This attribute indicates the current value of parameter N401 for
V.42 which is negotiated during Exchange Information (XID). This
is the maximum number of octets that can be carried in the
information field of an information frame that the IWF V.42
transmits to the Public Switched Telephone Network (PSTN)
modem. The IWF V.42 puts this or even smaller size of data into the
outgoing information frame. The value used for XID negotiations
can be provisioned by component GsmIwfV42 attribute
txN401FrameSize.