What is the interface between gNodeB and eNodeB?

In the context of 5G, there isn’t a direct interface between the gNodeB (gNB) and the eNodeB (eNB) as they operate in separate radio access technologies. The gNB is part of the 5G New Radio (NR) system, while the eNB is associated with the Long-Term Evolution (LTE) system. The gNB and eNB communicate indirectly through the Xn interface, which facilitates coordination and handover procedures between 5G and LTE networks. Here’s a detailed explanation of the indirect interaction between gNB and eNB through the Xn interface:

1. Evolved NodeB (eNB) Overview:
   • The eNB is a key component in the LTE network architecture, responsible for radio communication with User Equipment (UE) and managing radio resources within its coverage area.
2. Next Generation NodeB (gNB) Overview:
   • The gNB is a central element in the 5G NR network architecture, handling radio communication with UEs and managing radio resources within its coverage area.
3. Xn Interface Functionality:
   • The Xn interface is an inter-gNB interface that supports communication and coordination between gNBs. It also plays a role in facilitating handovers between gNBs and coordination with other radio access technologies, including LTE.
4. Handover Support:
   • The Xn interface enables gNBs to communicate with each other for handover procedures. This is essential when a UE moves across different cells or coverage areas served by different gNBs or eNBs. The Xn interface ensures a seamless transition of the connection from one node to another.
5. Inter-Cell Coordination:
   • The Xn interface allows gNBs to coordinate their activities, optimizing network performance, managing radio resources, and mitigating interference. This coordination is crucial for providing a smooth and efficient user experience.
6. Mobility Management:
   • The Xn interface supports mobility management functions, ensuring that UEs experience smooth handovers and maintain connectivity as they move across cells served by different gNBs or eNBs.
7. Dual Connectivity:
   • Dual Connectivity is a feature supported by the Xn interface, allowing a UE to be connected to both a 5G gNB and an LTE eNB simultaneously. This feature enhances data rates and user experience by aggregating resources from both 5G and LTE networks.
8. Protocol Stack:
   • The Xn interface uses a protocol stack for communication between gNBs. The protocol stack includes various layers, such as:
     • PHY (Physical Layer): Manages the physical transmission of signals over the air interface.
     • MAC (Medium Access Control): Controls access to shared radio resources and handles scheduling.
     • RLC (Radio Link Control): Manages segmentation and reassembly of data packets.
     • PDCP (Packet Data Convergence Protocol): Handles compression and decompression of data packets.
     • RRC (Radio Resource Control): Manages radio resources and control signaling.
9. Dual Connectivity Architecture:
   • In scenarios where dual connectivity is utilized, the Xn interface enables coordination between the gNB and eNB to manage the simultaneous connections and ensure efficient use of resources from both 5G and LTE networks.
10. Load Balancing:
    • The Xn interface supports load balancing strategies, allowing the network to distribute traffic across different cells and nodes, optimizing resource usage, and enhancing overall network performance.
11. Security Considerations:
    • Security mechanisms are implemented within the Xn interface to protect communication between gNBs. This includes encryption and integrity protection to ensure the confidentiality and authenticity of transmitted data.

In summary, the interaction between gNB and eNB is indirect, occurring through the Xn interface that enables communication and coordination between gNBs in 5G and supports handovers and dual connectivity between 5G and LTE networks.