HYBRID Solution

ADDAX AMI makes use of different solutions for last mile communications (between Data Concentrator and e-meters).The most spread solutions being based on PLC technologies like PRIME or G3-PLC, there are many use cases for wireless solutions like RF mesh. To get better coverage and combine the advantages of both PLC and RF technologies, a hybrid solution is proposed.

The top layer in the communication profile is DLMS/COSEM application layer. It provides services to establish a logical connection between the client and the server(s). It also provides the xDLMS messaging services to access attributes and methods of the COSEM interface objects. The e-meter acts as a server from which client applications retrieve data. The DC acts as a DLMS client and queries the COSEM objects exposed by e-meters.

The lower layers are based on G3-PLC specification. The G3-PLC data link layer is adapted for hybrid network.

The crucial part in this stack is the 6LoWPAN adaptation layer. The main goal of this layer is to optimize the transmission of IPv6 packets over low-power and noisy networks. The 6LoWPAN layer solves following tasks:

  • Header compression.
    The 40-byte IPv6 and 8-byte UDP headers are compressed by assuming the usage of common fields. Header fields are elided when they can be derived from the link layer.
  • Fragmentation and reassembly.
    The PLC and RF channels framing does not match the MTU of IPv6, which is 1280 bytes, that makes the adaptation layer to take care of fragmentation and reassembly.

  • Stateless auto configuration.
    Stateless auto configuration is the process where devices inside the 6LoWPAN network automatically generate their own IPv6 address. There are methods to avoid the case where two devices get the same address (duplicate address detection).


Architecture
A typical 6LoWPAN network has two device types – routers and hosts. Routers can route data destined to other nodes in the 6LoWPAN network. Hosts are just end devices that are not able to route data to other devices in the network. The host may be a battery powered device that wakes up periodically to check its router for data. As the e-meters are always powered devices, for stable network configuration, all devices in ADDAX solution act as routers. The DC also acts as a border (edge) router, providing data exchange between the 6LoWPAN network and the backbone (via Ethernet or 3GPP).

The DC is responsible not only of translating (or routing) the requests coming from HES to the 6LoWPAN network, it also provides 6LoWPAN network generation and maintenance, and manages the local data exchange between devices inside the 6LoWPAN network.

Data exchange
Every meter has PLC or RF, or PLC+RF connectivity to other meters. The route is built hop-to-hop, selecting between the best channel. The channel selection is dynamically adjusted based on media status.
After a new e-meter is discovered in the network, the DC application first queries identification and configuration information then starts performing the tasks for data collection.

Alarm handling
The meter may send asynchronous messages as an alarm occurs. The message is transmitted as an Event Notification to DC, then forwarded to HES or registered in DC, depending on alarm severity and configuration.

Security features
Security features are implemented at several layers.
AES-128 based encryption and authentication, defined in G3-PLC specification, is used at data link layer.
The DC also uses encryption/decryption of all input and output information at application layer. Meter-DC security architecture is based on the DLMS UA 1000-2 Ed.7.0 concepts.
AES-GCM-128 (Galois/Counter Mode with AES-128) Security Suite ID: 0 is implemented for data encryption and authentication and key transport methods.