Planetary systems containing two or more planets sometimes appear to exhibit resonant configurations, where the period ratio between the planets is close to the period ratio of two small integers. These configurations enhance dynamical interactions between the planets, which can be detected by variations in the time of transits of individual planets (the so-called TTVs). In addition, resonant configurations are commonly thought to be the result of convergent migration, a process by which young planets migrate in a gaseous discs at different speeds so that the outer planet "catches up" with the inner one and captures it in a resonance. In this talk, we will demonstrate what is the imprint of disc migration on the TTV signals that are observed today. We will focus on two systems, K2-24 and Trappist-1, and link their current architecture to their past history.
