Services Digital Network is an all-digital communications line
that allows the transmission of voice, data, video, and graphics,
at very high speeds, over standard communication lines.
There are two ways to provide the ISDN services to the customers.
Basic Rate Access Interface (BRI) provides:
two full-duplex 64 kbps bearer (B) channels
full-duplex 16 kbps D channel
Rate Access Interface (PRI) consists of:
up to 23 (for T1 lines) and
(for E1 lines) 64 kbps B channels
main transport medium for ISDN is the T1 /E1 digital line. The
T1 /E1 interfaces are used to transmit digital voice and data
at a maximum 1.544 Mbps / 2048 Mbps rate. E1 and T1 belong to
the physical layer in the OSI reference model, thus Layer 2 technologies
such as ATM and FR are carried over it. A T1 /E1 line connects
two points: in one point the information is multiplexed and in
the second demultiplexed.
of digital telephony are: