# NDN Content Store and Caching Policies: Performance Evaluation
## 5 Simulation and Discussion
### Simulation Environment Setup  
We use ndnSIM [60] for the simulation. ndnSIM is an open-source network simulator for the NDN architecture. It is based on and leverages the _network simulator_ (NS-3) [61] specifically to (a) create the simulation topology and specify the respective parameters; (b) simulate the link layer protocol model; (c) simulate the communication between the different NDN nodes; and (d) record the simulation events. This simulator is implemented to simulate the NDN network layer protocol model, and can work on top of any link layer protocol model [62]. Two topologies are considered: (1) Topology 1--generic, using the NDN testbed [63] (as shown in Figure 1a) composed by 42 routers. Connected to each of these routers, there is just one leaf where the consumer (or producer--the only producer in the network) is installed on; and (2) Topology 2--more suitable for ISP, using the Abilene network (see Figure 1b) composed by 11 routers. Connected to each of these routers, there are 4 or 5 leaves where the consumers are installed. One of the 11 routers is reserved, and the unique producer in the network is installed on a leaf connected to this router. For both topologies, the simulation is performed with the consumer request rate fixed to (a) 5 packets per second, and (b) 100 packets per second. To further evaluate the performance with a relatively more complex network, both topologies were additionally configured with multiple producers (i.e., 10 producers and 32 consumers requesting at a rate of 100 packets per second). Furthermore, the consumer request rate was incremented to 1000 packets per second for Topology 1, with all routers equipped with CS. A generic network and another network more suitable for ISP are chosen. Combining these topologies with different skewness factors, from MZipf, one observed in ISP networks and other for general user-generated content, will provide a more general view of the performance of the network, with the varying number of the CS. Seven different scenarios are prepared for both topologies. The scenarios are configured to have the routers equipped with CS at the following levels: 100%, 80%, 50%, 40%, 30%, 20% or 5% of the total routers. In scenarios where the percentage of nodes equipped with content stores is less than 100%, the caching nodes are randomly selected, but the positions of the consumers and the producer(s) are fixed. Nodes without CS cannot cache contents but can forward packets. The simulation environment was configured with the parameters shown in Table 2. The producer provides a universe of \(10^{6}\) different contents. The size of each CS is 1000 chunks. Consumers request content at a rate of 100 packets/s and 5 packets/s in both topologies, following the _MZipf_ popularity model with a modeling factor \(\alpha=0.75\) and \(\alpha=1.1\). This is done to simulate a scenario with user-generated content and a scenario of an ISP network, respectively. The interests are sent at constant average rates with a randomized time gap between two consecutive interests. The best route forwarding strategy was used, and LCD was selected as the default caching strategy. As explained earlier, we only consider LCD given our interest in studying \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **Value** \\ \hline Topology (nodes) & NDN Testbed (42), Abilene (11) \\ Number of the catalogues & 10\({}^{6}\) different content \\ Number of producers & 1 (10) \\ Number of consumers & 41 (32) \\ Size of CS & 1000 contents \\ Popularity ratio & _MZIP_ (\(\alpha=1.1\), \(\beta=0.7\)) and (\(\alpha=0.75\), \(\beta=0.7\)) \\ Content request rate & 100 packets/s, 5 packets/s (10\({}^{3}\) packets/s) \\ Caching strategy & LCD \\ caching policy & LRU, LFU, FIFO, Random \\ Forwarding strategy & _Best Route_ \\ Cache scenarios & 5\%, 20\%, 30\%, 40\%, 50\%, 80\%, 100\% \\ Metric & Cache Hit ratio, Traffic, Delay, Re-transmissions, \# hops \\ Simulations per scenario & 20 \\ Duration of simulations & 240 s, 600 s \\ \hline \hline \end{tabular}
\end{table}