ISDN-Integrated Service Digital Networks
ISDN. ISDN - Integrated Services Digital Network was developed to replace the POTS - Plain Old Telephone Service and provide a reliable digital connection for both voice and data. The reality has proven to be much different. It hasn't replaced POTS and almost certainly won't because of the development of higher speed and still lower cost alternatives.
Some of the major characteristics of ISDN are contained in the following list.
it is a digital link
no need to convert data from digital to analog and back
improves reliability
improves performance
it is more readily available than many of its newer competitors such as DSL
it can be used as an always on link
it is more expensive than the PSTN
requires specialized equipment at both ends
it is made up of one or more channels that carry data
B channels for bearer channels
each channel carries 64 kbps worth of data
these channels can be aggregated using inverse multiplexing to create multiple channels in one high speed connection
it has a single control channel
D channel or delta channel
this channel provides 16 kbps or 64kbps depending on the implementation
ISDN is offered by the telephone companies in two standard access interfaces:
BRI - Basic Rate ISDN
two 64 kbps B channels
aggregate bandwidth of 128 kbps
one 16 kbps D channel
PRI - Primary Rate ISDN
23 different 64 kbps B channels
aggregate bandwidth of 1.472 Mbps
one 64 kbps D channel
BRI is implemented for residential or small business data transfer. PRI is typically used for digital voice transmission in conjunction with PBX - Private Branch Exchange telephone systems.
