PEER-TO-PEER NETWORK FORMATION

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Topology

Depending on the application requirements, an IEEE 802.15.4 LR-WPAN operates in two topologies: the star topology or the peer-to-peer topology. Both are shown in Figure 3-1. In the star topology communication is established between devices and a single central controller called a pan-coordinator. A device typically has some associated application and is either the initiation point or the termination point for network communications. A pan-coordinator may also have a specific application, but it can be used to initiate, terminate, or route communication around the network. The pan-coordinator is a primary controller of PAN. All devices operating on a network of either topology shall have unique 64-bit addresses. This address may be used for direct communication within the PAN, or a short address may be allocated by the pan-coordinator when the device associates and used instead. The pan-coordinator might often be main-powered, while the devices will most likely be battery powered. Applications that benefit from a star topology include home automation, personal computer (PC) peripherals, toys and games, and personal health care [7].
The peer-to-peer topology also has a PAN coordinator; however, it differs from the star topology in that any device may communicate with any other device as long as they are in range of one another. Peer-to-peer topology allows more complex network formations to be implemented, such as mesh networking topology. 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. It may also allow multiple hops to route messages from any device to any other device on the network.
PAN selects a unique identifier. This PAN identifier allows communication between devices within a network using short addresses and enables transmissions between devices across independent networks. The mechanism by which identifiers are chosen is outside the scope of this standard [6].

Star-Network Formation

The basic structure of a star network is illustrated in figure 3-1. After an FFD is activated, it can establish its own network and become the pan-coordinator. All-star networks operate independently from other star networks. This is achieved by choosing a PAN identifier that is not currently used by any other network within the radio sphere of influence. Once the PAN identifier is chosen, the PAN coordinator allows other devices, potentially both FFDs and RFDs, to join its network.

Peer-to-Peer Network Formation

In a peer-to-peer topology, each device is capable of communicating with any other device within its radio sphere of influence. One device is nominated as the pan-coordinator, for instance, by virtue of being the first device to communicate on the channel. Further network structures are constructed out of the peer-to-peer topology and it is possible to impose topological restrictions on the formation of the network.
An example of the use of the peer-to-peer communications topology is the cluster tree. The cluster tree network is a special case of a peer-to-peer network in which most devices are FFDs. An RFD connects to a cluster tree network as a leaf device at the end of a branch because RFDs do not allow other devices to associate. Any of the FFDs may act as a coordinator and provide synchronization services to other devices or other coordinators. Only one of these coordinators can be the overall pan-coordinator, which may have greater computational resources than any other device(s) in the PAN. The pan-coordinator forms the first cluster by choosing an unused PAN identifier and broadcasting beacon frames to neighboring devices.
A candidate device receiving a beacon frame may request to join the network at the pan-coordinator. If the pan-coordinator permits the device to join, it adds the new device as a child device in its neighbor list. Then the newly joined device adds the pan-coordinator as its parent in its neighbor list and begins transmitting periodic beacons; other candidate devices may then join the network at that device. If the original candidate device is not able to join the network at the pan-coordinator then it will search for another parent device.
The simplest form of a cluster tree network is a single cluster network, but larger networks are possible by forming a mesh of multiple neighboring clusters. Once predetermined application or network requirements are met, the first pan-coordinator may instruct a device to become the pan-coordinator of a new cluster adjacent to the first one. Other devices gradually connect and form a multi-cluster network structure, such as the one seen in Figure 3-2. The lines in Figure 3-2 represent the parent-child relationships of the devices. The advantage of a multi-cluster structure is increased coverage area, while the disadvantage is an increase in message latency [7].

Multiple star topology

Wireless LAN technology in its current implementation require the nodes to be in the vicinity of an access-point attached to the wired data network, the star topology is necessary to combine with many access points spread across a building to ensure wireless coverage; All the access points report back into the main star hub, where server resources would reside on the network as shown in figure 3-3, in this topology devices are connected to their own central device and form a star, if any node get disconnected from its access point then it waits for the time to get reconnected with the same hub or switch, this situation cause alot of packet loss in the network and isolate a particular disconnected device from the network for a very long time ; since there is no routing technique in this topology therefore the disconnected device will never connect to other station (Switch/hub).

1 Introduction 
1.1 BACKGROUND
1.2 AIMS AND OBJECTIVES
1.3 REASON FOR DESIGN
1.4 GOAL
1.5 LIMITATIONS
2 Theoretical background 
2.1 WIRELESS TECHNOLOGY
2.2 PHYSICAL LAYER
2.3 MAC LAYER
2.4 APPLICATION OF IEEE 802.15.4
2.4.1 Zigbee
3 Topology 
3.1 STAR-NETWORK FORMATION
3.2 PEER-TO-PEER NETWORK FORMATION
3.3MULTIPLE STAR TOPOLOGY
4 Wireless Star-based Mesh topology Analysis
4.1 INTRODUCTION 
4.2 TOPOLOGY OVERVIEW
5 Radio Simulator based on NS-2 
5.1 SOFTWARE STRUCTURE AND WORKING OF NS-2
5.2 RESEARCH METHODOLOGY
5.3 STEPS REQUIRED FOR SIMULATION
5.4 DEFINING TCL SCRIPT TO EXECUTE WIRELESS SIMULATION
5.5 NODES IN NS-2 (NETWORK SIMULATOR-2)
5.6 TRACE FILE ANALYSIS
5.7 RADIO PROPAGATION MODEL IN NS-2
6 Simulation of scenarios 
6.1 SCENARIO 1: (1 COORDINATOR, PROPAGATION MODEL: TWO-RAY GROUND REFLECTION, TOPOLOGY: MESH NETWORK)
6.2 SCENARIO 2: (1 COORDINATOR, PROPAGATION MODEL: SHADOWING MODEL, TOPOLOGY: MESH NETWORK)
6.3 SCENARIO 3 (MULTIPLE PAN-COORDINATOR, SHADOWING MODEL, STAR – BASED MESH NETWORK)
7. Simulation results and analysis 
7.1 INTRODUCTION
7.2 ANALYSIS OF SCENARIO 1: 1 COORDINATOR, TWO-RAY GROUND REFLECTION, MESH NETWORK
7.3 ANALYSIS OF SCENARIO 2: 1 COORDINATOR, SHADOWING-MODEL, MESH NETWORK
7.4 ANALYSIS OF SCENARIO 3:MULTIPLE PAN COORDINATORS, SHADOWING-MODEL, STAR-BASED MESH NETWORK
7.5 HOP-COUNT ANALYSIS
7.6 NETWORK DISCOVERY POLICY
8 Conclusions and Future Work 
8.1 CONCLUSION
8.2 FUTURE WORK
References
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Implementation and performance analysis of star-based mesh network