 pre-processing allowed in 5G (see Section 7.2), such a scenario is indeed expected to be common. After updating the mapping rule, packets from the QoS flow will therefore reach the receiver from both the old bearer and the new bearer in parallel for as long as the old bearer contains packets from that QoS flow (please note that a solution requiring 7 5G Radio Protocols the UE to pull all pre-processed data on the old bearer from the QoS flow to be remapped was not considered feasible). In-order delivery then necessitates buffering of fresh data on the new DRB for as long as data remains on the old DRB. Such buffering can either take place at the receiver or at the transmitter. Buffering in the transmitter relies on the following principle: transmission of fresh data on the new bearer starts only after having transmitted all packets from the relocated QoS flow on the old bearer. It is transparent to the receiver but requires the transmitter to buffer fresh data from the relocated QoS flow. Buffering in the receiver relies on the following principle: fresh data from the new bearer is only delivered to the upper layers once all the packets from the relocated QoS flow on the old bearer have been received and delivered in sequence to the upper layers. It is transparent to the transmitter but requires the receiver to buffer fresh data from the QoS flow. In order to minimize the buffering requirements on the UE, buffering in the transmit- ter (i.e. gNB) is used in the downlink while buffering in the receiver (i.e. also gNB) is used in the uplink. However, in order to help the gNB confirm that all data from the relocated QoS flow has been sent on the old bearer, an end marker is introduced. The end marker is always transmitted by the UE on the old bearer after updating a mapping rule. An example of QoS flow relocation in the downlink is depicted in Figure 7.5, where a QoS flow A initially mapped onto RB1 together with a QoS flow B is remapped to RB2 (Step 1 in the figure). After updating the mapping rules, fresh data fr