TAD Protocol Documentation¶
TAD Protocol Analysis for SINTRAN III
Overview¶
TAD (Terminal Access Device) protocol documentation, analyzing communication protocols used in SINTRAN III systems, particularly X.25 over HDLC encapsulation.
Documents¶
| Document | Purpose | Description |
|---|---|---|
| TAD-Analysis-Summary.md | Overview | Summary of TAD protocol analysis |
| TAD-Protocol-Analysis.md | Protocol Details | Complete protocol analysis |
| TAD-Message-Formats.md | Message Structure | TAD message formats |
| TAD-Protocol-Flows.md | Flow Diagrams | Protocol flow sequences |
| TAD-HDLC-Encapsulation.md | HDLC Layer | How TAD uses HDLC |
| TAD-X25-CUD-Specification.md | X.25 Details | X.25 Call User Data |
| TAD-Evidence-vs-Inference.md | Analysis Notes | What's verified vs. inferred |
Key Topics¶
Protocol Layers¶
┌─────────────────────────┐
│ TAD Application Layer │ - Terminal access
├─────────────────────────┤
│ X.25 Packet Layer │ - Virtual circuits
├─────────────────────────┤
│ HDLC Link Layer │ - Frame transmission
├─────────────────────────┤
│ Physical Layer │ - Serial communication
└─────────────────────────┘
HDLC Encapsulation¶
TAD uses HDLC for reliable frame transmission: - Frame structure with FCS (Frame Check Sequence) - Sequence numbers for reliability - Flow control (RR, RNR) - Error recovery (REJ frames)
See: TAD-HDLC-Encapsulation.md
X.25 Integration¶
TAD implements X.25 packet layer: - Virtual circuits - Call setup/teardown - Call User Data (CUD) fields - Packet types (CALL REQUEST, CALL ACCEPTED, DATA, CLEAR)
See: TAD-X25-CUD-Specification.md
Message Formats¶
TAD-specific message structures: - Connection requests - Data transfers - Acknowledgments - Control messages
Quick Start¶
- Start with: TAD-Analysis-Summary.md - Get overview
- Understand layers: TAD-HDLC-Encapsulation.md - How HDLC is used
- Detailed analysis: TAD-Protocol-Analysis.md - Complete protocol
- Message structure: TAD-Message-Formats.md - Data formats
Related Documentation¶
HDLC Layer¶
- ../Devices/HDLC/ - HDLC hardware and driver
- ../Devices/HDLC/learning/03-Hardware-Overview.md - COM5025 controller
Protocol Implementation¶
- ../Devices/HDLC/reference/Protocol-Reference.md - HDLC/LAPB protocols
OS Integration¶
- ../OS/18-DEVICE-DRIVER-FRAMEWORK.md - Device drivers
- ../OS/15-DISK-IO-SUBSYSTEM.md - I/O subsystem
Evidence-Based Analysis¶
TAD documentation is based on: - ✅ Packet captures and traces - ✅ Protocol behavior observation - ✅ Message format analysis - ⚠️ Some specifications inferred from behavior
See: TAD-Evidence-vs-Inference.md for what's verified vs. inferred.
Use Cases¶
For Protocol Analysis¶
- Understanding TAD communication
- Reverse engineering protocol
- Implementing TAD clients/servers
For Emulation¶
- Emulating TAD endpoints
- Testing protocol implementations
- Debugging communication issues
For Historical Preservation¶
- Documenting legacy protocols
- Understanding SINTRAN networking
- Educational purposes
Version History¶
| Date | Version | Changes |
|---|---|---|
| 2025-10-17 | 1.0 | Initial TAD protocol documentation structure |
Parent: ../README.md - SINTRAN Documentation