# Neighbor Session Solutions for Integrated Routing Protocols
## 4 Modeling Protocol Integration Solution Classes
### PISC 3--L3 Transport, Multiple Adjacencies
#### 4.1.1 Sending Part
In contrast, simulation runs of the first-class model consist of either 180 or 175 steps, with 180 steps occurring the most frequently. Based on the results shown in Table 2, we can state that the best PISC class based on the comparison according to the number of simulation steps is the PISC 2, that is, creating a single adjacency along with sending routing messages only at the link layer. The efficiency of the PISC 2 class is also shown by the state space size presented in Table 1. \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Mode** & **Arithmetic Mean** \\ \hline First PISC model simulations & 180 & 179.98 \\ Second PISC model simulations & 90 & 90 \\ Third PISC model simulations & 252 & 252 \\ Fourth PISC model simulations & 131 & 131 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of simulation runs of PISC models. Figure 16: PISC 1 simulation output excerpt. ## 7 Recommendations for the Design of Integrated Routing Protocols

The main goal of the research published in this paper, outlined in the introduction, is the creation of recommendations for the design of future or modification of existing integrated routing protocols. Therefore, we created models of the four identified PISC from the point of view of the number of neighbors and the protocol used for transporting routing messages, described in Section 3. Based on the verification of individual models and subsequent comparison using the criterion of the number of simulation steps, we found that the most suitable PISC is class two. Therefore, based on the research presented in this paper, it is possible to formulate the following recommendations for the design of integrated routing protocols from the point of view of the number of adjacencies and transport. Routing protocols designed for use in networks where multiple network protocols are used, i.e., integrated routing protocols, should create only one common adjacency for all network protocols. Also, they should only use link layer protocols to transmit routing protocol messages and thus encapsulate routing messages directly into link layer frames. As the basis of routing messages, it is advisable to use TLV structures, which allow great flexibility for future protocol expansion. Acknowledgment of receipt must be handled by the routing protocol, as the link layer does not provide such services. As another benefit of the PISC 2 model, we see its simplicity, which was also confirmed by the calculation of the state space in Section 5, since the state space was the smallest of the models of all PISC. Since the model is simple enough, after adding appropriate extension elements, it can also be used to verify the design of a specific implementation of the routing protocol based on the formulated recommendations after reading the description of the creation procedure as well as the functionalities of the individual class models in Section 4. The relatively small state space of the created model can potentially signal the advantage of this model even when compared based on other criteria or other parts of the routing protocol designed based on these recommendations. However, this hypothesis would need to be verified by further research. The advantage of the PISC 2 model is that it is unnecessary to solve the problem of which protocol to use to create a neighborship as in the case of the fourth class, described in Section 4.2. Even though both models create only one adjacency, since the second class model uses a link layer protocol to transmit routing messages, it is sufficient to indicate the supported network protocols by parameters in the routing message header. A graphical representation of the entire model of the second PISC can be found in Figure S2. When we look at the currently used dual-stack routing protocols, as mentioned in Section 2, the only protocol whose design fits into the second class of protocol integration solution is IS-IS, which was not originally developed for IP networks.