 section are now considered to have integrated softswitch capability. They set up end-to-end paths for voice, data, and video calls. Gateways are servers that convert protocols SO that networks and equipment that use different signaling protocols or other incompatible protocols can interoperate with one another. The following are the key software functions that support VoIP services. Application servers These are the workhorses in VoIP networks. They process calls and contain applications. The term "processing calls" means that they issue commands to set up and end calls. Application servers, referred to as feature servers by some manufacturers, also communicate with the billing systems used to generate customer invoices. Moreover, they contain subscriber profiles indicating features assigned to each user and which applications each customer has permission to access. These func- tions provide the capability of acting as network control points. In addition, application servers hold applications such as call forwarding, call waiting, video and audio conferencing, and unified messaging (the ability to access voicemail, e-mail, and fax messages on personal computers). Media servers Media servers generate and detect touch-tone signals, play announcements and voicemail prompts, record audio, and set up paths (routes) for audio and video conferences. Application servers issue com- mands to media servers that indicate which announcements to play and paths to set up. Carrier Networks The term media, as used in the context of IP traffic, refers to any call, whether it comprises audio or video content. Network servers These servers keep track of maps for routing instruc- tions and master directories to applications. They can contain databases that specify how each call should be billed and whether a call is charged at long-distance, intrastate, local, or international rates. Network servers use the maps for routing policies SO that traffic is sent to the softswitch closest to the called party. Session Border Controllers (SB