私有综合服务网络（PISN）是一种专用的通信网络，用于在组织内部提供电话和其他通信服务。PISN可以提供许多不同的服务，例如呼叫等待、呼叫转移、呼叫保持和会议呼叫等。其中，单步呼叫转移是一种常见的服务，允许用户将呼叫转移到另一个用户或呼叫转移到另一个电话系统。

ISO/IEC 19459:2001标准规定了PISN中单步呼叫转移补充服务的规范、功能模型和信息流。该标准定义了单步呼叫转移的功能和信息流程，以确保在PISN中实现单步呼叫转移的一致性和互操作性。该标准还规定了单步呼叫转移的各种情况和条件，例如呼叫转移的目标地址、呼叫转移的时间限制和呼叫转移的费用等。

在ISO/IEC 19459:2001标准中，单步呼叫转移被定义为一种补充服务，它可以与其他补充服务一起使用，例如呼叫等待和呼叫保持等。该标准还规定了单步呼叫转移的信息流程，包括呼叫转移请求、呼叫转移确认和呼叫转移完成等。

总之，ISO/IEC 19459:2001标准是关于PISN中单步呼叫转移补充服务的规范、功能模型和信息流的标准。该标准规定了单步呼叫转移的功能和信息流程，以确保在PISN中实现单步呼叫转移的一致性和互操作性。

相关标准
- ISO/IEC 11579-1:1995 Information technology -- Telecommunications and information exchange between systems -- Private Integrated Services Network -- Inter-exchange signalling protocol -- Part 1: Protocol specification
- ISO/IEC 11579-2:1995 Information technology -- Telecommunications and information exchange between systems -- Private Integrated Services Network -- Inter-exchange signalling protocol -- Part 2: Protocol implementation conformance statement (PICS) proforma
- ISO/IEC 11579-3:1995 Information technology -- Telecommunications and information exchange between systems -- Private Integrated Services Network -- Inter-exchange signalling protocol -- Part 3: Abstract test suite (ATS) and protocol implementation extra information for testing (PIXIT)
- ISO/IEC 11579-4:1995 Information technology -- Telecommunications and information exchange between systems -- Private Integrated Services Network -- Inter-exchange signalling protocol -- Part 4: Protocol implementation extra information for testing (PIXIT) for the support of supplementary services
- ISO/IEC 11579-5:1995 Information technology -- Telecommunications and information exchange between systems -- Private Integrated Services Network -- Inter-exchange signalling protocol -- Part 5: Protocol implementation conformance statement (PICS) proforma for the support of supplementary services