E1 connections have 32 channels in total.
Typically, for E1 CCS and CAS protocols, 30 channels are used as B-channels and 2 channels are used as D-channels. For this reason, the frame structure of an E1 PRI connection is said to be 30B+2D where the 2 D-channels are located on timeslots 0 and 16 and the remaining channels are used as B-channels. Hence;
|Channel 0||D-channel (Used mainly for clocking and synchronisation)|
|Channel 1-15||B-channel (Voice)|
|Channel 16||D-channel (Signalling)|
|Channel 17-31||B-channel (Voice)|
The word 'typically' is used above because there are certain protocols that allow for a different D-channel configuration, for instance, SS7.
For information on T1 connections please look at the knowledgebase entry 'How many voice channels does a T1 Primary Rate Interface have'?