# Neighbor Session Solutions for Integrated Routing Protocols
## 4 Modeling Protocol Integration Solution Classes
### PISC 3--L3 Transport, Multiple Adjacencies
#### 4.1.1 Sending Part
The number of nodes is expressed by the item nodes, the item arcs by the number of edges, and, the most important item, status indicates whether the full state space has been calculated (the simulation has ended after establishing the neighborship and exchanging routing information). As we can notice from the statistics output, the state space contains tens of thousands of items even though the model only consists of 22 places and 14 transitions. This is because, in the PISC 1 model, both neighborships are created simultaneously, which increases the number of possible active transition combinations. Other items of interest include the data in the Best Integer Bounds section, where we can see for specific places the maximum and minimum token occurrences simultaneously. As the last interesting part of the state space calculation output, we can mention the Dead Markings item, which shows the state space nodes at which the simulation ends. In the case of the PISC 1 model, there are three nodes, which is again due to two neighbors forming at the same time. The most important part of the PISC 2 state space calculation output is shown in Figure 5.1

Since the PISC 2 model creates only one neighborship and is simpler than the other models, its state space is smaller and contains only one node at which the simulation can terminate. The PISC 3 state space is similar in properties to the PISC 1 model, in that it also creates two neighborships. The main difference is only in the larger number of nodes and edges of the state space. The calculation of the PISC 4 state space is as successful as it was for the other models. Even though it forms a single neighborship, the state space contains more nodes and edges than in the PISC 1 model. This situation is caused by solving the problem of which network protocol to use to exchange routing messages. The comparison of all four PISC classes state space computation statistics is shown in Figure 5.2

Figure 5.3 PISC 1 state space calculation output excerpt. Figure 5.4 PISC 2 state space calculation output excerpt. The full-text outputs of the state space computation for each PISC model are given in Text S1-S4. To create a methodology for the design of dual-stack routing protocols, we have to rigorously compare individual PISC models. One of the biggest challenges is the selection of a suitable criterion, based on which the results of the comparison can be used to create a methodology for the design of integrated protocols, which will be independent of a specific future implementation; therefore, the selected criterion must be sufficiently general. Therefore, we perform an analysis of the available literature dealing with the creation of colored Petri net models [44] as well as various scientific papers dealing with the use of colored Petri nets for the improvement in network protocols, which are mentioned in the introduction of this paper. The first criterion we consider based on its use in simulating different protocol models is the length of neighbors establishment along with the time required for the subsequent exchange of routing information. Using the time criterion assumes that each transition in the model is assigned its duration. But the problem arises when determining these time intervals since the duration is an implementation-dependent parameter. For example, we will present the Encapsulate L3 transition, which in the third and fourth class models is used to wrap the routing message into an IP packet. This operation can be performed in software in a real router implementation. This can be an example of low-cost routers not optimized for operation in high-speed networks but for price. In contrast, in software implementation, it can take on the order of microseconds. On the contrary, this operation can be implemented by a hardware element, which is the case of current high-speed routers, where this operation can take on the order of nanoseconds to picoseconds.