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标题: sndcp分片的接收重组的困惑，及粗浅的理解，忘指点 [打印本页]

作者: 梦幻情缘 时间: 2013-2-20 09:37:22 标题: sndcp分片的接收重组的困惑，及粗浅的理解，忘指点

下面是我对sndcp分片重组的理解，不知是否正确还请多多指正。

在收到sndcp分片后对数据的处理和重组的理解：

如果收到的第一数据不是第一个分片，丢弃；
继续接收，如果仍不是第一个分片，仍然丢弃，直到接收到第一个分片；
然后准备接收后续数据：
如果收到的数据是最后一个分片，把数据排序重组，如果数据完整说明全部收到；如果数据片段缺失，则将收到的所有数据丢弃，并进入接收另外一个N-PDU的第一片的状态；
如果收到的数据不是最后一个分片，则判断是否是第一个分片，如果不是第一个分片，则保存，继续接收后面的数据；如果是第一个分片，则判断DCOMP 和PCOMP是否与接收到的第一个分片的一致，如果一致则将该数据覆盖原数据或不做任何处理，继续接收后面的数据；如果不一致，则将前面接收的数据全部丢弃，并进入接收另外一个N-PDU的第一片的状态；

对协议不是很明白，附在下面以供参考。
附：
6.7.4 Exception situations
6.7.4.1 Receive First Segment state
If an SN-UNITDATA PDU is received with the F bit set to 0, the SN-UNITDATA PDU shall be discarded. The
Receive First Segment state shall be entered if the M bit is set to 0, otherwise the Discard state shall be entered.
If an SN-DATA PDU is received with the F bit set to 0, the SN-DATA PDU shall be discarded, and the acknowledged
LLC operation shall be re-established for the SAPI used.
6.7.4.2 Receive Subsequent Segment state
If an SN-UNITDATA PDU is received with the F bit set to 1, and if DCOMP or PCOMP is different from those in the
first segment, then the SN-UNITDATA PDU and all previous segments belonging to the same N-PDU shall be
discarded. The Received First Segment state shall be entered if the M bit is set to 0, otherwise the Discard state shall be
entered.
If an SN-DATA PDU is received with the F bit set to 1, and if DCOMP, PCOMP or N-PDU number is different from
those in the first segment, then the SN-DATA PDU and all previous segments belonging to the same N-PDU shall be
discarded, and the acknowledged LLC operation shall be re-established for the SAPI used.
6.7.4.3 Discard state
If an SN-PDU is received with the M bit set to 1, the SN-PDU shall be discarded and the SNDCP entity shall remain in
the Discard state.
If an SN-PDU is received with the M bit set to 0, the SN-PDU shall be discarded and the Receive First Segment state
entered.

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