This attribute defines the framing of the DS1 line.
d4 defines a framing pattern of 12 frames per multiframe.
esf defines a framing pattern of 24 frames per multiframe.
d4Cas defines a framing pattern of 12 frames per multiframe with
channel associated signalling.
esfCas defines a framing pattern of 24 frames per multiframe with
channel associated signalling.
unframed defines an unknown framing pattern for clear channels.
For cell-based cards only the default option esf is permitted.