The size of the network

The last category of the simulated tests intends to realize the limitation of the COVN algorithm, through completing three objectives, these are: (1) Confirming the possibility of increasing the number of controllers which are placed by the COVN placement algorithm, if the network size is increased; (2) Exploring the increment of the connection flow-setup latency with growing the size of network; (3) Investigating the increment of the execution time for both parts (part one and part two) of the COVN placement algorithm. The strategy which is used to apply these tests is as follows:

Page | 170  Choosing a suitable number of controllers for the topology.

 Considering the complete topology as a single VN.

 Applying the COVN placement algorithm with the closeness and reliability weights equal to 0.5 for both.

 Presenting and discussing the resulting controller placement.

 _{Presenting and discussing the latency and reliability metrics which resulted from} applying the controller placements.

 _{Calculating and viewing the computation time for applying the two parts of the} COVN placement on every topology.

 Implementing the previous steps on three topologies which are: Us-Carrier, Generated-2 and Kentucky.

Implementing the COVN placement algorithm on the three topologies produces the controller placements, which are presented in Figure 6.40 below. The graph of US- Carrier network shows that the network is partitioned into seven clusters with a balanced number of nodes (see Figure 6.40(A)). Also, Figure 6.40(B), displays that Generated-2 topology has nine clusters and controllers. Finally, the graph in Figure 6.40(C), presents the controller placement of the Kentucky network. This network is sectioned into eighteen clusters with a balanced number of nodes. However, there are two clusters (C1 and C17) which received only half the number of nodes of other clusters. This is because the nodes of these two clusters are connected linearly and intersected with their neighbour by cut-vertices. The cut-vertex prevents a small number of nodes from moving from the big cluster to the small cluster because disconnecting the cut-vertex from the big cluster creates a separate group of nodes, which generates unbalanced clusters, whether it is added to the original (big cluster) or to the small cluster. This prevents the clustering algorithm from balancing the clusters. Otherwise, the COVN placement algorithm is able to balance all of the clusters.

The number of the controllers is increased from six controllers in the previous three topologies (Generated-1, Internet2 and India), into 7, 9 and 18 controllers in the last three topologies to prove the ability of COVN placement algorithm to increase the number of controllers when the size of the network is increased.

Page | 171 The second objective intends to indicate the increment in the latency and reliability metrics when the network size becomes larger. Figure 6.41 reveals that the increment of the latency metrics is related to two factors: the size of the network and the expansion of the network. However, the expansion of the network has a greater effect in raising the latency metrics. For example, the second test of Generated-2 topology with 400 nodes,

C1 23 C2 22 C3 25 C4 25 C5 21 C6 24 C7 18 Total 158

(A) The controller placement of Us-Carrier topology. C1 49 C2 49 C3 45 C4 48 C5 48 C6 38 C7 48 C8 36 C9 39 Total 400

(B) The controller placement

of the Generated-2 topology.

C1 21 C10 46 C2 45 C11 43 C3 45 C12 50 C4 50 C13 46 C5 36 C14 31 C6 45 C15 49 C7 44 C16 41 C8 49 C17 21 C9 46 C18 46 Total 754

(C) The controller placement of Kentucky topology.

Figure 6.40: The implementation of the COVN placement algorithm on three different size topologies.

Page | 172 obtains the maximum connection flow-setup latency equal to 1,253.42 ms; while, the first test of Us-carrier with 154 nodes produces 3,014.29 ms for this latency metric due to the larger expansion of the network. Finally, the last test of Kentucky topology, which has the largest network size and expansion demonstrates that the maximum connection flow-setup latency could grow up until 4,780.79 ms.

The reliability metrics, which are presented in Figure 6.42, demonstrate that the length of the control-path (Min-hops to farthest node) is effected by increasing the network size. For instance, the maximum value of this metric equals 23 hops for Us-carrier and

Figure 6.41: The comparison of the minimum, average and maximum values of the resulted latency metrics for three different topologies.

Figure 6.42: The comparison of the minimum, average and maximum values of the resulted reliability metrics for three different topologies.

Page | 173 34 hops for Kentucky networks, while it is only ten hops for Generated-2 network. Also, Figure 6.42 proves that controller-connectivity ratio is relevant to the connectivity of the topology. For example, the minimum value of this metric is 14.37 for Us-Carrier topology, while it is 59.11 for Generated-2 topology. However, Generated-2 topology has a larger number of controllers, which reduces the value of the controller-connectivity ratio. The reason for this, is Generated-2 network has more connection between its nodes.

The execution times of the COVN placement algorithm in Table 6.13 are calculated, to achieve the third objective, which aims to determine the limits of this time. This table discloses that the execution time of the first part (the placement of physical controllers) of the COVN placement algorithm is higher than the second part (the placement of the virtual controllers) of the algorithm. This is corresponding to the design of this algorithm because the second part is applied more frequently than the first part (see Table 4.2 in chapter four). Also, the last network (Kentucky) in Table 6.13, proves that

the COVN placement algorithm has a fast exaction time because it can place eighteen physical controllers on a large network (754 nodes) in only 49.53 seconds and eighteen virtual controllers in 28.85 seconds (see Figure 6.40 (C)).

The findings of the sixth category of tests:

 _{The COVN placement algorithm can efficiently increase the number of the placed} physical and virtual controllers when the size of the network is increased.

 The latency of VN raises when the size of the network is increased. However, it acquires a higher increment with the network of the wider expansion like Us- carrier and Kentucky.

Topology name Number of controllers Time of physical controller placement (Second)

Time of virtual controller placement (Second) Generated-1 6 5.70 4.93 Internet2 6 5.44 4.30 India 6 6.86 5.22 Us-Carrier 7 7.07 6.29 Generated-2 9 20.16 11.25 Kentucky 18 49.53 28.85

Table 6.13: The execution time of the COVN placement algorithm for six different topologies and a different number of controllers.

Page | 174  The COVN placement algorithm keeps a low execution time even when the size of

the network and number of placed controllers are increased.