Select the correct statement$($s$)$ regarding DCE and DTE interfaces.

a$.$ the DCE and DTE convention describes devices and not interfaces

b$.$ to establish data flow, DTE interfaces must always be connected to other DTE interfaces, and DCE interfaces must always be connected to other DCE interfaces

c$.$ DCE and DTE device descriptions are unique to IEEE $802\mathrm{.}3$ Ethernet LANs

d$.$ the DCE and DTE convention describes the interfaces associated with devices; a single device may have both a DTE and DCE interface to enable correct data flow