本文件定义了GMR-1移动卫星系统中物理层向MES-GS接口上层提供的服务。其主要目的是为45系列和44系列的GMR-1技术规范之间的接口提供指导。它还规定了信令信道、业务信道（Iu模式）的格式以及比特传输的顺序。本文件尽可能使用ITU-T建议X.200[i.1]和X.210[i.2]中所载开放系统互连（OSI）参考模型的分层原则。

The present document defines the service offered by the physical layer to the upper layers of the MES-GS interface in the GMR-1 Mobile Satellite System. Its main objective is to provide guidance for the interface between the GMR-1 Technical Specifications in the 45-series and the 44-series. It also specifies the format of signalling channels, traffic channels (Iu mode) and the order of bit transmission.As far as possible, the present document makes use of the layering principles of the Reference Model for Open System Interconnection (OSI) as contained in ITU-T Recommendations X.200 [i.1] and X.210 [i.2].