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Table of Contents: 1. Introduction 2.
IoT Data Link Protocols 2. Comparative Study 3.
Summary References List of Acronyms 1. It is regarded as an extension of today's Internet to the real world of physical objects, which is often associated with such terms as 'ambient intelligent', 'ubiquitous network', and 'cyber-physical system'.
In recent years, with the development of computer science, communication technology and the network of things has made a great breakthrough.
The IoT applications has been used in many fields, from the earliest wireless sensor networks such as the smart grid, smart healthcare, smart agriculture, military and so on. A combination of technologies, including low-cost sensors, low-power processors, scalable cloud computing, and ubiquitous wireless connectivity, has enabled this revolution. Many companies are using these technologies to embed intelligence and sensing capabilities in their products, thereby enable objects to sense, learn from, and interact with, their environment.
Some of these devices engage in machine-to-machine communication.
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For example, sensors on the roadway electronically alert cars to potential hazards, and the smart grid sends dynamic electricity pricing data to home appliances in order to optimize power consumption.
The wireless technology standards are everywhere.
Bluetooth, ZigBee, Wi-Fi, and cellular technologies are the most well known standards. A combination of these standards is envisaged to be used to construct the smart home.
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Effectively all wireless technologies that can support some form of remote data transfer, sensing and control are candidates for inclusion in the smart home portfolio. Interacting with individual devices and appliances can introduce a basic level of intelligence to the home environment. However, the level of intelligence can be greatly enhanced once devices, be it simple sensors or complex appliances, can exchange information and effectively share the decision making process to offer a certain type of service to the occupant of an intelligent environment.
The remainder of this paper is organized as follows. For each protocol, separate alliances of companies worked to develop specifications covering the network, security and application profile layers so that the commercial potential of the standards could be realized.
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The major goal of this paper is not to contribute to research in the area of wireless standards, but to present a comparison study of the six main short-range wireless networks. ZigBee is a new technology of a short-range, low complexity, low-power consumption, low-data-rate, low-cost and duplex wireless communication [ li14 ]. It is applied on the low- data-rate wireless data communication between various electronic equipment within a short distance.
IEEE ZigBee is characterized by short distance wireless communication and low power consumption. Though the maximum transmission speed is kbps and lower than Bluetooth and Bluetooth LE, it is suitable for the application for which data traffic is a little and a lot of devices are necessary.
Radio modules corresponding to this specification are provided from many vendors. So it is convenient to construct sensor network, and try to apply to a variety of monitoring and control applications such as air-conditioning control, lighting control, physical distribution management, house control, the measurement instrument and so on. With power-saving, reliable, low-cost, large capacity, security, and many other advantages the ZigBee networks pay the way for its widely applications in various fields of Automatic Control.
Currently, ZigBee mainly used in transmitting information among the various electronic equipment which are within short-distance and data transmission rate is not very high.
Usually, any applications which are small space between equipment; low cost, low data rate transmission; small equipment size, inadmissibility of big power module; hard to frequent replace or repeat recharge battery can be considered to use ZigBee technology.
It can also complete transmission and exchange of information among physical things, so we can use the technology to complete the same mission in the construction of Internet of Things, then combined with Internet and database technology, we would set up Internet of Things.
However, mesh networks enable high levels of reliability and longer coverage range by providing more than one path through the network for any wireless link. Note that in any ZigBee network there are three types of ZigBee devices [ zhou11 ]: PAN coordinator: There is only one coordinator in a network that is responsible for starting the network, binding together devices.
Also it routes data between different devices. A router: It cannot start the network however it scans a network to join it. It is a FFD and it is usually mains powered device. An end device: It cannot start a network however it scans a network to join it. Bluetooth LE is the hallmark feature of the Bluetooth 4. It has been designed for ultra- low-power applications, yet keeping similarities with classic Bluetooth [ chris15 ].
Remarkably, a Bluetooth LE implementation can reuse classic Bluetooth circuitry components. Therefore, the upside potential for Bluetooth LE is enormous given that future mobile phones that have a Bluetooth chipset are expected to include Bluetooth LE as well.
Nevertheless, in order to achieve the goal of ultra-low-power consumption, major changes have been made to the Bluetooth LE protocol stack.
The number of channels is reduced from 79 in classic Bluetooth to 40 [Kuor11]. In terms of coverage, Bluetooth LE typically has a range of up to a few tens of meters.
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The Link Layer specifies, among others, the functionality for bidirectional communication between two devices, which requires them to establish a connection.
As defined in [ chris15 ], two roles for connected devices, called master and slave. Prior to connection establishment, the devices that will be in the slave role announce their presence and connect ability, while the device that will be in the master role listens for those announcements and initiates the connection establishment by transmitting a message called Connection Request to each device it attempts to connect to.
A master can manage multiple simultaneous connections with several slaves, whereas a slave can only be connected with a single master. Therefore, Bluetooth LE defines a star topology. The connection establishment time between a master and a slave takes less than 3 ms.
Once two devices are connected, a Time Division Multiple Access TDMA scheme is used by the master for scheduling the start of connection events, in which communication between master and slave takes place. The Connection Request message serves as a reference for synchronization between master and slave [ hansen15 ].
Using Bluetooth LE for Internet connectivity and applications poses challenges beyond IPv6 packet transport, including gateway operation, application protocol efficiency, and security. A central piece of this solution is the IPv6 over Bluetooth LE specification that is currently being produced by the IETF [ chris15 ] and is expected to become a standard in the near future.
It is crucial to understand the capabilities and performance trade-offs of the solution. Figure 2: Physical Layer Communication [ chris15 ].
Both Bluetooth LE and Spectrum spreading allows uncoordinated, low data rate wireless connections to share the radio spectrum without interfering. Frequency hopped spread spectrum, used by Bluetooth LE, changes the radio frequency in each transmission burst according to a pseudo random pattern [ hansen15 ].
Different networks employ different hopping patterns. Thus, the likelihood of two networks simultaneously sharing a channel is low. If a particular hop results in interference, there will not be interference on the next hop, so any lost data can be re-transmitted without error. Direct sequence spread spectrum works in a different way.
It makes data transmissions more immune to noise or interference by modulating the data with sequences that switch much faster than the data's bit rate. The result is a transmitted signal that occupies a wider swath of radio spectrum.
The effect for uncoordinated radio links is the same, however. More radio links can share a given slice of radio spectrum without interfering.
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In contrast, IEEE This has an advantage of allowing high speed, bandwidth efficient communications [ nieman14 ]. However, there is a cost in power consumption because all devices must actively sense the medium before transmission. Furthermore, bandwidth efficient communication is inherently more power consuming because the physical layer must be designed to accommodate high dynamic range signals.
Two examples are provided for internetworking with Bluetooth LE.
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The first, shown in Figure 3, is a fixed infrastructure model. A router gateway can be added to the home to provide connectivity to Bluetooth LE enabled IoT devices. The gateway can either be a stand-alone device or it could be incorporated into another fixed device.
In Figure 3, it is shown as a stand-alone device. An Internet-based application for controlling the lamp or washing machine will employ the 6LoWPAN protocol from the device to the gateway. As with any Bluetooth connection, the devices must first be paired for authentication and for key generation. The Z-Wave protocol was explicitly developed by Zensys for home control applications [ zwave15 ]. It is a proprietary protocol, with two basic types of devices: controlling and slave devices.
Slave nodes reply and execute commands sent by controlling devices that initiate messages within the network. There is always a single controller primary controller that holds authoritative network topology information.
Slave nodes can have several forms depending on their function. Routing slaves forward commands to other.
At data frame creation the whole route is known, meaning a source routing is used. Networks can be formed with up to devices. FSK frequency shift keying modulation is used at Since it is intended for wireless home control applications, Z-Wave radio networking is designed for relatively few nodes maximum, but manufacturers recommend no more than that communicate on average every 5 to 15 minutes.
Its messages are variable length, with a payload averaging 4 to 6 bytes. Message latency requirements are relaxed to milliseconds or more. Figure 4: AMR infrastructure architecture [ zwave15 ]. The Z-Wave protocol consist of 4 OSI layers as illustrated in Fig 5, the MAC layer that controls the RF media, the Transfer Layer that controls that handles frame integrity checks, acknowledgements, and retransmissions, the Routing Layer that controls the routing of frames in the network and application interface and the application layer that controls the payload in the transmitted and received frames.
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The SRA requires message initiator devices to know the arrangement of other devices in the network the topology so that they can compute the best route for messages to travel.
Maintaining and distributing a network topology database is an intricate software task, especially when some devices in the network are mobile. Therefore, to keep costs down, Z-Wave defines different kinds of devices, with the lowest cost devices, called slaves, unable to initiate messages.
The minimum length of a properly formatted Z-Wave message is 9 bytes, but a routed message requires 12 bytes plus repeater data plus the payload. The message protocol includes routing, frame acknowledgement, collision avoidance with random back off and a frame checksum with retransmission if necessary.
The Z-Wave network is self-organizing and self-healing.