The Idea Of Zigbee Style Networks Computer Science Essay

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Wireless technology dates back to as late as the 1800s and was developed by heinrich hertz. He explored the theories of scientist before him such as a guy called Maxwell. He demonstrated the transmission and reception of the electromagnetic waves predicted by Maxwell and therefore being the first person to intentionally transmit and receive radio. Thereafter the evolution of wireless technology took place. In the late 1980's gsm was formed and in 1992 the first mobile phone call was recorded in Finland. 1997 saw the introduction of WIFI and from then on the wireless technology industry has developed rapidly seeing the beginning of many wireless technologies such as Bluetooth, WImax, WIFI, Zigbee and many more.

Introduction to Zigbee

The idea of Zigbee-style networks began to be conceived around 1998, when many technicians realized that both Wi-Fi and Bluetooth were not going to be suitable for many applications in the future. Moreover many engineers saw a need for self-organising ad-hoc digital radio networks. The first Zigbee devise to be made was a phone controlling different household devices from one location and with a touch of a button, it was exhibited in Asia but still needed ratification as a standard. Zigbee as a technology hasn't yet taken off in the UK but is widely used in America for household use.

How was it named?

The idea of Zigbee was taken from one of nature's beauty and that is the honeybee. It references to the behaviour of honey as they travel from flower to flower collecting pollen by creating invisible paths then returning home the central unit.

What is ZigBee?

The Zigbee protocol was designed to provide an easy-to-use wireless data solution characterized by secure, reliable wireless network architectures. It is simply a low powered, low cost, wireless technology for personal area networks. It operates at 2.4GHZ industrial, scientific and medical (ISM) radio band, the same frequency as Bluetooth, microwave ovens, car alarms and many other devices. It has a capacity of 255 devices per network which for home use is more than enough. It can support data transmission up to 250kbps up to a range of 30 meters. Although it is much slower than Bluetooth's 11 Mbps, its consumption is significantly less too, therefore making it more efficient to use.

 How does it work?

Almost every household device can incorporate the Zigbee technology so the user does not have to move from their seat. They can control the heating system, oven, alarm, lights, AC, PC, home entertainment and many more, all from a remote, phone or PDA

It can operate star, mesh or cluster topologies. A major component of the ZigBee protocol is the ability to support mesh networking. In a mesh network, nodes are interconnected with other nodes so that multiple pathways connect each node. Connections between nodes are dynamically updated and optimized through sophisticated, built-in mesh routing table.

Mesh networks are decentralized in nature; each node is capable of self-discovery on the network. Also, as nodes leave the network, the mesh topology allows the nodes to reconfigure routing paths based on the new network structure. The characteristics of mesh topology and ad-hoc routing provide greater stability in changing conditions or failure at single nodes.

Where can it be used?

Consumer Electronics- the ZigBee Remote Control liberates the consumers from having to point remotes at devices the traditional way. It allows consumers to have more flexibility, giving them control of devices from nearby rooms and placement of those devices almost anywhere including behind wood, interior walls or glass.

Health Care - ZigBee Health Care provides a global standard for interoperable wireless devices enabling secure and reliable monitoring and management of noncritical, low-acuity healthcare services targeted at chronic disease. It promotes aging independence, overall health, wellness and fitness by providing more information about one's state of health.

It has been designed for use in homes, fitness centres, retirement communities, nursing homes and a variety of medical care facilities.

Home Automation- ZigBee technology allows for control of many household appliances, lighting, energy management, safety, and security

Telecommunication Service- ZigBee enables peer-to-peer data sharing, mobile gaming, GPS, secure mobile payments, mobile advertising, mobile office access. It offers mobile network operators with a new way to deliver value added services that can increase revenues.

It can also be used in offices and industrial buildings to regulate the flow of energy controlling switches and many more uses for it.

Who is involved?

Over 300 leading semiconductor manufacturers, technology firms, OEMs and service companies comprise the Zigbee Alliance membership. Companies which are actively involved in the development of this Wireless LAN topic are: Philips, Texas instrument, NEC ember and reliant energy to name a few. The participants are many, to name some are Intel, LG, Samsung, Siemens etc.

IEEE Standard

The IEEE standard for this product is 802.15.4. It was created to explore a low data rate solution with a long battery life and very low complexity. It is operating in an unlicensed, international frequency band at 2.4GHz.

Frames are the basic unit for data transport, for which there are four fundamental types (data, acknowledgment, beacon and MAC command frames), which provide a reasonable tradeoff between simplicity and robustness. Additionally, a superframe structure, defined by the coordinator, may be used, in which case two beacons act as its limits and provide synchronization to other devices as well as configuration information. A super frame consists of sixteen equal-length slots, which can be further divided into an active part and an inactive part, during which the coordinator may enter power saving mode, not needing to control its network.

Within superframes contention occurs between their limits, and is resolved by CSMA/CA. Every transmission must end before the arrival of the second beacon. As mentioned before, applications with well-defined bandwidth needs can use up to seven domains of one or more contention less guaranteed time slots, trailing at the end of the superframe. The first part of the superframe must be sufficient to give service to the network structure and its devices. Superframes are typically utilized within the context of low-latency devices, whose associations must be kept even if inactive for long periods of time.

Data transfers to the coordinator require a beacon synchronization phase, if applicable, followed by CSMA/CA transmission (by means of slots if superframes are in use); acknowledgment is optional. Data transfers from the coordinator usually follow device requests: if beacons are in use, these are used to signal requests; the coordinator acknowledges the request and then sends the data in packets which are acknowledged by the device. The same is done when superframes are not in use, only in this case there are no beacons to keep track of pending messages.

Point-to-point networks may either use unslotted CSMA/CA or synchronization mechanisms; in this case, communication between any two devices is possible, whereas in "structured" modes one of the devices must be the network coordinator.

In general, all implemented procedures follow a typical request-confirm/indication-response classification.

In CSMA/CA a Wireless node that wants to transmit performs the following simplified basic sequence:

Listen on the desired channel.

If channel is idle (no active transmitters) it sends a packet.

If channel is busy the node waits until transmission stops and then waits an additional time period *(DIFS).

If the channel is now idle at the end of the time period the node transmits its packet otherwise it repeats the process defined in 3 above until it gets a free channel.

The physical medium is accessed through a CSMA/CA protocol. Networks which are not using beaconing mechanisms utilize an unslotted variation which is based on the listening of the medium, leveraged by a random exponential back off algorithm; acknowledgments do not adhere to this discipline. Common data transmission utilizes unallocated slots when beaconing is in use; again, confirmations do not follow the same process.

Confirmation messages may be optional under certain circumstances, in which case a success assumption is made. Whatever the case, if a device is unable to process a frame at a given time, it simply does not confirm its reception: timeout-based retransmission can be performed a number of times, following after that a decision of whether to abort or keep trying.

Because the predicted environment of these devices demands maximization of battery life, the protocols tend to favour the methods which lead to it, implementing periodic checks for pending messages, the frequency of which depends on application needs.

Regarding secure communications, the MAC sub layer offers facilities which can be harnessed by upper layers to achieve the desired level of security. Higher-layer processes may specify keys to perform symmetric cryptography to protect the payload and restrict it to a group of devices or just a point-to-point link; these groups of devices can be specified in access control lists. Furthermore, MAC computes freshness checks between successive receptions to ensure that presumably old frames, or data which is no longer considered valid, does not transcend to higher layers.

In addition to this secure mode, there is another, insecure MAC mode, which allows access control lists merely as a means to decide on the acceptance of frames according to their (presumed) source.

Vulnerabilities

open source wireless communication protocol stack used in its ZigBee radio modules, generates pseudo-random numbers makes it easier for an attacker to eavesdrop on encrypted communications.

The weakness allows attackers to eavesdrop on wireless communications for devices such as automation systems and sensors and potentially even to access these devices. The vulnerability is of particularly concern in view of the widespread use of smart electricity meters in the USA. Some electricity providers use ZigBee to transfer data from electricity meters to base stations.

The crux of the problem is that the numbers generated by the random number generator (PRNG) for initialising the elliptic curve cryptography functions (ECC) used for asymmetric encryption are predictable. This not only makes calculating the ECC key used easier, it is then also possible to crack the AES key for symmetrical communication with other ZigBee modules, since this is transferred using ECC encryption.

According to developer Travis Goodspeed, the problem is the result of multiple factors. Firstly, the 16 bit seed used to initialise the PRNG is too short. Z-Stack also uses a relatively insecure version of a linear feedback shift register (LFSR) to generate its (pseudo) random numbers. Furthermore, tests carried out by Goodspeed show that the seed itself possesses only minimal entropy. Although the seed is derived from a digitally converted analogue signal from the radio module, the values are apparently not as scattered as might be expected. The stack also fails to support reseeding, so that as long as the module is turned on, the LFSR always generates random numbers from the same seed.

ZigBee modules with integrated 8051 compatible controllers, such as the CC2430 and CC2530, containing Z-Stack version 2.2.2-1.30 are affected, as are earlier versions. TI is planning to release Z-Stack version 2.3, which should use an improved PRNG.

 

Reliability

The reliability measures employed by ZigBee allow a wireless network to operate in a protected environment, even when there are other ZigBee networks nearby operating in the same frequency band. Adjacent ZigBee networks will not interfere with each other. In addition, ZigBee networks can operate in the neighbourhood of networks based on other standards, such as Wi-Fi and Bluetooth.

ZigBee offers a range of techniques to ensure reliable communications. These are described below.

Listen Before Send

The transmission scheme used in ZigBee avoids transmitting data when there is activity on the chosen channel - this is known as Carrier Sense, Multiple Access with Collision Avoidance (CSMA-CA).

Put simply, this means that before beginning a transmission, a node listens on the channel to check whether it is clear. If activity is detected on the channel, the node delays the transmission for a random amount of time and listens again. If the channel is now clear, the transmission can begin, otherwise the delay-and-listen cycle is repeated.

Acknowledgements

An acknowledgement mechanism is built into ZigBee to ensure that messages reach their destinations.

When a message arrives at its destination, the receiving device sends an acknowledgement to say the message has been received. If the sending device does not receive an acknowledgement within a certain time interval, it resends the original message (it can resend the message several times until the message has been acknowledged).

Alternative Routes

In a Mesh topology, the network has built-in intelligence to ensure that messages reach their destinations. If the default route to the destination node is down, due to a failed intermediate node or link, the network can "discover" and implement alternative routes for message delivery.

Security Measures

ZigBee networks are highly secure. They incorporate measures to prevent intrusion from potentially hostile parties and from neighbouring ZigBee networks. To this end, a "Security Toolbox" is included with ZigBee, offering the following features:

AES-based Encryption

A very high-security, key-based encryption system is used to prevent external agents from interpreting ZigBee network data. Data is encrypted at the source and decrypted at the destination using the same key - only devices with the correct key can decrypt the encrypted data.

A 128-bit encyption system is employed based on the AES (Advanced Encryption Standard) algorithm.

Message Timeout

This feature allows timed-out messages to be rejected, preventing message replay attacks on the network.

A frame counter is added to a message, which helps a device determine how old a received message is - the appended value is compared with a value stored in the device (which is the frame counter value of the last message received). This value only indicates the order of messages and does not contain time/date information. This allows protection against replay attacks in which old messages are later re-sent to a device.

An example of a replay attack would be a malicious individual recording the open command for a garage door opener, and then later replaying it to gain entry to the property.

Access Control Lists

A provision of the underlying IEEE 802.15.4 standard is that a node is able to select the other network nodes with which it is prepared to communicate. This is achieved using an Access Control List (ACL), maintained in the device, which contains the MAC addresses of nodes with which communication is allowed.

The source node of an incoming message is compared against this list, and the result is passed to the higher layers which decide whether to accept or reject the message. However, note that if messages are not encrypted, the alleged source of a message could be falsified.

Zigbee Future...

It looks promising ..................

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