BOAC has the answer, Data is sent via VHF/UHF and HF link.
The 2 providers are ARINC (American company) and SITA (Asian company) but they share some resources to give almost global coverage. If SATCOM is not used by the airline, then coverage is more limited.
Data tends to be periodic unless requested for increased frequency on demand. Data is also send data burst so very short transmission time required. All manner of data can be sent from flight plan info, company info air traffic info in the form of preset messages or an open text based format. Data for aircraft performance and engine performance is virtually continual and direct to company engineering, manufactures etc.