
Several forms of B-ISDN exists. Some are listed below:
Frame relay service. Frame relay is considered to be a B-ISDN service. Frame relay is a packet switching protocol service offered by telephone corporations to replace the X-25 protocol. It is a WAN network.
Switched Multimegabit Digital Service (SMDS). SMDS is a digital service that provides a high speed digital path. The transport speed of SMDS is usually 155 Mbps.
ATM. The transport speed of most ATM applications are 155 Mbps.
B-ISDN uses the same functional groupings of N-ISDN. But named as B-NT1, B-NT2, B-TE1, B-TE2 and B-TA. B-ISDN uses the same R, S, T and U reference points. However B-ISDN uses three different access methods to satisfy the user needs. They are symmetrical 155.52 Mbps, asymmetrical 155.520 Mbps and symmetrical 622.080 Mbps.
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