Are you building an access device or want to use an access device? And what is the application.
T1/E1 channels/time slots can be configured differently for different purposes.
Unstructured or unchannelised T1/E1 have no time slots and the full bit rate is dedicated for data transmission. this is the typical use for serial links between routers.
Structured or channelised T1/E1 have channels/time slots 24 for T1 and 32 for E1. But dependent on the application certain time slots can be reserved for signalling and worse certain bits can be reserved for signalling.
Can you be more specific with what you are trying to achieve?