Cognitive Networks: Towards Self-Aware Networks

6.3. General Motivations for Cross-Layer Design

What motivates designers of wireless networks to violate the layered communication architectures? There are a three broad motivations. Several cross-layer design proposals aim to solve some unique problems created by wireless links. An example of such a problem is the classic case of a TCP sender mistaking a wireless error to be an indication of network congestion ^[]. Another category of cross-layer design ideas aim to exploit the fundamental characteristics of the wireless medium opportunistically, for example by utilizing channel variations from fading at the higher layers. This is in line with the general goal of an adaptive protocol stack that responds dynamically to the changes in the network conditions. Yet another category of cross-layer design ideas make use of the new modalities of communications that wireless medium creates and that cannot be accomodated within the constraints of layering. An example here is node cooperation, as we discuss later. Cross-layer design with all three motivations are important in the context of cognitive networks of the future.

In this section, we elaborate further on the motivations for cross-layer design. We draw examples from the published research literature. Apart from clarifying the main motivations for cross-layer design, taking relevant examples from the literature also gives a good measure of the wide range of scenarios in which cross-layer design has been applied.

Since there is no ...