Transcript Evaluating Mobility Support in ZigBee Networks

Evaluating Mobility Support
in ZigBee Networks
Tony Sun1, Nia-Chiang Liang1, Ling-Jyh Chen2,
Ping-Chieh Chen1, and Mario Gerla1
1University
of California at Los Angeles
2Academia Sinica
Motivation
• Simple appliances and numerous traditional
wired services can now be efficiently
connected wirelessly.
• The ZigBee standard is the latest attempt to
realize the wireless network vision.
• Understanding the performance of ZigBee
networks becomes important in determining
the applicability of many applications.
Our Contribution
• Dissecting ZigBee routing and its
current support for device mobility.
• Running a rich set of preliminary
simulations, illustrating the inefficacy
of current standard in handling mobility.
Background - ZigBee
• Based on the Low
Power, Low Rate
IEEE 802.15.4
Standard
– ZigBee is the network
and application
specification developed
by the ZigBee alliance.
– Back by 150+ member
companies and numerous
adopters
– Released June 2005
OEM
Applications
Application Interface
Security
Network Layer
Star/Cluster/Mesh
IEEE
802.15.4
MAC Layer
PHY Layer
ZigBee
Background- ZigBee
• Three device types
– Coordinator: FFD
– Routers: FFD
– End devices: RFD or FFD
• End devices with limited
functionality to control
cost
ZigBee Coordinator
ZigBee Router
ZigBee End Device
– Can only communicate to
parent router
– Rely on their parent router
for routing functionality
• ZigBee node has two
addresses
– 16-bit network address
– 64-bit MAC address
Mobility support in ZigBee mesh
topology
• Mobile end device:
– When an end device moves out of the range of his parent
router,
– if this end device is receiver
• the source nodes will receive a route error message and trigger
Device Discovery primitive in the application layer.
– if this end device is sender
• transmission will be temporally disrupted for the duration it
takes for the mobile to find a new parent router to associate
itself with.
• Mobile router:
– Whenever an existing route failed,
– whether an router is sender or receiver
• Built-in route recovery mechanism (via router discovery and
route error)
• ZigBee routers are robust to effects from most mobility cased.
Mobility support in ZigBee Tree
topology
• Every other device is a descendant of the ZigBee
coordinator and no device is the descendant of any
ZigBee end device.
• Each node can check the destination address against
its own to determine where the destination is.
• When a node change its parent router due to mobility,
a new network address will be automatically assigned
to preserve the tree addressing structure.
• Simple mobility of a router can cause cascading
address changes across entire tree branches.
Mobility support in ZigBee Tree
topology
• Mobile end device:
– Route discovery and Device Discovery
– Device Discovery mechanism would only work under very
limited mobility scenario.
– When there are persistent or multiple occurrences of
mobility, the longer routes and slower throughput of tree
routing tends to hinder the responsiveness of the recovery
scheme.
• Mobile router:
– A cascading network address change to all of its descendant
nodes on impacted branches.
– Creating varying levels of inconsistency to the tree
addressing scheme, thereby reducing the routing protocol’s
ability to function properly.
Evaluation
• The NS-2 simulator with Samsung’s IEEE 802.15.4
extension
• Network component: 36 nodes(70% routers and 30%
end devices)
• Testing parameters:
– Varying percentage of mobile nodes
– Mobile node with varying speed
• Performance metrics
– Packet delivery ratio
• The average over the number of flows in the network
– Relative routing overhead
• A Normalized value of the total overhead of the network with
respect to the traffic in the network
Scenarios
Scenario 1
Scenario 2
Sender
Receiver
Device type
Mobile
Stationary
Router
Mobile
Stationary
End device
Stationary
Mobile
Router
Stationary
Mobile
End device
Varying percentage of
mobile nodes
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary
device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Varying percentage of
mobile nodes
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Varying percentage of
mobile nodes
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Varying percentage of
mobile nodes
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Scenarios with mobile nodes of
varying speed
•
•
20% nodes are selected randomly to
be mobile nodes.
the speed of mobile node are constant.
(1m/s to 5m/s in 1m/s increments)
Mobile nodes of
varying speed
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary
device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Mobile nodes of
varying speed
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary
device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Mobile nodes of
varying speed
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary
device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Mobile nodes of
varying speed
Source
Dest
Type
Station
Router
ary
1
Station End
Mobile
ary
device
Station
Mobile Router
ary
2
Station
End
Mobile
ary
device
Mobile
Conclusion
• We discussed ZigBee routing and its support
for device mobility
• We analyzed the adequacy of current
provision in dealing with different mobility
cases.
• The packet loss rate increases under the
multiple instances of mobility and when mobile
nodes travel at higher speed.
• We found that the end devices suffer more
packet loss than router under mobile
scenarios.
Thank You!