# Future Sustainable Internet Energy-Defined Networking
## 4 Future Internet Energy-Defined Networking--Design Methods
### Methods for Network Energy Management and Associated Research Challenges
#### 4.4.4 Connectivity-Level Energy Design Methods  
Connectivity /forwarding operational support functions (\(\sim\)40% of energy consumption); the methods' main goal is ensuring forwarding decisions consume the most energy among data-plane operations).  
The specific critical methods include the following:  
1. The proposed programmability [5] of the traffic sending rate is designed to conserve energy, maintain the network topology's connectivity, and not require new routing information distribution and re-convergence.
2. Energy-aware semantic routing and approaches are mainly aimed at consolidating traffic on the part of the infrastructure so that some network components, such as links or even entire routers, can be put into standby mode and thus reduce the network energy consumption.
3. Programming and encoding the entire routing path in packet headers to circumvent table lookups, which consume the most energy among data-plane operations.
4. Flexibility in supporting and addressing multiple semantics will be crucial in designing new schemes to cope seamlessly with changing network topologies due to infrastructure components going into sleep mode. This will not only avoid the need to maintain and update topological IP addresses frequently but can allow for richer policies that enhance packet treatment according to the expected energy performance. Connectivity/traffic engineering functions (~10% of energy consumption); the methods' main goal: traffic optimization. The specific critical methods include the following: 1. Designing protocols to reduce wasteful data transmission enables greater energy consumption efficiency. 2. The dynamic reconfiguration of network components for the activation/deactivation of services is contingent on network-changing conditions. 3. New network addressing schemes allow for the minimization of lookup table sizes and their associated energy use. 4. Optimizing energy efficiency involves directing traffic towards other areas; some isolated equipment may be brought into energy-saving mode. 5. Calculating alternative traffic paths for which the incremental energy cost is low or zero. 6. Alternative transmission duration optimizations are envisaged as, mainly, the transmission period determines the energy consumption, not the actual data rate. A device's energy consumption is not correlated linearly with the volume of data traffic. As such, energy consumption increases are a scale function (i.e., consumption is the constant for a specific traffic volume, and when support for higher traffic volume is needed, the energy consumption is changed to another level). 7. New transport protocols that react to congestion without dropping packets. The Transmission Control Protocol (TCP) and QUIC transport protocol respond to congestion by dumping packets, which is a highly energy-inefficient method since the effort to transmit the packet until it is dumped is wasted. 8. Segment routing (SR) has been employed for energy-efficient networking in various contexts [52], usually through combining Software-Defined Networking (SDN) and SR. In [53], the authors provide a solution for reducing energy consumption in backbone networks by describing a three-step process that includes the selection of nodes to switch off, the computation of new routes excluding the latter harvesting on an intra-domain SDN, and employing segment routing [52; 53] to reroute traffic dynamically. [54] proposes an energy-aware SDN-based routing solution targeting Data Center Networks utilizing segment routing, mainly focusing on per-packet load balancing instead of per-flow load balancing, and improved results regarding the number of links switched off were reported. Designing new SR methods involves the following: (i) green routing approaches harvesting on segment routing to reduce necessary information to deliver traffic; (ii) P4 models for data-plane programmability, supporting energy-aware routing techniques; and (iii) techniques to reduce SR headers to minimize packet size, with respective energy benefits.