| C194 | Byte Stream File Transfer (BSFT) |
| C209 | Protocols for X/Open PC Interworking: SMB, Version 2 |
| C303 | ACSE/Presentation Services API (XAP) |
| C305 | Message Store API |
| C315 | OSI-Abstract-Data Manipulation API (XOM), Issue 2 |
| C316 | API to Electronic Mail (X.400), Issue 2 |
| C317 | API to Directory Services (XDS), Issue 2 |
| C408 | Remote Operations Service Element (XAP-ROSE) API |
| C411 | X.25 Programming Interface using XTI (XX25) |
| C415 | FTAM High-level API (XFTAM), Version 2 |
| C438 | Networking Services, Issue 4 |
| C520 | Multiprotocol Transport Networking (XMPTN): Address Mapper |
| C521 | Multiprotocol Transport Networking (XMPTN): Access Node |
| C522 | Multiprotocol Transport Networking (XMPTN): Data Formats |
| C523 | Networking Services, Issue 5 |
| C607 | OSI-Abstract-Data Manipulation API (XOM), Issue 3 |
| C608 | API to Directory Services (XDS), Issue 3 |
| C609 | API to Electronic Mail (X.400), Issue 3 |
| C702 | Protocols for Interworking: XNFS, Version 3W |
| C808 | Networking Services, Issue 5.2 |
| C809 | Resource Reservation Setup Protocol API (RAPI) |
| C810 | Transport Provider Interface (TPI) Version 2 |
| C811 | Data Link Provider Interface (DLPI) Version 2 |