Wireless Sensor Networks : Technology, Protocols, and Applications

WSN DESIGN ISSUES 287
WSNs Routing Protocols
Network structure
Protocol operation
Locationbased
routing
Hierarchical
network
routing
Flat
network
routing
Coherentbasebased
QoS-
routing routing
Querybased
routing
Multipathbased
routing
Negotiationbased
routing
Figure 11.2
[11.15].)
Classification of routing protocols for wireless sensor networks. (From
protocol, open shortest path first, border gateway protocol) do not meet the
requirements of WSNs. Data-centric routing is more suitable for WSNs because
it can be deployed easily, and due to data aggregation, it saves energy. Traffic
models and system characteristics can be utilized to design efficient routing protocols.
To conserve energy, most routing protocols for WSNs employ certain technique
to minimize energy consumption (e.g., data aggregation and in-network
processing, clustering, node role assignment). Al-karaki and Kamal [11.15] classify
routing protocols in several categories shown in Figure 11.2. For example,
directed diffusion [11.16] is a data-centric routing scheme with three phases in
its operation:
1. A sink broadcasts its interest across the network in query messages with a
special query semantic at a low rate.
2. All the nodes cache the interest. When a node senses that an event matches
the interest, it sends the data relevant to the event to all the interested nodes.
Sink will also get the initial data and ‘‘reinforce’’ one of source nodes by
resending the interest at a higher rate.
3. After the reinforcement propagation, the source nodes send data directly on
the reinforced path. The performance of a routing protocol can be expressed
through such measures as computational overhead, communications
overhead, path reliability, path length, convergence rate, and stability.
11.3.3 Transport Protocols
The following factors should be considered carefully in the design of transport protocols:
a congestion control mechanism and especially, a reliability guarantee. As
discussed in Chapter 7, since most data streams are convergent toward the sink,
congestion is likely to occur at nodes around the sink. Although a MAC protocol
can recover packet loss as a result of bit error, it has no way to handle packet loss as
a result of buffer overflow. Therefore, transport protocols should have mechanisms
for loss recovery; to guarantee reliability, mechanisms such as ACK and selective
ACK [11.4] used in the TCP would be helpful. At the same time, reliability