1. An apparatus comprising a processor and a memory, the memory storing computer-executable instructions which, when executed by the processor, cause the apparatus to operate as an interworking function of a communications network, the computer-executable instructions further causing the interworking function to provide an application data delivery service for enabling communication between a first application that is hosted on a user equipment and a second application that is hosted on a server, the application data delivery service configured to perform operations comprising:receiving, from the second application on a first interface that comprises an application programming interface exposed by the application data delivery service to the second application, a first request to send a packet to the first application via the communications network, the first request comprising an indication of whether the second application desires the packet to be acknowledged and an identifier of the first application;
encoding, based on the first request, a header comprising the indication of whether the packet should be acknowledged, the identifier of the first application, and a field that is used to support sequencing of packets; and
sending, to a mobility management entity of the communications network, via a second interface that comprises a diameter interface, a second request requesting that the header and the packet be sent to the user equipment, the second request comprising the packet and the header, wherein the application data delivery service is first configured for communication with the first application by:
receiving, from the second application, a third request to configure a connection between the second application and the user equipment that hosts the first application, the third request comprising an identifier of the user equipment, the identifier of the first application, and an identifier of the second application;
sending a fourth request to a home subscriber server of the communications network to authorize the connection to the user equipment, the fourth request comprising the user equipment identifier;
receiving a response to the fourth request, the response comprising an international mobile subscriber identity and an indication of whether or not the connection to the user equipment is authorized;
maintaining a mapping between the user equipment identifier, the identifier of the first application, the identifier of the second application, and the international mobile subscriber identity; and
responding to the third request, the response indicating that the application data delivery service between the first and second applications is supported.