This document outlines recommended practices for the management of communications traffic formatted as an ICS213 “General Message.” These standards were developed using a variety of input from emergency management agencies, Amateur Radio Emergency Service® organizations and the traffic community. This was followed by a period of peer review consisting of the Radio Relay International Emergency Communications Committee and the ARRL NTS 2.0 Committee.
[Download link] Guidelines for Origination, Relay and Delivery of Radiogram-ICS213 Messages F-A
ARRL's National Traffic System for the 21st Century