Q：4_5G互操作场景，PGW-C_SMF如何根据PDU会话参数产生EPS PDN连接参数？

PDN Type，如果支持，则映射为Ethernet类型，否则PDN Type映射为Non-IP。

- EPS Bearer ID：4/5G互操作中的EBI分配作为PDU会话建立流程的一部分，在23502的4.11.1.4.1节定

义。EBI和Qos流的关联关系保存在SMF。

- APN-AMBR：根据运营商策略来映射（例如，根据Session-AMBR来映射。）

- EPS Qos参数：包括ARP、QCI、GBR、MBR。映射原则如下：

1）如果Qos流映射到一个EPS承载，则EPS承载的ARP、GBR和MBR参数根据Qos流的APR、GFBR、

MFBR来映射。如果是标准5QI，则一对一映射到QCI。如果是非标准5QI的值，PGW-C/SMF应根据5QI

和运营商策略派生出QCI。

2）如果分配了EBI的话，一个GBR的Qos流一对一映射到一个GBR的专有承载。

3）如果多个Qos流映射到一个EPS承载，则EPS承载参数根据运营商策略来映射。例如EPS承载的Qos

参数根据所有映射的Qos流的最高Qos来设置。

4）在切到4G后，对于没有分配到EBI的Non-GBR Qos流可以继续使用EPS的缺省承载。

原文如下：

Annex C (informative):Generating EPS PDN Connection parameters from 5G PDU Session parameters

This annex specifies how to generate the EPS PDN connection parameters from the 5G PDU Session

parameters in PGW-C+SMF.

When the PGW-C+SMF is requested to set up/modify either a PDN connection or a PDU session

supporting interworking between EPS and 5GS, the PGW-C+SMF generates the PDN Connection

parameters from the PDU session parameters.

When the PGW-C+SMF generates the PDN Connection parameters based on the PDU Session

parameters, the following rules hold:

- PDN type: the PDN type is set to IPv4, IPv6 or IPv4v6 if the PDU Session Type is IPv4, IPv6 or

IPv4v6,respectively. The PDN Type is set to Ethernet if the MME, SGW and UE support Ethernet PDN

Type, otherwsie the PDN type is set to Non-IP for Ethernet and Unstructured PDU Session Types

- EPS bearer ID: the EBI is requested from the AMF during the establishment of a QoS Flow as

described in clause 4.11.1.4.1 for PDU Sessions supporting interworking between EPS and 5GS. The

EBI is obtained from MME during the establishment of an EPS Bearer (that is triggered by an

establishment of a QoS Flow) as defined in TS 23.401 [13] for PDN Connections hosted by PGW-

C+SMF. The association between EBI and QoS Flow is stored by the SMF.

- APN-AMBR: APN-AMBR is set according to operator policy (e.g. taking the Session AMBR into

account).

- EPS QoS parameters (including ARP, QCI, GBR and MBR):

If QoS Flow is mapped to one EPS bearer, ARP, GBR and MBR of the EPS Bearer is set to the ARP,

GFBR and MFBR of the corresponding QoS Flow, respectively. For standardized 5QIs, the QCI is one

to one mapped to the 5QI. For non-standardized 5QIs, the PGW-C+SMF derives the QCI based on the

5QI and operator policy.

A GBR QoS Flow is mapped 1 to 1 to a GBR dedicated EPS Bearer if an EBI has been assigned. After

mobility to EPS traffic flows corresponding to GBR QoS Flow for which no EBI has been assigned will

continue flowing on the default EPS bearer if it does not have assigned TFT.

If multiple QoS Flows are mapped to one EPS bearer, the EPS bearer parameters are set based on

operator policy, e.g. EPS bearer QoS parameters are set according to the highest QoS of all mapped

QoS Flows.

After mobility to EPS traffic flows corresponding to Non-GBR QoS Flows for which no EBI has been

assigned will continue flowing on the default EPS Bearer if it does not have assigned TFT.