Flexible production processes and applications for Industry 4.0 expect a seamless, deterministic communication over scalable infrastructure networks that rely on a combination of wired and wireless technologies. Time-Sensitive Networking (TSN) and 5G are considered key technologies to meet the communication requirements of Industry 4.0. To integrate 5G into TSN, the 3rd Generation Partnership Project (3GPP) specified the 5G system (5GS) as Ethernet bridge, to exchange time synchronization and Quality of Service (QoS) requirement information between wired TSN entities and 5GS. QoS mapping between TSN and 5G is non-trivial and requires a deeper analysis of relevant parameters and QoS processing. In this paper, different solution approaches for QoS mapping between TSN and 5G are presented and discussed. The contribution covers fundamentals and prerequisites on the way to a 5G QoS model for TSN, which has not yet been addressed in 3GPP nor IEEE.