Cross-Layer Security in Wireless Sensor Networks - Security for Wireless Sensor Networks Using Identity-Based Cryptography - page 161

wireless channel. A similar idea based on explicit loss notification has been discussed in
Zhengrong et al. (n.d.), where simulations indicate improved throughput performance.
Such an approach is an example in which a cross-layer view of physical layer information
(channel conditions) is used at the network layer to significantly improve network-layer
throughput performance. Additionally, the wireless medium offers some new modalities
of communication that the layered architectures do not accommodate. For instance,
the physical layer can be made capable of receiving multiple packets at the same time.
The nodes can also make use of the broadcast nature of the channel and cooperate with
one another in involved ways. Making use of such “novel” modes of communication in
protocol design also requires violating the layered architectures.
8.3 Cross-Layer Design Proposals
In recent times, several cross-layer design schemes have been proposed. Cross-layer feed-
back optimization could be implemented on the sink node or the sensor nodes. The
cross-layer interactions among the layers can be categorized in different ways. For exam-
ple, Lower to Upper (violation in the flow control from bottom to top), Upper to Lower
(violation in the flow control from top to bottom), and Lower and Upper (Figure 8.1).
In all these cases, new interfaces will be created between layers. In addition, cross-layer
designs can be categorized by the integration of adjacent layers, design coupling without
interfaces, and horizontal calibrations (Figures 8.2 and 8.3).
• Lower to Upper. The requirement of information from the lower layer to the
upper layer at runtime results in the creation of a new interface between these
two layers. In this case, the lower layers update necessary information to the
appropriate upper layers via the interface. For example, the data-link layer is
made aware of the transmit power and the bit error rate information by the
Figure 8.1. Cross-Layer Architecture—Vertical Violation