VoIP is the digital transmission of voice communications through a data network based on Internet Protocol (IP). IP is an open, standards-based set of rules that can route data around network failures and dependably transport data with minimal delay and loss of content. IP also has mechanisms that can automatically discover the best route through a network with multiple paths. The potential benefits of IP-based voice technology for public safety activities include reduced communications costs, increased reliability, enhanced scalability, and interconnectivity. Communications costs are reduced by combining voice and data communications into a single, well-designed network. Reliability is increased by rerouting data around contested network paths. IP for routing data are scalable, so as to support a large number of users. Regarding interconnectivity, IP-based radio interoperability equipment is often used to interconnect older or different private radio systems if traditional radio techniques cannot be used. Issues that must be considered in deciding how to use VoIP are the Internet's security vulnerabilities and unpredictability. There may also be the potential for loss of clarity or delay in transmission. Further methods of encoding and signaling differ from vendor to vendor. The Project 25 (P25) InterSubSystem Interface (ISSI) is emerging as the most mature public safety IP standard. The ISSI has been partially approved within the Telecommunications Industry Association and will allow for P25 trunked radio system interconnectivity over a wide geographic area using IP-based technology. 3 notes and 2 suggested resources