The Security Status Request message provides for the ability to request the status of a security. One or more Security Status messages are returned as a result of a Security Status Request message.
The Security Status Request message contains a SubscriptionRequestType <263> field. This tells the counter party what type of request is being made:
0 indicates that the requestor only wants a snapshot or the current status.
1 indicates that the requestor wants a snapshot (the current status) plus updates as the status changes. This is similar to subscribing for information and can be implemented in applications as a subscription mechanism.
2 indicates that the requestor wishes to cancel any pending snapshots or updates in essence making this an unsubscribe operation.
Security Status Request