Attach rate limit is the maximum number of new connections that AMF can process. The new connections include Initial Registration Request, Namf_Communication_CreateUEContext Request, and N26 Forward Relocation Request.

Setting the rate limit enables the operators to manage the traffic and reduce the signaling on the external nodes.

Note	AMF does not throttle emergency, periodic, and mobility registration.

This section describes how this feature works.

When you enable the attach rate throttling feature, AMF buffers and queues new connection requests (excluding Emergency Registration). The AMF prioritizes the processing of these requests in the FIFO (first in, first out) order.

If the queue is full, AMF drops or rejects packets with a cause code which is based on the configured action.

To configure this feature, use the following configuration:

config 
   amf-global 
      network-protection-overload 
         attach-rate 
            rate-limit permitted_connection_count 
            queue-size queue_size 
            action 
               drop  
               initial-registration reject-with-cause { congestion | protocol_error_unspecified } 
               in14-create-ue-context reject-with-http-code {403} 
               in26-fwd-reloc reject-with-cause { gtpc-entity-congestion | relocation-failure | no-resources-available } 
               end 

NOTES:

• amf-global —Enter the AMF global configuration mode.

• attach-rate —Configure the attach rate feature.

• rate-limit permitted_connection_count —Specify the number of new connections that AMF accepts per second. permitted_connection_count must be an integer in the range 50—5000.

• queue-size queue_size —Specify the size of queue that AMF uses for buffering the packets. AMF uses this queue when the new connection requests exceed the value that you have specified for rate-limit .

  queue_size must be an integer in the range 50—1000. The default queue_size is 50.

• action —Configure the action that AMF takes when the queue is full. The default action is Reject for all requests with #default reject cause.

  The following options are available for Action:

  • drop —Configure to drop all the new connection requests.

  • initial-registration reject-with-cause { congestion | protocol_error_unspecified }—Configure AMF to reject the UE-initiated Initial Registration Request with the one of the following causes in the reject message:

    • congestion—The message is congestion (22).

    • protocol_error_unspecified—The message is protocol_error_unspecified (111) #default.

  • n14-create-ue-context reject-with-http-code {403} —Configure AMF to reject the new Namf_Communication_CreateUEContext Request with the HTTP error code. The AMF receives this request in the source AMF during the UE-initiated inter-AMF N2 handover. With the error code as 403, the Cause attribute of the ProblemDetails is set to HANDOVER_FAILURE #default.

  • n26-fwd-reloc reject-with-cause { gtpc-entity-congestion | relocation-failure | no-resources-available }—Configure AMF to reject the new MME-initiated forward relocation requests through the N26 interface.

    If AMF rejects the inbound forward-relocation requests, it uses one of the following cause codes:

    • No resources available (73)

    • gtpc-entity-congestion (120)

    • relocation-failure (81) #default

Note	AMF does not support dynamic change configuration. The configured rate-limit and queue-size are applied to each amf-service pod and not at the aggregation of all service pods.

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