Protocol Fundamentals
The TCP Streaming Protocol serves as the foundation for ultra-low latency, high-volume data exchange within the Subject Interface ecosystem. This section covers the core protocol specifications including version management, data encoding, and security options.
Protocol Overview
The TCP Streaming Protocol provides continuous asynchronous bidirectional stream of datagrams between connected parties. Unlike traditional request-response patterns, this protocol maintains persistent connections optimized for real-time data exchange scenarios common in transportation systems.
Protocol Flow Overview
Core Protocol Characteristics
| Characteristic |
Description |
| Persistent Connections |
Long-lived TCP connections; eliminates overhead; supports continuous operation; automatic keep-alive |
| Asynchronous Communication |
Independent bidirectional flow; no request-response coupling; parallel processing; queue-based transmission |
| Message-Agnostic Design |
Handles any payload type; no inspection/validation; supports binary/text/structured data; single byte type identifier |
| Frame-Based Structure |
Structured frames with integrity checking; fixed header; variable payload; boundary detection |
| Built-in Monitoring |
Connection health monitoring; time sync verification; performance metrics; automatic violation detection |
Protocol Version Management
Current Protocol Version
| Aspect |
Details |
| Version |
0x01 (single-byte identifier) |
| Exchange |
During connection establishment |
| Support |
Only supported version currently |
Version Compatibility
| Aspect |
Details |
| Current Support |
Version 0x01 only |
| Future Versions |
Incremental numbering; backward compatibility evaluation |
| Negotiation |
May be enhanced in future protocols |
Byte Order and Data Encoding
Byte Order
| Aspect |
Details |
| Order |
Big-endian (network byte order) throughout |
| Application |
All multi-byte fields; MSB transmitted first |
| Standards |
Consistent with network protocols; no byte order marks |
Encoding Standards
| Data Type |
Encoding |
Details |
| Text Data |
ASCII |
Tokens, identifiers, disconnect reasons; no null termination; length by frame size |
| Timestamps |
UTC milliseconds since epoch |
8 bytes (64-bit); big-endian integer |
| Numeric Fields |
Big-endian |
Unsigned integers; size as specified; no padding |
| Binary Payloads |
Pass-through |
No encoding; application-specific |
Frame Structure
+------------------+------------------+----------------------+
| Fixed Prefix | Data Size | Datagram Content |
| 0xAA 0xBB | 2 bytes | Variable Size |
| (2 bytes) | (big-endian) | (0-65535 bytes) |
+------------------+------------------+----------------------+
| Component |
Details |
| Fixed Prefix |
0xAA 0xBB - frame synchronization; start of every frame; loss of frame sync terminates connection |
| Data Size |
2 bytes big-endian; 0-65535 range; datagram content size only (excludes Fixed Prefix and Data Size fields) |
| Datagram Content |
Variable size; datagram type byte + data; length must match size field |
Transport Layer Security
Security Mode Options
The protocol supports two security modes:
| Mode |
Description |
Performance |
Use Cases |
| NONE |
Plain TCP without encryption |
Optimal, no overhead |
Isolated networks, development, non-sensitive data, legacy systems |
| TLSv1.2 |
Encrypted using TLS 1.2 |
Additional latency and CPU usage |
Production, public networks, sensitive data, compliance |
TLS Configuration
| Component |
Details |
| TLS Version |
TLS v1.2 exclusively; SSL/TLS v1.0/v1.1 prohibited; TLS v1.3 not supported |
| Cipher Suite |
TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 only; ECDHE key exchange; AES-128-GCM; SHA-256 |
| Authentication |
Standard TLS handshake; no client certificates; session auth via tokens |
Connection Establishment
All communication patterns follow a consistent connection establishment sequence regardless of session type or protocol variant.
Connection Establishment Sequence
| Step |
Process |
| 1. API Session Creation |
Create session via JSON-REST API; specify type/protocol; receive connection details and token |
| 2. TCP Connection |
Establish TCP to assigned Streaming Node; use host:port from session details |
| 3. Protocol Version Exchange |
Client sends version 0x01; service validates and responds; connection closed if mismatch |
| 4. Token Authentication |
Client sends Token datagram; contains session token; service validates against active sessions |
| 5. Operational State |
Enter active streaming; enable bidirectional exchange; begin time sync monitoring |
Connection Requirements
| Category |
Requirements |
| Prerequisites |
Valid session via JSON-REST API; network connectivity; synchronized clock; valid token |
| Protocol Support |
Version 0x01; mandatory datagram types; time sync response; frame parsing/generation |
| Security |
TLS support if enabled; encryption capability; cipher suite support; token security |