# An Efficient Probe-Based Routing for Content-Centric Networking
## 4 Performance Evaluation
### Simulation Parameters  
In the simulations, an open network topology with 12 city nodes, Abilene topology [40] is adopted as illustrated in Figure 4(a). Each node is a router with both a producer and a consumer configuration. Each producer (router) generates 100 unique contents with its name prefix and numbering from 0 to 99. Taking the router \"Atlanta\" as an example, the contents are \"Atlanta/0\",..., \"Atlanta/99\". The Abilene network topology contains 12 routers so the total number of contents is 1200. Each consumer randomly selects a content name from the 1200 contents to send the interest packet. In other words, the contents are chosen with the same uniform probability. Consumers send new interest packets to the network at a frequency of 1 per second.  
In addition, a more complicated network topology, PoP-level Rocketfuel SPRINT topology [7; 33], as shown in Figure 4(b) is also adopted for simulation. The network topology has 52 nodes, including 8 producers (red stars), 11 consumers (green squares), and 33 routers (blue circle). Each producer generates 200 unique contents with its name prefix, such as \"R9/0\",..., \"R9/199\", and so on. Therefore, the total number of contents is 1600.  
For basic CCN, the interest packet and data packet sizes are 5 bytes and 133 bytes respectively. The _probe_ field is a 2 byte string. The _probe-response_ field is recording the router IDs. The router ID is a 4 byte int. Therefore, the _probe-response_ field is \(n*4\) bytes in size. In this paper, the _probe-response_ only records the nearest 5 potential content providers, so n is 5. In Abilene topology, to see the impact of cache size and cache update ratio, increasing cache size ratio ranging from 1% to 40% and cache update ratio ranging from 1% to 50% are used. In PoP-level SPRINT topology, the bandwidth of the emulator is set to 1024 bits. To evaluate the impact of traffic variations on the performance of our approach, we changed the frequency of consumers sending new interest packets. The frequency was set to send from 1 to 30 interests per second. Cumulative number of router failures was used to evaluate the impact of router failure behavior on CCN performance. The faulty router was randomly selected from 33 routers. The replacement policy for cache and FIB was FIFO and LRU. Forwarding strategies included broadcast and best route. All the simulations ran 480 s each time. Basic CCN, EEGRP [31] and ReCIF + PIF [41] as comparison methods adopted the same settings in this paper. Table 1 lists the detailed experimental parameter settings.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Description** \\ \hline Number of routers & Abilene: 12 \\  & PoP-level SPRINT: 52 \\ Propagation delay & 1 s \\ Interest packet size & Name: 2 bytes; Selector: 2 bytes; Nonce: 1 byte; Probe: 2 bytes; Probe-response: 20 bytes. \\  & 2 bytes; Probe-response: 20 bytes. \\ Data packet size & Name: 2 bytes; Signature: 2 bytes; Signed info: 1 byte; \\  & Data: 1 kb; Probe: 2 bytes; Probe-response: 20 bytes. \\ Frequency & Abilene: 1 interest/s \\  & PoP-level SPRINT: 1-30 interest/s \\ Number of contents & Abilene: 1200 \\  & PoP-level SPRINT: 1600 \\ Cache size ratio & 1\%, 5\%, 10\%, 15\%, 20\%, 25\%, 30\%, 35\% and 40\% \\ Cache update ratio & 1\%, 5\%, 10\%, 15\%, 20\%, 30\%, 40\% and 50\% \\ Cumulative number of router failures & 1\(-\)20 \\ Cache replacement policy & FIFO and LRU \\ Forwarding strategy & broadcast and best route \\ Timeout timer of interest trails & 0.5 s \\ Simulation time & 480 s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experimental parameters setting.  
Figure 5: Topology. (**a**) Abilene topology [40]; (**b**) PoP-level SPRINT topology [7; 33], where including producer (red star), consumer (green square), and router (blue circle).