The MTP3 software aids to data flow control are based on layer 2 inputs. When a link is congested, as indicated by a flow control indication from layer 2, MTP3 starts queuing traffic meant for that link. MTP3 also maintains thresholds for the queued messages. For each threshold, MTP3 performs one of the following actions:
- Send a transfer controlled message at an STP in response to a data received from the adjacent point code for routing to a remote point code
- Send a status indication to its service users at an SP in response to a data transfer request received from user
- Drop the data if the priority with which the data to be sent is lower than the current congestion threshold (only for national networks with multiple congestion priorities).
The above actions allow the data originating entities to take appropriate actions in case of heavy loads and also prevents system crashes due to lack of resources.