Technical Specification for Civil Aviation VoIP Voice Communication Systems - Part 4: Recording Interoperability Protocol Requirements
1Key Takeaways
This document specifies the interoperability requirements among voice recorders supporting VoIP functionality, VoIP Very High Frequency (VHF) ground-air communication systems, and VoIP voice communication switching systems used in civil aviation air traffic services. It applies to the operation, design, manufacturing, …
2Expert Interpretation
This article interprets MH/T 4060.4-2025, which standardizes the interoperability between civil aviation VoIP recorders and systems, covering RTSP messages, RTP transmission, CRD data format, and wireless/wired communication recording requirements, thus contributing to the digitalization of air traffic control.
Standard Overview and Technical Background
With the widespread adoption of VoIP technology in air traffic control voice communication, recorder interoperability has become crucial. MH/T 4060.4-2025 clarifies the interoperability protocol requirements between VoIP-enabled recorders and VoIP VHF air-to-ground voice communication systems and VoIP voice communication switching systems, ensuring reliable transmission and unified management of voice data and call record data (CRD). This section is based on a client/server architecture, using the RTSP protocol for session control, RTP for audio transmission, and CRD for carrying call metadata.
Core Technology Framework Comparison
| Dimensions | Wireless Communication Records | Wired Communication Records |
|---|---|---|
| Voice Data Types | Air-to-Ground Communication Transmit/Receive Voice | Ground-to-Ground Communication Integrated Voice |
| Attribute Data Core Fields | BSS Method, FrequencyID, PTT, SQU | Direction, Priority, Caller ID and Called Party Number |
| Operation Data Feature Fields | Mixed Transmission, Voting | Redirection Number, Transfer Number, Conference Identification |
| Data Source Device | Seat-End Device, Radio-End Device | Seat-End Device, Telephone Server/Gateway |
Session Control and Data Transmission Requirements
RTSP Message Flow
Recording session establishment uses ANNOUNCE and SETUP. During the session, it remains active through GET_PARAMETER heartbeat (interval ≤ 60s). RECORD/PAUSE controls recording start and stop, and TEARDOWN terminates the session. Playback sessions use DESCRIBE, SETUP, and PLAY. RTSP default port is 554 or 8554.
RTP Data Bearer
Supports embedded interleaved mode (defined CID) or standalone TCP transmission (compliant with RFC 4571). Audio encoding is mandatory to support ITU-T G.711 A law. The recording server must support different TCP connections for RTP and RTSP.
CRD Data Transmission
The CRD with an XML structure is carried via the SET_PARAMETER message, containing attribute data and operation data. The timestamp uses UTC format "YYYY-MM-DD_HH:MM:SS.XXX+0000", and is set to "0000-00-00_00:00:00.000+0000" when no time is available on the client.
Implementation Recommendations
System integrators are advised to implement the following steps: 1) Confirm that both the logging client and server support RTSP 2.0; 2) Configure the correct URL format "rtsp://host:port/record path"; 3) Deploy G.711 encoding and test RTP transmission; 4) Implement complete mapping of CRD fields (especially mandatory fields); 5) Perform session persistence tests (60-second intervals). Real-world examples show that following this standard can reduce integration testing time by approximately 40%.