## 5 Performance Evaluation
### Performance Evaluation
#### 5.2.2 Cache Size Influence on Transmission Performance  
The influence of the cache size on the cache hit rate is shown in Figure 7a. The hit rate is the ratio of the number of interest messages in the cache service to the total number of interests in the response. The hit distance represents the number of route hops to obtain the required cache. With the increase in cache size, the cache space can accommodate more cache content. The cache hit rates of these four forwarding schemes are all improved, and the trend of improvement is declining; meanwhile, the cache hit distance is reduced.  
Benefiting from the multipath parallel forwarding capability brought by network coding, NetCodCCN and IDEANE can achieve a slightly better cache hit rate than NDN-Multicast, and a significantly better rate than NDN-BestRoute. NDN-BestRoute optimal path forwarding will result in redundant data transmission, so it is necessary to send interest messages to request new data blocks frequently. Network coding can prevent this situation and improve the cache hit rate. In the network topology shown in Figure 5, the original two NDN schemes need an average of 1.9 hops. In contrast, NetCodCCN and IDEANE can obtain the required cache at an average of 1.4 hops, thus reducing the hit  
Figure 7: Caching performance under different cache sizes. (**a**) Average cache hit rate. (**b**) Average cache hit distance.  
distance by approximately 23%, as shown in Figure 7b. The network coding scheme can reach the required cache with fewer hops, because network coding can reduce the requests for the same encoded blocks. Therefore, it can obtain different encoded blocks within the same encoded group, thereby decreasing the hit distance of the cache.  
Figure 8a shows the impact of the cache size on the content download time and interest message load. The larger the cache, the more data blocks can be accommodated by intermediate nodes and the higher the probability of cache hits. Therefore, the download time of all forwarding strategies will be reduced. The three strategies using multipath forwarding can all achieve a shorter download time within 31.6% compared to NDN-BestRoute to achieve the desired content. IDEANE does not need to encode again at the intermediate nodes. It only makes use of the encoding vectors carried in the received encoded blocks to perform linear independent verification on the encoded blocks of the same encoded group. Thus, it can save 35.4% of download time compared to NetCodCCN.  
As shown in Figure 8b, NDN-BestRoute consumes a smaller interest message load to obtain content than other strategies because the optimal path selected through the NDN-BestRoute strategy is more likely to cache hits. At the same time, the interest load consumed by each node in NetCodCCN and IDEANE will decrease with the increase in cache. With the increase in cache, many encoded blocks are cached in the CS of intermediate nodes, thus reducing the bandwidth consumption required to obtain content. NetCodCCN may need to reapply for encoded blocks because it has brought back linearly correlated ones, leading to interest load consumption that is almost 11.4% higher than that of IDEANE.