Nowadays, social networks have been widely used by different people for different purposes in the world. The discovering of communities and clustering is a widespread subject in the space of social networks analysis. Many interesting solutions have been proposed in the literature, such as the algorithms of Newman and Girvan. However, most solutions have common problems: the stability and the community structures quality. In this paper, we give a state of the art, from 1970 until 2018 on the approaches as well as the algorithms of communities' detection in social networks. This study aims to gives a comparison between the different proposed architectures.

Lookup services is still a key challenge in all distributed systems and particularly for P2P based services (e.g. distributed SDN node controllers, social networking…). In these networks, node searching for a specific service or resource has to discover the “best” path to the node offering the requ ested resource or service. Since P2P networking is implemented at application layer, the given optimized path from a source node to a destination one, in terms of number of hops is not necessarily the best path in terms of physical parameters (e.g. delay, physical proximity). For this, the lookup process optimization is still a real challenge in some environments, particularly for delay sensitive services. In this context, various topologies have been proposed in the literature such as: ring, tore, star, hypercub, De Bruijn graph, and skip graph. In this paper, we propose a new approach using Pancake graphs, for structuring the P2P topology in order to optimize the lookup process. The proposed solution is compared to some main existing solutions. Under certain conditions, the simulation results show better performance compared to existing approaches.

Multicast avoids sending repeated packets over the same network links and thus offers the promise of supporting multimedia streaming over wide-area networks. Previously, two opposite multicast schemes forward-path forwarding and reverse-path forwarding have been proposed on top of structured peer-to-peer (p2p) overlay networks. In this paper, we propose a new model for optimizing application layer multicast in the context of Peer-to-Peer networks (structured and unstructured). In this contribution, we consider two approaches for multicast tree construction: a "primitive " approach, and an optimized one based on a distributed algorithm. The proposed model inherits from main P2P attributes such as: scalability, fault tolerance, while taking into consideration the respective characteristics of "one to many" and "many to many" applications. We also give a performance evaluation for validation and comparison purposes. For this we consider some main existing application layer multicast protocols.

Application layer multicast (ALM) is considered as an attractive approach for implementing wide area multicast services. In ALM, multicast functionality is implemented at the edge instead of the core network (routers). As opposed to network-layer multicast, application layer multicast requires no infrastructure support and can be easily deployed in the Internet. In this paper, we propose a new generic and scalable approach for optimizing application layer multicast in the context of Peer-to-Peer networks (structured and unstructured). This approach benefits from P2P properties and characteristics. In this contribution, we consider two approaches for multicast tree construction: a primitive approach, and an optimized one based on a distributed algorithm. The proposed protocol inherits from main P2P attributes such as: scalability, fault tolerance. Performance evaluation shows that results are globally satisfactory compared to the main existing application layer multicast protocols.