The purpose of this document is to define the Space Link Extension (SLE) Return Channel Frames (RCF) service in conformance with the SLE Reference Model (reference [1]).° The RCF service is an SLE transfer service that delivers to a mission user all telemetry frames from one master channel or one virtual channel.

This document defines, in an abstract manner, the RCF service in terms of:

1. the operations necessary to provide the service;
2. the parameter data associated with each operation;
3. the behaviors that result from the invocation of each operation; and
4. the relationship between, and the valid sequence of, the operations and resulting behaviors.

It does not specify:

1. individual implementations or products;
2. the implementation of entities or interfaces within real systems;
3. the methods or technologies required to acquire telemetry frames from signals received from a spacecraft;
4. the methods or technologies required to provide a suitable environment for communications; or
5. the management activities required to schedule, configure, and control the RCF service.

NOTE°° °°°°°° Reference [1] defines the Return Master Channel Frames (Rtn MC Frames) service and the Return Virtual Channel Frames (Rtn VC Frames) service as two distinct services. Subsequent study has indicated that it is preferable to define one service that provides the functionality of both. The RCF service defined here does just that. It is anticipated that a future issue of reference [1] will take the same approach, deleting the Rtn MC Frames and Rtn VC Frames services and replacing them with the RCF service.

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