A survey on Congestion Handling Techniques in Opportunistic Networks Ahthasham Sajid Khalid Hussain Imran Baig Department of Computing Department of Computer Science Department of Electrical & Computer Engineering Shaheed Zulfiqar Ali Bhutto Institute Muslim Youth university College of Engineering Science and Technology Islamabad, PAKISTAN Dhofar University Salalah Islamabad, PAKISTAN Sultanate of OMAN Abstract: Opportunistic Networks an emerging research area that encompasses Mobile Adhoc Networks (MANETs) and a subset of Delay Tolerant Network (DTNs). In such networks one of the most dynamic and challenging tasks is to detect congestion timely and effectively. Congestion both at link and node level can occur due to Irregular Connectivity, Long and Variable Length Delays, and Heterogeneous Networks Infrastructure. Intermediate nodes between source and destination are seems to be critical for detecting a congestion issue as they have to store data in their respective buffer until a next best forwarding opportunistic node is found. The prime objective of our research is to evaluate different congestion handling techniques that addressed issues of storage/node level congestion in opportunistic networks. Consequently it may help to detect congestion issue at node level in a Pre-active manner rather than pro-active manner. Key Words: Estimation/ probability theory, DTN, MANETs, ICN 1) INTRODUCTION: An opportunistic network belongs to the subclass of Delay Tolerant Network (DTNs) in which chances for the communication to be successfully established between source and destinations are discontinuous / irregular. TCP protocol if applied in opportunistic networks will not be suitable in this environment [1]. The network is said to be opportunistic when it is not sure about the future both in terms of connectivity and topology. Routing in opportunistic networks indeed gets importance in the last few years that how an intelligent mechanism could be introduce; which can overcome the overhead caused by a congestion issue in the shape of long delay, retransmissions flooding [2]. Opportunistic networks have a lot of common features like MANET’s therefore general techniques which are used in forming a MANET’s network could be used in opportunistic networks as well and vice versa. Congestion to be detected timely is a key challenge faced in MANET’s among other challenges; Routing, Energy etc. But congestion to be detected and control at node level needs a key focus of researchers in the last few years in opportunistic networks [19]. 2) BACKGROUND: In the last few years a lot of research has focused on multi-hop Adhoc networks rather than single hop fashion to be established. Several application from military domain and lately proposed in civil applications as well belonging from multi-hop. Mesh networks and opportunistic networks are the two main evolutions of multi-hop networks. This research focuses on opportunistic networks; routing and forwarding in such networks are the latest research which gets focus by the researcher in the last few years. The terms “opportunistic networks” and “delay tolerant networks” are often used interchangeably [2]. Network is said to be opportunistic when it is not sure about the future both in terms of its connectivity and also about its topology, so in such scenario routing of information to the end node becomes difficult and therefor it incorporates such mechanism which can add overhead in terms of delay and congestion like flooding, store and forward. [02] International Journal of Computer Science and Information Security (IJCSIS), Vol. 14, No. 7, July 2016 490 https://sites.google.com/site/ijcsis/ ISSN 1947-5500