ISDN interfaces
ISDN uses TDM technology to divide a physical interface into one data (D) signaling channel and multiple bearer (B) channels.
The D-channel transmits control signaling.
The B-channels transmit data or voice.
The ITU-T I.412 recommendation specifies the basic rate interface (BRI) and the primary rate interface (PRI).
BRI interface
The BRI interface provides two 64 kbps bearer (B) channels and one 16 kbps D-channel. This interface is also referred to as "2B + D."
The B-channels use timeslots 1 and 2 in the BRI interface.
PRI interface
The PRI interface has two variants: CE1 PRI (ITU-T recommended) and CT1 PRI (ANSI recommended). CE1 PRI provides 30 B-channels and CT1 PRI provides 23 B-channels. Different countries use different PRI variants, as shown in Table 3.
Table 3: PRI interface specifications
Item | CE1 PRI (30B + D) | CT1 PRI (23B + D) |
|---|---|---|
Total bandwidth | About 2 Mbps | About 1.5 Mbps |
Timeslots | 32 | 24 |
Timeslot assignment |
NOTE: CEI PRI uses timeslot 0 for clock synchronization. |
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Countries/areas |
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