Define a protocol as an implementable contract
A controller protocol package should let an independent software team build and verify an integration without reverse engineering. A command list alone is insufficient; the package needs transport rules, message framing, a data dictionary, state behavior, errors, examples, timing and version management.
Minimum document set
| Document | Required content | Acceptance question |
|---|---|---|
| Transport profile | Physical/network interface, addressing, session and reconnect behavior | Can a client establish and recover a connection? |
| Message specification | Frame, fields, byte order, length, checksum and examples | Can two teams encode the same bytes? |
| Object/data dictionary | Identifiers, units, ranges, access and update rules | Does every value have one meaning? |
| State model | Operating modes, transitions, command preconditions and priority | Can unsafe or conflicting commands be rejected? |
| Error catalogue | Codes, causes, recovery and operator message | Can support diagnose a failure remotely? |
| Version policy | Protocol version, compatibility and deprecation rules | Can old and new fleets coexist? |
Include real request and response examples
Provide at least one valid example for each command family and examples of invalid length, checksum, authorization, unsupported object and wrong-state requests. Show timestamps, units and endianness explicitly. A packet capture and a human-readable field breakdown should describe the same exchange.
Document timing and connection recovery
State the expected response time, retry rule, keep-alive behavior, maximum outstanding requests, event delivery method and reconnection sequence. Define what happens to queued commands and alarms after a network interruption. These details determine whether the central platform remains predictable on a weak mobile connection.
Ship a test companion
The strongest package includes a controller simulator or test mode, sample client, conformance cases and known-good traces. The supplier and integrator should run the same test IDs during development and final acceptance. Record the controller firmware and protocol revision with every result.
Frequently asked questions
Is an API command list enough for controller integration?
No. A command list does not define framing, units, valid ranges, timing, state preconditions, errors or reconnection behavior. The integrator needs enough detail to encode messages, interpret every response and recover predictably when the controller, network or central platform changes state.
Should a controller protocol include version negotiation?
Yes when multiple firmware generations may share one central system. The connection or capability exchange should identify supported protocol features so the platform can select compatible behavior, reject unsupported commands and avoid assuming that every installed controller has the latest firmware.
What proves that protocol documentation is complete?
Give the specification to a software engineer who did not help create it. If that engineer can implement a client, pass the agreed conformance tests and diagnose deliberate error cases without private explanations, the package is close to being independently usable and supportable.
Related buyer resources
- Traffic Controller Communication Protocols
- Traffic Light Remote Monitoring Guide
- Controller Programming Guide