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transmission period in the order of minutes), cyclic and acyclic network traffic.
Messages have different priorities, depending on their nature. In a decreasing order of priority, the message categories are command (which contains network management payloads), process data, normal and alarm.
At the network layer, WirelessHART defines a full mesh network, where all devices source and sink packets and route data for other devices. Unicast, broadcast and multicast are supported. Communication paths are continuously verified for reliability. Two routing paradigms are supported. The main one is graph routing (as in TSMP), whereby each device stores a network graph generated by a device called the network manager the source of a packet includes a graph ID in the packet header and intermediate devices must know which devices the packet can be forwarded to. Source routing is another available option.
Network bandwidth for a communication is assigned in an on-demand basis. A simple transport layer offers reliable and unreliable end-to-end communication. In the reliable mode, automatic retries are supported.
WirelessHART uses the standard HART Application Layer, which is command-based.
WirelessHART provides security services which are essentially those offered in TSMP. One difference is the use of public keys, which are used at the MAC layer to offer frame authentication/integrity for devices aimed at joining a network and which are not yet authenticated. Key management is the responsibility of the network administrator/engineer.
11.3.3. ISA100.11a In 2005, the International Society of Automation (ISA)  created a committee called SP100 / Wireless Systems for Automation, which was chartered with the goal of creating an open standard for industrial wireless monitoring and con
trol. The result is a standard focused on industrial automation, including feedback loop control within its scope. The generic name of the standard is ISA100 and the specific standard covering the wireless access is called ISA100.11a, which was finally released in September 2009. Despite the publication of WirelessHART, the ISA justified the development of ISA100.11a because of the limited application of WirelessHART, the lack of formal support (WirelessHART is promoted by a group of companies) and the possibility of ISA100.11a transporting information from different buses such as Profi, HART, Mod or FF.
ISA100.11a defines a protocol stack which covers the functionality of the physical layer, the data link layer, the network layer, the transport layer and the application layer. Security is also provided. Like WirelessHART, ISA100.11a is based on the functionality defined by TSMP. ISA100.11a uses IEEE 802.15.
4-2006 as the physical and MAC layers. A relevant factor is that the frame format defined by 6LoWPAN in RFC 4944  is used at the network layer. This layer also provides addressing, routing, quality of service and management functions. The transport layer offers services that include both reliable (i.e. acknowledged) and unreliable data transport, secure transport, flow control and segmentation and reassembly. The application layer provides support for enabling an open and interoperable ISA100.11a application environment, which includes legacy and non-legacy ISA100.11a applications. ISA100.11a also offers a tunnelling object, which provides generic services for protocol translation and can be used in a gateway, that is, the element which connects an ISA100.11a network with another network. Security services are provided at the MAC and transport layers.
11.4. Other solutions This section presents the following WSN solutions: SensiNet, XMesh, ANT, DigiMesh, Ambiosystems, Ambient Systems and RuBee.
11.4.1. SensiNet A company called SENSICAST  has developed a proprietary solution called SensiNet. The 900 MHz and 2.4 GHz bands are available. In the first Chapter 11. Wireless sensor network architectures and technologies case, FHSS is used, while in the second one the radio used is IEEE 802.15.4, with the addition of Distributed Frequency Spread Spectrum (DFSS). DFSS is a technique which is able to change a channel if it is busy and offers better resistance to interference than the default IEEE 802.15.4 PHY.
The transmitted power is limited to 15 dBm and offers a range up to 212 m in the 2.4 GHz band outdoors.
SensiNet defines two types of devices:
Mesh Routers  and Smart Sensors. The former ones perform are in charge of routing. SensiNet defines a self-healing network.
Due to the physical layer enhancements against interference, SensiNet is particularly appropriate for industrial environments.
XMesh is a multi-hop networking protocol stack developed by Crossbow for low-power networks . Some of the features of XMesh include time synchronization, flexible topologies, support for various QoS levels, integrated network health messages and partial support of ZigBee.
XMesh developers claim that XMesh enables reliable routing links to third party ZigBee devices . However, some researchers have found interoperability issues between XMesh and ZigBee .
XMesh is offered as a software library, on top of devices that have IEEE 802.15.4 radio interface and run TinyOS.
ANT  is a wireless networking protocol developed by a company called Dynastream Innovations Inc. that operates in the 2.4 GHz band.
Multiple frequencies can be used within this band. The raw data rate is 1 Mbps and the transmission range is up to 30 m. Acknowledged transmission is supported, yielding a net data rate of up to 20 kbps.
All devices in ANT perform the same roles and there is no coordinator node. ANT allows peer-to-peer, star, tree and mesh networks, besides formation of other topologies. An ANT network may be composed of up to
232 devices. ANT technology has a significant market share in sports & fitness applications. Fig. 11.7 shows a chip-based solution that includes the ANT protocol stack.
Dynastream plans to get into markets related to home automation and industrial automation.
11.4.4. DigiMesh DigiMesh is a proprietary solution (peer-to-peer networking topology for use in wireless end-point connectivity) developed by Digi . This solution operates in the 900 MHz and 2.4 GHz bands, where FHSS and DSSS are used, respectively. In the first band the data rates available are 10, 125 and 150 kbps, while in the second one the data rate is 250 kbps.
DigiMesh supports long transmission range (up to 64 km in the Xtend product). In some products, the data payload is up to 256 bytes. DigiMesh device identifiers are 64-bit MAC addresses. DigiMesh supports only one type of node. DigiMesh offers security based on the application of the AES algorithm.
11.4.5. AmbioSystems AmbioSystems offers a proprietary WSN solution based on the AmbioMote platform  (see Fig. 11.8); which operates in the 2.4 GHz band at a raw data rate of 2 Mbps and with an application layer data rate of 500 kbps. This solution has been designed on the assumption that energy is Chapter 11. Wireless sensor network architectures and technologies harvested from vibration, strain or light, although a back-up battery can also be used. The transmission range is up to 80 m and a simple star topology is supported.
11.4.6. Ambient Systems The so-called Ambient Product Series 3000 is a WSN solution developed by Ambient Systems . The device radio is based on the 2.4 GHz IEEE 802.15.4 interface. Three types of devices are defined: SmartPoints, MicroRouters (see Fig. 11.9) and a Gateway. The first are battery-enabled, include various types of transducers, are capable of determining their own location and have additional storage capabilities for performing active RFIDlike tasks (e.g. information tracing). The MicroRouters carry out multi-hop routing operations. The Gateway collects the information obtained by the SmartPoints.
For data transmission, a SmartPoint communicates with a MicroRouter.
The latter transmits beacons periodically, while a SmartPoint selects the MicroRouter it will communicate with according to the signal strength of the beacons received. The SmartPoint uses CSMA as the MAC mechanism.
RuBee is a bidirectional, on-demand, peer-to-peer network protocol which uses a low-frequency carrier . The default frequency band is 131 kHz, but RuBee can operate in other frequencies, e.g. 450 kHz. The protocol is targeted on tagging networks offering speeds from 300 to 9600 baud and using IP addresses. The IEEE P1902.1 standard is based on the RuBee protocol.
One of the main advantages of RuBee is its ability to operate in harsh environments due to the physical properties of the low frequencies used by the protocol (in an area range of up to 15 metres).
 “ZigBee specification”, r17, ZigBee Alliance, October 2007.
 ZigBee Alliance website: http://www.zigbee.org/en/about/.
 C. Perkins, E. Belding-Royer, S. Das, “Ad hoc On Demand Distance Vector Routing (AODV)”, RFC 3561, July 2003.
 “ZigBee Home Automation Public Application Profile”, Revision 25, Version 1.0, ZigBee Alliance, October 2007.
Chapter 11. Wireless sensor network architectures and technologies
 “ZigBee Smart Energy Profile Specification”, Revision 15, ZigBee Alliance, December 2008.
 D. Gislason, “ ZigBee Wireless Nerworking”, Elsevier. Inc, 2008.
 J. Hui, D. Culler, “IP is dead, long live IP for wireless sensor networks”, in Proceedings of the 6th ACM Conference on Embedded Networked Sensor Systems, pp. 15-28, Raleigh, NC, USA, November 2008.
 N. Kushalnagar, G. Montenegro, C. Schumacher, "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals", RFC 4919, August 2007.
 6LoWPAN protocol stack data sheet from Jennic.
 6LoWPAN development platform from Sensinode.
 C. Bormann, D. Sturek, Z. Shelby, “Problem Statement for 6LoWPAN and LLN Application Protocols”, Internet Draft, (Work in progress) July 2009.
 US NIST Smart Grid home page: http://www.nist.gov/smartgrid  “Z-Wave protocol overview”, Version 4, May 2007.
 C. Dougas, “Configuring and managing a large-scale monitoring network: solving real world challenges for ultra-low powered and longrange wireless mesh networks”, International Journal of Network Management, 15: 269–282, 2005.
 Wavenis Open Standard Alliance website: www.wavenis-osa.org  EnOcean website: http://www.enocean.org  EnOcean Alliance website: http://www.enocean-alliance.org/  “INSTEON. The Details”, August 2005.
 “ONE-NET Specification”, Version 1.5.0, February 2009.
 “Technical Overview of Time Synchronized Mesh Protocol (TSMP)”, Dust Networks.
 K. Pister, L. Doherty, “TSMP: Time Synchronized Mesh Protocol”, in Proceedings of the International Symposium on Distributed Sensor Networks (DSN 2008), Florida, USA, November 2008.
 Dust Networks website: www.dustnetworks.com  HART Communications Foundation (HCF) website:
http://www.hartcomm.org/  WirelessHART Technical Datasheet, May 2007.
 ISA website: http://www.isa.org  N. Kushalnagar, G. Montenegro, J. Hui, D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, September 2007.
 SENSICAST website: http://www.sensicast.com/  Crossbow Technology: Mesh Networking website http://www.xbow.com/Technology/MeshNetworking.aspx  M. Turon, M. Horton, J. Hill, A. Broad, “XMesh Routing Layer”, February 2005.
 J.-S. Lee, Y.-C. Huang, “ITRI Zbnode: A ZigBee/802.15.4 Platform for Wireless Sensor Networks”, 2006 IEEE Conference on Systems, Man and Cybernetics, Taipei, Taiwan, October 2006.
 ANT website: http://www.thisisant.com  Digi Networks website: http://www.digi.com  AmbioSystems website: http://www.ambiosystems.com/  Ambient Systems website: http://www.ambient-systems.net/  J. K. Stevens, “RuBee Visibility Networks – IEEE P1902.1”, November 2006.
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Chapter 11. Wireless sensor network architectures and technologies
 C. Dugas, “Wavenis ULP long range wireless platforms, sensing, and M2M monitoring solutions”; presented at M2M Workshop ETSI, Sophia Antipolis, June 04-05, 2008.
 EnOcean, “Energy harvesting made easy with the EnOcean wireless standard”.
 ZigBee web site: http://www.zigbee.org  SmartMesh XT 2.4 GHz M2030 details, from Dust Networks web site:
http://www.dustnetworks.com/products/SmartMesh_XT_2_4_GHz/ M2030  SensiNet Mesh Router details, from SENSICAST web site:
http://www.sensicast.com/mesh_nodes.php  D. Sturek, “ZigBee IP Stack Overview”, ZigBee Alliance, 2009.
12. Sensed data management WSNs have a great potential for collecting data, but without additional context information the data cannot be transformed into information.
Sensor data have to be correlated in time and space in order to derive conclusions and provide useful information. To make this kind of processing possible, data has to be tagged with additional information (e.g. time, location, source, user, type of attribute, etc.). This kind of metadata is quite verbose and contrary to the memory and transmission capabilities of the sensor nodes. To reconcile these opposing interests, it is possible to use specific compact formats or intermediate nodes40 capable of providing semantic content to the raw data provided by the sensor node.