对于该新功能，需要在消息描述符中附加字段来保留分段和分组信息。

For this new function, additional fields in message descriptor were needed to keep information for the segmenting and grouping.

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自v 5以来，可以对消息分段或分组。

Since V5, messages can be segmented or grouped.

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实现层还执行用于底层协议的消息分段和并置。

The Implementation Layer also performs segmentation and concatenation of messages for the underlying protocol.

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