Admission Control xApp

Owned by Matti Hiltunen
Last updated: Nov 27, 2019
3 min read

This page will provide documentation of the AC xApp that is an example of an xApp that controls the execution of a gNB.

Additional documentation related to the Amber release version of the xApp can be found here.

Background

AC xApp is responsible for:

  • Subscription for SgNBAdditionRequest message in the gNB
  • Executing logic to determine if a dual connection should be accepted or rejected and generating the RIC CONTROL message
  • Update metrics: dual connections accepted/rejected

Control via A1 type (pre-standard) interface 

The following 4 parameters can be set via the control interface

  • Parameter 1: enforce , type = Boolean, description = whether to apply admission control or not
  • Parameter 2: window length , type = number , description = range over which to measure request volume
  • Parameter 3: trigger threshold, type = number , description = threshold above which to trigger blocking
  • Parameter 4: Blocking rate , type = number, description = percentage of requests to reject

A policy sent to the Admission Control xAPP must be a JSON that  conforms to the xAPP Policy Schema maintained by A1 Mediator.  The Admission Control instance of the schema is adm-ctrl-xapp-schema.json

  • An example of received policy :   { "enforce":true, "window_length":10, "blocking_rate":20, "trigger_threshold":10  }
  • Example of response from Admission Control xAPP on successful application of policy  : {  "status":"SUCCESS",  "message":"Config applied" }

Deployment

  • On the RIC, the Admission Control xAPP can be deployed using xApp Manager REST API interface
  • Or, appmgrcli command provided by xApp Manager:
    • appmgrcli -h appmgr-service p 8080 deploy admin xapp
  • Or, curl-command: 
    • curl -X POST http://appmgr-service:8080/ric/v1/xapps  -d '{"name:" "admin xapp}'
  • The Admission Control xAPP provides a configuration json and schema in its helm chart, conforming to the template structure dictated by the xAPP Manager
  • The configuration descriptor is config-file.json
    • The configuration descriptor describes the RMR messages that the xAPP expects to consume, send as well as a static route table for preliminary testing.
    • In addition, it exposes key configuration parameters under the 'env' block which can be used to configure behaviour of the xAPP. Notable 'env' parameters are :
      1. GNODEBID : Specifies the gNodeB connection identifier (as defined by the E2 manager when setting up connection) to which to send subscription request
      2. VES_COLLECTOR_URL :  URL of VES collector to which the xapp sends metrics
      3. VES_MEASUREMENT_INTERVAL : How often to post metrics
      4. LOG_LEVEL : Log level to set for testing/production
      5. TEST_MODE : If this key is defined (value does not matter), then the xAPP will send a subscription request, wait for VES_MEASUREMENT_INTERVAL and then send a subscription delete request. It will continue to process any E2AP indication messages independent of the subscription flow.
  • The schema of the descriptor is schema.json
  • The latest docker image for deployment is available at  snapshot.docker.ranco-dev-tools.eastus.cloudapp.azure.com:10001/ric-app-admin:0.1.2
  • Helm Chart for deployment is stored in the Helm repo specified by Integration team. Linked here for convenience Admission Control xAPP Helm Chart

Testing :

The admission control xAPP has 3 interfaces which can be tested :

  • A1- interface to get/set policies
  • VES interface to report metrics
  • E2 interface to interact with RAN. On this interface it currently supports
    • E2AP subscription request/delete messages
    • E2AP indication/control messages

A simple script check_status.sh   can be run in the RIC K8 environment to report if the Admission Control xAPP has successfully received/posted messages for each of these interfaces.

Note : The script does not (currently) identify any RMR related routing issues.

Metrics

The Admission Control xAPP collects metrics related to dual connections accepted/rejected and reports them via VES protocol to VES Collector.  The URL of the VES collector and the interval for posting metrics can be configured in the XAPP configuration descriptor during deployment.  The metrics posted are a JSON body that conforms to VES schema

An example JSON of posted metric is here