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computer science topics
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23-06-2010, 10:42 PM


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The cellular network was a natural extension of the wired telephony network that became persistent during the mid-20th century. As the need for mobility and the cost of laying new wires increased, the motivation for a personal connection independent of location to that network also increased. Coverage of large area is provided through (1-2km) cells that cooperate with their neighbours to create a seemingly seamless network. Examples of standards are GSM, IS-136, IS-95. Cellular standards basically aimed at facilitating voice communications throughout a metropolitan area. During the mid-1980s, it turned out that an even smaller coverage area is needed for higher user densities and the emergent data traffic. Wireless communication is the transfer of information over a distance without the use of electrical conductors or "wires". The distances involved may be short (a few meters as in television remote control) or long (thousands or millions of kilometers for radio communications). When the context is clear, the term is often shortened to "wireless". Wireless communication is generally considered to be a branch of telecommunications.It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets, satellite television and cordless telephones.
The IEEE 802.11 working group for Wireless Local Area Network (WLAN) is formed, to create a wireless local area network standard. Whereas IEEE 802.11 was concerned with features such as Ethernet matching speed, long range(100m), complexity to handle seamless roaming, message forwarding, and data throughput of 2-11Mbps. Wireless personal area networks (WPANs) are used to convey information over relatively short distances. WPANs are focused on a space around a person or object that typically extends up to 10m in all directions. The focus of WPANs is low-cost, low power, short range and very small size. The IEEE 802.15 working group is formed to create WPAN standard. This group has currently defined three classes of WPANs that are differentiated by data rate, battery drain and quality of service (QoS).
The high data rate WPAN (IEEE 802.15.3) is suitable for multimedia applications that require very high QoS.
Medium rate WPANs (IEEE 802.15.1/Bluetooth) will handle a variety of tasks ranging from cell phones to PDA communications and have QoS suitable for voice communications.
The low rate WPANs (IEEE 802.15.4/LR-WPAN) is intended to serve a set of industrial, residential and medical applications with very low power consumption, with relaxed needs for data rate and QoS. The low data rate enables the LR-WPAN to consume very little power. This feature allows small, power-efficient, inexpensive solutions to be implemented for a wide range of devices.

IEEE 802 IEEE 802.11 IEEE 802.15.4 Zigbee Technology

Wireless networking (i.e. the various types of unlicensed 2.4 GHz WiFi devices) is used to meet many needs. Perhaps the most common use is to connect laptop users who travel from location to location. Another common use is for mobile networks that connect via satellite. A wireless transmission method is a logical choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless technology:
¢ To span a distance beyond the capabilities of typical cabling,
¢ To provide a backup communications link in case of normal network failure,
¢ To link portable or temporary workstations,
¢ To overcome situations where normal cabling is difficult or financially impractical, or
¢ To remotely connect mobile users or networks.
Applications of wireless technology
Security systems
Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings.
Television remote control
Modern televisions use wireless (generally infrared) remote control units. Now radio waves are also used.
Cellular telephone (phones and modems)
Perhaps the best known example of wireless technology is the cellular telephone and modems. These instruments use radio waves to enable the operator to make phone calls from many locations worldwide. They can be used anywhere that there is a cellular telephone site to house the equipment that is required to transmit and receive the signal that is used to transfer both voice and data to and from these instruments.
Wi-Fi is a wireless LAN technology that enables laptop PCs, PDAs, and other devices to connect easily to the internet. Technically known as IEEE 802.11 a,b,g,n, Wi-Fi is less expensive and nearing the speeds of standard Ethernet and other common wire-based LAN technologies. Several Wi-Fi hot spots have been popular over the past few years. Some businesses charge customers a monthly fee for service, while others have begun offering it for free in an effort to increase the sales of their goods.

Wireless energy transfer

Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of interconnecting wires.
Computer Interface Devices
Answering the call of customers frustrated with cord clutter, many manufactures of computer peripherals turned to wireless technology to satisfy their consumer base. Originally these units used bulky, highly limited transceivers to mediate between a computer and a keyboard and mouse, however more recent generations have used small, high quality devices, some even incorporating Bluetooth. These systems have become so ubiquitous that some users have begun complaining about a lack of wired peripherals. Wireless devices tend to have a slightly slower response time than their wired counterparts, however the gap is decreasing. Initial concerns about the security of wireless keyboards have also been addressed with the maturation of the technology.
Many scientists have complained that wireless technology interferes with their experiments, forcing them to use less optimal peripherals because the optimum one is not available in a wired version. This has become especially prevalent among scientists who use trackballs as the number of models in production steadily decreases.
IEEE 802.11
IEEE 802.11 is a set of standards carrying out wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).
2.1 General description

A Compaq 802.11b PCI card

The 802.11 family includes over-the-air modulation techniques that use the same basic protocol. The most popular are those defined by the 802.11b and 802.11g protocols, and are amendments to the original standard. 802.11-1997 was the first wireless networking standard, but 802.11b was the first widely accepted one, followed by 802.11g and 802.11n. Security was originally purposefully weak due to export requirements of some governments, and was later enhanced via the 802.11i amendment after governmental and legislative changes. 802.11n is a new multi-streaming modulation technique. Other standards in the family (c“f, h, j) are service amendments and extensions or corrections to previous specifications.
802.11b and 802.11g use the 2.4 GHz ISM band, operating in the United States under Part 15 of the US Federal Communications Commission Rules and Regulations. Because of this choice of frequency band, 802.11b and g equipment may occasionally suffer interference from microwave ovens, cordless telephones and Bluetooth devices. Both 802.11 and Bluetooth control their interference and susceptibility to interference by using spread spectrum modulation. Bluetooth uses a frequency hopping spread spectrum signaling method (FHSS), while 802.11b and 802.11g use the direct sequence spread spectrum signaling (DSSS) and orthogonal frequency division multiplexing (OFDM) methods, respectively. 802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 19 non-overlapping channels rather than the 3 offered in the 2.4 GHz ISM frequency band. Better or worse performance with higher or lower frequencies (channels) may be realized, depending on the environment.
The segment of the radio frequency spectrum used varies between countries. In the US, 802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the FCC Rules and Regulations. Frequencies used by channels one through six (802.11b) fall within the 2.4 GHz amateur radio band. Licensed amateur radio operators may operate 802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.

2.2 Protocols

In the field of telecommunications, a communications protocol is the set of standard rules for data representation, signaling, authentication and error detection required to send information over a communications channel. An example of a simple communications protocol adapted to voice communication is the case of a radio dispatcher talking to mobile stations. Communication protocols for digital computer network communication have features intended to ensure reliable interchange of data over an imperfect communication channel. Communication protocol is basically following certain rules so that the system works properly.
802.11-1997 (802.11 legacy)
The original version of the standard IEEE 802.11 was released in 1997 and clarified in 1999, but is today obsolete. It specified two net bit rates of 1 or 2 megabits per second (Mbit/s), plus forward error correction code. It specifed three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequencespread spectrum operating at 1 Mbit/s or 2 Mbit/s. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz. Some earlier WLAN technologies used lower frequencies, such as the U.S. 900 MHz ISM band.
Legacy 802.11 with direct-sequence spread spectrum was rapidly supplanted and popularized by 802.11b.


Release date Op. Frequency Throughput (typ.) Net Bit Rate (max.) Gross Bit Rate (max.) Max Indoor Range Max Outdoor Range
October 1999 5 GHz 20 Mbit/s 54 Mbit/s 72 Mbit/s ~50 ft/15 meters ~100 ft/30 meters
The 802.11a standard uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface (physical layer). It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net. achievable throughput in the mid-20 Mbit/s
Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively un-used 5 GHz band gives 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: The effective overall range of 802.11a is less than that of 802.11b/g. In theory, 802.11a signals are absorbed more readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of 802.11b. In practice, 802.11b typically has a higher range at low speeds (802.11b will reduce speed to 5 Mbit/s or even 1 Mbit/s at low signal strengths). However, at higher speeds, 802.11a often has the same or greater range due to less interference.
Release date Op. Frequency Throughput (typ.) Net Bit Rate (max.) Gross Bit Rate (max.) Max Indoor Range Max Outdoor Range
October 1999 2.4 GHz ~5 Mbit/s 11 Mbit/s Mbit/s ~150 feet/45 meters ~300 feet/90 meters
802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. 802.11b products appeared on the market in early 2000, since 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.
802.11b devices suffer interference from other products operating in the 2.4 GHz band. Devices operating in the 2.4 GHz range include: microwave ovens, Bluetooth devices, baby monitors and cordless telephones.


Release date Op. Frequency Throughput (typ.) Net Bit Rate (max.) Gross Bit Rate (max.) Max Indoor Range Max Outdoor Range
June 2003 2.4 GHz ~22 Mbit/s 54 Mbit/s 128 Mbit/s ~150 feet/45 meters ~300 feet/90 meters
In June 2003, a third modulation standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b), but uses the same OFDM based transmission scheme as 802.11a. It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput. 802.11g hardware is fully backwards compatible with 802.11b hardware and therefore is encumbered with legacy issues that reduce throughput when compared to 802.11a by ~21%.
The then-proposed 802.11g standard was rapidly adopted by consumers starting in January 2003, well before ratification, due to the desire for higher data rates as well as to reductions in manufacturing costs. By summer 2003, most dual-band 802.11a/b products became dual-band/tri-mode, supporting a and b/g in a single mobile adapter card or access point. Details of making b and g work well together occupied much of the lingering technical process; in an 802.11g network, however, activity of an 802.11b participant will reduce the data rate of the overall 802.11g network.
Like 802.11b, 802.11g devices suffer interference from other products operating in the 2.4 GHz band.

2.3 Standard and amendments

Within the IEEE 802.11 Working Group, the following IEEE Standards Association Standard and Amendments exist:
IEEE 802.11 - The WLAN standard was original 1 Mbit/s and 2 Mbit/s, 2.4 GHz RF and infrared [IR] standard (1997), all the others listed below are Amendments to this standard, except for Recommended Practices 802.11F and 802.11T.
IEEE 802.11a - 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001)
IEEE 802.11b - Enhancements to 802.11 to support 5.5 and 11 Mbit/s (1999)
IEEE 802.11c ” Bridge operation procedures; included in the IEEE 802.1D standard (2001)
IEEE 802.11d - International (country-to-country) roaming extensions (2001)
IEEE 802.11e - Enhancements: QoS, including packet bursting (2005)
IEEE 802.11F - Inter-Access Point Protocol (2003) Withdrawn February 2006
IEEE 802.11g - 54 Mbit/s, 2.4 GHz standard (backwards compatible with b) (2003)
& many more.

Standard (or) amendment

Both the terms "standard" and "amendment" are used when referring to the different variants of IEEE 802.11.
As far as the IEEE Standards Association is concerned, there is only one current standard; it is denoted by IEEE 802.11 followed by the date that it was published. IEEE 802.11-2007 is the only version currently in publication. The standard is updated by means of amendments. Amendments are created by task groups (TG). Both the task group and their finished document are denoted by 802.11 followed by a non-capitalized letter. For example IEEE 802.11a and IEEE 802.11b. Updating 802.11 is the responsibility of task group m. In order to create a new version, TGm combines the previous version of the standard and all published amendments. TGm also provides clarification and interpretation to industry on published documents. New versions of the IEEE 802.11 were published in 1999 and 2007.
The working title of 802.11-2007 was 802.11-REVma. This denotes a third type of document, a "revision". The complexity of combining 802.11-1999 with 8 amendments made it necessary to revise already agreed upon text. As a result, additional guidelines associated with a revision had to be followed.


In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node. The throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second or data packets per time slot.
The system throughput or aggregate throughput is the sum of the data rates that are delivered to all terminals in a network.
The throughput can be analyzed mathematically by means of queueing theory, where the load in packets per time unit is denoted arrival rate , and the throughput in packets per time unit is denoted departure rate µ.
Throughput is essentially synonymous to digital bandwidth consumption.
Bit rate
In telecommunications and computing, bitrate (sometimes written bit rate, data rate or as a variable R or fb) is the number of bits that are conveyed or processed per unit of time.
The bit rate is quantified using the bits per second (bit/s or bps) unit, often in conjunction with an SI prefix such as kilo- (kbit/s or kbps), mega- (Mbit/s or Mbps),giga- (Gbit/s or Gbps) or tera- (Tbit/s or Tbps). Note that, unlike many other computer-related units, 1 kbit/s is traditionally defined as 1,000 bit/s, not 1,024 bit/s, etc, also before 1999 when SI prefixes were introduced for units of information in the standard IEC 60027-2.The formal abbreviation for "bits per second" is "bit/s" (not "bits/s"). In less formal contexts the abbreviations "b/s" or "bps" are often used, though this risks confusion with "bytes per second" ("B/s", "Bps").

2.4 Advantages and Disadvantages of WLANs

WLANs have advantages and disadvantages when compared with wired LANs. A WLAN will make it simple to add or move workstations and to install access points to provide connectivity in areas where it is difficult to lay cable. Temporary or semipermanent buildings that are in range of an access point can be wirelessly connected to a LAN to give these buildings connectivity. Where computer labs are used in schools, the computers (laptops) could be put on a mobile cart and wheeled from classroom to classroom, provided they are in range of access points. Wired network points would be needed for each of the access points. A WLAN has some specific advantages:
¢ It is easier to add or move workstations.
¢ It is easier to provide connectivity in areas where it is difficult to lay cable.
¢ Installation is fast and easy, and it can eliminate the need to pull cable through walls and ceilings.
¢ Access to the network can be from anywhere within range of an access point.
¢ Portable or semipermanent buildings can be connected using a WLAN.
¢ Although the initial investment required for WLAN hardware can be similar to the cost of wired LAN hardware, installation expenses can be significantly lower.
¢ When a facility is located on more than one site (such as on two sides of a road), a directional antenna can be used to avoid digging trenches under roads to connect the sites.
¢ In historic buildings where traditional cabling would compromise the façade, a WLAN can avoid the need to drill holes in walls.
¢ Long-term cost benefits can be found in dynamic environments requiring frequent moves and changes.
WLANs also have some disadvantages:
¢ As the number of computers using the network increases, the data transfer rate to each computer will decrease accordingly.
¢ As standards change, it may be necessary to replace wireless cards and/or access points.
¢ Lower wireless bandwidth means some applications such as video streaming will be more effective on a wired LAN.
¢ Security is more difficult to guarantee and requires configuration.
¢ Devices will only operate at a limited distance from an access point, with the distance determined by the standard used and buildings and other obstacles between the access point and the user.
¢ A wired LAN is most likely to be required to provide a backbone to the WLAN; a WLAN should be a supplement to a wired LAN and not a complete solution.
¢ Long-term cost benefits are harder to achieve in static environments that require few moves and changes.

3.1General description

A LR-WPAN is a simple, low-cost communication network that allows wireless connectivity in applications with limited power and relaxed throughput requirements. The main objectives of an LR-WPAN are ease of installation, reliable data transfer, short-range operation, extremely low cost, and a reasonable battery life, while maintaining a simple and flexible protocol.
A wireless personal area network (WPAN for short) is a low-range wireless network which covers an area of only a few dozen meters. This sort of network is generally used for linking peripheral devices (like printers, cell phones, and home appliances) or a personal assistant (PDA) to a computer, or just two nearby computers, without using a hard-wired connection. There are several kinds of technology used for WPANs.
The main WPAN technology is Bluetooth, launched by Ericsson in 1994, which offers a maximum throughput of 1 Mbps over a maximum range of about thirty meters. Bluetooth, also known as IEEE 802.15.1, has
the advantage of being very energy-efficient, which makes it particularly well-suited to use in small devices.
HomeRF (for Home Radio Frequency), launched in 1998 by HomeRF Working Group (which includes the manufacturers Compaq, HP, Intel, Siemens, Motorola and Microsoft, among others) has a maximum throughput of 10 Mbps with a range of about 50 to 100 metres without an amplifier. The HomeRF standard, despite Intel's support, was abandoned in January 2003, largely because processor manufacturers had started to support on-board Wi-Fi (via Centrino technology, which included a microprocessor and a Wi-Fi adapter on a single component).
The three license-free frequencies of the IEEE 802.15.4 standard include sixteen channels at 2.4 GHz, ten channels at 915 MHz, and one channel at 868 MHz, to support global or regional deployment. The maximum data rates for each band are 250 kbps, 40 kbps and 20 kbps, respectively. The air interface is direct sequence spread spectrum (DSSS) using binary phase shift keying (BPSK) for 868 MHz and 915 MHz and offset-quadrature phase shift keying (OQPSK) for 2.4 GHz. Other features of the IEEE 802.15.4 PHY include receiver energy detection, link quality indication and clear channel assessment. Both contention-based and contention-free channel access methods are supported. Maximum packet size is 128 bytes, including a variable payload of up to 104 bytes. IEEE 802.15.4 employs 64-bit IEEE and 16-bit short addresses, which supports over 65,000 nodes per network. The IEEE 802.15.4 MAC also enables network association and disassociation, has an optional super frame structure with beacons for time synchronization, and a guaranteed time slot (GTS) mechanism for high priority communications. The access method is carrier sense multiple access with collision avoidance (CSMA-CA). Network routing schemes
are designed to ensure power conservation, and low latency through guaranteed time slots. A unique feature of ZigBee network layer is communication redundancy eliminating single point of failure in mesh networks.IEEE and ZigBee Alliance have been working closely to specify the entire protocol stack. IEEE 802.15.4 focuses on the specification of the lower two layers of the protocol (physical and data link layer). On the other hand, ZigBee Alliance aims to provide the upper layers of the protocol stack (from network to the application layer) for interoperable data networking, security services and a range of wireless home and building control solutions.

3.2 Zigbee and IEEE 802.15.4

The IEEE 802.15.4 standard is a simple packet data protocol for lightweight wireless networks and specifies the Physical (PHY) and Medium Access Control (MAC) layers for Multiple Radio frequency (RF) bands, including 868 MHz, 915 MHz, and 2.4 GHz. The IEEE 802.15.4 standard is designed to provide reliable data transmission of modest amounts of data up to 100 meters or more while consuming very little power. IEEE 802.15.4 is typically less than 32 kb in size, featuring a 64-bit address space, source and destination addressing, error detection, and advanced power management.
ZigBee technology takes full advantage of the IEEE 802.15.4 standard and extends the capabilities of this new radio standard by defining a flexible and secure network layer that supports a variety of architectures to provide highly reliable wireless communications in harsh or dynamic RF environments. ZigBee technology also offers simplicity and a cost-effective approach to building, construction and remodelling with wireless technology. ZigBee is all set to provide the consumers with ultimate flexibility, mobility, and ease of use by building wireless intelligence and apabilities into every day devices. ZigBee is expected to provide low cost and low power connectivity for equipment that needs battery life as long as several months to several years but does not require data transfer rates as high as those enabled by Bluetooth. This kind of network eliminates use of physical Ethernet cables. The devices could include telephones, hand-held digital assistants, sensors and controls located within a few meters of each other. Thus, ZigBee technology is a low data rate, low power consumption, low cost; wireless networking protocol targeted towards automation and remote control applications.

3.3 ZigBee Alliance

The ZigBee Alliance is an association of companies working together to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard.
The goal of the ZigBee Alliance is to provide the consumer with ultimate flexibility, mobility, and ease of use by building wireless intelligence and capabilities into every day devices. ZigBee technology will be embedded in a wide range of products and applications across consumer, commercial, industrial and government markets worldwide. For the first time, companies will have a standards-based wireless platform optimized for the unique needs of remote monitoring and control applications, including simplicity, reliability, low-cost and low-power.

4.1 WHY the name Zigbee

It has been suggested that the name evokes the haphazard paths that bees follow as they harvest pollen, similar to the way packets would move through a mesh network Using communication system, whereby the bee dances in a zig-zag pattern, worker bee is able to share information such as the location, distance, And direction of a newly discovered food source to her fellow colony members. Instinctively implementing the ZigBee Principle, bees around the world actively sustain productive itchiness and promote future generations of Colony members.

4.2 Zigbee characteristics

The focus of network applications under the IEEE 802.15.4 / ZigBee standard include the features of low power consumption, needed for only two major modes (Tx/Rx or Sleep), high density of nodes per network, low costs and simple implementation. These features are enabled by the following characteristics
2.4GHz and 868/915 MHz dual PHY modes.
This represents three license-free bands: 2.4-2.4835 GHz, 868-870 MHz and 902-928 MHz The number of channels allotted to each frequency band is fixed at 16 channels in the 2.45 GHz band, 10 channels in the 915 MHz band, and 1 channel in the 868 MHz band
Maximum data rates allowed for each of these frequency bands are fixed as 250 kbps @2.4 GHz, 40 kbps @ 915 MHz, and 20 kbps @868 MHz Allocated 16 bit short or 64 bit extended addresses.
Allocation of guaranteed time slots (GTSs)
Carrier sense multiple access with collision avoidance (CSMA-CA) channel access Yields high throughput and low latency for low duty cycle devices like sensors and controls.
Fully hand-shake acknowledged protocol for transfer reliability.
Low power consumption with battery life ranging from months to years.
Energy detection (ED).
Link quality indication (LQI).
Multiple topologies : star, peer-to-peer, mesh topologies

Device Types

ZigBee devices are required to conform to the IEEE 802.15.4-2003 Low- Rate Wireless Personal Area Network (WPAN) standard. ZigBee wireless devices are expected to transmit 10-75 meters, depending on the RF environment and the power output consumption required for a given application, and will operate in the unlicensed RF worldwide (2.4GHz global, 915MHz Americas or 868 MHz Europe). The data rate is 250kbps at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz. There are three different ZigBee device types that operate on these layers in any self-organizing application network. These devices have 64-bit IEEE addresses, with option to enable shorter addresses to reduce packet size, and work in either of two addressing modes “ star and peer-to-peer.
The ZigBee (PAN) coordinator node: The most capable device, the coordinator forms the root of the network tree and might bridge to other networks. It is able to store information about the network.There is one, and only one, ZigBee coordinator in each network to act as the router to other network. It also acts as the repository for security keys.
The Full Function Device (FFD): The FFD is an intermediary router transmitting data from other devices. It needs lesser memory than the ZigBee coordinator node, and entails lesser manufacturing costs. It can operate in all topologies and can act as a coordinator.
The Reduced Function Device (RFD) : This device is just capable of talking in the network; it cannot relay data from other devices. Requiring even less memory, (no flash, very little ROM and RAM), an RFD will thus be cheaper than an FFD. This device talks only to a network coordinator and can be implemented very simply in star topology.
An FFD can talk to RFDs or other FFDs, while an RFD can talk only to an FFD. An RFD is intended for applications that are extremely simple, such as a light switch or a passive infrared sensor; they do not have the need to send large amounts of data and may only associate with a single FFD at a time. Consequently, the RFD can be implemented using minimal resources and memory capacity.

4.3 Network Topologies

Types of topologies that ZigBee supports: star topology, peer-to-peer topology and cluster tree.

Star Topology

In the star topology, the communication is established between devices and a single central controller, called the PAN coordinator. The PAN coordinator may be mains powered while the devices will most likely be battery powered. Applications that benefit from this topology include home automation, personal computer (PC) peripherals, toys and games. After an FFD is activated for the first time, it may establish its own network and become the PAN coordinator. Each start network chooses a PAN identifier, which is not currently used by any other network within the radio sphere of influence. This allows each star network to operate independently.

Peer-to-peer Topology

In peer-to-peer topology, there is also one PAN coordinator. In contrast to star topology, any device can communicate with any other device as long as they are in range of one another. A peer-to-peer network can be ad hoc, self-organizing and self-healing. Applications such as industrial control and monitoring, wireless sensor networks, asset and inventory tracking would benefit from such a topology. It also allows multiple hops to route messages from any device to any other device in the network. It can provide reliability by multipath routing.

Cluster-tree Topology

Cluster-tree network is a special case of a peer-to-peer network in which most devices are FFDs and an RFD may connect to a cluster-tree network as a leave node at the end of a branch. Any of the FFD can act as a coordinator and provide synchronization services to other devices and coordinators.
Only one of these coordinators however is the PAN coordinator. The PAN coordinator forms the first cluster by establishing itself as the cluster head (CLH) with a cluster identifier (CID) of zero, choosing an unused PAN identifier, and broadcasting beacon frames to neighbouring devices. A candidate device receiving a beacon frame may request to join the network at the CLH. If the PAN coordinator permits the device to join, it will add this new device as a child device in its neighbour list. The newly joined device will add the CLH as its parent in its neighbour list and begin transmitting periodic beacons such that other candidate devices may then join the network at that device. Once application or network requirements are met, the PAN coordinator may instruct a device to become the CLH of a new cluster adjacent to the first one. The advantage of this clustered structure is the increased coverage area at the cost of increased message latency.


The LR-WPAN architecture is defined in terms of a number of blocks inorder to simplify the standard. These blocks are called layers. Each layer is responsible for one part of the standard and offers services to the higher layers. The layout of the blocks is based on the open systems interconnection (OSI) seven-layer model. The interfaces between the layers serve to define the logical links between layers. The LR-WPAN architecture can be implemented either as embedded devices or as devices requiring the support of an external device such as a PC.
An LR-WPAN device comprises a PHY, which contains the radio frequency (RF) transceiver along with its low-level control mechanism, and a MAC sub layer that provides access to the physical channel for all types of transfer.

Network and Application
Support layer :

The network layer permits growth of network sans high power transmitters. This layer can handle huge numbers of nodes. This level in the ZigBee architecture includes
The ZigBee Device Object (ZDO)
User-Defined Application Profile(s)
The Application Support (APS) Sub-layer.
The APS sub-layer's responsibilities include maintenance of tables that enable matching between two devices and communication among them, and also discovery, the aspect that identifies other devices that operate in the operating space of any device.
The responsibility of determining the nature of the device (Coordinator / FFD or RFD) in the network, commencing and replying to binding requests and ensuring a secure relationship between devices rests with the ZDO (Zigbee Define Object). The user-defined application refers to the end
device that conforms to the ZigBee Standard.

Physical (PHY) layer:

The PHY service enables the transmission and reception of PHY protocol data units (PPDU) across the physical radio channel. The features of the IEEE 802.15.4 PHY physical layer are Activation and deactivation of the radio transceiver, energy detection (ED), Link quality indication (LQI), channel selection, clear channel assessment (CCA) and transmitting as well as receiving packets across the physical medium.

Media access control
(MAC) layer:

The MAC service enables the transmission and reception of MAC protocol data units (MPDU) across the PHY data service. The features of MAC sub layer are beacon management, channel access, GTS management, frame validation, acknowledged frame delivery, association and disassociation.

IEEE 802.15.4 PHY

The PHY provides an interface between the MAC sub layer and the physical radio channel, via the RF firmware and RF hardware. The PHY conceptually includes a management entity called the PLME. This entity provides the layer management service interfaces through which layer management functions may be invoked. The PLME is also responsible for maintaining a database of managed objects pertaining to the PHY. This database is referred to as the PHY PAN Information base (PIB).
Figure 3.1 depicts the components and interfaces of the PHY. The PHY provides two services, accessed through two SAPs: The PHY data service accessed through the PHY Data SAP (PD-SAP).
The PHY data service enables the transmission and reception of PHY protocol data units (PPDUs) across the physical radio channel. The PHY management service, accessed through the PLMEâ„¢s AP (PLMESAP). The features of the PHY are activation and deactivation of the radio transceiver, energy detection(ED), link quality indication (LQI), channel selection, clear channel assessment (CCA) and transmitting as well as receiving packets across the physical medium.
The standard offers two PHY options based on the frequency band. Both are based on direct sequence spread spectrum (DSSS). The data rate is 250kbps at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz. The higher data rate at 2.4GHz is attributed to a higher-order modulation scheme. Lower frequency provides longer range due to lower propagation losses. Low rate can be translated into better sensitivity and larger coverage area. Higher rate means higher throughput, lower latency or lower duty cycle. This information is summarized in Figure 3.2.
There is a single channel between 868 and 868.6MHz, 10 channels between 902.0 and 928.0MHz, and 16 channels between 2.4 and 2.4835GHz as shown in Figure 3.3. Several channels in different frequency bands enables the ability to relocate within spectrum. The standard also allows dynamic Channel selection, a scan function that steps through a list of supported channels in search of beacon, receiver energy detection, link quality indication, channel switching.

Data Transfer model

Three types of data transfer transactions exist: from a coordinator to a device, from a device to a coordinator and between two peer devices. The mechanism for each of these transfers depends on whether the network supports the transmission of beacons. The non-beacon mode will be included in a system where devices are Ëœasleep' nearly always, as in smoke detectors and burglar alarms. The devices wake up and confirm their continued presence in the network at random intervals. When a device wishes to transfer data in a no beacon-enabled network, it simply transmits its data frame, using the unslotted CSMA-CA, to the coordinator. On detection of activity, the sensors Ëœspring to attention', as it were, and transmit to the ever-waiting coordinator's receiver (since it is mains-powered). There is also an optional acknowledgement at the end as shown in Figure 4.3.

4.3 Beacon enabled model

In the beacon mode, a device watches out for the coordinator's beacon that gets transmitted at periodically, locks on and looks for messages addressed to it. If message transmission is complete, the coordinator dictates a schedule for the next beacon so that the device Ëœgoes to sleep'; in fact, the coordinator itself switches to sleep mode. While using the beacon mode, all the devices in a mesh network know when to communicate with each other. In this mode, necessarily, the timing circuits have to be quite accurate, or wake up sooner to be sure not to miss the beacon. This in turn means an increase in power consumption by the coordinator's receiver, entailing an optimal increase in costs. When a device wishes to transfer data to a coordinator in a beacon-enabled network, it first listens for the network beacon. When the beacon is found, it synchronizes to the super frame structure. At the right time, it transmits its data frame, using slotted CSMA-CA, to the coordinator. There is an optional acknowledgement at the end as shown in Figure 4.4.
The applications transfers are completely controlled by the devices on a PAN rather than by the coordinator. This provides the energy-conservation feature of the ZigBee network. When a coordinator wishes to transfer data to a device in a beacon-enabled network, it indicates in the network beacon that the data message is pending. The device periodically listens to the network beacon, and if a message is pending, transmits a MAC command requesting this data, using slotted CSMA-CA. The coordinator optionally acknowledges the successful transmission of this packet. The pending data frame is then sent using slotted CSMA-CA. The device acknowledged the successful reception of the data by transmitting an acknowledgement frame. Upon receiving the acknowledgement, the message is removed from the list of pending messages in the beacon as shown in Figure 4.5.
When a coordinator wishes to transfer data to a device in a non beacon enabled network, it stores the data for the appropriate device to make contact and request data. A device may make contact by transmitting a MAC command requesting the data, using unslotted CSMA-CA, to its coordinator at an application-defined rate. The coordinator acknowledges this packet. If data are pending, the coordinator transmits the data frame using unslotted CSMA-CA. If data are not pending, the coordinator transmits a data frame with a zero-length payload to indicate that no data were pending.
The device acknowledges this packet as shown in Figure 4.6.
In a peer-to-peer network, every device can communicate with any other device in its transmission radius. There are two options for this. In the first case, the node will listen constantly and transmit its data using unslotted CSMA-CA. In the second case, the nodes synchronize with each Other so
that they can save power.


ZigBee is an open and global standard for WSN. The first version v1.0 was ratified in December 2004 by the ZigBee Alliance that is an association of 186 companies. The standard is a part of the Low Rate Wireless Personal Area Network (LR-WPAN). The aim of the standard is to define low cost, low effect, wireless networks for short range and embedded applications. The purpose is that products based on ZigBee will, independent of implementer and manufacturer, produce interoperable, low cost and highly usable devices.

A. ZigBee Stack

It is divided in layers for the functions that are performed at specific level. The functions are called services. The architecture is based on the standard Open System Interconnection (OSI) seven layers model. The OSI model was developed for multi vendor equipment interoperability. It is intended for communication between hardware and software systems independent of underlying architecture. The first two layers, the physical (PHY) and Medium Access Control (MAC) are defined in the IEEE 802.15.4 standard. The other layers that build on they PHY and MAC layers are defined by the ZigBee alliance. Each layer has a defined set of services, a service entity. The Data Entity (DE) performs the data transmission 6 and the Management Entity (ME) performs all other services. The service entity communication between layers is performed through Service Access Points (SAP) that supports service primitives to perform the required functionality. The PHY layer contains the RF transceiver and access to the other hardware and control mechanisms. The function of the PHY is to activate and deactivate the radio transceiver and other hardware specific services such as radio frequency quality indicators and access to the channels. The PHY layer supports the IEEE 802.15.4 standard that can use three frequency bands. The three frequency bands are 868MHz, 916MHz and 2.4GHz. The 2.4GHz band reaches the maximum data rate of 250Kbps. The MAC layer is as described by the name a controlling device for the radio medium. It controls access to the physical radio channel andother services defined by the PHY service. It is also responsible for a reliable transmission system through its services. The services are about channel access and transmission techniques and validation of data packets.
Ad hoc is a Latin phrase which means "for this purpose". It generally signifies a solution designed for a specific problem or task, non-generalizable, and which cannot be adapted to other purposes. Common examples are organizations, committees, and commissions created at the national or international level for a specific task. In other fields the term may refer, for example, to a tailor-made suit, a handcrafted network protocol or a purpose-specific equation. Ad hoc can also have connotations of a makeshift solution, inadequate planning, or improvised events.
Multipath routing in wireless networks
To improve performance or fault tolerance:
CMR (Concurrent Multipath Routing) is often taken to mean simultaneous management and utilization of multiple available paths for the transmission of streams of data emanating from an application or multiple applications. In this form, each stream is assigned a separate path, uniquely to the extent supported by the number of paths available. If there are more streams than available paths, some streams will share paths. This provides better utilization of available bandwidth by creating multiple active transmission queues. It also provides a measure of fault tolerance in that, should a path fail, only the traffic assigned to that path is affected, the other paths continuing to serve their stream flows; there is also, ideally, an alternative path immediately available upon which to continue or restart the interrupted stream.
This method provides better transmission performance and fault tolerance by providing:
¢ Simultaneous, parallel transport over multiple carriers.
¢ Load balancing over available assets.
¢ Avoidance of path discovery when re-assigning an interrupted stream.
Shortcomings of this method are:
¢ Some applications may be slower in offering traffic to the transport layer, thus starving paths assigned to them, causing underutilization.
¢ Moving to the alternative path will incur a potentially disruptive period during which the connection is re-established.
A more powerful form of CMR (true CMR) goes beyond merely presenting paths to applications to which they can bind. True CMR aggregates all available paths into a single, virtual path. All applications offer their packets to this virtual path, which is de-muxed at the Network Layer, the packets then being distributed to the actual paths via some method such as round-robin or weighted fair queuing. Should a link or relay node fail, thus invalidating one or more paths, succeeding packets are not directed to that (those) paths. The stream continues uninterrupted, transparently to the application. This method provides significant performance benefits over the former:
¢ By continually offering packets to all paths, the paths are more fully utilized.
¢ No matter how many nodes (and thus paths) fail, so long as at least one path constituting the virtual path is still available, all sessions remain connected. This means that no streams need to be restarted from the beginning and no re-connection penalty is incurred.
It is noted that true CMR can, by its nature, cause Out-Of-Order-Delivery (OOOD) of packets, which is severely debilitating for standard TCP. Standard TCP, however, has been exhaustively proven to be inappropriate for use in challenged wireless environments and must, in any case, be augmented by a facility, such as a TCP gateway, that is designed to meet the challenge. One such gateway tool is SCPS-TP, which, through its Selective Negative Acknowledgement (SNACK) capability, deals successfully with the OOOD problem.
A wireless router is a device that performs the functions of a router but also includes the functions of a wireless access point. It is commonly used to allow access to the Internet or a computer network without the need for a cabled connection. It can function in a wired LAN (local area network), a wireless only LAN, or a mixed wired/wireless network. Most current wireless routers have the following characteristics:
¢ LAN ports, which function in the same manner as the ports of a network switch
¢ A WAN port, to connect to a wider area network. The routing functions are filtered using this port. If it is not used, many functions of the router will be bypassed.
¢ Wireless antennae. These allow connections from other wireless devices (NICs (network interface cards), wireless repeaters, wireless access points, and wireless bridges, for example).
¢ Routing (or routeing) is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network, electronic data networks (such as the Internet), and transportation networks. This article is concerned primarily with routing in electronic data networks using packet switching technology.
¢ In packet switching networks, routing directs packet forwarding, the transit of logically addressed packets from their source toward their ultimate destination through intermediate nodes; typically hardware devices called routers, bridges, gateways, firewalls, or switches. General-purpose computers with multiple network cards can also forward packets and perform routing, though they are not specialized hardware and may suffer from limited performance. The routing process usually directs forwarding on the basis of routing tables which maintain a record of the routes to various network destinations. Thus, constructing routing tables, which are held in the routers' memory, is very important for efficient routing. Most routing algorithms use only one network path at a time, but multipath routing techniques enable the use of multiple alternative paths.
¢ Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Because structured addresses allow a single routing table entry to represent the route to a group of devices, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging) in large networks, and has become the dominant form of addressing on the Internet, though bridging is still widely used within localized environments.

4.7 ZigBee Applications

The Zigbee Alliance targets applications "across consumer, commercial, industrial and government markets worldwide". Unwired applications are highly sought after in many networks that are characterized by numerous nodes consuming minimum power and enjoying long battery lives.
ZigBee technology is designed to best suit these applications, for the reason that it enables reduced costs of development, very fast market adoption, and rapid ROI. With ZigBee designed to enable two-way communications, not only will the consumer be able to monitor and keep track of domestic utilities usage, but also feed it to a computer system for data analysis.
A recent analyst report issued by West Technology Research Solutions estimates that by the year 2008, "annual shipments for ZigBee chipsets into the home automation segment alone will exceed 339 million units," and will show up in "light switches, fire and smoke detectors, thermostats, appliances in the kitchen, video and audio remote controls, landscaping, and security systems." Futurists are sure to hold ZigBee up and say, "See, I told you so".
The ZigBee Alliance is nearly 300 strong and growing, with more OEM's signing up. This means that more and more products and even later, all devices and their controls will be based on this standard. Since Wireless personal Area Networking applies not only to household devices, but also to individualized office automation applications, ZigBee is here to stay. It is more than likely the basis of future home-networking solutions.
The technology is designed to be simpler and cheaper than other WPANs such as Bluetooth. The most capable ZigBee node type is said to require only about 10% of the software of a typical Bluetooth or Wireless Internet node, while the simplest nodes are about 2%. ZigBee is aimed at applications with low data rates and low power consumption.


Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer.
Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from around 1980[1] to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET.
Applications areas :

Enterprise systems : health care and patient monitoring, environmental , Monitoring and hazard detection.
Industrial systems : remote controlled machines such as in tracking wind turbines.
Military and government systems : asset tracking, personnel monitoring and surveillance.
Transportation systems : audio control and automation, security and access control.
Consumer products : cellular handsets , computer peripherals, remote controls and other portable devices.
Climate control : customize the temperatures of ac machines or thermostats as differently needed.
Home automation : turn on or off ovens, air conditioners, geysers, lights without any hassles only when needed. Also sprinkle water to plants in garden monitoring moisture content in soil.
Private Security : this also acts like a private security to monitor kids or aged even from office and alert in case of medical emergencies.


It is crucial to keep a close look on the development of premature baby. Every year, in the United States, up to 1,300 babies are born prematurely and most of these babies are going to spend weeks or even months in the neonatal intensive care unit (NICU). The baby needs to receive special care in the NICU before he/she is able to go home. Sometimes, the babies may have to be kept in the incubator, nourished intravenously and placed on oxygen. Blood pressure, breathing levels, heart rate and also oxygen levels need to be observed closely. Currently most hospitals use ECG (Electrocardiography) for monitoring a babyâ„¢s heart rate. However, a reliable remote monitoring system is usually absent. Our project and implimentation proposes a solution to upgrade existing health monitoring systems in hospitals by providing remote monitoring capability. This solution may be applicable to any kind of patients apart from pre-mature babies. For example, monitoring the vital information such as heart rate, blood pressure, etc of the inmates of an old age home could be a potential application. In this paper, we develop a heart rate monitoring system for the babies who are kept in the incubators in different rooms.
The system will allow hospital personnel to remotely monitor the heart rate from the center monitoring system so that a baby can be given immediate assistance in case her/his heart rate falls or goes beyond limit. Wireless devices collect the heart rate information for babies kept in various incubators and transmit the heart rate information to the central wireless device which is kept in the incubator/hospital room through the wireless communication network. The central wireless device then sends the information to the central monitoring room over LAN. The central monitoring system along with the central wireless device in each incubator room is connected to the same LAN.
Fig 1 illustrates a ZigBee protocol based wireless sensor network of nodes which measures the heart rate of pre-mature babies inside incubators.
The information sensed by each ZigBee node is sent periodically to a ZigBee coordinator device in the same incubator room. The ZigBee coordinator is responsible for initiating the ZigBee network and collecting heart-rate information from each sensor nodes. The coordinator sends the collected information to a computer through RS 232 serial communication. A software running on the computer parses the information and passes on the data to a central monitoring system through LAN. The software maps the unique device ID of ZigBee sensor nodes to various incubators placed in the room. Fig 2 shows a LAN based remote monitoring architecture, in which each incubator room has a ZigBee based wireless sensor network.
A survey of heart rate monitors available in market is shown in TABLE 1. Most of these products use Bluetooth technology. They are costly and only few of these products have the capability of providing remote monitoring.


T.W..Nam et al. developed a wireless heart rate monitoring system for rehabilitation patients who are taking physical therapy inside a rehabilitation center. a monitoring system that can monitor patientsâ„¢ heart rates so that it gives physical therapist early warning if necessary. The whole system consists of the patientâ„¢s side device (PSD) and central monitoring system (CMS). The PSD was designed to be wearable and low power consumption. The CMS was designed to monitor multiple patientssimultaneously and generate a warning signal if necessary. They used the RF module based on the Nextronics's NEXAR_3A (receiver) and NEX-AT-3A (transmitter) for communication between PSD and CMS. Then the information was passed to the PC though RS-232C interface. The communication speed was found to be slow. Junho Park et al. [2] also proposed the similar approach replacing the wireless network with Zigbee. Jovanov et al. [3] developed a Wireless Body Area Network of Intelligent Sensors for Patient Monitoring using standard ZigBee compliant radio and a common set of physiological, kinetic, and environmental sensors.


We conducted a survey of various wireless technologies available today. Zigbee technology clearly has a lot of advantages over other wireless technologies. Some of the key advantages of ZigBee include the following
¢ Low power consumption
¢ Low cost
¢ High density of nodes in any network. Zigbee uses the IEEE 802.15.4 PHY MAC and networks can handle any number of devices.
¢ Zigbees protocol stack is very simple. Zigbees protocol stack is estimated to be 1/4th the size of blue tooth™s stack.
¢ Dual PHY (2.4GHz and 868/915 MHz)
¢ Data rates - 250 kbps (@2.4 GHz), 40 kbps (@ 915 MHz), and 20 kbps (@868 MHz)
¢ CSMA-CA channel access
¢ Uses 64 bit IEEE address which creates an address space for 18,450,000,000,000,000,000 devices. It supports up to 65,535 networks
¢ Flexible range between 5- 500m
¢ Supports periodic, intermittent and repetitive data
¢ AES encryption for security
¢ Rapid leaving and joining of the network by devices. In the order of milliseconds. Joining takes places in less than 30ms.
A survey of heart rate monitors available in market is shown in TABLE 1. Most of these products use Bluetooth technology. They are costly and only few of these products have the capability of providing remote monitoring. TABLE II shows a comparison of various features of ZigBee with other wireless technologies.


Some of the main concerns of the wireless heart rate monitoring system are:
“ Failure of either an end device or the coordinator in the wireless network
“ Determining when a node is losing its battery life so the battery of the node can be replaced.
“ Interference with other devices or networks
The following steps can be taken to make sure the above two concerns are met. The heart rate of each baby will be sent to the coordinator in the incubator room periodically. If the coordinator does not receive a heart-rate from a particular end-device, the coordinator will send an alert to the central monitoring room via the LAN network. There will be a watch dog daemon on the computer in the monitoring room that will periodically check if the coordinators in each of the incubator rooms are alive. This can be done by sending a specific message to the coordinator and expecting a specific message back from the coordinator periodically.
The nodes in the network will never sleep. This means a node is always consuming power from the battery to transmit, receive or even stay in idle state. Depending on the type of battery used on each end device and coordinator, the battery life for each device is very specific. The coordinator will keep track of the last time a new battery was installed on an end device. Knowing this, the coordinator can alert the remote monitoring room that the battery on a particular end device may die out soon. The coordinator will also keep track of when a new battery was installed on the coordinator itself and will report the remote monitoring room if the life-time of the battery is coming close. The coordinator can check for battery usage on all the nodes in the network (incubator room) periodically.Other wireless devices such as Wi-Fi, Bluetooth, etc could cause significant RF interference with the ZigBee communication depending on the signal strength of those devices.


The ZigBee Standard enables the broad-based deployment of reliable wireless networks with low complexity, low cost solutions and provides the ability for a product to run for years on inexpensive primary batteries (for a typical monitoring application). It is also, of course, capable of inexpensively supporting robust mesh networking technologies .ZigBee is all set to provide the consumers with ultimate flexibility, mobility, and ease of use by building wireless intelligence and capabilities into every day devices.
The mission of the ZigBee Working Group is to bring about the existence of a broad range of interoperable consumer devices by establishing open industry specifications for unlicensed, untethered peripheral, control and entertainment devices requiring the lowest cost and lowest power consumption communications between compliant devices anywhere in and around the home. We have proposed a low-cost solution to enhance the remote monitoring capability of existing health care system. It is cheap, secure, robust and low-power consuming. It can operate on multiple channels so as to avoid interference with other wireless devices or equipments in the hospital. An extension of this work would be to develop a software that transmits heart rate information to a central monitoring system over Ethernet LAN. The interface between the ZigBee Coordinator and a computer in LAN, could be developed using IEEE 1451, which is a smart transducer interface standard. It makes it easier for transducer manufacturers to develop smart devices and to interface those devices to networks, systems and instruments by incorporating existing and emerging sensor and networking technologies.
CHAPTER 1..............................................................................................................................4
CHAPTER 2..............................................................................................................................7
IEEE 802.11
CHAPTER 3............................................................................................................................14
IEEE 802.15.4
3.2 ZIGBEE AND IEEE 802.15.4
CHAPTER 4............................................................................................................................16
CHAPTER 5............................................................................................................................30
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