ETSI TS 100 392-18-4定义了针对TETRA空中接口进行优化的网络辅助协议2。它定义了服务:允许将信息传递给位置确定实体（也称为MS（移动站））；允许位置确定实体向协助服务器请求协助信息。辅助服务器传递给位置确定实体的信息（如果相关）反映了内容 以及从卫星传递到定位点的等效信息（导航数据）的格式 实体该协议能够支持多种定位技术。目前它涵盖了多个领域 GNSS，并可扩展到所有网络定位方法。

ETSI TS 100 392-18-4 defines Net Assist Protocol 2 that is optimized for TETRA air interface. It defines services:allowing information to be passed to a location determining entity also called MS (Mobile Station);allowing a location determining entity to request assistance information to an assistance server.The information passed to the location determining entity by the assistance server, when relevant, reflects the content and format of the equivalent information (navigation data) which passes from satellites to the location determining entity.The protocol is capable of supporting more than one position determining technology. Presently it covers multiple GNSS, and is extensible to all network positioning methods.