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.