In this paper, we are defining techniques for reducing the isolated nodes in the Zigbee network. To reduce the isolated nodes, a connectivity improving mechanism is proposed which utilizes a connection shifting scheme to increase the join ratio of established devices.

1. www.ijcsit-apm.com International Journal of Computer Science & Information Technology 1
IJCSIT, Vol. 1, Issue 3 (June 2014) e-ISSN: 1694-2329 | p-ISSN: 1694-2345
A REVIEW ON TECHNIQUES FOR
INCREASING CONNECTIVITY AND LIFE
OF ZIGBEE NETWORKS1
Roop kamal kaur, 2
Dr. Dinesh Arora
1,2
Gurukul Vidyapeeth Institute of Engg. & Technology, Banur, Punjab, India
1
roopkamal7@gmail.com, 2
drdinesh169@gmail.com
Abstract: Zigbee is a wireless communication standard
based on IEEE 802.15.4. Zigbee standard is designed for
wireless sensor network and control networks with low
power consumption, low data rate and low cost. Sensor
devices are randomly established in some applications and
some of these devices may become isolated from the
network due to the constraints of configuration parameters
in Zigbee networks. Due to the isolated nodes, an expected
network operation become unreached. In this paper, we
are defining techniques for reducing the isolated nodes in
the Zigbee network. To reduce the isolated nodes, a
connectivity improving mechanism is proposed which
utilizes a connection shifting scheme to increase the join
ratio of established devices. Another approach to reduce
isolated node is Extended joining procedure which can
efficiently reconstructs the part of the network. We also
introduce a swapping method which extends the life of the
network and balance the energy consumption of the
nodes. This paper also proposes an optimized connectivity
scheme which decreases the isolated nodes and prolongs
the life of the network. In this paper we are describing
these approaches in detail.
Keywords: Zigbee network, connectivity, isolated,
wireless sensor networks.
I. INTRODUCTION
Zigbee is a wireless communication standard based on
IEEE 802.15.4. Zigbee standard is designed for wireless
sensor network and control networks with low power
consumption, low data rate and low cost. Zigbee is used in
various applications: Electrical meters with in home
displays, traffic management systems, industrial
automation, building automation, lighting control, energy
automation etc.
Zigbee includes two layers specified by 802.15.4 : PHY
and MAC. The PHY layer defines the physical and
electrical characteristics of the network. The basic task of
the PHY layer is data transmission and reception. The
MAC layer is responsible for beacon generation if device
is a coordinator, implementing carrier sense multiple
access with collision avoidance (CSMA-CA), handling
guaranteed time slot (GTS) mechanism, data transfer
services for upper layers.
Zigbee Stack
This gives an overview of Zigbee specification. ZigBee is
built on top of the IEEE 802.15.4 standard. ZigBee
provides routing and multi-hop functions to the packet-
based radio protocol.
Fig. 1 Zigbee stack
Zigbee stack resides on a Zigbee logical device and there
are three logical device types:
a. Coordinator
b. Router
c. End device
Wireless standards comparasion
Wireless
parameter
Bluetooth Wi-fi Zigbee
Frequency 2.5GHz 2.5GHz 2.5GHz
Physical/MA
C layers
IEEE
802.15.1
IEEE
802.11b
IEEE
802.15.4
Range 9m 75 to 90m Indoors:
upto 30 m
Outdoors(li
ne of
sight): upto
100m
Current
Consumption
60 mA
(Tx mode)
400 mA
(Tx mode)
20 mA
(Standby
mode)
25-35 mA
(Tx mode)
3 µA
(Standby
mode)
Raw data rate 1 Mbps 11 Mbps 250 Kbps
Protocol stack
size
250 KB 1 MB
32 KB
4 KB (for
limited
function
end
devices)
Typical >3 sec variable, 1 30 ms

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network join
time
sec
typically
typically
Interference
avoidance
method
FHSS(Fre
quency
hopping
spread
spectrum)
DSSS(Dire
ct sequence
spread
spectrum)
DSSS(Dire
ct sequence
spread
spectrum)
Minimum
quiet
bandwidth
required
15
MHz(dyn
amic)
22
MHz(static
)
3MHz(stati
c)
Maximum
number of
nodes per
network
7
32 per
access
point
64 K
Number of
channels
19 13 16
Zigbee Features
Throughput: 250 Kbps at 2.4 Ghz with 16 Channels/40
Kbps at 915 Mhz with 10 Channels.
Battery life: Low power design ,Around 1000 Days.
Scalability: Highly scalable network that can accomodate
up to 64,000 nodes using a single coordinator.
Cost: As compared to Wi-Fi,Zigbee Routers and sensors
cost very less and hence are more suitable for bulk
deployment.
Network Topology: Zigbee uses Mesh Topology, Star
Topology and Peer-to-peer Topology and and can work
any one of them.
Zigbee Network Joining Scheme
Three types of devices are defined by Zigbee are: Zigbee
Coordinator (ZC), Zigbee Router (ZR), Zigbee End
Device (ZED). In Zigbee Neworks only one ZC and
multiple ZRs are used. In Zigbee only ZC and ZRs are
responsible for packet
forwarding and can accepts join request. Every device can
join to one device at most. Zigbee can support three types
of topologies: Star , Mesh, Tree. Hardware requirement of
a device is very simple to join in a network with tree
topology. Figure shows Zigbee network with tree
topology.
Fig. 2 Zigbee Network with tree topology
A mechanism that is Distributed Address Assignment is
designed which is also known as Cskip, to allocate
network addresses for the joined node in Zigbe networks.
To allocate their child nodes, each device has an address
space. Three configuration parameters defined by Zigbee
to control the network are nwkMaxChildren,
nwkMaxDepth and nwkMaxRouters.
[I] Connectivity Improving Mechanism
Figure 3 shows an example of Zigbee network. The
network configuration parameters described in the
previous section will cause some join failures is shown in
Fig 3(a). Now assume that three parameters
nwkMaxChildren, nwkMaxRouters, nwkMaxDepth are
equal to 3, 2, and 3 respectively. Through node A or B
node will get ZR node will get failures to join the network
due to the excesses of the children of A or B even though A
and B are both in the communication range of D.Due to
the excess of depth limitation, D will still get failure to
join to C. Due to this reason, node D becomes an isolated
node of the Zigbee network.Because only the joined nodes
are allowed to accept the join requests of other unjoined
nodes in the network so it is unable to accept any join
request comes from other nodes. So the ZR device M and
ZED device N will become isolated nodes, too. The node
P will become isolated from the network because of the
similar situation. Fig 3(b) shows the network connectivity
improvement. Node G has a capacity of one ZR children,
in fact, the ZR child E of node A does not have to join the
network through A.An other choice can be node G to
which allows ZR node E to join. Node A will become
joinable for the isolated node D, if node E selects G rather
than node A to join. Then ZR node M and ZED node N
will be allowed to join to D. After the ZED node R
performed the change of join target from Z to G, similarly
ZED node P can successfully join to node Z. Connection
change of node E from node A to G and connection
change of node R from Z to G is called shifting. Shifting
node E and R will make the Zigbee network an increase of
four nodes. By this improvement not only the reduction of
isolated sensors and wasted costs is improved but the
performance growth of the Zigbee sensor network is also
improved.
Fig. 3 Illustration of Zigbee connectivity issue
Zigbee MAC Beacon Format
Figure 4 shows the format of Zigbee MAC beacon. MAC
payload consists of four fields: Superframe specification,
GTS Field, Pending address field and Beacon payload.
And beacon payload is further divided into 10 fields.
Every fields do different tasks. Figure 4(a) shows that
reserved field consists of tw parts. Each part is of one bit.
One bit is for swapping and one bit is for shifting
information.

3. www.ijcsit-apm.com International Journal of Computer Science & Information Technology 3
Fig. 4 Payload format of zigbee MAC beacon
Fig. 4(a) The MAC beacon payload with the shiftable flag
[II] Extended Joining Scheme
Extended joining scheme consists of two methods. First
method is to reconstructs the part of the network to
connect more devices (Enhancement Connectivity
Scheme) and the second method is swapping to improve
the connectivity. If a potential parent receives join requests
from multiple isolated nodes then its selection cannot
achieve the best connectivity of the network while using
the method in the previous scheme.
Description
Extended joining process is shown in the figure 5. In this
example there are five isolated nodes that contains B and I
as ZRs and J, K and R as ZEDs. In Fig. 5, node G has a
capacity to accept one more child so children C of
potential parent A and children M of potential parent L
can connect to G. In this method, beacons are used to
announce the acceptance of th child. So nodes A and L use
beacons to announce the acceptance of more children.If
node B wants to join to its potential parent A and node I
wants to join to its potential parent L then they have to
scan how many isolated nodes come within their
communication range. Now, From an example, node B has
one child and node I has two children. Due to network
parameters, node G has capacity to accept one more child.
After the joining of So node M to node G, node L accepts
node I as its child and isolated nodes J and K can
successfully join in the network through node I but nodes
B and R cannot join in the network. Our Extended Joining
Procedure decreases three isolated nodes. After the first
part of Extended Joining Process, Fig. 6 shows the Zigbee
Network of Fig. 5.
Fig. 5 An example of Extended Joining Process
Fig. 6 The Zigbee Network of Fig. 5 after our Extended Joining
Process
[a] Swapping Process
In the Swapping process, swapping of nodes will be done
so that connectivity and life of the Zigbee Networks can
be improved. In Fig. 5, node P announces the acceptance
of more ZRs as its children. When node P receives the
joining request from the node B then node P disconnects
its child node Q and connects a new node B as its child.
Now, node B is successfully connected with a node P and
node B has capacity to accept more nodes as its child. So,
node Q and node R will be connected to node B as its
child. Figure 7 shows our Swapping process.
Fig. 7 Zigbee Network of Fig. 5 after our Swapping process
The Swapping Process is stopped when two
situations occur. First, when all residual energies of leaf
ZRs are lower than that of internode ZR, then the
swapping process is stopped. Second, it is necessary that
the communication range of the selected node has to reach
to all those nodes that connects to the internode ZR. If this
condition is not satisfied by all children then the swapping
process is stopped. The process of swapping is as follows:
Step 1. The ZR sets the swapping flag as TRUE, if the
residual electric voltage of the battery in an internode ZR

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is lower than the threshold and announces that its energy is
exhausted.
Step 2. The internode ZR selects highest residual electric
voltage leaf ZR after receiving statuses of residual electric
voltages from all leaf ZRs. Swapping process is terminated
if residual energies of all the leaf ZRs are lower than that
of internode ZR.
Step 3. The internode ZR, then notifies about the selected
leaf ZR and also then transfer the routing infomation to the
selected leaf ZR.
Step 4. After that, the selected leaf ZR announces to all the
nodes that it is the new router and wait for the replies from
all the devices.
Step 5. If the selected leaf ZR fails to receive replies from
some devices that connecs to the internode ZR then leaf
ZR has to send the transfer failure message to the
internode ZR.
Step 6. If the transfer failure message is received by the
internode ZR then the leaf ZR with the highest residual
electric voltage is selected by the internode ZR from the
remaining leaf ZRs.
Step 7. The selected leaf ZR becomes a new internode ZR
after receiving all the replies and send acknowledge to the
old internode ZR that the tranfer is successfully done.
Step 8. The old internode ZR stops routing while it
receives the successful transfer message and becomes the
leaf ZR of the new internode ZR.
[III] Optimized Connectivity Scheme
An energy depletion limitation is found in the swapping
process. When energy is depleted then the internode
Zigbee router send requests to its child nodes and then find
all the replacements bases of residual energy that should
be more than threshold. Swapping process is terminated if
energy level is less and router goes to sleep[3].
A new technique is proposed called Optimized
Connectivity Scheme.In Optimized Connectivity Scheme
the Zigbee router swapping process is updated by energy
level checking of the isolatd nodes. Energy level of each
isolated is checked. By selecting nodes having better
energy carrying capacity, the connectivity and life of the
Zigbee Networks is increases. These all techniques shows
how the connectivity and life of the Zigbee Networks
increases and isolated nodes decreases. These can be
implemented using Opnet simulator.
CONCLUSION
Zigbee is a wireless communication standard based on
IEEE 802.15.4. Zigbee standard is designed for wireless
sensor network and control networks with low power
consumption, low data rate and low cost. Zigbee is uesd is
in various applications like home automation, industrial
automation, building automation etc. This paper is based
on increasing the connectivity and life of the Zigbee
Networks by various techniques and hence improve the
network efficiency. In these techniques specific depth is
considered so that scalability can be increased. As
compared to the previous techniques, throughput is high in
optimized connecivity scheme due to the energy saving
while swapping devices.
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