This document specifies the access network requirements for Callback to an Emergency Call Origination (CECO). These requirements pertain to 1x Circuit Switched (1xCS) calls routed to a 1xCS access network and 1xCS calls routed to a non-1xCS access network. For example, the requirements pertain to Circuit-Switched Fall Back (CSFB) for a Long Term Evolution (LTE) access network. The requirements are subject to regional regulation.