多项选择题
A. class of service
B. bandwidth profiles
C. user-network interface
D. Ethernet LAN circuit attributes
E. Ethernet virtual circuit attributes
多项选择题 Which two of these Metro Internet services map to E-LAN services that are defined by the MEF?（）
多项选择题 Which three of these Metro Ethernet services map to E-Line services that are defined by the MEF?（）
单项选择题 What is the recommended practice regarding UDLD when implementing it in all fiber-optic LAN ports?（）