Overview

Introduction to NOS

The New Observing Strategies (NOS) initiative within the NASA Earth Science Technology Office Advanced Information Systems Technology program envisions future Earth science missions with distributed sensors (nodes) interconnected by a communications fabric that enables dynamic and intelligent operations. Some NOS concepts resemble systems-of-systems or collaborative systems where operational authority is distributed among multiple systems, necessitating new methods for systems engineering and design to cope with more decentralized control over constituent systems.

NOS-T Architecture

NOS-T is best suited for conceptual, systems-level design of NOS components and operational concepts. The system architecture follows a loosely-coupled event-driven architecture (EDA) where member nodes communicate through events in the form of notification messages sent over a network.

Key characteristics of the NOS-T architecture:

Flexible Node Types: Nodes can be software applications, simulation models, science databases, or hardware
Enhanced Scalability: The EDA provides scalability and reliability by using consistent event-handling functions
Modular Design: Participants can join and leave experiments without reconfiguring the testbed
Security: Maintains protection of proprietary software and data while enabling cross-organizational tests

Event Broker Infrastructure

The NOS-T architecture relies on a centralized infrastructure component called an event broker (or message broker) to exchange event notifications between applications. A broker simplifies communication by requiring each application to connect only to the broker, rather than directly to every other application.

NOS-T adopts RabbitMQ, an open-source message broker implementing the Advanced Message Queuing Protocol (AMQP). RabbitMQ uses a publish-subscribe messaging pattern with:

Publishers: Applications that produce events
Subscribers: Applications that consume events
Topics: Categories for event types that applications can publish to or subscribe to

        ---
config:
theme: redux
---
flowchart LR
subgraph User_Apps["User Apps"]
   direction TB
      UserApp1["User App 1"]
      UserApp2["User App 2"]
      UserApp3["User App 3"]
end
   UserApp1 <-. Publish/Subscribe .-> Network["Network"]
   UserApp2 <-. Publish/Subscribe .-> Network
   UserApp3 <-. Publish/Subscribe .-> Network
   Network -- Publish --> EventBroker["Event Broker<br>(AMQP Protocol)"]
   EventBroker -. Subscribe .-> Network
   UserApp1:::red
   UserApp2:::blue
   UserApp3:::green
   Network:::gray
   EventBroker:::darkorange1
   classDef red fill:#ff0000,stroke:#000000,stroke-width:2px
   classDef blue fill:dodgerblue,stroke:#000000,stroke-width:2px
   classDef green fill:#00ff00,stroke:#000000,stroke-width:2px
   classDef gray fill:#808080,stroke:#000000,stroke-width:2px
   classDef darkorange1 fill:#ff8c00,stroke:#000000,stroke-width:2px

System Components

NOS-T consists of two top-level system components:

User System (tailored to each test case):
- Consists of user applications developed by users
- Applications run on separate hosts controlled by each user
- Can model entire observing systems or individual components (sensors, communication links, algorithms, etc.)
- Must meet basic NOS-T interface requirements for orchestration
NOS-T System (fixed for all test cases):
- Managed by an NOS-T operator
- Includes the event broker infrastructure
- Contains a manager application that orchestrates test runs
- Ensures proper application synchronization, topic configuration, and consistent message structure

        ---
config:
theme: redux
---
flowchart LR
subgraph cluster0["User System"]
   direction TB
      PI1["NOS PI"]
      PI2["NOS PI"]
      PI3["NOS PI"]
      UserApp1["User Apps"]
      UserApp2["User Apps"]
      UserApp3["User Apps"]
end
subgraph cluster2["NOS-T Operator"]
      EventBroker["Broker<br>(AMQP)"]
      ManagerApplication["Manager"]
      Monitor["Monitor"]
end
subgraph cluster1["NOS-T System"]
   direction TB
      NOSTInfrastructure["NOS-T Infrastructure"]
      cluster2
end
   PI1 --> UserApp1
   PI2 --> UserApp2
   PI3 --> UserApp3
   UserApp1 --> NOSTInfrastructure
   UserApp2 --> NOSTInfrastructure
   UserApp3 --> NOSTInfrastructure
   NOSTInfrastructure --> EventBroker & ManagerApplication & Monitor
   TestCase["NOS Test Case"] --> PI1 & PI2 & PI3
   PI1:::red
   PI2:::blue
   PI3:::green
   UserApp1:::red
   UserApp2:::blue
   UserApp3:::green
   NOSTInfrastructure:::orange
   TestCase:::oval
   classDef red fill:#ff0000,stroke:#000000,stroke-width:2px
   classDef blue fill:dodgerblue,stroke:#000000,stroke-width:2px
   classDef green fill:#00ff00,stroke:#000000,stroke-width:2px
   classDef orange fill:orange,stroke:#333,stroke-width:2px
   classDef oval shape:oval,fill:lightgrey,stroke:#333,stroke-width:2px

%% Increase the line width of all arrows and change color to black
linkStyle default stroke-width:3px, stroke:black;

Development Tools

To aid in application development, the open-source[*] NOS-T tools library provides templates for implementing basic NOS-T functionality:

Manager application template: Orchestrates test execution
Network Time Protocol (NTP) capabilities: Synchronizes applications across distributed systems
Observer templates: For implementing sensor applications
Observable templates: For science applications
Publisher templates: For regular messaging (e.g., “heartbeat” messages)
Broker connection utilities: For connecting to the message broker

../_images/NTP_request.png — Network Time Protocol (NTP) Round Trip Time Delay

Language Compatibility

While the NOS-T tools and most example applications are coded in Python, the system supports multiple programming languages:

Any language with RabbitMQ interface libraries can be used
Supported protocols include AMQP and MQTT
Examples of compatible platforms:
- JavaScript (used in the “scoreboard” geospatial visualization)
- MATLAB (via available RabbitMQ libraries)

Applications in a test suite can use different programming languages as long as they maintain a common message structure.