# Cross-Layer Methods for Ad Hoc Networks--Review and Classification
## 4 Discussion
\begin{table}
\begin{tabular}{c c} \hline \hline
**Frequency** & **Goal Combination** \\ \hline
0.36 & (line throughput) \\
0.21 & (energy consumption) \\
0.015 & (line packet error rate) \\
0.06 & (line latency) \\
0.1 & (route packet error rate) \\
0.33 & (route throughput) \\
0.09 & (interference) \\
0.13 & (route stability) \\
0.09 & (route latency) \\
0.09 & (data overhead) \\
0.06 & (route throughput, energy consumption) \\
0.06 & (line throughput, energy consumption) \\
0.01 & (line packet error rate, energy consumption) \\
0.04 & (line throughput, line latency) \\
0.01 & (route stability, line latency) \\
0.03 & (line latency, energy consumption) \\
0.01 & (route stability, line throughput, line latency) \\
0.01 & (line throughput, line latency, energy consumption) \\
0.03 & (route packet error rate, energy consumption) \\
0.04 & (route throughput, route packet error rate, energy consumption) \\
0.01 & (route throughput, route packet error rate, energy consumption) \\
0.03 & (route throughput, interference) \\
0.04 & (interference, line throughput) \\
0.01 & (interference, route packet error rate) \\
0.01 & (interference, energy consumption) \\
0.01 & (route throughput, route packet error rate, interference) \\
0.01 & (interference, route packet error rate, energy consumption) \\
0.01 & (interference, route throughput, energy consumption) \\
0.01 & (route stability, route throughput, energy consumption) \\
0.01 & (route stability, line throughput) \\
0.04 & (route stability, line throughput) \\
0.06 & (route throughput, route latency) \\
0.01 & (route latency, route packet error rate) \\
0.01 & (route stability, route latency) \\
0.01 & (line throughput, route latency) \\
0.01 & (route throughput, route latency, route packet error rate) \\
0.01 & (route stability, line throughput, route latency) \\
0.01 & (route stability, data overhead) \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Goal frequency of the methods in the reviewed publications. classification of cross-layer methods in ad hoc networks (Figure 7) according to the purpose pursued by using multiple layers. The proposed classification can help to simplify the goal-oriented cross-layer protocol development. The overall objectives for network control protocols are always throughput, latency, and packet error rate. These objectives remain invariant regardless of the number of layers involved in the optimization process. At the same time, these objectives can be achieved in a variety of ways. The proposed classification helps to systematize these ways. Quite often, when developing a new cross-layer protocol, there is a goal to achieve (it can be a routing protocol, channel access protocol, etc.). Figure 7 helps to choose the publications to base the research of new cross-layer protocols upon, given the protocols in publications were already categorized using the proposed classification. The proposed classification is goal-based, contrary to usual combination-based classifications. Combination-based classifications may be ambiguous. For example, let one cross-layer method use physical, channel, and network layers. This method can be categorized equally as channel access protocol, routing protocol, or protocol with independent layers and information sharing. At the same time, the proposed classification provides an explicit reasoning about the considered protocol. This circumstance makes the proposed classification more useful. The proposed classification helped us to highlight the 10 problems that can be  
Figure 7: Cross-layer methods for ad hoc network classification. solved using a cross-layer approach. These 10 problems are enumerated above. These problems were solved earlier in the confines of one corresponding layer.