LLS (lower layer split (gNB))

The lower layer split (LLS) in 5G cellular networks refers to the functional separation of the base station (gNB) into two parts: the Distributed Unit (DU) and the Central Unit (CU). This separation allows for a more flexible, scalable, and efficient deployment of the 5G network.

In the traditional cellular network architecture, the base station (eNodeB in LTE) comprises a single entity responsible for all the functions related to radio access, control, and management. However, with the emergence of 5G and its diverse requirements, a more versatile and dynamic approach was needed to meet the demands of different use cases, services, and deployment scenarios.

The LLS solution aims to address these challenges by splitting the base station into two distinct components: the DU and the CU. The DU is responsible for the radio access functions, while the CU takes care of the higher-level processing tasks. This separation allows for greater flexibility and scalability in the deployment of the 5G network, as well as improved resource utilization and performance.

The DU and CU communicate with each other via a standardized interface called the F1 interface. This interface allows for the exchange of control and user plane data between the two components. The DU is responsible for the lower layers of the protocol stack, including the physical layer, the MAC layer, and the RLC layer. The CU, on the other hand, is responsible for the higher layers of the protocol stack, including the RRC layer, the PDCP layer, and the SDAP layer.

One of the key advantages of the LLS solution is its ability to support different deployment scenarios. For example, in a centralized deployment scenario, multiple DUs can be connected to a single CU, enabling a more centralized management and control of the network. In a distributed deployment scenario, the DUs can be deployed closer to the edge of the network, allowing for better coverage and reduced latency.

Another advantage of the LLS solution is its flexibility in supporting different radio access technologies. For example, the DU can support both 5G NR and LTE radio access technologies, while the CU can support different 5G core network architectures, such as standalone (SA) and non-standalone (NSA) modes.

The LLS solution also enables more efficient resource utilization and improved performance. By separating the lower and higher layers of the protocol stack, the LLS solution allows for more efficient allocation of processing resources, reducing processing latency and improving overall network performance. The solution also enables dynamic scaling of resources based on network traffic and demand, allowing for more efficient use of network resources and improved user experience.

In summary, the LLS solution in 5G cellular networks provides a flexible, scalable, and efficient approach to network deployment, management, and control. By separating the base station into two distinct components, the DU and the CU, the LLS solution enables the support of different deployment scenarios, radio access technologies, and core network architectures, as well as more efficient resource utilization and improved network performance.

Another advantage of the LLS solution is its ability to support network slicing. Network slicing is a key feature of 5G networks that enables the creation of multiple virtual networks on top of a single physical network infrastructure. Each virtual network, or slice, can be customized to meet the specific requirements of different use cases and services, such as enhanced mobile broadband (eMBB), ultra-reliable low latency communication (URLLC), and massive machine type communication (mMTC).

The LLS solution enables network slicing by allowing for the creation of multiple DUs and CUs that can be dedicated to specific slices, providing a more efficient use of network resources and improved performance for each slice. This allows network operators to offer customized services and applications to their customers, while also improving the overall network performance and efficiency.

The LLS solution also facilitates the integration of cloud computing and edge computing into the 5G network architecture. By deploying DUs closer to the edge of the network, the LLS solution enables edge computing capabilities, allowing for more efficient processing of data and reduced latency for services and applications that require real-time processing.

Furthermore, the LLS solution enables the integration of cloud computing into the 5G network by allowing for the deployment of CUs in cloud data centers. This enables network operators to offer network functions and services as a service (NFaaS), enabling a more flexible and scalable approach to network management and control.

In addition to its many advantages, the LLS solution also presents some challenges that need to be addressed. One of the key challenges is the complexity of the F1 interface, which can make the integration of DUs and CUs from different vendors difficult. To address this challenge, standardization bodies such as 3GPP are working on developing standardized F1 interface specifications to ensure interoperability and compatibility between different vendors' equipment.

Another challenge of the LLS solution is the increased signaling traffic and latency introduced by the F1 interface. To mitigate this challenge, the F1 interface needs to be designed to minimize the signaling traffic and latency while still providing the necessary control and user plane data exchange between the DUs and CUs.

In conclusion, the lower layer split (LLS) in 5G cellular networks provides a flexible, scalable, and efficient approach to network deployment, management, and control. By separating the base station into two distinct components, the DU and the CU, the LLS solution enables the support of different deployment scenarios, radio access technologies, and core network architectures, as well as more efficient resource utilization and improved network performance. While the LLS solution presents some challenges, the benefits it offers make it a key feature of 5G networks, enabling the support of diverse use cases and services and the integration of cloud and edge computing into the network architecture.