In single-hop WSNs, the sensor nodes are directly connected to the base station. And in the case of multi-hop WSNs, peer nodes and cluster heads are used to relay the information to reduce energy consumption. 

In non-Self Configurable WSNs, the sensor networks cannot organize themselves in a network and consider a control unit to gather data.

In many WSNs, the sensor nodes can be able to organize and maintain the connection and work collaboratively with other sensor nodes to accomplish the task. 

More info: What is SaaS?