Mobility Handover (Xn/N2) Collision Control

Feature Summary and Revision History

Summary Data

Table 1. Summary Data

Applicable Products or Functional Area

AMF

Applicable Platforms

SMI

Feature Default Setting

Enabled – No settings required as it's always enabled

Related Documentation

Not Applicable

Revision History

Table 2. Revision History

Revision Details

Release

First introduced.

2022.04

Feature Description

The AMF interacts with multiple nodes, such as UE/GNB, UDM, AUSF, and SMF. When multiple nodes send simultaneous request toward AMF, there's a possibility of collision at the AMF node. The AMF Collision Support feature supports handling the collision between different procedures at the AMF node.

How it Works

AMF supports collision handling for the following UE-initiated procedures:

  • Initial Registration Request

  • Deregistration

While the initial registration procedure is running, collision can occur for UE-initiated deregistration, or for an extra initial registration that gets triggered. In such cases, the current procedure is waiting for any of the following cases:

  • Security mode complete message

  • Initial context setup response

  • AM policy establishment from PCF

In each of the preceding specified case, the AMF aborts the running procedure, clears up the corresponding messages, and proceeds with the new incoming procedure.

The UE-level procedure takes precedence over the PDU-level procedure, or aborts or suspends the PDU-level procedure depending on the call flow needs.

All procedures have equal priority—The collision handling gets provision for every combination.

Limitations

This feature has the following limitations in this release:

  • Currently, the AMF supports collision control for single procedure collision with another single procedure.

  • The AMF doesn't support collision control for simultaneous multiple procedure collisions.

OAM Support

This section describes operations, administration, and maintenance support for this feature.

Bulk Statistics Support

The following statistics are supported for the Mobility Handover (Xn/N2) – Collision Control feature.

  • amf_collision_stats —Used for tracking and debugging the AMF collision

    The statistics includes the name of the running procedure, the new procedure, and the action taken by the collision resolver.

The following is an example when the AMF received the subsequent UE Registration while one UE Registration procedure was in progress. The collision resolver aborts the first procedure. 

amf_collision_stats{action_type="abort_old",app_name="amf",cluster="clu001",
data_center="sys001",instance_id="0",new_proc="UERegistration",old_proc="UERegistration",
service_name="amf-service"} 1