What an E1 contains

An E1 carries 30 DS0s, per ITU-T G.704 and ITU-T G.702.

E1 → 30 × E0 → 1 × DS0

Down to DS0

30 × E0 ITU-T G.70430 voice channels in 32 timeslots. TS0 is framing and TS16 is channel-associated signalling.
1. 1 × DS0 ITU-T G.702E0 and DS0 are each one 64 kbit/s PCM channel.