# OpenCare5G: O-RAN in Private Network for Digital Health Applications
## 3 Proposed Solution
### 5G NR/NGC Protocol Framework Stack  
Figure 4 depicts the conceptual model of the open systems interconnection (OSI) being used in 5G, based on the functionalities of each layer and distinguished by the concepts of services, interfaces and protocols. The OSI model divides functions into seven layers that serve as a reference for developers to program networks and so that they can communicate and work independently of the manufacturer. It is a theoretical model for developers and scholars and the great secret is standardization and interoperability [32]. The TCP/IP model is a four-layer oriented model, forming the stack of the protocol structurecurrently in use, but we need to know both models to interpret the 5G Protocol Framework Stack. With the implementation of the structure of the datacenter LAN/4G/LTE stacks for the 5G NR/NGC, the layers and sublayers of the structured stack of protocols for interconnection, communication and other functionalities of hardware and software underwent alterations and were included in the functional division options proposed by 3 GPP in conjunction with disaggregated O-RAN. Based on the simplified Radio Protocol Stacks in the comparison of UMTS/LTE/5G Air Interface or datacenter LAN with 4G/LTE/5G RAN network stacks, we will have the \"5G NR/NGC SA Protocol Stack\" with different technical terms and a functional division\"Intra-MAC split\" among RU/DU/CU, as shown in layers L1, L2 and L3 and their sublayers in Figure 4[33]. Based on the OSI model, each layer has its own structure called Protocol Data Unit for data, segments, packets, frames and bits (PDU). This division into layers brings several advantages, such as the decomposition of network communications into smaller, simpler parts and standardization of network components, enabling communication between different types of hardware and network software, preventing changes in one layer from affecting the others. Each layer of the model must provide its services exclusively to the layer immediately above and, consequently, the function of each layer depends on the services of the layer immediately below [32]. Therefore, based on the OSI/TCP-IP model, the \"5G NR/NGC SA Protocol Structure Stack\" was formed, in which 3 GPP released the 38.300 v1 specification on NR and NG-RAN. These standards, termed Phase 2, include details about the 5G NR network and the protocol architecture shown in Figure 4 with the three layers L1, L2 and L3 and their sublayers [34,37]:  
* Layer L1 on sublayer RF, PHY Low(L) and High(H);
* Layer L2 on sublayer MAC (L/H)/(SCH), RLC (L/H) and PDCP (L/H);
* Layer L3 on sublayer RRC and SDAP, only SA and not NSA, NAS and IP. Figure 5 demonstrates the architecture of layers L1, L2 and L3 for DownLink (DL) and UpLink (UL), where the:  
* PHY sublayer offers transport channels to the MAC sublayer;
* MAC sublayer offers logical channels to the RLC sublayer;
* RLC sublayer offers RLC channels to the PDCP sublayer;
* PDCP sublayer offers Radio Bearers to the SDAP sublayer;
* SDAP sublayer provides the QoS flows. The \"5G NR/NGC SA Protocol Framework Stack\" is designed to support lower delays and higher data rates with QoS in the sublayers shown in Figure 6 for UE and 5G gNB base station with DL or UL directions of data packets [37]. Figure 4: Radio protocol stack simplified in the UMTS/LTE/5G air interface or datacenter LAN with 4G/LTE/5G RAN Network stacks—Comparison to have the “5G NR/NGC SA Protocol Stack”. Based on [32, 33, 34, 35, 36]. As shown in Figure 5:  
* Packet Data Convergence Protocol (PDCP) is the first sublayer in the 5G NR protocol stack that receives/transmits network layer traffic (TCP/IP traffic);
* Data Radio Bearer (DRB) has the logical connection used within the 5G protocol stack to carry protocol data units (PDUs);
* The Service Data Adaptation Protocol (SDAP) functionality is to map the QoS flows for the DRB in the PDCP sublayer in the DL and UL directions [40]. The channels shown in Figure 5 help us organize and simplify the design of the stack for each sublayer.