DOCSIS标准中对上行流量的频道有没有规定？

iamxiaop

请懂cable modem或CMTS的高手来解答。谢谢！
问题1：
DOCSIS标准中对上行流量的频道有没有规定？查了很多资料都没有提上行流量的频道是怎样的，只提到了下行流量使用一个6MHz（或欧洲8MHz）的频道。
问题2：
下面的一道题目答案是D，不知道是不是正确？（似乎C有可能正确，如果标准没有规定上行频道的话。）
Which HFC cable network statement is true about the downstream data channel to
the customer and the upstream data channel to the service provider?
A. The upstream data path is assigned a channel in a higher frequency range than the
downstream path has.
B. The downstream data path is assigned a 30 MHz channel and the upstream data path is
assigned a 1 MHz channel.
C. The downstream data path is assigned a fixed bandwidth channel and the upstream
data path uses a variable bandwidth channel.
D. Both upstream and downstream data paths are assigned in 6 MHz channels.
E. None of the above.
Answer: D