Table X-2: ITU-T X Series Recommendation Groups Recommendation Group Description 100 Data communications and networks 200 Open systems interconnection 300 Data transmission services between public networks, and between public net- works and other networks 400 Message Handling Services and Systems (MHS) 500 Open Systems Interconnection (OSI): Directory services 600 Open Systems Interconnection (OSI): Multi-peer communications 700 Open Systems Interconnection (OSI): Systems Management 800 Open Systems Interconnection (OSI): Security 900 Open Distributed Processing |