This attribute specifies how channel associated signalling
information is transported through the network.
none specifies that channel associated signalling information is not
transported through the network.
transparent specifies signalling information is transported
transparently through the network. transparent can be used when
both sides are using equivalent signalling tables.
interpret specifies signalling information is interpreted for idle and
seize codes. interpret can be used when both sides are not using
equivalent signalling tables but only require two unique codes (seize
and idle) for signalling.
Using a value of interpret requires correct idleCode and seizeCode
attributes. interpret mode must be used if silenceSuppression is set
to casIdleCode.