E to monitor the downlink for the QoS that has been applied by the RAN to the traffic. It then applies the observed QoS parameters in the uplink for the traffic it generates toward the RAN. Packet Data Convergence Protocol (PDCP) In earlier versions of Global System for Mobile communication (GSM) and 3GPP standards, PDCP was only used for the packet data bearers, and the circuit switched bearers connected directly from the host to the RLC layer. Because LTE is all-packet, this is now a place for higher layer functions that sit above the packing and unpacking that goes on in the RLC. PDCP functions in the UP include encryption/decryption, RoHC header decompression, sequence numbering, and duplicate removal. PDCP functions in the CP include encryption/ decryption, integrity protection, sequence numbering, and duplicate removal. There is one PDCP instance per radio bearer. Table 2-1 4G and 5G QoS parameters. 5G/NR 4G/LTE QoS identifier 5G QoS Identifier (5QI) QoS Class Identifier QoS granularity QoS flow EPS bearer Flow/bearer identifier QoS Flow Identifier (QFI) EPS bearer ID (EBI) Reflective QoS Supported through Reflective QoS Indicator (RQI) Not supported 56 Open Radio Access Network (O-RAN) Systems Architecture and Design Dual and multiconnectivity The concept of multiconnectivity means that a single UE/client device is connected to multi- ple radios (RUs, TRPs) at the same time. DC was first introduced in Release 12 specification for LTE, assuming a UE to be connected to two eNBs at the same time, where the eNBs are connected over the X2 link. The concept of a Master and Secondary eNB (MeNB and SeNB in 4G or MgNB and SgNB in 5G) was established to define a single base station (the master) that maintains the CP connectivity, where the UP connectivity can be provided by both eNBs. Consider the scenario with the MeNB as a macro cell and a SeNB as a small cell as a typical deployment scenario in Fig. 2-11. 3GPP defines different multiconnectivity options that allow deployment in various opera- tor core network and