pp and Tencent's Chinese Weixin-W chat in English-IMS is meant to be globally interoperable on carriers' networks and not part of a closed network. Initiation Protocol SIP signaling to control (Voice overLTE)functions www.TechnicalPDF.com Multimedia Subsystem Databases Router Firewal connects to IMS & broadband Internet networks Servers with security software, deep inspection, and signaling software LTE Enhanced Packet Core Figure 7-8 IP Multimedia Subsystem (IMS) for mobile subscribers. A Session Border Controller converts signals from the mobile network to those compatible with VoIP equipment. www.TechnicalPDF.com IMS is based on IP protocols. Interoperability and control of sessions in interactive online games, conference calls, instant messages, and SO on are managed in Session Border Controller (SBCs) and signaling gateways. SBCs are located at sites where carriers connect their IP networks to one another. These controllers have functions such as security, session management, policy control, and address translation. Policy control refers to the ability to prioritize certain traffic based on agreements between carriers. The following is a sampling of applications that users can access from both mobile and landline devices: Presence SO that subscribers are able to determine if friends and colleagues are available online Advertising that works across wired and wireless platforms Gaming SO that users can participate in online games together Text messaging Video calling Connections to Customers and Mobile Networks via the Cell Site, Towers, and Mobile Switches A cell site is the physical area in which a set of frequencies is used. The link between users' devices and towers or antennas is the only part of mobile networks that is always wireless. The increase in data traffic in shopping malls and downtown areas with heavy pedestrian traffic areas requires dense arrays of cell sites. The air interface between mobile handsets and equipment at antennas and towers are the only parts of mobile network that are wireless.