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The wireless market has been traditionally dominated by high end technologies, but so far Wireless Personal Area Networking products have not been able to make a significant impact on the market. While some technologies like the Bluetooth have been quite a success story, in the areas like computer peripherals, mobile devices, etc, they couldn’t be expanded to the automation arena. This led to the invention of the wireless low data rate personal area networking technology, Zigbee (IEEE 802.15.4),... Continue Reading
During the last decade there has been an explosion of devices using sensor technologies for control and monitoring purposes. Wired Sensors are now intended to be replaced with wireless technologies. Corporates have been envisioning of a digital home where every device is connected, and remotely controlled and monitored. Even though a perfect digital home is yet a mirage, we are now able to apply several technologies to suite our home and industrial networking needs. However, this concept of a digitally connected home has received a luke warm response due to lack of viable solutions... Continue Reading
The objective of our project is to build a simulation model of LR-WPAN and simulated the model using the Network simulator NS2. The WPAN Low Rate Task Group (TG4) is chartered to investigate a low data rate solution with multi-month to multi-year battery life and very low complexity. This standard specifies two physical layers: an 868 MHz/915 MHz direct sequence spread spectrum PHY and a 2.4 GHz direct sequence spread spectrum PHY. The 2.4 GHz PHY supports an over air data rate of 250 kb/s and the 868 MHz/915 MHz PHY supports over the air data rates of 20 kb/s and 40 kb/s.... Continue Reading
There has been tremendous excitement on part of the corporates, the market and the consumers alike because of the wide spectrum of applications that zigbee has to other. It is a revolutionary new technology built to compliment or replace existing not so successful technologies. Automation is the buzz word for zigbee. It stands to automate our household, corporate buildings and industries.... Continue Reading
Compared with wired networks, wireless networks provide advantages in deployment, cost, size, and distributed intelligence. Wireless technology not only enables users to set up a network quickly, but also enables them to set up a network where it is in-convenient or impossible to wire cables. The “care free” feature and convenience of deployment make a wireless network more cost-efficient than a wired network in general... Continue Reading
A Low rate WPAN supports three different types of topologies.
Network formation is part of the network layer functionalities. An example run of the various steps involved for a network formation is presented:
Star-Topology
The LR-WPAN architecture is defined in terms of a number of blocks in order 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 similar to the structure of the OSI layered architecture. But the IEEE 802.15.4 standard only defines the PHY and the MAC layers. The upper layers of networking and application have been left for the application developers. 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. The figure 2.3 depicts the layered architecture of IEEE 802.15.4
The Superframe structure
The superframe structure (Fig: 2.4) is an optional part of a WPAN. It is the time duration between two consecutive beacons. The structure of the superframe is determined by the coordinator. The coordinator can also switch off the use of a superframe by not transmitting the beacons. The superframe duration is divided into 16 concurrent slots. The beacon is transmitted in the first slot. The remaining part of the superframe duration can be described by the terms, CAP, CFP and Inactive. The superframe is used to provide vital statistics like synchronization, identifying the PAN and the superframe structure, to the devices connected in a Wireless PAN. This information is critical for the operation of the PAN in a Beacon enabled network... Continue Reading
There can be three different types of data transmission possible. They are
Ø Transmission from a device to the coordinator
Ø Transmission from the coordinator to the device
Ø Transmission between any two devices.
IEEE 802.15.4 Service Primitives
The new IEEE standard, 802.15.4, defines the physical layer (PHY) and medium access control sublayer (MAC) specifications for low data rate wireless connectivity among relatively simple devices that consume minimal power and typically operate in the Personal Operating Space (POS) of 10 meters or less. An 802.15.4 network can simply be a one-hop star, or, when lines of communication exceed 10 meters, a self-configuring, multi-hop network. A device in an 802.15.4 network can use either a 64-bit IEEE address or a 16-bit short address assigned during the association procedure, and a single 802.15.4 network can accommodate up to 64k (216 ) devices. Wireless links under 802.15.4 can operate in three license free industrial scientific medical (ISM) frequency bands. These accommodate over air data rates of 250 kb/sec (or expressed in symbols, 62.5 ksym/sec) in the 2.4 GHz band, 40 kb/sec (40 ksym/sec) in the 915 MHz band, and 20 kb/sec (20 ksym/sec) in the 868 MHz. Total 27 channels are allocated in 802.15.4, with 16 channels in the 2.4 GHz band, 10 channels in the 915 MHz band, and 1 channel in the 868 MHz band... Continue Reading
The primitives indicate the functions organized by each layer. The PHY layer is responsible for the following tasks:
Ø Activation and deactivation of the radio transceiver
Ø Energy Detection
Ø Link Quality Indication Measurement
Ø Clear Channel Assessment
Ø Data Transmission and Reception
Data Transmission
When ever there is data to be transmitted, the MAC layer Management Entity calls upon the PHY layer with these primitives to transmit a data frame
Data Transmission
The following primitives are used for data transmission from the next higher layer. The result is indicated with confirm primitive. These responses are prepared with respect to its own requests for data transmission to the PHY layer.
MCPS-DATA.request : Requests the transmission of a data unit from the local SSCS entity. It prepares the corresponding MPDU from the incoming SPDU and this is passed on to the PHY layer for transmission
Purpose
NS (version 2) is an object-oriented, discrete event driven network simulator developed at UC Berkely written in C++ and OTcl. NS is primarily useful for simulating local and wide area networks. Although NS is fairly easy to use once you get to know the simulator, it is quite difficult for a first time user, because there are few user-friendly manuals. Even though there is a lot of documentation written by the developers which has in depth explanation of the simulator, it is written with the depth of a skilled NS user. The purpose of this project is to give a new user some basic idea of how the simulator works, how to setup simulation networks, where to look for further information about network components in simulator codes, how to create new network components, etc., mainly by giving simple examples and brief explanations based on our experiences. Although all the usage of the simulator or possible network simulation setups may not be covered in this project, the project should help a new user to get started quickly.
3.1.2 Overview
NS is an event driven network simulator developed at UC Berkeley that simulates variety of IP networks. It implements network protocols such as TCP and UPD, traffic source behavior such as... Continue Reading
This section shows a simple NS simulation script and explains what each line does. An OTcl script that creates the simple network configuration and runs the simulation scenario is shown... Continue Reading
EXPLANATION FOR A SIMPLE PROGRAM
The following is the explanation of the script above. In general, an NS script starts with making a Simulator object instance.
set ns [new Simulator]: generates an NS simulator object instance, and assigns it to variable ns (italics is used for variables and values in this section).
What this line does is the following:
Initialize the packet format (ignore this for now)
Create a scheduler (default is calendar scheduler)
Select the default address format (ignore this for now)
The "Simulator" object has member functions that do the following:
Create compound objects such as nodes and links (described later)
Connect network component objects created (ex. attach-agent)
Set network component parameters (mostly for compound objects)
Create connections between agents (ex. make connection between a "tcp" and "sink")
Specify
Etc... Continue Reading
The network simulator (ns) comes along with an interesting tool, called the Network Animator (NAM).
First the simulation model of star and peer-to-peer technology is designed. The following steps are done to simulate the model,
· Generate the scripts for node arrangement
· Creating TCL scripts for both the topologies
· Running the simulation... Continue Reading
The node scenario generation is done using the star.scn file. The Start topology model has the following parameters simulated
Simulation is a flexible means for assessment of the performance offered by a telecommunication system. However, identifying the correct simulation parameters is key for a successful and nearly realistic analysis
Model of Peer-to-peer topology
The simulation parameters for peer-to-peer topology are mostly simulated similar to that of star topology but for some parameters. The peer-to-peer topology has main advantage that the node can transmit data to different... Continue Reading
The simulation process is carried out systematically as shown,
· Running Ns2
· Path setting for NS2
· Opening Terminal window
· Running Star.tcl an d Peer.tcl
·
Steps to Simulate our project
Ø Firstly the Terminal window in fedora is opened
Ø The path for the NS is loaded
Ø Run the command ns star.tcl or peer.tcl
[1] IEEE 802.15.4 Standard-2003, “Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low Rate Wireless Personal Area Networks (LR WPANs)”, IEEE SA Standards Board, 2003.
[2] slides by John Heidemann
[4] ns-2 Tutorial: http://www.isi.edu/nsnam/ns/tutorial/nsindex.html
[5] Tcl/Tk tutorial : http://hegel.ittc.ukans.edu/topics/tcltk/tutorial-noplugin/
[6] IEEE computer society, “Wireless MAC and PHY Specifications For LR-WPANS” IEEE,2003.
[7] Jianliang Zheng, and Myung J. Lee, “Will IEEE 802.15.4 Make Ubiquitous Networking a Reality?: A Discussion on a Potential Low Power Low Bit Rate Standard” IEEE Communications magazine, pp. 140-146, June 2004.
LR-WPAN is a promising new wireless short range communications technology. It may not have yet swept the short range communications market but it is surely making its presence felt. An alliance of companies called the Zibgbee alliance, have already joined hands to benefit from this new technology and share information and develop new applications. With its promises of short range communications with very low datarates and ultra low power consumption, it has created a market for itself.
A detailed study of the zigbee technology with its internal architecture, and the layered structure has been conducted. Followed by it is a similar study of the simulator environment (ns-2). A detailed study of the zigbee modules built under ns-2 with reference to its implementation in the standard also has been done. Later a well behaved and near realistic simulation scenario is built in TCL. The zigbee modules have been exclusively tested for the simulator environment and several loopholes have been identified. These loopholes are further investigated to replace them with working modules. Both Star and Peer-to-peer topologies have been studied and finalized that the star topology can be used effectively for short range application whereas the peer-to-peer can be used for large application which involves many number of devices.
The simulation parameters for peer-to-peer topology are mostly simulated similar to that of star topology but for some parameters. The peer-to-peer topology has main advantage that the node can transmit data to different nodes, that is the communication is possible between the nodes.
Parameter
Value
Traffic Type
FTP
Number of nodes
11
Number of coordinator
1
Traffic direction
Node à node
Simulation time
100 seconds
Figure 4.2 Peer topology parameters
The node scenario generation is done using the star.scn file. The Start topology model has the following parameters simulated
4.1.1 Simulation Parameters
Simulation is a flexible means for assessment of the performance offered by a telecommunication system. However, identifying the correct simulation parameters is key for a successful and nearly realistic analysis
of any study. The following discussion focuses on the task of identifying the correct parameters to generate a realistic network scenario, while explaining their meaning and their reason of choice (if any) in detail. General parameters for basic simulations are described here. However, the parameters that impact the network performance are discussed in the next chapter where we introduce the performance analysis of the system.
Traffic Parameters
Traffic Type
This project report is based on results simulated with a FTP application, based on the internet protocol, UDP (User Datagram Protocol). Its primary features are:
. Single Way Transmission (No Acknowledgements)
. Defined Packet size
. Defined Packet Interval
. Unreliable Data Transmission
FTP traffic with a TCP connection is done due to its advanced features like congestion control, requiring dynamic adjustment of the transmission rate based on the traffic conditions; it is hard to implement simplistic and power efficient devices, for menial applications.
Packet Size
The packet size is assumed be to 70bytes. This is exclusive of the RTR, MAC and PHY layer headers.
Traffic Direction
The traffic flows are all one way, with the communication directed to the coordinator. The study is being investigated with particular focus on low datarate wireless sensors communicating with a central node updating it with the application information.
Number of Nodes
The simulation is carried out with 7 active nodes. One of them being the coordinator.
Coordinators
Since a simple star network topology is being simulated, only a single coordinator is present.
Node Movement
The nodes remain stationary.
Node Position
The nodes are placed along an imaginary circle around the coordinator, with radius equal to the personal operating space of the nodes.
The trace and node parameters are summarized in the following table.
Figure 4.1 Star topology parameters
scen_gen
. Parameters: It accepts the following command line parameters
– scen_gen [number-of-nodes] [X-Pos-of-coord] [Y-Pos-of-coord] [Personal-Operating-Space]
Number-of-nodes: Number of nodes to be placed around the coordinator.
X-Pos-of-coord: X position of the coordinator, with respect to the area of the network dimensions.
Y-Pos-of-coord: Y position of the coordinator, with respect to the area of operation of the network.
Personal-Operating-Space: The operating space or the reachabilitiy of the coordinator. The nodes are required to be placed equidistantly around the coordinator, for the test scenarios in this report, within the operating space of the coordinator, this parameter is utilized to arrange the nodes along an imaginary circle drawn around the coordinator with this value
as radius.
Example: scen gen 11 25 25 10
. Functionality: This utility would automatically generate the coordinates of the nodes to place them around the coordinator, along an imaginary circle drawn with a radius equal to the Personal Operating Space. The node position file, holding the positions of all the nodes around the coordinator is generated from star.scn. Currently this file is being generated with the utility, scen gen. However, it is a simple text file, which can be easily edited to place the nodes at desired positions. Note that the positions of the nodes should respect the boundaries of the network mentioned in the source file, star.tcl
Working: Running the utility would create a file, star.scn, to be used by the source scenario file, star.tcl.
The scn file for star.tcl
$node_(0) set X_ 25
$node_(0) set Y_ 25
$node_(0) set Z_ 0
$node_(1) set X_ 20
$node_(1) set Y_ 16.34
$node_(1) set Z_ 0
$node_(2) set X_ 15
$node_(2) set Y_ 25
$node_(2) set Z_ 0
$node_(3) set X_ 20
$node_(3) set Y_ 33.66
$node_(3) set Z_ 0
$node_(4) set X_ 30
$node_(4) set Y_ 33.66
$node_(4) set Z_ 0
$node_(5) set X_ 35
$node_(5) set Y_ 25
$node_(5) set Z_ 0
$node_(6) set X_ 30
$node_(6) set Y_ 16.34
$node_(6) set Z_ 0
The resultant position file for the nodes would like some think like this:
Figure 4.1 Node arrangement
SIMULATION MODEL
First the simulation model of star and peer-to-peer technology is designed. The following steps are done to simulate the model,
· Generate the scripts for node arrangement
· Creating TCL scripts for both the topologies
· Running the simulation in network simulator
· Analyzing using network simulator
System Requirements
· Operating system – Linux fedora 7
· Package – Ns allinone 2.30
· Scripts – TCL, C++
A Simple Network Topology and Simulation Scenario
This network consists of 4 nodes (n0, n1, n2, n3) as shown in above figure. The duplex links between n0 and n2, and n1 and n2 have 2 Mbps of bandwidth and 10 ms of delay. The duplex link between n2 and n3 has 1.7 Mbps of bandwidth and 20 ms of delay. Each node uses a DropTail queue, of which the maximum size is 10. A "tcp" agent is attached to n0, and a connection is established to a tcp "sink" agent attached to n3. As default, the maximum size of a packet that a "tcp" agent can generate is 1KByte. A tcp "sink" agent generates and sends ACK packets to the sender (tcp agent) and frees the received packets. A "udp" agent that is attached to n1 is connected to a "null" agent attached to n3. A "null" agent just frees the packets received. A "ftp" and a "cbr" traffic generator are attached to "tcp" and "udp" agents respectively, and the "cbr" is configured to generate 1 KByte packets at the rate of 1 Mbps. The "cbr" is set to start at 0.1 sec and stop at 4.5 sec, and "ftp" is set to start at 1.0 sec and stop at 4.0 sec.
A Simple NS Simulation Script is shown below
set ns [new Simulator]
$ns color 0 blue
$ns color 1 red
$ns color 2 white
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]
set f [open out.tr w]
$ns trace-all $f
set nf [open out.nam w]
$ns namtrace-all $nf
$ns duplex-link $n0 $n2 5Mb 2ms DropTail
$ns duplex-link $n1 $n2 5Mb 2ms DropTail
$ns duplex-link $n2 $n3 1.5Mb 10ms DropTail
$ns duplex-link-op $n0 $n2 orient right-up
$ns duplex-link-op $n1 $n2 orient right-down
$ns duplex-link-op $n2 $n3 orient right
$ns duplex-link-op $n2 $n3 queuePos 0.5
set udp0 [new Agent/UDP]
$ns attach-agent $n0 $udp0
set cbr0 [new Application/Traffic/CBR]
$cbr0 attach-agent $udp0
set udp1 [new Agent/UDP]
$ns attach-agent $n3 $udp1
$udp1 set class_ 1
set cbr1 [new Application/Traffic/CBR]
$cbr1 attach-agent $udp1
Set null0 [new Agent/Null]
$ns attach-agent $n3 $null0
set null1 [new Agent/Null]
$ns attach-agent $n1 $null1
$ns connect $udp0 $null0
$ns connect $udp1 $null1
$ns at 1.0 "$cbr0 start"
$ns at 1.1 "$cbr1 start"
set tcp [new Agent/TCP]
$tcp set class_ 2
set sink [new Agent/TCPSink]
$ns attach-agent $n0 $tcp
$ns attach-agent $n3 $sink
$ns connect $tcp $sink
set ftp [new Application/FTP]
$ftp attach-agent $tcp
$ns at 1.2 "$ftp start"
$ns at 1.35 "$ns detach-agent $n0 $tcp ; $ns detach-agent $n3 $sink"
puts [$cbr0 set packetSize_]
puts [$cbr0 set interval_]
$ns at 3.0 "finish"
proc finish {} {
global ns f nf
$ns flush-trace
close $f
close $nf
puts "running nam..."
exec nam out.nam &
exit 0
}
$ns run
The new IEEE standard, 802.15.4, defines the physical layer (PHY) and medium access control sublayer (MAC) specifications for low data rate wireless connectivity among relatively simple devices that consume minimal power and typically operate in the Personal Operating Space (POS) of 10 meters or less. An 802.15.4 network can simply be a one-hop star, or, when lines of communication exceed 10 meters, a self-configuring, multi-hop network. A device in an 802.15.4 network can use either a 64-bit IEEE address or a 16-bit short address assigned during the association procedure, and a single 802.15.4 network can accommodate up to 64k (216 ) devices. Wireless links under 802.15.4 can operate in three license free industrial scientific medical (ISM) frequency bands. These accommodate over air data rates of 250 kb/sec (or expressed in symbols, 62.5 ksym/sec) in the 2.4 GHz band, 40 kb/sec (40 ksym/sec) in the 915 MHz band, and 20 kb/sec (20 ksym/sec) in the 868 MHz. Total 27 channels are allocated in 802.15.4, with 16 channels in the 2.4 GHz band, 10 channels in the 915 MHz band, and 1 channel in the 868 MHz band.
Wireless communications are inherently susceptible to interception and interference. Some security research has been done for WLANs and wireless sensor networks, but pursuing security in wireless networks remains a challenging task. 802.15.4 employs a fully handshaked protocol for data transfer reliability and embeds the Advanced Encryption Standard (AES) for secure data transfer.
In the following subsections, we give a brief overview of the PHY layer, MAC sublayer and some general functions of 802.15.4. The services of a layer are the capabilities it offers to the user in the next higher layer or sublayer by building its functions on the services of the next lower layer. This concept is illustrated in 3.1, showing the service hierarchy and the relationship of the two correspondent N-users and their associated N-layer (Or sublayer) peer protocol entities.
The services are specified by describing the information flow between the N-user and the N-layer. This information flow is modeled by discrete, instantaneous events, which characterize the provision of a service. Each event consists of passing a service primitive from one layer to the other through a layer SAP associated with an N-user. Service primitives convey the required information by providing a particular service. These service primitives are an abstraction because they specify only the provided service rather than the means by which it is provided. This definition is independent of any other interface implementation.
Services are specified by describing the service primitives and parameters that characterize it. A service may have one or more related primitives that constitute the activity that is related to that particular service. Each service primitive may have zero or more parameters that convey the information required to provide the service.
Figure 2.10: Service Primitive
A primitive can be one of four generic types:
Ø Request: The request primitive is passed from the N-user to the N-layer to request that a service is initiated.
Ø Indication: The indication primitive is passed from the N-layer to the N-user to indicate an internal N-layer event that is significant to the N-user. This event may be logically related to a remote service request, or it may be caused by an N-layer internal event.
Ø Response: The response primitive is passed from the N-user to the N-layer to complete a procedure previously invoked by an indication primitive.
Ø Confirm: The confirm primitive is passed from the N-layer to the N-user to convey the results of one or more associated previous service requests.
The IEEE 802.15.4 standard describes 14 PHY and 35 MAC primitives. The IEEE 802.15.4, WPAN supports two types of devices, The FFD and the RFD. The FFD is a full function devices supporting all the defined primitives of the standard. While, the RFD, is a reduced function device, degraded in terms of functionality. It supports a subset of these primitives. A total of 38 primitives are supported by RFDs. A few of those primitives are described here which are quite frequently used and are implemented in the zigbee modules.
Network formation is part of the network layer functionalities. An example run of the various steps involved for a network formation is presented:
Star-Topology
Ø Assume a full function device is switched ON for the first time.
Ø It starts scanning its operating channels for possible beacon transmissions, from other PANs.
Ø If it finds a beacon, it can try to associate with the PAN or it can choose to form its own PAN.
Ø assuming it chooses to form a new PAN, It chooses a PAN ID unique within its operating space.
Ø Now it allows other devices to be associated to it. This ends the Star network formation phase, as initiated by the PAN-Coordinator.
Peer-to-Peer Topology
Ø Assume a full function device is switched ON for the first time.
Ø It starts scanning its operating channels for possible beacon transmissions, from other PANs.
Ø If it finds a beacon, it can try to associate with the PAN or it can choose to form its own PAN.
Ø Assuming it chooses to form a new PAN, It assumes the role of a PAN Coordinator and assigns a Cluster ID (CID) of 0 to itself.
Ø Now it allows other devices to be associated to it.
Ø Other devices which intend to join a PAN, look for the beacon transmissions and upon receiving the beacon transmissions from the coordinator, would request association to the network.
Ø The coordinator shall decide if it would like to add the device into the network.
Ø If it wants to add the device, it will assign a CID value to it. The new device shall add the coordinator as its neighbor, while the coordinator will add it as its child.
Ø And this new device can now act as a cluster head and transmit beacons.
Ø Other devices can now join the network at this node.
A Low rate WPAN supports three different types of topologies.
. Star Topology
. Peer-to-Peer Topology
. Cluster Tree/Mesh Topology
Star Topology
The star topology (Fig: 2.1) is one of the most common forms of network formation. This type of topology can be used in monitoring applications where several devices monitor their applications and report to the coordinator. And the coordinator, a highly capable FFD, reacts to the situation at hand. In this type of network formation the communication between any two devices is forbidden. All devices can only communicate with the coordinator irrespective of their device type. Thus, a device can communicate with the coordinator and vice versa. No routing of information is possible. Given this reduced functionality of the system, routing functionalities like Address Resolution, and Routing finding to certain extent can be disabled.
Peer-to-Peer Topology
The Peer-to-Peer topology (Fig: 2.2) is a mode of communication where routing of data among devices is possible, as long as they are with in the operating space of each other. Complicated applications where devices need sharing of information are intended targets for the implementation of a peer-to-peer topology. Thus possible communication scenarios are between node-to-node, node-to-coordinator, and coordinator-to-node. As is evident if two devices need to transfer data, both have to be full function devices. Applications such as industrial control and monitoring, wireless sensor networks, asset and inventory tracking, intelligent agriculture, and security would benefit from such a network topology. A peer-to-peer network can be ad hoc, self-organizing and self-healing.
Cluster-Tree Topology
The cluster tree topology can in a way be considered as a derivative of the peer-to-peer topology. Several small clusters, each being able to communicate peer-to-peer, can be controlled with a PAN coordinator. And each cluster can have its own coordinator. And the coordinators are answerable to the PAN Coordinator. Among several existing clusters, the coordinators can compete with each other to choose a PAN coordinator.
Compared with wired networks, wireless networks provide advantages in deployment, cost, size, and distributed intelligence. Wireless technology not only enables users to set up a network quickly, but also enables them to set up a network where it is in-convenient or impossible to wire cables. The “care free” feature and convenience of deployment make a wireless network more cost-efficient than a wired network in general.
The release of IEEE 802.15.4 (referred to as 802.15.4 hereinafter), "Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low Rate Wireless Personal Area Networks (LR-WPANs)”, represents a milestone in wireless personal area networks and wireless sensor networks.
AW ireless personal area network conforming to the IEEE 802.15.4 standard is composed of several devices and its functionality and features can be illustrated by several terms. Some of them are listed here.
Co-ordinator: It is a device which is authorized to provide synchronization services in an established network. There can be two different kinds of co-ordinators based on their operation scope. First is the PAN-Coordinator, which acts as a coordinator for the entire PAN. Where as an ordinary co-ordinator can only function within the scope of a cluster.
Cluster: A cluster is a small section of a bigger network, which has its own co-ordinator. Groups of clusters communicate with a central PAN-Coordinator to form the PAN in a mesh topology.
Device/End Node: A device is either a reduced/full function device that can be visualized as a leaf of a tree structure. Any device that is not a co-ordinator is an end node (device).
Personal Operating Space (POS): It is the operating range of a node in all directions, and is a constant irrespective of being in motion or stationary.
There are 14 PHY and 35 MAC Primitives defined by the IEEE 802.15.4 standard. The LR-WPAN supports two types of devices called the Full Function Device and the Reduced Function Device.
Full Function Device It is a device which supports all the 49 primitives supported by the technology. It is a fully functional device which is capable of assuming the role of either a PAN Coordinator, a Coordinator, or just as an end node (device). Also an FFD can function as a routing device in certain network topologies where data transfer among FFD is allowed (EX: peer-to-peer communication).
Reduced Function Device It is a device with reduced functionality which can only function as an end device or node. It cannot communicate with any other device other than the coordinator. Given their extremely low functionality, these devices are normally intended for simple applications like a light switch, etc. They merely send information to the coordinator at regular intervals about the status of the device it is monitoring. It can only support a maximum of 38 primitives.
A basic LR-WPAN comprises of a mixture of these devices, an FFD being the most common device used in a PAN. But any PAN network should have at least one FFD, to act as the PAN-Coordinator. However, depending on the application when a RFD is not feasible, to fulfill the needs of the application, an FFD can be applied. The devices of a network monitor the applications and reply back to the coordinator. The devices within the pan should be around the operating space of the coordinator. But given the dynamic propagation characteristics of the channel a definite operating space for each device cannot be defined.
Operating Frequencies and Datarates
Any technology cannot achieve wide ranging popularity if it not flexible enough to be used worldwide. This is also one of the primary reasons for the failure of several proprietary technologies. However, IEEE 802.15.4 has been designed to be applied worldwide. This allows manufactures to concentrate on devices that can work in any of the available channels based on channel characteristics, bandwidth requirements, local regulations, etc. It supports three different operating frequency bands, with different number of supporting channels and datarates.
There has been tremendous excitement on part of the corporates, the market and the consumers alike because of the wide spectrum of applications that zigbee has to other. It is a revolutionary new technology built to compliment or replace existing not so successful technologies. Automation is the buzz word for zigbee. It stands to automate our household, corporate buildings and industries. Its control and monitoring capabilities offer an excellent platform for automation. A host of application categories/scenarios are presented here:
· Monitoring: Surveillance systems, Fire alarms, Pressure sensors, Meter reading monitors, Health and Environment monitors.
· Control: Health, Environment, Sensors, Home, Building and Industry Automation
· Efficiency
· Conservation
Theoretically there can be innumerable number of applications. It only depends on how better we tend to harness the flexibility and services offered by zigbee. As already stated, these are merely applications that are intended or desired and there may be scenarios where this technology cannot be successfully applied. Firstly, these application scenarios can be applied broadly into three application spheres, based on the complexity, feasibility and requirements posed by each sphere of application.
. Home
. Building
. Industrial
1 INTRODUCTION
1.1 Motivation
1.2 Evolution of ZigBee
1.3 Overview of our project
1.4 Applications
2 overview of ieee 802.15.4
2.1 Operating Frequencies and Datarates
2.2 Network topology
2.2.1 Star topology
2.2.2 Peer-to-peer topology
2.2.3 Cluster tree topology
2.3 Network formation
2.3.1 Star topology
2.3.2 Peer-to-peer topology
2.4 Architecture
2.5Functional overview
2.5.1 The Superframe structure
2.5.2 Data Transmission
2.6IEEE 802.15.4 Service Primitives
2.6.1 PHY Primitives
2.6.1.1 Data Transmission
2.6.1.2 Data Reception
2.6.1.3 Clear Channel Assessment
2.6.1.4 Energy Detection
2.6.1.5 PAN Inftn Management
2.6.1.6 Radio Transceiver
2.6.2 MAC Primitives
2.6.2.1 Data Transmission
2.6.2.2 Data Reception
2.6.2.3 Association
2.6.2.4 Disassociation
2.6.2.5 PAN Inftn Management
2.6.2.6 Orphaning
2.6.2.7 Receiver Maintenance
2.6.2.8 Channel Scanning
3.The Simulation Environment
3.1Network Simulator NS2
3.1.1 Purpose
3.1.2 Overview
3.2Simple simulation
3.3The Network Animator
4.SIMULATION SETUP AND RESULT
4.1Simulation Model
4.1.1 Simulation Parameters
4.1.2 Traffic parameters
4.2Model of Star topology
4.3Model of Peer-to-peer topology
4.4Simulation Results
4.1 Simulation Windows
5Conclusions
6.REFERENCES
