请教关于PDP上下文去激活的问题？

jianglibing

如果说是MS或者网络主动发起的PDP去激活PDP上下文是不是一定删除？在3G里面如果启用保留机制的话除了RAB释放可以保留PDP上下文以外，对于主动发起的这种去激活会不会保留PDP上下文？请各路大侠指点？不甚感激！

爱卫生

  请问下你说的3G下的PDP上下文保留机制，有规范的出处吗？因为我只知道在去附着之后，SGSN通常会保留用户的MM上下文。这样没有用完的鉴权参数，下次这个用户上来，就可以继续用，以此减少Gr接口的交互。但GGSN上如果去激活后，仍然保留PDP上下文，感觉没有什么好处啊！因为再次激活时，该走的流程都得再走一遍，且需要再次为用户分配地址。而且你保留PDP上下文的话，你的资源释不释放呢？例如最宝贵的MS IP地址资源？如果不释放，别的手机就用不了，将降低GGSN的性能。如果释放了，你保留也就没什么意义了。

mobileice

我还真没遇到过这种情况，我所见过的是：但凡是PDP去激活，无论是网络发起还是UE发起，PDP context都会被删除。
坐听其他朋友的解释

hycl5410

楼主恐怕搞混了一个概念，RAB release甚至Iu release不是一定会触发PDP释放。那是某些定时器超时，释放RRC资源的一个过程。跟MM,SM都没有关系的。所谓的“保留机制”严格说压根就不应该叫机制，而是必须这么做。而PDP去激活是跟SM直接联系的。貌似楼主接触RNC比较多，对核心网不太熟，建议好好看看23.060里的3G状态变迁图。

jianglibing

回复 hycl5410 的帖子

我就是做PS的，对原理不是很熟悉。但是23060里面有个保留流程的描述啊。那这个怎么解释呢？Preservation Procedures

By sending a RAB Release Request or IuRelease Request message to the SGSN, an Iu mode RAN initiates the release ofone or more RABs. The preservation procedure allows the active PDP contextsassociated with the released RABs to be preserved in the CN, and the RABscan then be re-established at a later stage, see clause 9.2.5.2and clause 9.2.3.5.

An Iu mode RAN uses the Iu Release Requestto request release of all RABs of an MS, and the RAB Release Request in othercases.

jianglibing

回复 爱卫生 的帖子

但是协议里面是有的呀。23060里面有这么一段描述；Preservation Procedures

By sending a RAB Release Request or IuRelease Request message to the SGSN, an Iu mode RAN initiates the release ofone or more RABs. The preservation procedure allows the active PDP contextsassociated with the released RABs to be preservedin the CN, and the RABscan then be re-established at a later stage, see clause 9.2.5.2and clause 9.2.3.5.

An Iu mode RAN uses the Iu Release Requestto request release of all RABs of an MS, and the RAB Release Request in othercases.

然后我认为保留的话也有好处呀，至少你下次做业务的时候可能只要重建个RAB就可以了，这样的话流程肯定会更快一点，做业务当然就更快。如果你重新走激活流程的话时间肯定会稍微长一点嘛，以前不是说什么“永远在线”的吗？不就是让用户感觉他好像没有脱离这个这个网络，随时可以进行业务吗？个人见解，爱总再帮我点拨一下。

jianglibing

回复 mobileice 的帖子

现网中一般是这样的，但是有时候为了对一些VIP用户会做一些特别的设置来提高用户感知。这个问题尚在讨论中。

爱卫生

回复 jianglibing 的帖子

   仔细查了下，确实是有的。我都没有注意到。惭愧。
   好处正如你说的那样，可以给用户带来更好的业务体验。
   更多的细节和背景我也不了解，抱歉。
   这里只补充下，R10做了下更新。
The following procedures shall be performed in the MS when the RRC layer indicate to higher layer that a RAB has been released and the RAB release was not initiated due to a PDP Context Deactivation Procedure:
- For a PDP context using background or interactive traffic class, the PDP context is be preserved with no modifications.
- For a PDP context using streaming or conversational traffic class and if the TFT include packet filter(s) set by the MS, the PDP context may be is preserved, but the maximum bit rate is downgraded to 0 kbit/s (for both uplink and downlink). If the TFT only include packet filter(s) set by the network or if the TFT include packet filter(s) set by the MS and the PDP context was not preserved, the PDP context is locally deactivated in the MS.
- At this point or at a later stage (for preserved PDP contexts), the MS may start a PDP Context Deactivation procedure or PDP Context Modification procedure. The MS shall use the PDP context modification procedure to re-activate the PDP context and to re-establish the RAB.

jianglibing

回复 爱卫生 的帖子

恩，多谢版主的补充。

hycl5410

回复 jianglibing 的帖子
9.2.5.2
Re-establishment of RABs

The procedure for re-establishment of RABs allows the SGSN to re-establish RABs for active PDP contexts that don't have an associated RAB.

The MS initiates the re-establishment of RABs by using the Service Request (Service Type = Data) message. This is described in the sub-clause "MS Initiated Service Request Procedure". SGSN shall not establish RABs for PDP contexts with maximum bit rate for uplink and downlink of 0 kbit/s. For these PDP contexts, the MS shall perform a MS-initiated PDP Context Modification or Deactivation procedure.

When RABs for an MS that has no RRC connection needs to be re-established, the CN must first page the MS. The clause "Network Initiated Service Request Procedure" describes this.

6.12.1
MS Initiated Service Request Procedure

4)
If the network is in PMM-CONNECTED state and the Service Type indicates Data, the SGSN shall respond with a Service Accept message towards the MS, in case the service request can be accepted. In case Service Type indicates Data, the SGSN sends a Radio Access Bearer Assignment Request (NSAPIRAB ID(s), TEID(s), QoS Profile(s), SGSN IP Address(es)) message to re-establish radio access bearer for every activated PDP context, except the ones having maximum bit rates for uplink and downlink of 0 kbit/s.

这个写的都比较清楚。3G里Iu-PS接口可以release而不用delete pdp，这是一个很基本的认知吧。。。想想RAB建立过程，U平面是SGSN和RNC的GTP-U地址和TEID。为了节约空口资源，当某些idle定时器超时，就可以release RRC和Iu-PS,Iu-PS release了必然会release所有的RAB。但是这完全没必要影响到用户的PDP啊，SGSN与GGSN之间的C和U通道都是好的。当有上行数据，MS可以发service request，有下行就SGSN先paging再MS发service request。
9.2.5
Preservation Procedures

By sending a RAB Release Request or Iu Release Request message to the SGSN, an Iu mode RAN initiates the release of one or more RABs. The preservation procedure allows the active PDP contexts associated with the released RABs to be preservedin the CN, and the RABs can then be re-established at a later stage, see clause 9.2.5.2 and clause 9.2.3.5.

An Iu mode RAN uses the Iu Release Request to request release of all RABs of an MS, and the RAB Release Request in other cases.

这段说的难道不是这个事？

为了能够更好的理解这个问题，可以参照23.401的EMM,ESM,ECM状态变迁图。23.060的PMM状态变迁图也有涉及，请看PMM-idle与PMM-connected变化，SM是active或inactive的。

hycl5410

哪个规范会写delete pdp之后还有Preservation Procedures么？这里一直都在说RAB，没有看到deactivate pdp或者delete pdp字眼哦。

爱卫生

hycl5410 发表于 2012-2-25 16:36
回复 jianglibing 的帖子
9.2.5.2
Re-establishment of RABsThe procedure for re-establishment of RABs ...

谢谢你的补充。我这个墙头草觉得你说得很有道理。呵呵。应该是RAB的释放流程，而不是PDP的去激活。

所以根据你的提示。总结一下这个问题。欢迎继续纠错。

“就是如果说有保留机制的话，那就是如果RAB因为某种原因（可能是无线信号不好、也可能是假设手机看小说，过长时间没有翻页）释放后，PDP上下文仍有可能会被保留，MM状态将切换到PMM-Idle。这样对UE来讲是透明的，用户可以重建RAB而不是重新发起PDP激活流程来访问后续的数据业务。但如果发生了PDP的去激活流程，那PDP上下文应该是会被删除的。”

jianglibing

回复 爱卫生 的帖子

赞同你的观点，那我上面的说法是错误的，只是在RAB释放的时候可能去启用保留机制，而不是PDP去激活。如果是去激活的话肯定会删除PDP上下文了是吧。