UE请求IPv4IP6的PDP激活请求失败，原因不明

snap0127

有个测试，情况如下：
UE请求一个IPv4v6的PDP激活，但是签约数据中只有IPv4，这个时候，SGSN对这个请求的回应是“unknown_pdp_ctxt”。我查看了协议 36.060 9.2.1.
，有这样的描述：

During the PDP Context Activation procedure the SGSN compares the requested PDP type to the PDP type in the subscription records for the given APN and sets the PDP type as follows:

-     If the requested PDP type is allowed by subscription, the S4-SGSN sets the PDP type as requested.

-     If the requested PDP type is allowed by subscription and if the requested PDP type is IPv4v6, the Gn/Gp SGSN sets the PDP type as requested if the GGSN supports PDP type IPv4v6. Otherwise, the SGSN shall set the PDP type to IPv4 or IPv6 where the selection between IPv4 and IPv6 is based on the result of the check.

NOTE 1:  The check for PDP type IPv4v6 is implementation specific and configuration may be shared in roaming agreements.

NOTE 2:  A Gn/Gp SGSN assumes coherent support for PDP type IPv4v6 across all SGSNs in a PLMN.

-     If the requested PDP type is IPv4v6 and subscription data only allows PDP type IPv4 or only allows PDP type IPv6, the SGSN sets the PDP type according to the subscribed value. A reason cause shall be returned to the UE indicating that only the assigned PDP type is allowed. In this case the UE shall not request for another PDP context to the same APN for the other IP version.

我的理解是，UE请求的IPv4v6的PDP，如签约里面有ipv4的，那么sgsn就应该根据签约的ipv4，给予UE一个ipv4的；如签约里面是ipv6的那么就给予IPv6。