I. Introduction  
A. Softwarized Network Scenarios  
B. Various Softwarized Network Scenarios  
C. Toward Energy-Efficient Softwarized Networks  
D. Survey Methodology  
E. Survey on Surveys  
F. Contributions and Paper Organization  

II. Energy Efficiency in Network Infrastructure  
A. Energy Consumption Contributors  
B. Energy Consumption Models  
C. Energy-Efficiency Strategies  
D. Energy Efficiency and Network Softwarization  

III. Network Softwarization: The Key Enablers  
A. Software-Defined Networking  
B. Network Functions Virtualization  
C. Network Slicing  
D. Management and Orchestration  

IV. Survey on Energy-Efficient Softwarized Networks  
A. Energy-Efficient SDN  
B. Energy-Efficient NFV  
C. Energy-Efficient NS  

V. Future Research Challenges  
A. Green Programmable Hardware and Green Software  
B. Energy Consumption in Control and MANO Layers  
C. Network Reconfiguration and Sharing  
D. Energy Savings at the Edge  
E. E2E Energy-Efficient Softwarized Networks  
F. Network Heterogeneity  
G. Energy Heterogeneity  
H. Optimization Approaches  
I. Metrics and Measurements  
J. Evaluation Environments  

VI. Conclusions