This European Standard specifies the requirements for alarm transmission systems using Packet Switched Networks (PSN), which are additional to those in EN 50136-1-1:1998. The alarm transmission system using PSN may use wired links, voice grade signalling links, mobile networks, radio or data links and may include ethernet switches, hubs, firewalls, ADSL-routers and DSL-modems. The standard is also applicable to alarm transmission systems in which signalling links are shared with other services within the above descriptions.