ok, i get it.
one transfer can use several links (= timeslots) to perform the exchange of data.
the transfer is defined at the LAYER 3, and the “LAYER 3” transfer occupies several “LAYER 1” timeslots. Therefore it can happen than one transfer uses the full E1 : 31 links.
(beware : all E1 have max 31 TS useable for transfer. 1 TS is always reserved for “framing”. And if there is one SS7, then you have only 30 TS useable for data).