Techniques, apparatuses, and systems include mechanisms for interworking circuit service fallback. In one implementation, a system for wireless communications can include one or more first base stations forming a first radio access network to provide wireless communications based on a first wireless technology; one or more second base stations forming a second radio access network to provide wireless communications based on a second wireless technology which is different from the first wireless technology, and an interworking service (IWS) module that is configured to provide the interworking between the first and second radio access networks for communications to a wireless device served by the system via either the first wireless technology or the second wireless technology, and uses a signal adaptation protocol to encapsulate messages in communicating with a wireless device served by the system. Other implementations are also provided in this document.