# IMU: A Content Replacement Policy for CCN, Based on Immutance Content Selection
## 4 Performance Evaluation
### Link Load  
Link load indicates the total number of bytes (consumer's request size and content size) traversed for retrieving the interesting content at the specific time limit. It measures bandwidth usage in the network and is defined as follows:  
\[\textit{Link Load}=\frac{(\textit{request}_{size}\times\textit{request}_{link \_count})+(\textit{content}_{size}\times\textit{content}_{link\_count})}{ Duration} \tag{4}\]  
\[\textit{Duration}=\textit{Content Retrieval Time}-\textit{Content Request Time} \tag{5}\]  
where, \(\textit{request}_{size}\) denotes the request's size in bytes, \(\textit{request}_{link\_count}\) designates the number of the links traversed that reach the source, \(\textit{content}_{size}\) is the content size to retrieve, \(\textit{content}_{link\_count}\) is the number of links where the content reaches the request's originator. Figure 5 illustrates that IMU performs better than other existing strategies in terms of link load. IMU does not replace such content from the cache, which has a frequency over a certain period of time. Therefore, consumer request is mostly satisfied with the routing path or close to the consumer. Therefore, most of the content in the cache is of interest to the user. In addition, content that increases in frequency for some time but does not become popular later also removes such content from the cache. However, IMU maintains the freshness of the content as well as the mature content in the cache. FIFO does not compete with the popularity of content because this technique only considers the order in which the content is cached and evicts the content from the cache in that order. Therefore, popular content is evicted from the cache. However, most consumer requests are satisfied with the publisher. Figure 5 demonstrates that LRU is better than LFU when the cache size is smaller. LFU performance improves as the cache size increases, as LFU takes into account the popularity of the content. Therefore, popular content stays in the cache for a long time, and the consumer's request is found in the cache space and not forwarded to the publisher. In addition, content that increases in frequency stays in the cache space, even if it is not popular. However, this is a misuse of cache space and leads to a higher link load. LRU ignores the popularity of the content as well as the maturity of the content. Therefore, popular content requested in the past is likely to be used in the future, but recently requested content may be replaced with less popularity; thus, it does not adapt to changing workloads. When the request rate is high in LFRU, the least recently used content is evicted from the privileged partition and pushed towards the unprivileged partition, with complete access history. However, this content is no longer popular but has a high access history; this content spends more time in cache space, which causes high \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \(\mathbf{\alpha}\) & **Cache Size** & **Placement** & **FIFO (\%)** & **LRU (\%)** & **LFU (\%)** & **LFRU (\%)** \\ \hline
0.6 & & LCE & 10.37 & 8.71 & 7.48 & 3.45 \\
0.6 & & CL4M & 7.58 & 6.79 & 6.17 & 5.49 \\
0.6 & 4\% to 20\% & ProbCache & 8.13 & 7.12 & 6.43 & 2.10 \\
0.6 & & LCD & 10.00 & 5.76 & 4.90 & 6.55 \\
0.6 & & opt-Cache & 7.12 & 5.37 & 4.51 & 2.26 \\ \hline
0.8 & & LCE & 14.01 & 11.55 & 10.08 & 6.08 \\
0.8 & & CL4M & 14.32 & 9.65 & 8.71 & 6.30 \\
0.8 & 4\% to 20\% & ProbCache & 7.39 & 6.12 & 5.44 & 1.95 \\
0.8 & & LCD & 10.12 & 7.01 & 6.36 & 4.07 \\
0.8 & & opt-Cache & 9.26 & 7.18 & 5.97 & 3.38 \\ \hline
1.0 & & LCE & 21.37 & 19.60 & 18.87 & 9.98 \\
1.0 & & CL4M & 18.36 & 15.96 & 15.24 & 13.53 \\
1.0 & 4\% to 20\% & ProbCache & 14.55 & 12.39 & 12.24 & 7.51 \\
1.0 & & LCD & 14.61 & 11.90 & 11.08 & 6.89 \\
1.0 & & opt-Cache & 17.67 & 14.39 & 12.74 & 9.05 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: IMU latency percentage improvement. link load. IMU outperformed FIFO, LRU, LFU, and LFRU in terms of link load by 18.04%, 13.61%, 12.49%, and 9.53%, respectively.