# A Comprehensive Survey on Knowledge-Defined Networking
## 7 Application Plane  
### Introduction to Application Plane  
The application plane is the top layer in KDN architecture and is responsible for providing a higher-level view of the network that is more closely aligned with business needs and objectives. These high-level goals and objectives of users are expressed in the application plane as intents. The application plane in KDN is designed to understand the requirements of the applications, while dynamically optimizing application policies based on the knowledge of the network. Additionally, it offers a centralized control point for network policies, allowing administrators to specify policies that are exclusive to a single application or a collection of apps and to reliably apply those policies throughout the network. Remember that an application policy is a set of high-level guidelines that control how an application behaves. Its scope is more specific (application-level scope) than an intent, and it may be established for a single application or a collection of apps. Due to the fact that KDN can be implemented in a variety of network types, including  
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Parameter** & **Wired** & **Optical** & **Wireless** \\ \hline Transmission range & Low (Cat6a—around 100 m) & High (single mode—2 km to 40 km, multi mode—300 m to 2 km) & Vary (4G—up to 10 km, 5G—up to few km, Wi-Fi6—50 m indoor and 200 m outdoor) \\ \hline Attenuation & Medium (Cat6a—0.02 to 0.10 dB/m) & Low (single mode—0.002 to 0.0004 dB/m, multi mode—0.0030 to 0.0100 dB/m) & Vary (4G—0.0005 to 0.0050 dB/m, 5G—0.0005 to 0.00200 dB/m, Wi-Fi6—0.10 to 10 dB/m) \\ \hline Propagation delay & Medium (Cat6a—5.3 μs/km) & Vary (single mode—around 5 μs/km, multi mode—6.7 μs/km) & Low (4G—3.5 μs/km, Wi-Fi6—4.4 μs/km) \\ \hline Maximum throughput & Medium (Cat6a—10 Gbps) & High (single mode—100 Gbps, multi mode—10 Gbps) & Vary (4G—1 Gbps, 5G—20 Gbps, Wi-Fi6—9.6 Gbps) \\ \hline Maximum bandwidth & Low (Cat6a—500 MHz) & High single mode—10 GHz, multi mode—2 GHz) & Vary (4G—20 MHz, Wi-Fi6—160 MHz) \\ \hline Error rate & Medium (Cat6a—10\({}^{-12}\)) & Low (single mode—10\({}^{-15}\), multi mode—10\({}^{-12}\)) & High (4G—10\({}^{-6}\), 5G—10\({}^{-9}\) to 10\({}^{-10}\), Wi-Fi6—10\({}^{-9}\) to 10\({}^{-10}\)) \\ \hline Communication cost & Low & Medium & High \\ \hline Installation and maintenance cost & Low & High & High \\ \hline Flexibility & Medium & Low & High \\ \hline Security & Medium & High & Low \\ \hline Electromagnetic interference & Medium & Low & High \\ \hline \hline \end{tabular}
\end{table}
Table 8: Comparison of transmission media parameters.  
wireless sensor networks, data center networks, optical networks, vehicular networks, internet of things networks, etc., a wide range of applications may be possible. We discuss KDN in different network scenarios in Section 8.3.7. The applications can be developed by third-party vendors or customized by network operators to suit their requirements. The application plane decouples the application logic from the hardware to express the desired intents/policies in a centralized manner. Routing, load balancing, access control, firewalls, etc. are typical examples of KDN applications.