ing algorithms are mostly vendor specific and are typically not standardized, several other enhancements of the NR protocol specification are required. Specification enhancements to support NTN have been studied and discussed on a per-layer basis in 3GPP: for MAC enhancements see 3GPP R2-1818511, for RLC see 3GPP R2-1818512, for PDCP see 3GPP R2-1818513, and for SDAP see 3GPP R2-1818514. Most of the enhancements of the NR radio protocol stack to support NTNs are related to timer values (3GPP R2-1900119), as the currently defined value ranges of many timers are not sufficiently large to cope with the propagation delays of NTNs. Two approaches are considered: adding an offset to the timer value equal to 5.3 Non-terrestrial Networks the increase in propagation delay or increasing the value range in the RRC configuration protocol. Furthermore, the size of sequence numbers at RLC and PDCP layers as well as the size of the layer 2 buffer will have to be increased to ensure sufficient eMBB throughput over satellite links. Of course, some of the QoS classes and respective radio bearer configurations defined for terrestrial networks (e.g. URLLC) may not be supported due to the large propagation delay. 5.3.4.3 NR Control-Plane Procedure Adaptations for NTN The latency of RRC control-plane procedures is another concern for NTN that may benefit from enhancements (3GPP R2-1901493). The time it takes to perform RRC procedures such as connection setup and RRC state transitions may have an impact on the actual user expe- rience. On the one hand, NTN cell sizes can be of several 100 km and not all the UEs in that area can be kept active. On the other hand, RRC state transitions toward an active state will take quite some time. Therefore, means must be found to reduce the duration between the arrival of a packet in idle state and the transmission of the first packet in connected state in order to maintain control-plane latency at reasonable levels. The use of the new RRC Inactive state (see Section 3.4) is one of the protocol enha