The German Ministry of transport (BMDV) has ask DFS to support the the distribution of the ICAO EUR OPS BULLETIN attached.
The purpose of the European Operations Bulletin 2021_001 is to promulgate principles and best practices in case of loss of air-ground communication. It aims to raise awareness amongst aircraft operators, flight crews, air traffic controllers and military stakeholders with a special emphasis on the recovery of communication as well as the required timely actions by all involved entities. The ICAO EUR OPS BULLETIN also describes measures and possibilities to shorten the phase of uncertainty in case of loss of air-ground communication.
You can find the document here.