Hello Ruben,
Regarding your query,When using a CAS signalling which belongs to SS7 also, channelling is associated ,I mean CH 16 is fixed as a signalling but it can carry more than 2 traffic channels not only 2 CH within E1 connection ,unlike SS7 that uses common Signal (CSC),which differs from CAS ,a signal link can be assign any of the channels in E1 or a T1 connections but on some sort their signalling channel can be use as traffic channel.