# A Survey on an Energy-Efficient and Energy-Balanced Routing Protocol for Wireless Sensor Networks
## 5 Taxonomy for Energy-Efficient and Energy-Balanced Routing Protocols
### Multi-Hop Communication Method
#### 5.1.1 Multi-Hop Clustering Technique
In addition, some multi-hop clustering routing algorithms transmit the message from the source node to the CH directly as shown in Table 3. The authors only use the multi-hop technique during the inter-cluster communications. Note, in Table 3, all these clustering routing protocols use the multi-hop communication method during either intra-cluster or inter-cluster communications. In most cases, the multi-hop communication method is used in both the intra-cluster and inter-cluster communications. The clustering algorithms studied in this paper that do not use the multi-hop communication method are classified in Table 6 under single-hop communication. Also, some of the studied clustering algorithms select the relay nodes during the intra-cluster communications based on a probability that depends on two or more of the aforementioned design decision variables. The algorithms attempt to balance the trade-off in selecting the most energy-balanced route to the CH. For instance, as shown in Table 3, some literature jointly uses the transmitting distance between SNs and the residual energy of the SNs as the input decision variables in selecting the relaying nodes during the intra-cluster communications. In so doing, they reduce, to the nearest minimum, the disadvantages of using either the shortest distance or residual energy only in selecting the relay nodes. The disadvantage with some of these approaches is the high network delay as a result of the complexity in the proposed mathematical formulations. Furthermore, some of these studied clustering routing protocols concentrated more on the clustering formation. Since the focus of these papers is on producing a load-balanced cluster, the authors do not give a clear explanation on the intra-cluster and inter-cluster communications. The mode of communication used in transmitting the sensed information towards the BS in these papers can either be the multi-hop or single-hop communication method. However, we classified these papers under multi-hop communication as shown in Tables 2 and 3. Additionally, as shown in Table 3, since the design decision variables used for both the intra-cluster and inter-cluster communications in these papers are not mentioned, we grouped the papers under \"Cluster only\". Also, we classified the clustering routing protocols that do not use any of these mentioned design decision variables in Table 3 under \"Others\". Lastly, we classified any other design decision variables not mentioned in Table 3 that are used in selecting the routes to the CH and/or BS, together with those mentioned in Table 3, under \"Others\". Likewise, we classified the design decision variables used in selecting the route to the BS during the inter-cluster communications. In a similar way to the intra-cluster communication classifications, we grouped the inter-cluster communications under \"Direct\", \"Residual Energy (RE)\", \"Distance\", \"Hop count\", and \"Others\". Another important factor to be considered during the inter-cluster communication phase is the tier of the SNs acting as part of the relay node's chain in forwarding the aggregated information from a CH node to the BS. Since clustering WSNs are regarded as a two-tier hierarchical network, the tier of the node used to form the relay node's chain towards the BS plays a vital role in balancing the load traffic in the network. Some authors use the upper tier nodes (CH nodes) only to form the relay node's chain towards the BS. Although this approach is better than sending the aggregated data directly over a large distance to the BS, the approach tends to increase the work load of the CH nodes. In this case, beside aggregating and forwarding the information from their respective cluster members, the CH nodes are given the sole responsibility of also serving as relay nodes in forwarding the aggregated information to the BS. Accordingly, this increases the duty of the CH nodes, thereby increasing the energy dissipated by the CH nodes in that particular data transmission round.