Progress in Signals and Telecommunication Engineering Sunil Kumar, Maninder Singh 7 1 2018 http://www.dline.info/pste/fulltext/v7n1/pstev7n1_1.pdf Mobile Ad hoc networks are defined as the category of wireless networks that utilize multi-hop radio relaying and are capable of operating without the support of any fixed infrastructure Mobile Ad hoc Network (MANET) is more vulnerable to various attacks since it has no centralized or any pre-existing network structure. At the time of framing of a new security mechanism for MANET various attack variations as well as their characteristics must be known. Jelly Fish periodic drop attack is a new Denial of Service (DoS) attack and passive attack which is difficult to detect as it follows the protocol rules and it works against closed loop flows such as TCP. In jellyfish attack, JF nodes randomly discard some packets over a specified period during communication process over the network. In this paper, periodic drop attack is implemented using AODV and OLSR routing protocols over voice based traffic in MANET. In addition to this, simulation results also illustrate the seriousness of the attacks caused by JF nodes and their effects on data communication.