## 3 Existing Chain Oriented Topologies
Each chain has a leader that gathers data from its neighbours and sends aggregated data to the upper level leader. The delay may decrease with 3-level PEGASIS. However, 3-level PEGASIS raises the problem of wireless interference as it does not consider the relative location of nodes. Another problem is that unexpected long transmission may occur because the leader of a chain sends a packet to the upper leader or the sink node by one hop transmission. Reference [38] provides an algorithm for constructing the energy efficient chain called the minimum total energy (MTE) chain. These chain construction algorithms use centralised approaches for constructing the chain and elect the leader node for transmitting data back to the sink by taking turns. However, if the remaining energy of each node is not taken into account in the leader election, the nodes with low remaining energy will easily run out of energy, leaving just a small number of survival nodes to perform the sensing task. From the viewpoint of network lifetime, this is not ideal. Both PEGASIS and MTE approaches use centralised chain construction, which has a number of disadvantages. Firstly, their transmission cost calculation based on distance may not reflect the exact cost in different practical environments due to radio irregularity as indicated in [39]. Secondly, these centralised approaches may not scale well for large network or large number of nodes. Moreover, after some time, nodes far away from the sink easily run out of battery since they consume more energy to transmit to the sink as a leader. Power Aware Chain (PAC) [19] addresses these issues by constructing the chain using a distributed algorithm. PAC is a chain oriented routing scheme, and here the distributed algorithm presented for constructing the routing chain is based on the minimum cost tree. In this protocol, the transmission cost  
Figure 2: PEGASIS protocol chain. (**a**) chain formation using greedy method; (**b**) Data fusion at the leader node, and transmitting it to BS. is calculated based on the received signal strength between nodes. Therefore, it does not require global knowledge of nodes' location information and provides more accurate communication cost calculation among nodes under different practical deployment environments. The proposed power aware mechanism for leader node election in the chain ensures more uniform energy consumption among nodes. Thus, in PAC, all nodes die at approximately the same time, which provides better active network operation time than the case where there are only a few nodes still functioning while almost all other nodes have died. However, the problem of PAC is that it constructs a single chain, which causes a delay in gathering data from all the sensor nodes of the network. This protocol also requires very high processing complexity for a large network, and thus is not applicable for a large-scale WSN. The chain oriented topology proposed in this paper is a multiple-chain oriented topology. In other words, multiple chains are constructed using the deployed sensor nodes in the target field. The chains are constructed in a way to solve the abovementioned problems of different chain oriented protocols. Furthermore, a network management protocol is associated with the proposed logical topology, so that the network can be managed in such a way as to contend with the resource constraints of WSNs