Working of a Zigbee Network:
A Zigbee Network consists of a
- Zigbee Coordinator: It is the root of the network and also acts as a bridge between the other networks as well. Every network consists of one coordinator. Its main functions are to (I) Store Information about concerning networks and routing tables, & (ii) Pretends as a depository for security keys.
- Zigbee Router: It behaves as an intermediate router that is capable of passing data and information to and from other devices namely coordinator or to the end devices.
- Zigbee End device or Reduced Function End Device: Can pass the information to Zigbee coordinator or Zigbee router but could not establish communication with other end device. It utilizes reduced amounts of memory.
- An alarm device is activated to indicate that certain measures are required to take attention.
Zigbee network can work in any topology like star, Mesh and so on. It also consists of a Full Function Device (FFD) and Reduced Function Device (RFD). The end systems may be RFD’s and it must contain one FFD at least to work as coordinator in a Zigbee network.
In order to reduce or lower power utilization and boost long battery life of the devices, End devices are made to sleep to most of their time and wake up at the time when a communication is required and get back to sleep mode after the desired function. The cost of the devices and other materials required to establish a network is relatively low as compared to the other wireless sensor devices.
The framework potentially has the capability to create and form, and work in Mesh networks. For the aim of saving energy the beaconless system will attach to the network only when there is scope for communication and disconnects immediately. The algorithms are built to support low – speed Ad-hoc communication among nodes automatically in a network. Zigbee stack affirm beacon and non-beacon enabled networks. It uses Ad-hoc on Demand Distance Vector Routing Protocol (AODV) an improved version of routing protocol that takes care of transmitting content.
Example: Lights turns off immediately (Sleep) when there is no sense in the area and turns on when it recognizes a sense – saving energy.
As discussed above; Zigbee networks are capable of supporting mesh networks. The nodes are interlinked with other individual nodes to establish transmission from as many paths as possible.
The routing table takes the responsibility of dynamically updating the routing information which is readily built in the architecture. The concepts of mesh topology and potential towards ad-hoc routing capability configure greater stableness in changing conditions or failure at single nodes.
The nodes cooperate with each other in leveraging or in transmitting the data with the nearby devices which further send them to the end device limiting their power consumption.
CSMA (Carrier Sense Multiple Access):
There is an assumption that collisions takes place in the signal whenever a device transmits data it wishes to. Zigbee devices are able to find a free sharing channel on itself to avoid interference with other packets. This approach is motivated by CSMA, which does not require any synchronization between sharing devices. It adopts “Listen before you talk” criteria before initiating a call. If a desired channel is often too busy then it creates wait intervals which increases exponentially and randomly to find a clear channel and gives access to the devices prioritizing the waiting intervals of the nodes. Therefore no collision takes place that results in the data packet loss.
The algorithm for collision free access is given below:
Association process in Zigbee:
The formation of a network by the devices begins the life of a Zigbee network structure. When a new device joins the existing network it sends requests to the nearby devices to reconfigure routing paths. It is the function of the Zigbee router or the co-ordinator to allow devices to join a network. This process in Zigbee framework is termed as “Association”. The newly joined devices are termed as child nodes.
Zigbee differs from other wireless standards (say Wi-Fi) by allowing hierarchy of associations which router creates more than a one single parent – child relation achieving multiple levels of associations.
Path Diversity in Zigbee:
Dynamic routing enables the path diversity in Zigbee by using CSMA (Carrier Sense Multiple Access). If interference occurs in a selected path due to reasons like failure in intermediate node, device or link, then an alternative path will chosen by the network among the available nodes for the delivery of the content from coordinator to end device. Therefore transmission of packets takes place even if a failure occurs in one path. This makes it more robust in its deployment. This is to make the communication more reliable.
Support for Multiple Channels:
Zigbee supports multiple channels co-exist together without overlapping. Presently, Zigbee is operating unlicensed frequency bands world-wide at the following frequencies. 2.400 GHz-2.48 GHz (16 Non-overlapping Channels), 902 MHz – 928 MHz (10 Channels), & 868.0 MHz – 868.6 MHz (1 Channel) by allowing different modulation schemes.
This paper is written and submitted by sandeep k