Version: 2 Status: Review Woo web of Objects Project
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- Navigate this page:
- Networking technologies
- Internet Protocol Version 6
- ZigBee
- IPv6 over Low Power Wireless Personal Area Network
- Bluetooth
- Near Field Communication
- Radio Frequency ID
Virtual ObjectsIt is not always possible that real infrastructures are directly available to the main applications. Such as if there is an application that provides information about any process running in remote places consisting resource constrained objects like sensors, it will be difficult to provide real time information all the time. It is because sensors normally have limited resources that they cannot sustain long communication session. Also, if there is large number of requesters, a resource-constrained object may not be able to handle such large number of requests at a time. In such situation, it is a convenient solution to provide those resource constrained devices and their functionalities as a virtual objects through some capable devices. Virtualizing objects via gateway, middleware or various APIs has become a common solution in the field of wireless sensor and actuator networks. With this approach, processing load of the data can be shifted from resource-constrained objects to the resourceful one. Better quality of service can be maintained in service provisioning and data access. Use of middleware-based approach in sensor network has been discussed extensively in previous section of this document. Middleware normally is used in data processing, service provisioning, providing access to the devices etc. With virtualization, it is possible to emulate the real objects as it is so that any operation can be performed on objects as in real case. We believe that rather than providing access to the objects via modified interfaces, virtual object concept can provide better view of the device.
IoT refers to uniquely identifiable objects (things) and their virtual representations in an Internet-like structure. The idea is so simple but to make it real is the real challenge. But which technology could we use to connect these objects to the network? Basically we have two methods, the wired and the wireless networks. For static elements we don´t need to take in account the mobility so the connection could be done by the telephone lines as we do with our home internet connection. This connections use an Internet Protocol (IPv4) to communicate with other devices around the world, but this was getting obsolete because of the number of devices that was able to identify. So it was necessary to develop a new protocol to expand the addressing to all this objects that we want to connect to the network. The other possibility to connect things to the network is to do it wirelessly. Figure 5.8 shows different network topologies to connect objects. During the last years the wireless technologies are getting more and more strength in our lives, and this is due to the development of new technologies that provide communication possibilities to low power devices. A lot of things we want to monitor and measure are in movement so to connect it to a static connector maybe is not the best choice. So the solution is to use this wireless devices to create a wireless sensor network, which will help us having all this moving data on our hands, with low energy consumption and safely. Depending on the type of device we could have different kind of networks:    
Fig. 5.: Different types of networking topologies.
The Internet Protocol Version 6 was developed in order to substitute the actual IPv4 defined in RFC 791. Designed by Steve Deering and Craig Mudge, its greatest advance is to give the possibility of expanding the number of net addresses that was getting obsolete in IPv4. This will give the chance of giving all new devices like mobile phones its own permanent address. IPv6 brings many benefits compared to IPv4. The most important one is the extension of the addressing capacity. With IPv6, addresses are stored in 128 bits which provides approximately 3.4 x 1038 compared to the 32 bits of IPv4 which provide 4.3 x 109 addresses. IPv6 addresses are represented by eight groups of two bytes in hexadecimal. The blocks having a 0 value can be omitted and are represented using a :: (two colons). This way the address is simpler to read. A sample address is: 2607:f8b0:4002:802::1018. There are two types of IPv6 addresses: unicast and multicast. A globally addressable unicast address is split in three parts: a routing prefix and a subnet ID which forms the network address and a last part which is the interface identifier (relative to a device). A link-local unicast address, which is only known inside its private network, always begins with fe80:: and followed by a 64 bits interface identifier usually calculated using the MAC address in an Ethernet network. Multicast addressing in IPv6 uses benefits of larger address space to broaden usage of multicast across the Internet and on an inter-domain basis. The addresses include the scope of the packets. For example, an address beginning with ff02:: is a local multicast address but an address beginning this ff0e:: will be global to the Internet. IPv6 has simplified the configuration of hosts by removing the need of companion protocols of IPv4 like ARP and DHCP. The addresses of each host are configured through Neighbor Discovery Protocol part of ICMPv6. The host will send a router solicitation request when it gets connected. The router responsible of the network will reply to the host with a reply advertisement packet containing the needed parameters to let the host self-configure. IPv6 also simplifies the headers first used in IPv4 and the processing done by routers by removing the fragmentation feature. With IPv6 any packet which is too big to be transmitted by a router is just rejected and the sender is notified. In IPv4 the router was responsible of splitting packets which were too big. Headers are also expanded in IPv6 by allowing them to have a maximum length of one packet. They are now chained. These headers directly include IPSec information which is integrated in the IPv6 specification. They can also include Jumbogram option to create IPv6 packets which can have at most 4GB data. IPv6 options are also used by Mobile IPv6 to allow roaming of devices between different networks.
This ZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on an IEEE 802.15.4 standard for personal area networks. The differences of this technology with others are:
ZigBee is a network layer specification build upon the IEEE 802.15.4 standard defined to LR-WPAN (Low Rate Wireless Personal Area Network). Aiming develop the entire protocol stack, while IEEE 802.15.4 work group specifies the lowers layers of the protocol stack, the ZigBee Alliance focus its efforts on define the upper layers, from network to application layer. The IEEE 802.15.4 and ZigBee Alliance work has the objective to develop a standard that can be used for devices manufactured by different companies that work well together and provide a framework that makes easier the development of application in the application layer. The IEEE 802.15.4 uses three different bands to transmit data : the 868MHz, 915Mhz and 2.4GHz bands. Each band is split in non-overlapping channels for a total of 11 channels in the 868/915Mhz band and 16 channels in the 2.4GHz band. IEEE802.15.4 provides a data rate of 20kbps in the 868MHz band, 40kbps in the 915MHz band and 250kb/s in the 2.4GHz band. Each IEEE802.15.4 packet is composed of a preamble, a start-of-packet delimiter and an additional header to indicate the length of the following data which can’t be more than 127 bytes. The MAC layer defined in IEEE 802.15.4 defines two operation modes: beacon-enabled and without beacons. Using beacons, a device can obtain guaranteed bandwidth but synchronization is needed. As a consequence, this mode is more complex and needs more computation power. The IEEE 802.15.4 defines two devices types, the reduces-function device (RFD) and the full-function device (FFD). In the ZigBee network a node can assume three roles; it can be a personal area network coordinator, a coordinator or an end device. The role of each node depends on witch type of device it is according to IEEE 802.15.4 definition. If the node is a FFD, it can be perform all roles, but is it is a RFD; it can be just an end device and only communicate to a FFD device. The communication between the devices in the network depends on the topology used to represent the network. ZigBee supports the three topologies defined by the IEEE 802.15.4 standard that are: star, tree and mesh topologies. When a star topology is used, the communication is established just between each end device called ZigBee end device and the ZigBee Router or ZigBee Coordinator. If a mesh or a tree topology is chosen, the ZigBee Router can communicate to others ZigBee Routers and the ZigBee Coordinator. A PAN must have one and only one ZigBee Coordinator which is responsible of network starting and initial address configuration. ZigBee network layer is responsible for starting a network, doing the procedure of association and dissociation, routing discovery, maintenance and addressing the devices that join the network. A simple example of a mesh wireless network could be as depicted in the Fig. 5.9.
Fig. 5.: ZigBee wireless mesh network.
6LoWPAN (IPv6 over Low Power Wireless Personal Area Network) was created with the idea of bring the Internet protocol to the low power small devices, to give them the gate to participate in IoT. The 6LoWPAN has defined encapsulation and header compression mechanisms that allow IPv6 packets to be sent to and received from over IEEE 802.15.4 based networks. The compression methods use information present in the underlying layers to compress and remove redundant data in 6LoWPAN. In addition, 6LoWPAN defines a compression method for the UDP headers. As a consequence, 6LoWPAN is a cross-layer protocol taking information from data link layer and going up to transport layer. 6LoWPAN can use RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks) to ensure efficient routing between all devices. Each router is then member of a DAG (Directed Acyclic Graph) to prevent loops in the network and to enable shortest path discovery. Routers get routes information thanks to RPL and devices use Neighbor Discovery Protocol to get the routing information. Figure 5.10 could be a typical architecture of a 6LoWPAN network: 
Fig. 5.: 6LoWPAN.
The Bluetooth technology it’s an industrial specification for the wireless personal area network that gives the opportunity to share voice and data between different devices trough a radiofrequency link in the ISM band at 2,4 GHz .This specification was designed especially to low consumption devices , with low coverage and designed with low power transceiver. Table 5.: Three Classes of Bluetooth.
The Bluetooth SIG completed the Bluetooth Core Specification version 4.0, which includes Classic Bluetooth, Bluetooth high speed and Bluetooth low energy protocols. Bluetooth high speed is based on Wi-Fi, and Classic Bluetooth consists of legacy Bluetooth protocols. Nowadays there is a Bluetooth v4.0 developed with a 24 Mbit/s band width.
Near Field Communication (NFC) technology allows a simpler way to make payments, pair/connect devices or exchange content just with proximity contact. A standards-based connectivity technology, NFC harmonizes today's diverse contactless technologies, enabling solutions in areas such as: Access control, consumer electronics, Healthcare, Information collection and Exchange, Loyalty and coupons, Payments or Transport. NFC-Forum promotes the use of NFC short-range, was founded in 2004 by Nokia, Philips and Sony, and now has more than 160 members. The Forum also promotes NFC and certifies device compliance. NFC standards cover communications protocols and data exchange formats, and are based on existing radio-frequency identification (RFID) standards including ISO/IEC 14443 and FeliCa. Structurally, NFC Forum specifications are based on existing radio-frequency identification (RFID) and recognized standards like ISO/IEC 18092 and ISO/IEC 14443-2,3,4, as well as JIS X6319-4 [NFC-FORUM12]. NFC structure is shown in the Fig. 5.11. 
Fig. 5.: NFC structure. NFC provides a range of benefits to consumers and businesses, such as [NFC12]:
RFID is a contactless system for wireless communication which uses frequency bands as shown in Table 5.2. This technology uses electromagnetic fields to transfer data between a passive component and a device or between enabled devices, for example mobile phones [RFID12]. Passive tags require no battery, there are powered by the electromagnetic field used to read them. RFID tags can be attached to any kind of objects (e.g. cloths, wallets, cars) or devices (e.g. mobile phones, tablets.), enabling the possibility of reading personally linked information. These are some examples of use cases: commerce, product tracking, telemetry, transportation payments, animal identification, access control or advertising. Main problems around the RFID technology are: data flooding, global standardization, privacy or XMPP temperature exposure. Table 5.: Common RFID frequency bands.
Standards that have been made regarding RFID technology include:
In order to ensure global interoperability of products several organizations have setup additional standards for RFID testing. These standards include conformance, performance and interoperability tests. Groups concerned with standardization are:
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