ISDN
1. Definition
ISDN(integrated services digital network). It is a set of CCITT/ITU standards for circuit-switched transmission of data over various media, including ordinary telephone-grade copper wire.
2. channels
It includes 2 channels:
1. B-channels carry payloads(e.g., data or voice streams)
2. D-channels carry control and signaling information
3. leves of service
There are two levels of services: the basic rate interface(BRI) and primary rate interface(PRI).
3.1 BRI
consist of two 64kbps B-channels and one 16kbps D-channel. Thus, a BRI delivers up to 128 kbps of data.
3.2 PRI
In the U.S.A, a PRI connection consists of 23 B-channels(1472 kbps total) and one 64 kbps D-channel. In Europe a PRI connection consists of 30 B-channels(1920kbps total) and 1 D-channel.