The following is the description of request_id in oaris 2.0 spec:

7.3.12.6 request_id_type
Type: IDLTypeDef unsigned long long
Package: Requests
The purpose of the request_id is to uniquely relate responses of the subsystem (server) to requests of the CMS (client). The request_id is set by the client. It is the responsibility of the client to specify a system-wide unique request_id (e.g. based on a combination of client id and a sequence number / time of request). Here it indicates that CMS as client should specify request_id. But in section 7.7.5.3 Provide_Subsystem_Identification, it documents that it should be the subsystem to initiate the communication to CMS, which implies subsystem will need to specify request_id required in receive_sub_identification_data_type before sending it to CMS.

There are track_priority_type typedefs defined in both the Track_Reporting and Tracking_Control Domain Model packages.