Performance with the resource utilization cost variation (R cost )(Rcost)

The following experiment evaluates the LSPs allocation in the NSFNET network (Fi-gure 5.4) when varying the R_cost value. To carry out the experiment, we have assumed a random uniform VC-3 demand matrix, which is scaled from [0,9] to [0,108].

Figure 5.7 shows the amount of paths used by the U_mean utility when R_cost varies and the traffic load is increased. As we can see (Figure 5.7 top-left) the amount of electronics paths changes depending on the Rcost parameter used. Moreover, the amount of paths remains similar while the traffic load increases. This means that the Bayesian decisor uses the IP paths first whenever possible and only uses the optical lightpaths when the IP layer is saturated. This behavior fits with the idea of first using the already deployed IP layer if

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(a) Working point 1 (see Figure 5.5)

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(b) Working point 2 (see Figure 5.5)

Figure 5.6: Paths used when the traffic load increases

possible, since it is cheaper in terms of risk. The same paths are used given a R_cost value, but they do not transport the same amount of traffic. Figure 5.7 (bottom-left) shows the mean occupation of the IP layer links. The U_mean function gradually fills in the paths.

At the beginning, when the traffic load is still low, the links occupation is low too, but, progressively, this mean occupation becomes higher. On key feature of the Bayesian decisor is that it does not saturate the IP layer. This remains at medium load levels, but they are never set congested (it does provide QoS).

However, although the number of electronic end-to-end paths remains constant with the traffic increment, the amount of optical by-passes increases with the traffic load (Figure 5.7 top-center). At the beginning, just a few optical end-to-end connections are used, but when the IP layer becomes saturated and can not accept more LSPs, new lightpaths are required to provide a proper service to the traffic demands. This behavior remains similar compared with the previous results in simpler networks or in the multi-hop scenario. It is worth noticing that the number of partly optical and electronic paths referred to as hybrid paths is very small. These paths are used when the hop-by-hop and direct end-to-end connections are saturated. Furthermore, as the traffic matrix is uniform the amount of traffic between one-hop destinations saturates the links when the traffic becomes high.

Such reasons imply that its number is minimum. The occupation of the hybrid paths is not displayed, since they used the lambdas of the electronic and the optical layer. Therefore, neither its occupation is the occupation of the IP layer, nor the occupation of the by-pass.

Once the U_mean function has been is analyzed, the performance of the U_step case is studied next. Its results are displayed in Figure 5.8. Like the U_mean function, the amount of paths used at the IP layer are constant when the traffic load increases. Moreover, the

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Maximum number of e2e LSPs Nmax

Rcost=1.6 Rcost=2 Rcost=3 Rcost=4

Figure 5.7: Number of paths used in each domain and their mean occupation when Rcost

varies (U_mean)

amount of electronic paths is almost constant when the R_costparameter varies. The number of IP layer connections for the U_stepcase does not change as much as for the U_meancase, only about 20 LSPs, whereas the U_mean case this difference was about 150 LSPs. The amount changes, but just 20 paths, while the variation of number of paths with the U_mean function is 150 LSPs. This behavior fits again with the numerical results explained in chapter 4.

The Ustep function sets a given working point depending on the QoS rather than the other parameters. Again the amount of optical paths increases with the traffic, but the amount of LSPs remains similar for all R_cost values. The number of hybrid by-passes is higher in the U_stepcase. Section 4.2.2 showed that when there is cross-traffic in the network and the U_step function is used, the decisor sends the incoming LSPs through the IP layer until they reach a congested node. At this node, the traffic is optically switched to the destination node. This behavior fits with the increment of the number of hybrid connections.

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Rcost=1.6 Rcost=2 Rcost=3 Rcost=4

Figure 5.8: Number of paths used in each domain and their mean occupation when Rcost

varies (U_step)

Concerning the path load, the occupation at the IP layer clearly remains constant in all cases in order to provide the desired QoS (see Figure 5.8 bottom). On the other hand, the optical links’ occupation increases when the amount of traffic becomes greater, since the traffic is transmitted optically, since the IP layer is congested. Again the occupation does not depend on the Rcost parameter for this utility function.

The results for the U_exp function are shown in Figure 5.9. Its behavior is similar to the Umean function, but the difference between Rcost = 1.6 and 2 are smaller. Both cases use the same amount of LSPs at the electronic domain. The number of optical and hybrid connections show the same behavior than at the U_mean case. The main difference between both utility functions is the link occupation. While the U_mean function takes into account the mean delay, the objective of the U_exp function is to provide a QoS to every service, thus filling the links more gradually.

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Rcost=1.6 Rcost=2 Rcost=3 Rcost=4

Figure 5.9: Number of paths used in each domain and their mean occupation when Rcost

varies (U_exp)

Let us review the path length in the three cases. Table 5.1 summarizes the mean length of the paths in each domain for all simulations. The mean is just shown, because there is almost no variation of the average path length with the traffic load increment. We may notice that the electronic paths are shorter than the optical or hybrid paths. This is because the one-hop demands can just send the traffic in the electronic domain, there is no choice of by-passing intermediate nodes. For instance, when Rcost is 1.6, only the one-hop demands are established at the electronic domain, while the others demands use the optical domain.

Electronic paths Optical paths Hybrid paths U_mean U_step U_exp U_mean U_step U_exp U_mean U_step U_exp Rcost = 1.6 1.0152 2.4570 1.7021 2.7620 2.7701 2.7479 − 3.3487 4.0238 R_cost = 2 1.2816 2.4973 1.7043 2.7324 2.7661 2.7362 3.4286 3.3247 4.0408 R_cost = 3 1.9278 2.5556 2.0630 2.7226 2.7724 2.7206 3.1972 3.3994 3.2214 R_cost = 4 2.1184 2.5865 2.2470 2.7287 2.8160 2.7227 3.1689 3.4820 3.1868

Table 5.1: Path length with the variation of the R_cost parameter

When the R_cost parameter is 1.6, the electronic paths becomes shorter than when its value is 3. The reason is that the optical resources cost is cheaper, thus enhancing their utilization. Moreover, when R_cost = 1.6, the design rule of R_cost > _{M +1}^2·M is not fulfilled for all path lengths, becoming the end-to-end ligthpaths cheaper than the hop-by-hop connections. The length of the optical resources does not change with the R_cost variation.

The optical paths length is fix by the network topology, but the end-to-end connections are used at lower or higher rates depending on the R_cost parameter. As previous results depicted, the utilization of the electronic layer is higher for the Ustepcase and, consequently, the average length of the electronic paths is higher than at the Umean or Uexp cases. The length of the hybrid paths highly varies with the traffic load, but it is caused because of the low amount of hybrid connections. If the utilization of new hybrid paths highly impact on the average length.