ABSTRACT : The Wireless Sensor Networks (WSNs) is one of the succeeded technology that being strongly considered in scientific and engineering fields. WSN is an ad-hoc network that consists of small nodes with sensing, computing and communicating wireless abilities. These Sensor nodes are usually have limited lifetime duration due to the sensors that powered by limited exhaustible batteries. The main aim of WSN is to sense all the information from the environment (The environment can be an Information Technological framework, a physical world, or a biological system) based on the kind of application for which is deployed and send this information to it is Base Station (BS). Sensor nodes have to ensure their task with their rigorousenergy budget, this constraint makes theenergy resource the most of critical importance in the WSNs. Sensor Nodes communicate with each other by different Routing Protocols, and Routing Protocols can be classified into different categories in WSNs. This paper will focus on the Hierarchical (cluster based) routing protocols. Also, we will go deeply in PEGASIS protocol backgrounds and improvements,complete description for each stage of improvements, models, and offering a complete vision for these protocols through making a comparison between them by knowing there positive and negative effects on WSN.

Keywords -Wireless Sensor Network, Cluster-based routing protocols, LEACH, PEGASIS, EEPB, PEGASIS-ANT, H-PEGASIS, PDCH, IEEPB, MIEEPB, ACO.