When WMM is disabled, it will work in 11G mode. Thus, the maximum speed will be 54Mbps. http://www.smallnetbuilder.com/wireless/wireless-features/30938-dont-mess-with-wmm

I use TP-LINK for several years but never heard of such a feature called "WLAN Client"... What's the model number of your old TP-LINK? What are you trying to fulfill with that feature?

As I know, none of TP-LINK indoor products support DFS...

That's called channel width... Not sure about the reason but it has been improved in some models using new user interface like C8... C7 V2's UI may be updated in future as well...

router(LAN)---(LAN)TL-SG1024D(LAN)---Server? Bypassing the switch, the server can access internet? The switch is a plug and play device. To figure out the problem, Any other PCs available there for...

L2 Features IGMP Snooping V1/V2/V3 802.3ad LACP (Up to 6 aggregation groups, containing 4 ports per group) Spanning Tree STP/RSTP/MSTP BPDU Filtering/Guard TC/Root Protect Loop back detection 802.3x...