Integrated Services Digital Network

:ISDN is also short for isosorbide dinitrate

Configurations

In ISDN, there are two types of channels, B and D:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• B channels are used for data--this refers both to voice and data information, and
• D channels are intended for signalling and control (but can also be used for data).

B stands for Bearer and D stands for Delta.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

There are two kinds of access to ISDN:

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

• Basic rate interface (BRI) - consisting of two B channels, each with bandwidth of 64 kbit/s, and one D channel with a bandwidth of 16 kbit/s. Together these three channels can be designated as 2B+D, and,
• Primary rate interface (PRI) - containing a greater number of B channels and a D channel with a bandwidth of 64 kbit/s, The number of B channels varies based on the country:
• North America and Japan: 23B+1D, aggregate bit rate of 1.544 Mbit/s (T1)
• Europe, Australia: 30B+D, aggregate bit rate of 2.048 Mbit/s (E1)

Using a variation of the alternate mark inversion encoding technique, call data is transmitted over the data (B) channels, with the signalling (D) channels used for call setup and management. Once a call is set up, there is a simple 64 kbit/s synchronous bidirectional data channel between the end parties, lasting until the call is terminated. There can be as many calls as there are data channels, to the same or different end-points. Bearer channels may also be multiplexed into what may be considered single, higher-bandwidth channels via a process called B channel bonding.

Related Topics:
Alternate mark inversion - Multiplexed

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The D channel can also be used for sending and receiving X.25 data packets, and connection to X.25 packet network. In practice, this was never widely implemented.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~