k implicitly tells the UE to use that same DRB for sending pack- ets from that same QoS flow in the uplink; that is, a mapping rule for QoS flow X to DRB y is implicitly configured. Furthermore, all QoS flows for which no mapping rules are configured are mapped by default on a default DRB. As a result, the 5G QoS framework allows a mode of operation where (1) a default DRB with radio protocols configured to provide a default QoS is used to carry the bulk of traffic; and (2) only QoS flows with specific requirements are dynamically (re)mapped onto dedicated DRBs as they appear, without involving 5GC. Together with RQoS, this greatly minimizes the amount of signaling required and reduces CP latency: not all DRBs need to be configured when transiting to CONNECTED from IDLE, and the relocation of QoS flows from one RB to another does not always require CP signaling. As a matter of fact, in a typical usage scenario, the number of flows to deal with is very high, and they come and go frequently. For example, when browsing the Internet, one click can initiate a dozen TCP/IP flows. With RQoS, the allocation of radio bearers is still controlled by the network, but CP sig- naling is limited to the setup of the bearers: explicit signaling of the mapping rules for the plethora of flows is not required. The configuration of the SDAP sublayer to handle the QoS flows of one PDU session is called an SDAP entity. In single connectivity (when only one gNB is used), there are as many SDAP entities as PDU sessions established by 5GC. 7.3.2 QoS Flow Remapping QoS flow remapping from one bearer to another is needed whenever the mapping rule of a QoS flow changes, for instance, at handover when the target gNB has a different mapping policy than the source gNB, or when the gNB moves a new QoS flow away from the default bearer (as explained in Section 7.3.1. above). When remapping a QoS flow from an old bearer to a new one, some packets from that QoS flow are likely still awaiting transmission on the old bearer - with the large amount of