pat- ible with wireline IP networks, as seen in Figure 4-6. It has the additional advantage of providing carriers that offer wireless, circuit-switched and broadband services with a way to merge operations in core networks SO that the same staff supports, for example, one voicemail server. IMS is based on IP protocols. It was first developed for 3G networks and later expanded to include Wireless Local Area Networks (WLANs), Wi-Fi, and wireline Convergence in Core and Metropolitan Networks IP Multimedia Subsystem (IMS) VolP applications in core network Session border controller Cable network Mobile network Fixed-broadband network Residential customer with Video call to a presence indicators showing customer on a which friends are online on Enterprise customers with broadband landline mobile devices access to a single voicemail box for landline and mobile devices Figure 4-6 IP Multimedia Subsystem (IMS) with common VolP applications for both mobile and landline subscribers. A Session Border Controller converts signals from the mobile network to those compatible with VolP equipment. networks. Interoperability and control of sessions in ongoing online games, confer- ence 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. IMS users with wireline devices are able to interact with people using wired broad- band for access. 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 Instant messaging Video calli