pynimomodem 0.4.16

A Python implementation of Viasat's NIMO modem interface project.

pynimomodem

A Python implementation of the Viasat NIMO modem interface for satellite IoT.

NIMO stands for Non-IP Modem Orbcomm waveform and represents a family of low cost satellite data modems that use network protocols developed by ORBCOMM including IsatData Pro and its successor, OGx.

These ORBCOMM protocols can operate over the Viasat L-band global network in cooperation with a varietry of authorized Viasat IoT service partners, and are intended for event-based remote data collection and device control.

Example NIMO modems available:

• ORBCOMM ST2100
• Quectel CC200A-LB
• uBlox UBX-S52

Additional Information

• API Documentation

[!NOTE] Obsoletes/replaces the Inmarsat idpmodem project, when combined with the pynimcodec library.

Installation

Example using pip, on a Linux-based platform including PySerial dependency:

pip install 'pynimomodem'

Background

Overview

IsatData Pro (IDP)is a store-and-forward satellite messaging technology with flexible message sizes:

• up to 6400 bytes Mobile-Originated (aka MO, From-Terminal, Return)
• up to 10000 bytes Mobile-Terminated (aka MT, To-Terminal, Forward)

Messages are sent to or collected from a Mobile using its globally unique Mobile ID, transacted through a Mailbox that provides authentication, encryption and data segregation for cloud-based or enterprise client applications via a REST Messaging API.

Data sources and controls in the field are interfaced to a modem using a serial interface with AT commands to send and receive messages, check network status, and optionally use the built-in Global Navigation Satellite System (GNSS) receiver to determine location-based information.

The first byte of the message is referred to as the Service Identification Number (SIN) where values below 16 are reserved for system use. SIN is intended to capture the concept of embedded microservices used by an application.

The second byte of the message can optionally be defined as the Message Identifier Number (MIN) intended to support remote operations within each embedded microservice with defined binary formatting. The MIN concept also supports the optional Message Definition File feature allowing an XML file to be applied which presents a JSON-tagged message structure on the network API.

Modem Concept of Operation

1. Upon power-up or reset, the modem first acquires its location using Global Navigation Satellite Systems (GNSS).
2. After getting its location, the modem tunes to the correct frequency, then registers on the network. Once registered it can communicate on the network.
3. MO messages are submitted by a microcontroller or IoT Edge device, which then must monitor progress until the message is complete (either delivered or timed out/failed due to blockage). Completed messages must be cleared from the modem transmit queue by querying state(s) either periodically or when prompted by the modem's event notification pin if configured.
4. MT messages that arrive are stored in the receive queue and the Edge device queries for New MT messages periodically or when prompted by the modem's event notification pin if configured.
5. Network acquisition status can also be queried using AT commands.
6. If the modem cannot find the target frequency it begins to search for other frequencies from a configuration map in its non-volatile memory. It will cycle through beam acquisition attempts for a period of time before falling back to a globally-accessible Bulletin Board frequency where it may need to download a new network configuration before re-attempting. Bulletin board downloads typically take less than 15 minutes but can take longer in low signal or high interference locations. A modem should not be powered off during Bulletin Board download.
7. Prolonged obstruction of satellite signal will put the modem into blockage state from which it will automatically try to recover based on an algorithm influenced by its power mode setting.