看包详解带3GDT的PDP上下文激活流程

yonka

In case of a pre-release 7 GGSN, error indications from the RNC are treated as if they came from the SGSN, and the GGSN deletes the PDP context without informing the SGSN. This results in a hanging PDP context in the SGSN and User Equipment (UE), which is resolved at the next connection establishment.

With a release 7 GGSN, the PDP context is not deleted but the SGSN is informed and the Radio Access Bearer (RAB) can be reestablished.

Therefore during an ISRAU, the SGSN checks if the GGSN supports 3GDT based on 3GPP release 7, using the optional Private Extension Information Element (IE) in the Forward Relocation Request and SGSN Context Response messages. If there is no optional Private Extension IE, it means the GGSN does not support 3GDT based on 3GPP release 7 or the old SGSN does not support the optional Private Extension IE, therefore 3GDT is not used.


在R7之前的GGSN中，来自RNC的错误指示error indication会被认为来自SGSN，于是GGSN会删除PDP上下文并且不会通知SGSN。这样会导致SGSN和MS中会吊死（该）PDP上下文。这个问题会在下一次连接建立时解决。

    对于R7 GGSN，该PDP上下文不会被删除，不过会通知SGSN，RAB可以重新建立。

    因此在ISRAU中，SGSN可以检查GGSN是否支持R7的3GDT，方式是在Forward Relocation Request和SGSN Context Response消息中使用可选的私有扩展IE。    如果没有可选的私有扩展IE的话，就意味着GGSN不支持R7的3GDT或者老的SGSN不支持该可选私有扩展IE，于是就不会使用3GDT。


爱总你看这段怎么理解？
虽然翻译出来了，但还是有些不理解。

R7之前GGSN收到错误指示会删除PDP上下文？
“对于R7 GGSN，该PDP上下文不会被删除，不过会通知SGSN，RAB可以重新建立。”怎么理解？