本文档的目的是根据SLE参考模型（参考文献[1]）定义空间链路扩展（SLE）返回信道帧（RCF）服务。？RCF服务是一种SLE传输服务，它从一个主信道或一个虚拟信道向任务用户传送所有遥测帧。 本文档以抽象的方式从以下方面定义了RCF服务: 提供服务所需的操作； 与每个操作相关联的参数数据； 调用每个操作所产生的行为；和 操作和结果行为之间的关系和有效序列。 它没有具体说明: 单个实现或产品； 实体或接口在真实系统中的实现； 从从航天器接收的信号中获取遥测帧所需的方法或技术；为通信提供合适环境所需的方法或技术；或 调度、配置和控制RCF服务所需的管理活动。 笔记？–？参考文献[1]将返回主信道帧(Rtn MC帧)服务和返回虚拟信道帧(Rtn VC帧)服务定义为两个不同的服务。随后的研究表明，最好定义一个提供两者功能的服务。这里定义的RCF服务就是这样做的。预期将来的参考文献[1]将采取相同的方法，删除Rtn MC帧和Rtn VC帧服务，并用RCF服务代替它们。

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.