Load and Overload Control on Junos Multi-Access User Plane
Load and Overload Control are a set of optional features within the 5G Core network (5GC). You can use these features to manage traffic loads on your network and maintain service to user equipment (UE) during extreme situations and peak traffic.
Load Control Information (LCI) and Overload Control Information (OCI) reports provide you with the information needed to manage your control plane traffic. LCI and OCI use the information collected from the user plane (UPF).
Load Control Information
Load Control allows the User Plane Function (UPF) to send specific traffic load information to the Control Plane Function (CPF) through the Sx/N4 interface. With this information, you are able to adaptively balance your session loads across various UPFs.
Load Control Information (LCI) reports gather specific information from the user plane:
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CPU Usage: CPU utilization on the current UPF.
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Session Capacity: The maximum number of sessions supported based on your system profile.
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Memory Usage: Maximum memory in use. Statistics for shared and heap memory, as well as the maximum usage.
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Bandwidth Usage: The amount of the available bandwidth in use on downlink and uplink paths.
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Metric Calculation: LCI is reported as a metric percentage from 0 to 100. If the metric reaches 90 percent, additional LCI reports generate for any change. If the metric reaches 95 percent, a full LCI and telemetry report generate each time the timer expires (every 15 seconds).
Overload Control Information
Overload Control allows the UPF to gracefully reduce its traffic load. It instructs peer control plane functions to reduce the amount of sessions being sent to the UPF. In this manner, overload control is able to avoid spreading an overload to other nodes in the network.
Like LCI, Overload Control Information (OCI) reports gather specific information from the UP:
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UE Registration Surges: A large number of UEs registering on the network will cause a surge of login sessions. OCI monitors the inflight number and reports an overload if the number of inflight sessions reach 80percent of the maximum.
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UE Mobility and Application Signal: A large number of UEs using specific applications can cause a lot of hand-over and QoS flow control signaling. This results in a surge of session modify messages. If the number of "session modify" messages exceeds a preset threshold, the UPF generates an overload report.
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Packet Forwarding Engine Congestion Signal: If the Packet Fowarding Engine receives more messages than it can handle, the Packet Forwarding Engine will send traffic in the Waiting-To-Send (WTS) queue. If any items are present in the WTS queue, an OCI report generates.
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Anchor Packet Forwarding Engine Failover: When an anchor Packet Forwarding Engine fails over and the secondary Packet Forwarding Engine boots, a 30 percent overload report is sent.
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Overload Metric Report: The OCI includes the metric of the load that needs to be reduced and how long the load reduction will last.
Maintenance Mode
Maintenance mode allows you to resolve an overload issue and perform other back-end network management tasks - such as a system upgrade. When you enter maintenance mode, the UPF sends a metric value of 100 percent to the CPF. Maintenance mode prevents new sessions from starting on the UPF, but allows existing sessions and traffic to continue. When you exit maintenance mode, the true load metric is sent to the CPF and normal session activity resumes.
To enter and exit maintenance mode, you will use service-mode
statements.
See service-mode (mobile-edge SAEGW) for additional information about using maintenance mode.
Mobile-Edge Configuration Commit Check
Whenever you modify or delete a configuration that supports mobile-edge features, Junos OS will check to see if any active sessions exist. If any active sessions exist, Junos OS provides an error message and rejects your modifications.