1）N4口确实不下发5QI。（As 5QI is not signalled over N4）。
2）UPF是否需要5QI？得先查下5QI的构成，主要是5个参数，在TS23.501的5.7.3 5G QoS characteristics定义。包括：
Resource Type
Priority Level
Packet Delay Budget
Packet Error Rate
Averaging Window
Maximum Data Burst Volume。
上述参数中，明确提到UPF需要的只有Packet Delay Budget和Averaging Window，这两个如果SMF没下发给UPF，那我的理解是：
- 在R16中，SMF可以通过下发SRR（Session Reporting Rule），要求对Qos进行监控，其中SRR可以包含Packet Delay Thresholds参数，即要求UPF计算时延，并上报给SMF，再由SMF来决定下一步怎么做。
- 平均窗口的话，可以在UPF预配置或者也可以下发，有这个单独的参数。（As 5QI is not signalled over N4, one default averaging window shall be pre-configured in the UPF.）
剩下那几个：
- Resource Type：取值是GBR还是Non-GBR，这个UPF是知道的。
- Priority Level：主要是做拥塞场景下的拥塞控制，个人理解主要是空口。【In the case of congestion, when all QoS requirements cannot be fulfilled for one or more QoS Flows, the Priority Level shall be used to select for which QoS Flows the QoS requirements are prioritised such that a QoS Flow。。。】
- Packet Error Rate：这个明确提到是基站侧来做。【The Packet Error Rate (PER) defines an upper bound for the rate of PDUs (e.g. IP packets) that have been processed by the sender of a link layer protocol (e.g. RLC in RAN of a 3GPP access) but that are not successfully delivered by the corresponding receiver to the upper layer (e.g. PDCP in RAN of a 3GPP access).】
- Maximum Data Burst Volume（简称MDBV）：这个也明确提到了是属于接入侧来做管控。【MDBV denotes the largest amount of data that the 5G-AN is required to serve within a period of 5G-AN PDB.】
在23501关于5QI的术语定义中还明确提到，这个是接入侧实现的，并没有提到UPF。原文是“
5G QoS Identifier: A scalar that is used as a reference to a specific QoS forwarding behaviour (e.g. packet loss rate,packet delay budget) to be provided to a 5G QoS Flow.
This may be implemented in the access network by the 5QI referencing node specific parameters that control the QoS forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.).”