SENSOR
network deployments may include hundreds or thousands of nodes. Since deploying
such large-scale networks has a high cost, it is increasingly likely that sensors
will be shared by multiple applications and gather various types of data:
temperature, the presence of lethal chemical gases, audio and/or video feeds,
etc. Therefore, data generated in a sensor network may not all be equally important.
With large deployment sizes, congestion becomes an important problem. Congestion
may lead to indiscriminate dropping of data (i.e., high-priority (HP) packets
may be dropped while low-priority (LP) packets are delivered). It also results
in an increase in energy consumption to route packets that will be dropped
downstream as links become saturated. As nodes along optimal routes are
depleted of energy, only nonoptimal routes remain, further compounding the
problem. To ensure that data with higher priority is received in the presence
of congestion due to LP packets, differentiated service must be provided. In
this work, we are interested in congestion that results from excessive
competition for the wireless medium. Existing schemes detect congestion while
considering all data to be equally important. We characterize congestion as the
degradation of service to HP data due to competing LP traffic. In this case,
congestion detection is reduced to identifying competition for medium access
between HP and LP traffic. Congestion becomes worse when a particular area is generating
data at a high rate. This may occur in deployments in which sensors in one area
of interest are requested to gather and transmit data at a higher rate than
others (similar to bursty converge cast [25]). In this case, routing dynamics
can lead to congestion on specific paths. These paths are usually close to each
other, which lead to an entire zone in the network facing congestion. We refer
to this zone, essentially an extended hotspot, as the congestion zone
(Conzone). In this paper, we examine data delivery issues in the presence of
congestion. We propose the use of data prioritization and a differentiated
routing protocol and/or a prioritized medium access scheme to mitigate its
effects on HP traffic. We strive for a solution that accommodates both LP and
HP traffic when the network is static or near static and enables fast recovery
of LP traffic in networks with mobile HP data sources. Our solution uses a differentiated
routing approach to effectively separate HP traffic from LP traffic in the
sensor network. HP traffic has exclusive use of nodes along its shortest path
to the sink, whereas LP traffic is routed over un-congested nodes in the
network but may traverse longer paths. Our contributions in this work are
listed as follows:
Design of Congestion-Aware Routing (CAR):
CAR is
a network-layer solution to provide differentiated service
in congested sensor networks. CAR also prevents severe degradation of service
to LP data by utilizing un congested parts of the network.
Modules:
1
Network Formation
2
Conzone Discovery
3
Routing Data via Differentiated paths