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by researchers who have made independent contributions in designing different layers
of the stack. Many of the cross-layer designs depend on other cross-layer designs and
hence raise the fundamental question of the coexistence of different cross-layer design
proposals. In addition, the question of time synchronization between various cross-layer
schemes and the roles each layer of the stack plays is an active area of research. In addi-
tion, the wireless medium allows richer modalities of communication than wired net-
works. For example, nodes can make use of the inherent broadcast nature of the wireless
medium and cooperate with each other. Employing modalities such as node cooperation
in protocol design also calls for cross-layer design. The goal of designing security solu-
tions with a cross-layer design approach takes us to a new paradigm of security research.
The main objective of security solutions in a network is to provide security services such
as authentication, integrity, confidentiality, and availability to the users. In wireless ad-
hoc networks, due to the unreliable nature of the shared radio medium, attackers can
launch varying attacks, ranging from passive reconnaissance attacks to active man-in-
the-middle attacks (Chapter 2). Routing in WSN is hop by hop and assumes a trusted,
cooperative environment as intermediate nodes act as relays. However, compromised
intermediate nodes can launch varying routing attacks, such as blackhole, wormhole,
flood rushing, and selective-forwarding attacks (Chapter 2). In this chapter, we review
the existing state of the art in the cross-layer design from a security perspective. In addi-
tion, as an example, we look at a cross-layer key-distribution mechanism.
8.2 Cross-Layer Design in WSN
8.2.1 Motivation
As in an Open Systems Interconnect (OSI) model, a layered architecture divides the
overall networking task into specific layers, where each layer specifies defined services
and direct communication between nonadjacent layers is forbidden. Subsequently, com-
munication between adjacent layers is limited to procedure calls and responses. Such lay-
ered architecture facilitates the framework for inter- and intracommunication and sets
the ground rules on which protocols can be designed. As a result, a higher layer protocol
will only avail the services offered by lower layers and not be concerned about the details
involved in implementation of such services. Second, the architecture also implies that
the protocol would aim to have standard Application Program Interfaces (API). On the
other hand, protocols can be designed by defying the reference layered architecture that
could facilitate direct communication between nonadjacent layers. Such violation of
layered architecture forms the basis for the cross-layer design architecture. For example,
violation of a layered architecture could include creating new interfaces between layers,
redefining the layered boundaries, and joint tuning of parameters across different layers.
In certain cases, where the violation is too drastic, the original architecture could be
replaced completely by the newer cross-layer design. Although, caution should be taken
in designing cross-layer design schemes in WSN, there are many incentives to adapting
to such schemes that have motivated cross-layer designers to violate the layered archi-
tecture. One of the main motivations is the prospect of leveraging on opportunistic
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