# Insights from the Experimentation of Named Data Networks in Mobile Wireless Environments
## 4 Experimentation Setup and Results
### NDN According to the Network Characteristics  
Over the course of our tests we have noticed that certain network conditions could have a significant impact in the NDN protocol operation, specially in the packet forwarding over the wireless medium. Such conditions can, in some cases, lead to a higher number of congestion situations. To this extent, we have performed a study on how different network characteristics affect the behavior of the NDN in an effort to further ascertain how better they can be utilized to minimize any negative consequences. The network parameters under study in this scenario are: (i) the Interest timeout, which represents the amount of time that a given node will wait for the corresponding Data packet to arrive; and (ii) the Maximum Transmission Unit (MTU), and consequently, the chunk size. We ran this experiment in the same laboratory environment used in the previous scenario. The main goal was the transmission of a 6 MB file from the infrastructure to the mobile node using wireless technologies, in an effort to obtain the lowest download time possible in a reliable manner. Finally, the indicators used to assess the performance of the NDN in this scenario are as follows:  
* **Download duration:** measures the total time needed to download the Content starting from the moment that the first chunk is requested;
* **Number of timeout events:** every time a Consumer sends and Interest a timer is set, indicating the maximum amount of time available for the Data packet to arrive. If the timer expires, the Consumer retransmits the Interest packet, therefore increasing the network overhead.  
Figure 11a shows that increasing the timeout value slightly can bring benefits in the time needed to download the file, but can also be detrimental or present no significant results as this value is increased to higher values. It is also clear that the NDN packet size has notable improvements: by simply doubling the size of the packet we were able to download the file 60% faster. Improvements to download time stagnate as we approach higher values to this metric, due to the fact that it is easier for longer sized packet to be lost in the wireless channel. A safe value to assume as a _sweet-spot_ for our scenario would be an Interest timeout value of 6 seconds and a 4470 chunk-sized NDN packet, achieving one of the smallest download times while still leaving a window for any transmission errors to occur.  
These values can be further attested by verifying the number of occurred timeouts for the different network characteristics, as depicted in Figure 11b. As the number of Interest timeouts increases, the number of timeouts naturally decreases because more time is given for the data packet to be delivered. However, it also needs to be taken into account that higher Interest timeout values will result in delayed Interest retransmissions, if needed, and consequently longer download times. To this extent, it is emphasized that a middle term must be achieved for a proper and reliable behavior of the network altogether.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Time** & **OutInts** & **InData** & **TimedOuts** & **Average Delay per Chunk** \\ \hline
**Multicast** & 331 s & 39,298 & 1422 & 37,876 & 516.93 ms \\ \hline
**Unicast** & 37 s & 4201 & 4266 & 2779 & 2197.48 ms \\ \hline \hline \end{tabular}
\end{table}
Table 6: Total download time using multi-technology and pipelined application.