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在TS23.060 V5.5规范之前,提到了在Iu模式下,Iu 连接释放后,如果对应的PDP上下文业务类型是实时类业务,即steaming或conversational类型的业务,网络侧和UE是可以将这个PDP上下文保持起来不删除的.但规范并没有提到A/Gb模式中是否也应该有这种保持机制.可能3GPP认为GSM的空口带宽太小了,不足以承载实时类型业务.
基于这种现状,在2003年4月7日到11日在韩国首尔举行的3GPP TSG-SA2第31次会议上,由西门子提出了关于增加在A/Gb模式下,当终止数据传递时,在SGSN和MS侧保持实时类型业务的PDP上下文的支持.这个CR编号为435,对应的文档编号为S2-031595,对应的大文档编号为SP-030343.pdf,可以通过google搜索下载.
以下是CR的一些具体内容,在V5.5后进行了更新.
________________________________________________________________________________________
Title: Preservation procedure for realtime bearers in A/Gb mode
Source: Siemens
Work item code: TEI5
Date: 04/02/2003
Reason for change: (为什么要改)
The preservation procedure for realtime PDP context is only described for Iu mode. But realtime PDP contexts, especially of traffic class streaming, are also supported in A/Gb mode. The reservation for realtime PDP context in A/Gb mode is needed for the same reasons as for such contexts in Iu mode.
The triggers for the preservation in A/Gb mode are slightly different but the handling for the preservation is the same as well as the handling to return the bearer provision. The triggers are:
• Radio Status procedure as defined in 48.018 for the causes “Radio contact lost with MS” and “Radio link quality insufficient to continue communication” (but not “cell-reselection ordered”)
• Intra- and inter-SGSN Suspend procedure as defined in 48.018 (inter SGSN only in Rel-5)
Summary of change:
Preservation in A/GB mode can be triggered by Suspend or Radio Status procedures. The return to normal bearer service provision for realtime PDP contexts is done via PDP context modification procedure.
Consequences if not approved: (如果不这样做的后果)
No stop of downlink traffic for realtime PDP contexts in A/Gb mode. Incompatible mechanisms for A/Gb and Iu modes.
________________________________________________________________________________________
以上部分简单来说,就是A/Gb模式下也支持实时类型业务并且有很多,但规范中只写了对Iu模式的支持,建议补充A/Gb模式.所以,在规范中的9.2.3.4,原来的章节名字叫RNC-Initiated PDP Context Modification Procedure,现在改成了RNC/BSS-Initiated PDP Context Modification Procedure.
在本章的内容中,主要还补充了这样几段话:
The BSS may terminate the downlink data transfer to a MS by the Suspend procedure (which is triggered by the MS) or by the Radio Status procedure with cause "Radio contact lost with MS" or "Radio link quality insufficient to continue communication" both defined in GSM 08.18 [21]. After Iu Release in Iu mode, or after termination of the downlink data transfer in A/Gb mode, the PDP contexts are modified as follows:
- For the A/Gb mode the value of 0 kbit/s for the maximum bit rate for both uplink and downlink indicates that the SGSN shall not send any downlink data for this PDP Context.
主要意思是BSS可以在收到MS的挂起流程或者因为无线质量的原因终止用户的数据传输,在终止以后,A/Gb模式下PDP上下文将按下面的规则进行修改:
- 对于A/Gb模式,对于流媒体和会话类业务(前面有提,不在这段话里)应将MBR设置为0 kbps用于指示SGSN不为这个PDP上下文发送下行数据.并且要保持这个PDP上下文.
In A/Gb mode the following procedures shall be performed in the MS when radio coverage is lost, when the radio link quality is insufficient or when the MS suspends GPRS:
- For a PDP context using background or interactive traffic class, the PDP context is preserved.
- For a PDP context using streaming or conversational traffic class, the PDP context is preserved, but the maximum bit rate is downgraded to 0 kbit/s (for both uplink and downlink). After coverage or radio link quality is regained or when GPRS services shall resume and if the MS did not deactivate the PDP Context locally the MS should start MS initiated PDP Context Modification procedure or the PDP Context Deactivation procedure.
The MS shall use the PDP Context Modification procedure to re-activate the PDP context.
主要意思就是,当A/Gb模式下,如果MS丢失了无线覆盖,或者无线质量不好,或者MS请求挂起GPRS业务,那对应的PDP上下文,如果是背景或交互式业务的,将继续保持.而如果是流媒体或会话类业务的,PDP上下文也将保持,但应将MBR(含上行和下行)都降为0 kbit/s.在重新获得无线覆盖的情况或者MS希望拾取原GPRS业务的情况下,并且此时如果MS没有将这个PDP上下文在本地去激活,MS应发起PDP上下文修改流程或PDP上下文去激活流程.MS应使用PDP上下文修改流程来重新激活这个PDP上下文.
后续16.2.1.1章节也做了相应补充,如下:
16.2.1.1 Suspend and Resume procedure (A/Gb mode)
In the following procedures, when a suspended MS is resumed, the MS should either deactivate the PDP context of
streaming or conversational traffic class, or the MS should modify the PDP context of streaming or conversational traffic class to reset the maximum bit rate to a proper value (see clause “RNC/BSS-Initiated PDP Context Modification Procedure”).
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