Embedded Networking#

While the term wireless network may technically be used to refer to any type of network that functions without the need for interconnecting wires, the term most commonly refers to a telecommunications network, such as a computer network. Wireless telecommunications networks are generally implemented with radios for the carrier or physical layer of the network.

One type of wireless network is a wireless local area network or LAN. It uses radios instead of wires to transmit data back and forth between computers on the same network. The wireless LAN has become commonplace at hotels, coffee shops, and other public places. The wireless personal area network (WPAN) takes this technology into a new area where the distances required between network devices is relatively small and data throughput is low.

In the control world, embedded systems have become commonplace for operating equipment using local special-purpose computer hardware. Wired networks of such devices are now common in manufacturing environments and other application areas. Like all computer networks, the interconnecting cable systems and supporting hardware are messy, costly, and sometimes difficult to install. To overcome these problems, wireless networking of embedded systems (that is, embedded networking) has become commonplace. However, the costly embedded networking solutions have only been justifiable in high-end applications where the costs are a secondary consideration. Low-cost applications with low data rate communications requirements did not have a good standardized solution until the IEEE 802.15.4 standard for wireless personal area PHY and MAC layers was released in 2003.

Note: The current version as of this writing is the IEEE 802.15.4-2006 standard.

The Connectivity Standards Alliance was formed to establish networking and application-level standards on top of the IEEE 802.15.4 standards, to allow flexibility, reliability, and interoperability. The Zigbee 802.15.4-2003 Specification 1.0 was ratified in 2005 and the Zigbee 2006 Specification was announced in 2006, obsoleting the 2004 stack. Working Groups (WGs) have been formed within the Internet Engineering Task Force (IETF) to establish open standard approaches for routing (roll WG) and interfacing low-powered wireless devices to IPV6 networks (6LoWPAN WG). More recently, the Thread Group was formed in 2014 to utilize open IP standards, mesh networking, and 802.15.4 to support a wide array of home networking products.

Although wireless networks eliminate messy cables and enhance installation mobility, the downside is the potential for interference that might block the radio signals from passing between devices. This interference may be from other wireless networks or from physical obstructions that interfere with the radio communications. Interference from other wireless networks can often be avoided by using different channels. Zigbee, for example, has a channel-scanning mechanism on start-up of a network to avoid crowded channels. Standards-based systems, such as Thread, Zigbee and Wi-Fi, use mechanisms at the MAC layer to allow channel sharing. In addition, Zigbee and Thread provide an interoperable standard for multi-hop wireless networking, allowing signals to reach their destination by traveling through multiple relay points. These networks can be comprised of many such relay points or "routers," each one within range of one or more other routers, creating an interconnected "mesh" of devices that can provide redundant paths for data within the network that are automatically rediscovered and used to avoid interference in a local area. This concept is collectively referred to as "mesh networking."

Another potential problem is that wireless networks may be slower than those that are directly connected through a cable. Yet not all applications require high data rates or large data bandwidth. Most embedded networks function very well at reduced throughputs. Application designers need to ensure their system data rates are within the range achievable with the system being used.

Wireless network security is also a problem, because the data can easily be overheard by eavesdropping devices. Zigbee and Thread have a set of security services designed around Advanced Encryption Standard (AES) 128 encryption, so that application designers have a choice of security levels based on the needs of their applications. Careful design around these standards helps maintain high levels of network security.

Other networking standards exist such as Bluetooth Classic. Each standard has its own unique strengths and essential areas of application. The bandwidth of Bluetooth is 1 Mbps, while 802.15.4-based protocols are one-fourth of this value. The strength of Bluetooth Classic lies in its ability to allow interoperability and replacement of cables. Zigbee and Thread's strengths are low cost, long battery life, and mesh networks for large network operation. Bluetooth is meant for point-to-point applications such as handsets and headsets, whereas Zigbee and Thread are focused on the sensors and remote controls market, large distributed networks, and highly reliable mesh networking. Bluetooth Low Energy is emerging rapidly as another low power wireless technology very well suited for point-to-point applications such as controlling a single device with your smartphone.

While in the past each chip supported a single protocol, new developments have allowed two protocols to operate on the same chip. This multiprotocol operation may be as simple as chip technology that supports different protocols, with the application protocol of choice loaded during manufacturing. More recently, chips such as Silicon Labs EFR32 products and shared operational infrastructure allow two protocols to share the same radio. For example, a dynamic multiprotocol implementation might allow an end user to use a smartphone app working with a Bluetooth Low Energy application on the device to control the device or perform diagnostics, while the device remains connected to its Zigbee home automation network. Multiprotocol Fundamentals describes the four different multiprotocol modes, their operational requirements, and discusses some considerations to take into account when implementing a multiprotocol device.