This blog discusses how LoxiLB, an open-source, eBPF-based load balancer, addresses challenges in NGAP (NG Application Protocol) Layer 7 load balancing within 5G networks with Free5GC, an open-source implementation of a 5G core network (5GC). Traditional Layer 4 load balancing can lead to issues such as AMF (Access and Mobility Management Function) overload and problematic handovers, especially when gNBs (next-generation Node Bs) serve a large number of UEs (User Equipments). LoxiLB overcomes these challenges by comprehending both NGAP and NAS (Non-Access Stratum) protocols, enabling effective distribution of UEs across stateless AMFs and facilitating seamless handovers. More information about this topic can be found here.

This post provides a step-by-step deployment guide using open-source solutions like Free5GC, LoxiLB, and UERANSIM, all orchestrated in a cloud-native fashion with Kubernetes, to demonstrate this functionality.

Overview

LoxiLB is deployed as a load balancer in front of multiple AMFs in a Free5GC deployment to ensure high availability and seamless failover for NGAP connections originating from a gNB (UERANSIM). By proxying NGAP traffic, LoxiLB ensures that if an AMF instance goes down, the gNB's NGAP connection remains intact and continues to function without interruption. Additionally, when a failed AMF instance recovers, LoxiLB replays cached NG Setup requests, etc to restore connectivity automatically.

Flow Diagram

1. Normal Operation:

• UERANSIM (gNB) establishes an NGAP connection through LoxiLB.
• LoxiLB load balances NGAP traffic across multiple Free5GC AMFs.
• The NG Setup procedure is completed with the selected AMF.

2. AMF Failure Handling:

• If an AMF fails, LoxiLB detects the failure and reroutes the gNB's NGAP session, along with its associated UEs, to a healthy AMF.
• The gNB does not experience connection loss because LoxiLB maintains the session.

3. AMF Recovery & NGAP Replay:

• When the failed AMF is restored, LoxiLB replays cached NG Setup requests and other related messages.
• The AMF resumes handling NGAP traffic without requiring the gNB to reinitiate the setup.

                          +-------------------+
                          |   UERANSIM gNB    |
                          | (Simulated gNB)   |
                          +-------------------+
                                   |
                     NG Setup Req  |  NGAP Signaling
                                   v
                          +-------------------+
                          |      LoxiLB       |
                          | (NGAP Proxy/LB)   |
                          +-------------------+
                               /     |     \\
       +----------------+    +----------------+    +----------------+
       |   AMF 1 (UP)   |    |   AMF 2 (DOWN)  |   |   AMF 3 (UP)   |
       |  (Processing)  |    | (Failure State) |   |  (Processing)  |
       +----------------+    +----------------+    +----------------+
                                        |
                         AMF 2 Recovers |
                                        v
                              +----------------+
                              |   AMF 2 (UP)   |
                              | (Cache Replay) |
                              +----------------+

This architecture significantly enhances 5G network reliability by ensuring the NGAP signaling plane remains operational even when individual AMF instances experience failures, making it ideal for production 5G deployments requiring high availability

Prerequisites