Handling DLMS Push Setup (Class 40) DataNotification APDU with TCP Wrapper on Port 4059

[marcus_vance]

Architecture & Implementation

In modern smart metering deployments, meters autonomously push alarm events and hourly load readings using COSEM Class 40 (Push Setup) and Class 41 (Data Notification), instead of relying on round-robin polling from the Head-End System.

Push APDU Format over TCP Wrapper (Port 4059)

00 01 00 01 00 01 00 28 0F 00 00 00 01 00 00 01 02 02 09 0C 07 EA 08 16 ...

Wrapper Header Analysis (8 bytes)

• 00 01: Protocol Version (0x0001 for DLMS TCP Wrapper)
• 00 01: Source WPort (Meter Logical Client ID)
• 00 01: Destination WPort (HES Receiver Server ID)
• 00 28: PDU Length (40 bytes)
• 0F: APDU Tag -> Data-Notification (Tag 0x0F / 15)

Key Considerations

1. Unsolicited Connection Management: The HES TCP server must maintain asynchronous socket listeners capable of handling thousands of simultaneous incoming TCP connections without blocking.
2. Association Context: Push notifications are often sent without full AARQ authentication handshake. The meter uses predefined ciphering parameters (General-Ciphering 0xDB or General-Signing 0xDF) with Dedicated Encryption Key (DEK).

[sarah_jenkins]

When parsing the push_object_list in Attribute 2 of the Push Setup object, ensure your server dynamically deserializes the structure array. Typical push payload includes:

1. Logical Device Name (0.0.42.0.0.255)
2. Timestamp (0.0.1.0.0.255)
3. Active Energy Import (+A) (1.0.1.8.0.255)
4. Active Power (+P) (1.0.21.7.0.255)

If the meter firmware adds an alarm code into the push list, dynamic schema decoding prevents parsing crashes.

[alex_turner]

For encrypted Push notifications (0xDB tag), the HES receiver must extract the System Title and Invocation Counter from the ciphered APDU header, lookup the corresponding Global Unicast Encryption Key (GUEK) in the HSM / Key Vault, and decrypt using AES-GCM-128.