Integrated Business Digital Network (ISDN) is a digital network system based on public telephone network. Also, telephone communications uses to simulate connection methods, and ISDN is the first defined protocol to digital communication, which supports high-speed transmission services such as voice, data, video, graphics, etc. on standard lines. ISDN's bearer channel (B channel) is responsible for simultaneously transmitting various media, occupying a bandwidth of 64 kb / s (some switches limit bandwidth to 56 kb / s). Data Channel (D Channel) is mainly responsible for transmitting signaling, transmission rates from 16 kb / s to 64 kb / s, depending on the type of service. ISDN is not limited by public telephone networks, and its transmission can also be done by packet switched networks, Telex, CATV networks, etc. ISDN has two basic service types:
Basic Rate Interface (BRI: Basic Rate Interface): Composed of two 64 kb / s B channels and a 16 kb / s D channel, the total rate is 144 kb / s. This service is mainly suitable for personal computer users. The BRI of the U interface provided by Telco supports the double line and the transmission rate is 160 kb / s. Reduce the noise effect by echo cancellation operation. Various data coding modes (North America use 2B1Q, European countries use 4B3T) to provide a higher data transfer rate for one-way local loops. Main Rate Interface (PRI: Primary Rate Interface): Can meet users' higher requirements. A typical PRI consists of a 23 kb / s B channel and a 16 kb / s D channel, with a total rate of 1536 kb / s. In Europe, PRI consists of 30 kb / s B channel and a 64 kb / s D channel, with a total rate of 1984kb / s. With NFAS (Non-Facility Associated Signaling), PRI also supports multi-PRI lines with a 64 kb / s D channel.
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