Through most of its history, the Internet has been limited to connecting people and applications. Now, advances...
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in semiconductor technology have made it possible to embed a powerful processor and a network interface in everyday objects. This development has in turn enabled the Internet of Things (IoT), networks through which objects communicate and are controlled via the Internet. Specialized machine-to-machine network technologies provide the last hop for many IoT applications. Each application is different. No single set of network technologies or protocols can support all of them.
Three examples illustrate how specialized networks that share some characteristics differ to meet specific requirements generated by the IoT. Each network is wireless and each operates over a limited distance. Still, the applications differ and each network protocol varies as a result to meet those specific requirements.
Automobile manufacturers, along with the U.S. Dept. of Transportation, are currently working to reduce highway accidents by developing a set of standards that vehicles will use to communicate with each other.
The goal is that eventually equipment based on these standards, known as vehicle-to-vehicle (V2V) and vehicle to infrastructure (V2I) communications, will be installed in every automobile, truck, bus and motorcycle. IEEE 802.11p or WAVE, Wireless Access in Vehicular Environments, is a key component of the project.
Using WAVE, each vehicle will broadcast its location, speed and direction of travel 10 times per second. Nearby vehicles and roadside infrastructure will receive these broadcasts. Installed computers will use the information received to generate warnings to the driver or take action to prevent accidents.
While 802.11p is based on the IEEE 802.11 standard used in millions of Wi-Fi installations, it operates in a different environment with different design challenges. 802.11p must establish communications between vehicles that may be in proximity only very briefly. Widely-used 802.11 versions such as 802.11n require stations to exchange packets to set up the connection to a specific access point (AP), identified by its unique basic service set identification (BSSID). The 802.11p standard defines a wild card BSSID, so no initial exchange of packets is required. Each vehicle will transmit its location, speed and direction without establishing connections with nearby vehicles and process received data as soon as it arrives.
Because specifying location, speed and direction does not require a great deal of data, a high data rate is not a requirement for WAVE. Data loss caused by reflections from nearby buildings and large trucks and buses, however, does present a challenge. As a result, WAVE designers used 10 MHz bandwidth channels -- a narrower channel than other 802.11 versions -- to reduce the sensitivity to reflections.
Security is a major issue for the V2V project, due to the potential danger of an attacker sending erroneous messages. IEEE 1609 defines management and security operations used to protect data. Under that standard, vehicles and accompanying infrastructure elements obtain certificates via the public key infrastructure to enable secure operation. Other research continues. Topics include finding ways to build protection against distributed denial of service attacks and evaluating steps needed to prevent hackers from gaining access to infrastructure and vehicles. Other issues include beefing up the capabilities of the certificate authority as it supports the millions of vehicles and roadside infrastructure elements needed to support V2V and V2I.
ZigBee Alliance protocols are designed to satisfy the need to create low-power networks that cover a large area. Power consumption is a critical issue since many ZigBee devices are powered by batteries. ZigBee devices meet these goals by constructing a mesh of nodes.
Applications include monitoring and controlling temperature and lighting in homes and in commercial and industrial buildings. Other applications include tracking the location of portable equipment in hospitals, factories and schools. Environmental monitors and tracking devices send small amounts of data periodically. For these types of applications, a high data rate is not a requirement, but since devices are often scattered throughout a large area, having to replace batteries frequently would greatly reduce the value of the network.
The distance between adjacent devices in the mesh can be as little as 10 meters in extremely low-power applications. ZigBee networks can operate in the 2.4 GHz band and in the 915 MHz or 868 MHz bands. Maximum data rate is 256 Kbps in the 2.4 GHz band and at lower rates in sub-gigahertz bands. ZigBee supports encryption using the AES-128 standard. A variety of key distribution methods are provided.
A ZigBee network can consist of thousands of nodes. Messages are passed from node to node through the network. There is no need for any single node to be within transmission range of all of the members of the mesh. ZigBee devices can form either star or mesh networks. Mesh networks are self-configuring and self-healing, so loss of a node will not disrupt the entire network. ZigBee routers can be placed to extend the network where end nodes are too far apart to communicate with neighboring nodes.
ZigBee and 802.11p networks differ due to the nature of their applications. Like 802.11p applications, ZigBee applications do not require high data rates, but ZigBee applications do not require rapid connection setup since ZigBee nodes typically remain in contact for extended periods of time. IEEE 802.11p applications do not require the ability to construct a mesh. Each vehicle has access to alternator-generated power, and the brief time vehicles are in contact with each other prevents the creation of a long-lasting mesh.
Security requirements in ZigBee networks are less stringent than in 802.11p networks since all devices are owned and configured by the same organization. Static keys provide sufficient security for most applications.
The ZigBee Alliance, founded in 2002, maintains and updates the standards. The alliance consists of several hundred companies, including component manufacturers, such as Analog Devices and Texas Instruments; network equipment vendors including Cisco and Huawei Technologies; and end users of ZigBee products, such as Kroger and Pacific Gas and Electric.
Bluetooth was designed for a very different set of applications than 802.11p or ZigBee were, but like both, it is wireless and can act as the last hop in the IoT. It was originally designed to eliminate the wires connecting headsets and phones. There was no need to support the 1,000-meter range of 802.11p or the potential reach of a ZigBee mesh. The current Bluetooth standard specifies a 100-meter maximum distance, extending its uses to portable equipment such as medical devices or to eliminate the need to run speaker wires around a room.
Also unlike both 802.11p and ZigBee, there is no need to connect a large number of devices. Bluetooth networks are limited to a maximum of eight devices, with one acting as a controller and the remaining seven as slaves.
IoT will connect many other device types via specialized network technologies. 802.11p, ZigBee and Bluetooth are only a small subset of the networks that will be used to deploy IoT, but they illustrate how their designers modified existing technologies or invented new ones to meet specific application requirements.
About the author:
David B. Jacobs of The Jacobs Group has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted for Fortune 500 companies as well as software startups.
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David Jacobs asks:
Will you have to re-architect your IoT applications to take last hop capabilities into consideration?
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