# An Efficient Probe-Based Routing for Content-Centric Networking
## 4 Performance Evaluation
### Experimental Results
#### 4.4.2 The Impact of Cache Size Ratio  
The cache size to whole content ratio has a huge impact on routing performance [3]. The higher the ratio, the less the rate of cache misses. Due to the increasing cache size, a router can cache more content. In other words, because there are more candidate content providers for an interest, obtaining content responses from nearby routers is easier. As a result, the number of forwarded interests decreases, and network congestion decreases indirectly. Figure 6 exhibits the effect of the cache size ratio on different performance measurements of basic CCN and our _probe_-based approach. According to our observations, when the cache size ratio is more than 50%, the routing results between the basic CCN and our _probe_-based approach are scarcely different. The reasons above are that the _I router_ or its neighbor routers satisfy the majority of interest packets, and the _probe_'s exploration in CCN is limited. Generally, the cache size ratio is rarely larger than 50% in most actual network situations. The amount of network content is exponentially increasing, especially with the recent increasing network applications. The large size of cached contents becomes a burden on a router and causes processing time to be delayed. As a result, only the results of the cache size ratio less than 45% are presented and discussed in this paper. For the three approaches in Figure 5(a)-c, the number of forwarded interest packets, the number of timeout interest packets, and the average response time all decrease as the cache size ratio increases. Compared to the 1% cache size ratio, owing to increasing the cache size ratio to 40%, the number of forwarded interest packets is reduced by about 4.5% \begin{table}
\begin{tabular}{c c c} \hline \hline
**Methods** & **Accuracy of Content Provider** & **Routing Path** \\ \hline _PIT probe_ & 19.98\% & 6454 \\ _FIB probe_ & 21.39\% & 6320 \\ Sequential probe & 18.99\% & 6543 \\ Random probe & 18.77\% & 6430 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Effectivity of probe. Figure 6: Impact of cache size ratio. (**a**) Total number of forwarded interests; (**b**) number of timeout interests; (**c**) average response time. and the number of timeout interest packets by about 10%. In the simulations, the packet transmission delay in each router was set to 1 s, thus the average response time corresponds to the number of hops in the routing path. The average response time is roughly 3 to 5 s when the cache size ratio is 40%. In other words, the _I router_ or its neighbors satisfy the majority of interests. The results shown in Figure 6 illustrate that both the _PIT probe_ and the _FIB probe_ outperform basic CCN. _PIT probe_ and _FIB probe_ lower the number of forwarded interest packets of basic CCN by 1.024 and 1.034 times, respectively. The _PIT probe_ and the _FIB probe_ reduce the average response time of consumers by 1.08 s and 0.64 s, respectively. This also demonstrates that _probe_-based routing improves the accuracy of the routing table. It is evident that using a _probe_-based approach reduces basic CCN network congestion and improves the accuracy of the routing table, allowing for more efficient routing. Figure 6 also demonstrates that _FIB probe_ outperforms the other _probe_-based approaches in reducing network congestion. This agrees with the result of Table 2. Compared to _PIT probe_, _FIB probe_ routing is more accurate, resulting in more interests being satisfied by the expected content provider and a lower routing cost. It is evident that adopting _FIB probe_ as a FIB update algorithm improves finding the best content provider and the shortest path to the nearest content, resulting in the best performance in terms of the total number of forwarded interest packets and interest packet timeout. However, _PIT probe_ directly reduces customer waiting times by selecting the most popular entry in PIT as a _probe_ to find the best content provider. Hence, the _PIT probe_ gets superior performance on average response time than other approaches.