1. Introduction

1.1. What is a Unet?

The material in this section is also available as a short video .

The Internet has changed our lives beyond anyone’s wildest expectations, fundamentally changing the way we interact, the way we learn, and the way we work. More recently, devices have started connecting to the Internet, and communicating with other devices. This Internet of Things (IoT) has the potential to have a huge impact on the way we understand our environment, and interact with it. Given that most of our planet’s surface is covered with water, would it then not make sense that at least some of these devices might be in water? Some devices might measure ocean temperature and acidification to give us a handle on climate change, while other devices might monitor fresh water quality to ensure safe drinking water for us. Autonomous underwater vehicles (AUVs) may patrol our coastal waters looking for intruders, or tracking down sources of pollution or nutients that encourage harmful algal blooms. Be it static sensors or mobile AUVs, we need a way to connect them into a network that we can communicate and interact with. The Unet project strives to develop technologies that allow us to do precisely this. In this handbook, we explore how to use UnetStack3 , a technology developed as part of the Unet project, to build communication networks that extend underwater.

Most wireless technologies today rely on electromagnetic waves that don’t propagate well underwater. Therefore, to extend IoT underwater, we typically need a mix of technologies — cabled links where possible, otherwise radio frequency (RF) wireless links above water, and mid-to-long range wireless acoustic or short-range wireless optical links underwater. A "Unet" network (which we will simply call Unet henceforth) consists of several nodes (underwater, on the surface of water, or above water) that communicate over various types of links, as shown in Figure 1 .

Figure 1. A typical Unet consists of static and mobile nodes, both underwater and in air, with bidirectional acoustic, optical, electromagnetic and cabled links connecting pairs of nodes.

A Unet consists of many Unet nodes (e.g. underwater sensor nodes, Autonomous Underwater Vehicles (AUVs), gateway buoys, ground stations, boats/ships) that generate, consume or relay data over a variety of links:

  • Acoustic links are typically used for mid-to-long range communication underwater. These links usually offer low data rates and long propagation delay due to the slow speed of sound in water (as compared to EM waves).

  • Optical links are used for short range high data rate communications in water.

  • RF links are used for mid-range communication in air.

  • GSM links are used for near-shore connectivity through air.

  • Satellite links are used for nodes that are far out at sea, and cannot be reached through GSM or RF links. These links usually are expensive and offer relatively low data rates.

  • Wired links (Ethernet, serial, fiber optic) are used for long-term static deployments underwater, or over short distances where cabling is feasible.

  • In some cases, nodes are retreived and data is transferred from them to other nodes in the network on a regular basis, using physical media (e.g. USB drives, SD cards, etc). These links usually offer very high data rates, but are only available intermittently. We dub such links as Sneakernet links .

A link is simply a logical connection between two nodes, often provided by equipping both the nodes with modems. We summarize various types of links in Table 1 .

1.2. UnetStack

The material in this section is also available as a short video .

Unet nodes are equipped with one or more network interfaces that allow communication over some of these links. For example, to communicate over an underwater acoustic link, we need an underwater acoustic modem . For an underwater optical link, we use an underwater optical modem . Most RF, GSM, satellite or wired links would be accessed over a standard TCP/IP network interface. In all cases, each Unet node would run the UnetStack software that allows us to effectively communicate over all of these types of links using a common Application Programming Interface (API). UnetStack API bindings are available for several languages including Java, Groovy, Python, Julia, C, Javascript, etc.

UnetStack has a several components, as depicted in Figure 2 :

  • The Unet framework provides core services, messages, agents and APIs needed by UnetStack.

  • The Unet basic stack is a collection of agents providing services and functionality required by typical Unets. These agents, together with the Unet framework, are sufficient to build fully functional Unets.

  • The Unet premium stack is a collection of agents providing advanced functionality and/or higher performance. Many of the premium agents provide similar services as the basic ones, but used advanced techniques for better performance and bandwidth efficiency.

  • The Unet simulator is able to simulate Unets with many nodes on a single computer. It can run in realtime simulation mode for interactive testing of agents and protocols, working to provide the user with the same user experience as in a real Unet. It can also be run in discrete event simulation mode to perform a large number of simulations in a short time, allowing Monte Carlo testing and performance evaluation of network protocols.

  • The Unet IDE is an integrated development environment (IDE) for developers to develop, simulate and test Unet agents and protocols. It also enables the developer to visualize and interact with simulated networks.

  • Unet audio is a soundcard-based realtime software defined open architecture acoustic modem (SDOAM) that runs on desktop, laptop or single-board computers, and can be used to build and test simple Unets. It is a great tool for not only developing and testing network protocols, but also developing acoustic communication techniques.

The components are packaged into various editions . The community edition is downloadable free of charge for educational and research purposes. It has all the components required to develop, simulate, test and deploy Unets. The commercial and OEM editions package offer advanced functionality, better performance and tighter integration with vendor-specific hardware.

Figure 2. An overview of UnetStack components.

In the next few chapters, we will learn how to use UnetStack and how to customize it to meet our networking needs. In some cases, it may be necessary to prototype and simulate a Unet before it is actually implemented. We will also learn how to do that using the Unet simulator.

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