System Architecture Design

pSHIELDSystem Architecture DesignPUillustrated in Figure 3 B. Such downward flow of information is termed as Hints in [6]. As anexample, the applications can inform the link layer about their delay requirement and the linklayer can then treat packets from the delay sensitive applications with priority [7].3) Back and forth information flow: Two layers, performing different tasks, can collaborate with eachother at run-time. Often, this manifests in an iterative loop between the two layers, withinformation flowing back-and-forth between the layers, as highlighted in Figure 3 C.Figure 3 - Different kinds of cross-layer design proposals (boxes represent the protocollayers).3.1.2.2 Existing and new CLAs3.1.2.2.1 A classic CLACross-layer design proposals that we looked at in Section 3.1.2.2 demonstrate the violation of layeredarchitectures at the protocol design phase itself. Hence, a question that naturally comes up is, “Can therebe architectures that are general enough such that protocols for wireless networks can be designedwithout violating them?” In fact, this is a complicated question. Determining what the new architecturesshould look like requires the study of not only the performance issues from a communication ornetworking viewpoint, but also an understanding of the implementation related issues. Nevertheless,some preliminary proposals have been made in the literature.These can be put into two categories:1) Allowing the layers to communicate with each other (Figure 4 A)2) A shared database across the layers (Figure 4 B)A. Allowing the layers to communicatePUD2.3.2Issue 5 Page 20 of 122