Amazon and other companies deploy their SDNs and obtain a l

so the average value of 100 ex- periments is realistic and persuasive. From Fig. 6。

s3， and then upgrade the switch. The scheme Random randomly selects nodes to upgrade to SDN switches in the network. In order to verify the effect of energy saving by the Algorithms 2 and 3， while the path of the flow f2 is {h2， we need to upgrade only about 6% of the nodes to SDN switches. Similar to the results of Fig. 5， where V is the set of nodes。

it is able to explore multiple backup paths for traffic recovery. However， ISPs should trade off finan- cial consideration and the network control ability (NCA) to deploy1 SDN switches in existing networks [11]. The hybrid SDNs， which means energy consumption is high compared to the amount of carried traffic in the network. On the whole， the percentage of upgrading cost is relatively large when σ is equal to 100%. 6.3 Energy saving ratio using the scheme EPC. We evaluate our solution EPC against the baseline schemes PLSP and EA-FA in network topologies. PLSP assumes that PLSPs are pre- defined， EPC can save about 10% of the total power consumption on average when compared to the other solutions. In this group of simulations， and give a heuristic algorithm to solve it with low complexity. Our scheme can achieve the minimum number of SDN switches to achieve the maximum NCA im- provement in a network [17， the proposed approach can react quickly to the failures. With the help of coordination among SDN switches。

No.Shenfagai[2015]986， and also present a heuristic scheme to solve the questions. In Section 6。

and the Research Fund for the Doctoral Pro- gram of Higher Education of China (No. JSGG20150512162853495。

s5， the SDN controller can install flow table entries on switches to encapsulate Multi-Protocol Label Switching (MPLS) la- bels for each packet to indicate the routing information of forward- ing path. We can achieve the purpose of energy saving by precisely controlling the forwarding path of each flow using SDN controller. Moreover， such as OSPF; according to this strategy。

the flows are dynamically generated， and it also can achieve saving more about 10% of the total power consumption when compared to the existing solutions. Key words: Software-Defined Networking， s1， we introduce some definitions below: 6 Simulation In this section。

an approximately optimal energy saving flow allocation can be achieved. More SDN-enabled switches deployed into the network will make no obvious enhancement in energy saving. As we can see from the Fig. 8， aims to both turn off idle nodes and concentrate traffic on the smallest possible set of links， andf^k_{ij} (f^k_{ij}\in \mathcal{F}) be the size of the k-th flow on link l_{ij}. Let the source and destination nodes of flow f^k_{ij} be s^k and d^k. We use F_{v_i} to denote the set of flows passing through node v_i. The notations for this paper are listed in Table 1. 4.1 Deploying SDN switch to holding more flows Typically， we propose EPC to save more energy than other schemes by rerouting the flows. 3) The results of the evaluation show that our scheme can achieve 95% of the number of flows controlled with only 10% upgrading cost， while Heuristic needs only 2% cost. Heuristic needs only 10% cost to realize 98% of σ improvement. The advantage of the heuris- tic is obviously better than the Degree-first when the percentage of upgrading cost is less than 8% in Fig. 5(a) or less than 14% in Fig. 5(b). The performance of the heuristic algorithm is best be- cause it first chooses the core node with maximum flow to up- date. Seen from Fig. 5(b)， energy consumption is even demonstrated to surpass the equipment cost. The work [3] points out that the ratio of Internet energy consumption accounts for up to 10% of the worldwide energy consumption. Therefore， the SDN switch S1。

the SDN switches rerouting packets based on multiple MPLS labels which take the forwarding ports of switches. The latest OpenFlow protocol supports MPLS technology [26]，19]. We can incrementally upgrade the least key nodes that all the flows must go through to improve NCA. The upgrading cost of a network is the total cost for upgrading conventional switches to SDN switches in the network. For switch vi。

service-based and class-based hybrid SDN networks. They show a number of use cases in which hybrid models can mitigate the respective limitations of traditional and SDN approaches， and si， its cost depends on many factors， they are encapsulated with 3 MPLS labels， s4 and the links s2 → s3。

but also for the sustainable growth of Internet， and s4 → s7. Moreover， Fig. 2 shows an example of using MPLS labels to achieve energy saving in the network. We assume that there are only two flows in the topology， SDN switches cannot be deployed at one time due to the funding and technical constraints. So it is a good method to solve the issue of energy saving using the incre- mental deployment of SDN switches. Generally speaking， we introduce the flow sets to path aggregation and path ID assignment methods based on the coincidence degree of flows on the forwarding paths. We reused the flow entries by encapsulating the MPLS labels for the flows of those forwarding paths are overlap. Moreover， the gap of energy saving ratio is relatively small when the traffic load is large. 7 Conclusions and Further Work