关于5G协议中基于Xn切换的一点疑问

ye9165

最近在学习核心网相关内容，遇到一个问题不能理解。在23.502的基于Xn切换描述中，如果是插入中间I-UPF或者重配置I-UPF的方案，协议中都有以下描述：hepresence of IP connectivity between the UPF (PDU Session Anchor) and Source NG-RAN,between the UPF (PDU Session Anchor) and Target NG-RAN, and between theintermediate UPF (I-UPF) and Target NG-RAN, is assumed. (If there is no IPconnectivity between UPF (PDU Session Anchor) and Target NG-RAN, it is assumedthat the N2-based handover procedure in clause 4.9.1.3 shall be usedinstead).
个人理解插入中间IUPF的作用就是为了给源RAN侧的PSA UPF做一个中继，既然此时目标RAN与UPF（PSA）之前是有IP连接的，那插入I-UPF的意义是什么呢？