为什么规范中"MS可以限制N-PDU最大大小"这句话被删除了?

爱卫生

  对比3GPP规范的TS23.060的V5.5.0和V6.9.0就会发现，里面9.3章关于MS和GGSN之间传递的N-PDU的大小描述有一句话被删除了。
V5.5.0这段话是：
“The PDP PDUs shall be routed and transferred between the MS and the GGSN as N PDUs. In case of PDP type PPP, the maximum size of each N PDU shall be 1 502 octets. In other cases, the maximum size of each N PDU shall be 1 500 octets. When the MS or the GGSN receives a PDP PDU that results in an N PDU that is not larger than the maximum N PDU size, the PDP PDU shall be routed and transferred as one N PDU. When the MS or the GGSN receives a PDP PDU that results in an N PDU that is larger than the maximum N PDU size, the PDP PDU shall be segmented, discarded or rejected, depending on the PDP type and the implementation. The packet data protocol in the MS may limit the maximum size of the PDP PDUs that are routed and transferred, e.g. due to MS memory limitations.”
而V6.9.0这段话是：
"The PDP PDUs shall be routed and transferred between the MS and the GGSN as N PDUs. In case of PDP type PPP, the maximum size of each N PDU shall be 1 502 octets. In other cases, the maximum size of each N PDU shall be 1 500 octets. When the MS or the GGSN receives a PDP PDU that results in an N PDU that is not larger than the maximum N PDU size, the PDP PDU shall be routed and transferred as one N PDU. When the MS or the GGSN receives a PDP PDU that results in an N PDU that is larger than the maximum N PDU size, the PDP PDU shall be segmented, discarded or rejected, depending on the PDP type and the implementation."
   红色部分的The packet data protocol in the MS may limit the maximum size of the PDP PDUs that are routed and transferred, e.g. due to MS memory limitations这句话被删除了。为什么呢?
  因为在2003年4月12日到5月16日在美国圣地亚哥举行的3GPP TSG-SA WG2会议上，爱立信提出了一个Change Request，提出了对上述这句话的质疑，后面3GPP审核通过后，就将这句话删除了。
  这个CR编号为432，对应的文档编号为S2-032081。收录在SP-030343 (CRs on TS 23.060(PS domain Stage 2)).doc中。可以直接在Google中搜索“SP-030343 (CRs on TS 23.060(PS domain Stage 2)).doc",下载第一个链接得到SP-030343.pdf就包含了S2-032081对应我们这篇帖子提到的CR432。
   先截个图过来，这个CR432主要内容如下：

   如图红色圈标注的部分，既然在9.3中已经明确的提到，MS和GGSN之间传递N-PDU的时候，根据PDP类型的不同，类型为PPP的话，则N-PDU最大长度为1502字节，其他类型为1500字节。但后面又提到MS可以根据自己的内存大小等自身原因来限制最大N-PDU长度，感觉逻辑不是很顺。所以请求删除。最后3GPP采纳了，肯定也经过分组开会讨论的。要不这个会怎么开一个多月呢？

  这就是3GPP规范背后的故事举的一个例子，后续还会陆续推出供大家讨论。

  这些CR其实在每个3GPP规范的附录部分都说明了，并给出了文档编号，可直接去3GPP网站下载，了解这些背后的故事，应该对我们学习和了解协议是更有好处的，个人这样认为。

kathyjin

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