Update _3gpp-common-subscription-control.yang

      list HeartbeatControl {

        description "MnS consumers (i.e. notification recipients) use heartbeat

          notifications to monitor the communication channels between them and

          data reporting MnS producers emitting notifications such as

          notifications to monitor the communication channels between 

          themselves MnS producers configured to emit notifications such as

          notifyNewAlarm and notifyFileReady.

          A HeartbeatControl instance allows controlling the emission of

          Creation and deletion of HeartbeatControl instances by MnS Consumers

          is optional; when not supported, the HeartbeatControl instances may be

          created and deleted by the system or be pre-installed.

          created and deleted by the system or be pre-installed.  A single 

          HeartbeatControl instance may emit heartbeats for multiple MnS, 

          identified by MNSAgent in the notification. 

          Whether and when to emit heartbeat notifications is controlled by

          HeartbeatControl. Subscription for heartbeat is not supported via the