Architecture of MSNs
In the traditional communication way, the users obtain the data from the servers which store the data. However, MSNs require an increasing number of large-sized content delivery (e.g., audio or video contents), which may not be guaranteed with a satisfied QoE only through the traditional wireless communication networks. To this end, the short range wireless technologies (e.g. Wi-Fi and Bluetooth) can be leveraged and widely used in MSNs, as shown in Fig.1.2. With these technologies,
Fig. 1.2 User mobility and data delivery in MSNs
users can exchange data through mobile devices directly [3-7] when they encounter with each other. The structure of MSNs can be divided into two types, i.e., Web-based MSN and distributed MSN.
- • Web-based MSN. Web-based MSN is a centralized structure which relies on network infrastructures and content servers. Social users use mobile devices through social network services (e.g., Facebook, Myspace and Twitter) or mobile portal (e.g., m.4info.com) to communicate with the Web-based applications. There have been many Web-based MSNs to provide social services for mobile users. For example, “Iphone Facebook App” is a Web-based MSN which allows users to communicate with the “Facebook”. Similarly, “WhozThat”  uses the online information to obtain users’ characteristics and interest to recommend music to the users. “Google Latitude”  is another Web-based MSNs. It can help users obtain the location information of others who have the will to share the location information.
- • Distributed MSN. In a distributed MSN, users form a community to disseminate data between different social users without the central servers. The opportunistic contact between two users is defined as a link. When a user encounters another user, they can exchange or share the data directly through short-range wireless technology. In a distributed MSN, the community is formed to based on their opportunistic contacts, such as “EyeVibe” which is a video and chat community. Recently, most researches of MSNs focus on the distributed MSN.