← Reports Index
🌍 Technical Reference ⚡ OpenAMI Spec 🏭 IHM-4000 / 5000

OpenAMI Technical Reference Design:
Interoperable Smart Metering,
Wi-SUN Mesh & Grid Code Audits

A publication-grade technical blueprint for the OpenAMI smart-metering framework. Synthesizing physical hardware configurations, self-healing mesh radio downlinks, satellite backhaul uplinks, the 7 core communication use cases, 7-layer OSI & 5-layer SGAM mappings, and Type B earth-leakage life-safety thresholds for high-penetration solar grids.

ARMv7
Linux 4.1.15
Wi-SUN
400m Hop Limit
6 mA DC
Life-Safety Limit
Type B
RCM Protection
SGAM
Interoperable
Section 01

INHEMETER Customization & Physical Hardware Context

Smart metering systems in emerging markets fail when utilities treat them as standard consumer commodities. Real-world deployment requires adaptive, regional customizations matching specific localized electrical, environmental, and security requirements.

📱
The Non-Commodity Philosophy

Unlike standard consumer products (such as the iPhone), INHEMETER does not design a static "standard product." Rather, they utilize an adaptive architecture customized specifically for each market's project guidelines. Features are continuously evolved on a project-by-project basis, reflecting changes in regional regulations, utility objectives, and localized grids.

⚠️
Legacy Obsoleteness

Reusing old equipment models (such as older legacy variants designed for the Nigerian market) is highly discouraged for modern integration testing. Because smart grids introduce new security parameters, billing profiles, and radio environments, newer products (e.g. latest IHM-5000 and IHM-4000 concentrators) are critical to support current requirements and standard compliance.

🏭
Physical Hardware Profile

Gleaned from diagnostic audits, the physical Model IHM-4000 Data Concentrator Unit (DCU) features an industrial ARMv7 processor, NAND-based storage running a synchronized customized Linux kernel (4.1.15) with UBIFS filesystems, and dedicated local startup work daemons running out of temporal partitions.

🔧
Physical Hardware Specifications (Model IHM-4000 DCU)
  • CPU: ARMv7 Processor (Cortex-A core), system architecture armv7l, running with a 24MHz clocksource (resolution 41ns).
  • Memory: 256MB DDR RAM (with approximately 215MB available after kernel reservation).
  • Kernel Environment: Linux Kernel version 4.1.15 #27 SMP PREEMPT (built via Linaro GCC 4.9).
  • Storage & Partitioning: 256MB SLC NAND Flash (AMD/Spansion S34ML02G2 chip) running UBIFS (Unsorted Block Image File System). MTD partitions include:
    • ubi0:rootfs: Mounted read-only (R/O) on / (58.7M total, 11.4M free) for high durability.
    • ubi1_0:opt: Mounted read-write (R/W) on /opt (134.7M total, 123.0M free) for programs and configurations.
  • Networking Interfaces: Built-in eth0 (Freescale FEC Ethernet, connected at 100Mbps Full Duplex) and Realtek RTL8188EU USB Wi-Fi adapter (initialized with the 8188eu module).
  • Cellular Uplink: Dual SIM high-reliability automatic switching with 4G/3G/2G automatic network drop adaptation.
  • Startup Daemons: Booting sequence is governed by /home/startup script, which duplicates operational files to /tmp, unpacks update archives (update.tar.gz), and executes a local multi-threaded binary daemon ./daemon out of the RAM-based /tmp/work/ partition to maximize write endurance of NAND flash.
Section 02

Hybrid Network Topology: Downlink Mesh & Uplink Backhaul

Rural mini-grids represent a massive geographical and demographic diversity. The network architecture must bridge localized, high-density household clusters to remote central servers over long distances and thick vegetation.

📶
Wi-SUN RF Downlink Mesh

The preferred downlink communication between the HES/DCU and smart meters is a Wireless Smart Utility Network (Wi-SUN) mesh. Based on IEEE 802.15.4g and sub-GHz frequencies, it provides high penetrative power and low power consumption compared to standard Wi-Fi, making it ideal for rural density profiles.

🔄
Self-Healing Node Relaying

Wi-SUN networks use self-healing node mesh relaying. The maximum direct point-to-point equipment distance is capped at 400 meters. However, intermediate meters act as relays: if Meter A is 600m away from the DCU, it automatically forwards its packet to Meter B (300m away), which in turn relays the data to the DCU.

🛰️
Satellite & Cellular Uplink

The preferred uplink backhaul (DCU-to-HES) is structured dynamically. High-reliability Satellite backhaul is used for remote, off-grid locations where cellular systems are absent. However, the system is designed to dynamically drop back and utilize Cellular backhaul (4G/3G/2G) where terrestrial signals exist.

💡
Relay Topography Illustration
In typical rural SSA or South Asia villages, households are scattered along agricultural buffers: DCU Concentrator Base Node 300 m Smart Meter B Mesh Relay Node 300 m Smart Meter A Edge Endpoint Total relay path: 600 m — beyond single-hop 400 m limit This self-forming multi-hop routing bypasses vegetation blocks and topographic elevations without requiring expensive, high-altitude masts at each household.
Section 03

The 7 Core AMI Use Cases & Communication Flows

A functional interoperable Advanced Metering Infrastructure (AMI) relies on standardizing the execution sequence of core transactions between the Head-End System (HES), the DCU, and the edge smart meters.

Use Case Name Trigger & Frequency Communication Sequence & Protocols Data Payload & Objects
I Meter Automatic Registration Meter installation or power recovery. Meter scans for DCU beacons -> performs network sync -> initiates connection -> mutual cryptographic authentication (DLMS Security Suite 0/1 PKI exchange) -> DCU registers ID with HES database. Meter Serial Number, MAC, cryptographic public keys, hardware revision profile.
II On-Demand Energy Reading Utility operator request (via HES WebUI). Operator triggers request -> HES sends pull command via MQTT to DCU -> DCU sends DLMS GET-REQUEST over Wi-SUN -> Meter responds -> DCU returns JSON payload to HES. Active & Reactive registers, cumulative active energy (kWh), instantaneous voltage (V), current (A), instantaneous active power (kW), and maximum demand.
III On-Demand Profile Reading Scheduled audits or operator triggers. HES queries specific date/time block -> DLMS GET-BY-RANGE sent to target meter -> Meter extracts logged data from internal memory -> streams packet back via Wi-SUN -> HES stores in MDMS database. Load Profile (30-60 min intervals: voltage, current, active power), Daily Billing Profile (historical daily kWh), and Monthly billing profile.
IV Periodical Push of Data Autonomous scheduled (e.g. daily at 00:00). Meter autonomously packages cumulative load profiles -> initiates Wi-SUN push to DCU -> DCU collects and buffers neighborhood metrics -> uploads aggregated, compressed bundle to HES via Satellite/Cellular. Aggregated 24-hour interval load profiles, cumulative reactive/active energy indexes, and tampered event log registries.
V Remote Token Delivery Consumer prepayment purchase. Payment gateway notifies HES -> HES generates encrypted credit token -> sends OTA via MQTT/Wi-SUN -> Meter decodes token, updates internal credit register, and validates transaction. STS (Standard Transfer Specification) 20-digit token or custom encrypted credit injection payload containing transaction serial.
VI Clock Synchronization Daily or drift-triggered (drift > 2 seconds). DCU disciplines local clock using GPS/PTP PPS -> HES matches network time -> DCU broadcasts time-sync command to all Wi-SUN meters using DLMS clock object -> Meters correct internal RTC. Universal Coordinated Time (UTC) timestamp, local time zone shift, and leap-second parameters.
VII OTA Firmware Upgrade Ad-hoc utility system upgrades. HES uploads firmware image to DCU -> HES triggers broadcast upgrade -> DCU streams firmware blocks via Wi-SUN multicast -> Meters write to backup flash partition -> perform checksum verify -> swap partition and boot. Compressed binary image, block metadata, MD5/SHA256 signature verification code.
Section 04

Architectural Alignment: 7-Layer OSI & 5-Layer SGAM

Interoperability requires a structured mapping of technologies. Based on the Group of Experts on Sustainable Energy UNECE (2025) Interoperability Guidelines, we align the OpenAMI system across the 7 layers of the OSI model and the 5 layers of the Smart Grid Architecture Model (SGAM).

OSI Layer SGAM Layer UNECE Interoperability Dimension OpenAMI Technical Mapping / Protocol Description & Implementation Nuance
7. Application Business / Function Organizational / Informational DLMS/COSEM (IEC 62056), MQTT, JSON, HTTP/REST Defines the business rules and use cases. DLMS/COSEM models electrical parameters as logical objects (OBIS codes). HES and utility applications exchange metrics via JSON payloads over MQTT to coordinate billing.
6. Presentation Information Informational (Semantics) Common Information Model (CIM - IEC 61970/61968), STS, A-XDR Ensures that exchanged information has a uniform, semantic meaning. XDR (External Data Representation) encodes DLMS messages. STS tokens translate securely across manufacturer platforms.
5. Session Information / Function Technical (Syntax) COSEM Association System (COSEM-AS), TLS 1.3 Establishes, maintains, and secures communication sessions. Handles mutual cryptographic authentication and manages DLMS Security Suite 0/1 keys for active connection periods.
4. Transport Communication Technical (Syntax) TCP / UDP Provides end-to-end transport reliability. TCP is utilized for secure HES-to-DCU exchanges, while UDP handles low-overhead multicasts over mesh networks.
3. Network Communication Technical (Syntax) IPv6, 6LoWPAN, IPv4 Manages physical node addressing and packet routing. 6LoWPAN compresses IPv6 headers to enable internet-protocol packets to traverse narrow sub-GHz mesh bands.
2. Data Link Communication / Component Technical (Basic Connectivity) IEEE 802.15.4 MAC (Wi-SUN profile), IEEE 802.3 Ethernet MAC Controls logical link management and channel access. Wi-SUN profile specifies frequency-hopping spread spectrum (FHSS) mechanisms to mitigate noise in rural channels.
1. Physical Component Technical (Basic Connectivity) IEEE 802.15.4g PHY, 100BASE-TX Ethernet, 4G LTE RF The actual transmission of raw bits. Includes license-free sub-GHz radio bands (915MHz/868MHz) for Wi-SUN mesh, 4G cellular antennas, and copper Ethernet cabling on the DCU.
⚖️
UNECE Interoperability Dimensions Checklist
Our architectural layout satisfies the three-pronged UNECE context:
  • Technical: Managed via standardized communication interfaces (Wi-SUN, 6LoWPAN, TCP/IP, and local serial paths).
  • Informational: Standardized semantic modeling of utility metrics via DLMS/COSEM object registries (OBIS objects) and IEC CIM schemas.
  • Organizational: Connects grid physics directly to billing processes, regulatory compliance, and community equity strategies.
Section 05

RFP Technical Specifications & Life-Safety Protection

Traditional over-current protection is completely blind to hazardous earth-leakage currents. When grids integrate Distributed Energy Resources (DERs), they introduce complex electrical waveforms that demand a revolutionary approach to grid and human safety.

⚡
Life-Safety Current Thresholds

Human heart fibrillation and tissue burning occur at extremely low electrical leakages. OpenAMI establishes mandatory autonomous detection limits of 6 mA smooth DC and 30 mA AC current leakages. Individual tenant lines must isolate within milliseconds of crossing these safety lines.

🛡️
Type B RCM/RCD Requirement

Grids incorporating distributed solar PV or battery storage introduce complex DC components and pulsating waveforms. Standard Type A or Type AC RCDs are blind to smooth DC currents. Under high-penetration DER scenarios, Type B Residual Current Monitors (RCM) or Type B RCDs are mandatory to ensure protection.

🔄
Isolation & Secure Restoration

Each tenant line must incorporate a Solid-State Relay (SSR) or contactor for rapid autonomous isolation. Once a fault is cleared, the system allows remote-controlled electricity restoration, but internal verification logic must block remote re-energization if the leakage condition persists.

⚠️
Grid Standards Compliance Mapping
OpenAMI is engineered to fully satisfy international and national grid codes:
  • IEEE 1547-2018 Compatibility: Ensures interoperable interconnection of Distributed Energy Resources (DERs) with the grid, providing criteria for frequency and voltage ride-through, reactive power control, and dynamic support.
  • Kenya Electricity Grid Code Standards:
    • Frequency Ride-Through: All system equipment must remain in active service within the power system frequency range of 45.0 Hz to 52.0 Hz, unless directed otherwise by the System Operator for load shedding.
    • Voltage Tolerances: Steady-state operating voltages at grid-connection points must be maintained within 90% to 110% of the nominal voltage.
Earth Leakage Isolation Condition I_leakage >= I_threshold (6mA DC | 30mA AC) ==> SSR_Trigger = TRUE (T_isolation <= 40ms)
Where:
* I_leakage: Real-time vector sum of active and neutral phase currents. Any non-zero sum represents an active earth path.
* Type B RCM: Continually processes raw wave signals via DSP to extract high-frequency harmonics, pulsating DC, and smooth DC leakage vectors.
* Safety Override: Local microcontroller triggers the SSR directly, bypassing WAN latency to prevent fatal shocks.

🔗 Related Reports in This Suite