What are the DSL-specific factors that require additional bandwidth when supporting Voice-over-IP over an IPSec VPN?（）

• A、A voice packet is sent via multiple fixed-length cells; a portion of the last cell is padding, requiring more bandwidth.
• B、ADSL typically uses PPPoE encapsulation, which adds additional overhead to each voice packet.
• C、A voice packet is sent via multiple fixed-length cells; each cell has about 10% Layer-2 header overhead. 
• D、IPSec requires additional overhead for the header and hash. 
• E、ADSL carrier band requires additional bits to be carried over the wire to the DSL Access Concentrator.