There are two types of SIP proxy servers:
1) Stateless proxy server: A simple forwarding function that selects the destination and route of forwarding by requesting information. Messages are discarded as soon as they are forwarded.
2) Stateful proxy server: records incoming requests and sent request information (especially transaction status) and uses this to control future message processing. It also has a fork function for messages.
This is the Emergency Telephone functional specification for the ET system Implemented along the expressway. The document will be divided into three portions namely Road side Equipment Hardware, Control Room Equipment Hardware and Software and Graphical user interface section.
