This attribute indicates the current value of N401, that is negotiated
during Exchange Identification (XID). This is the maximum number
of octets that can be carried in the information field of an
information frame received from the Public Switched Telephone
Network (PSTN) modem. An incoming information frame carrying
data octets more than this size shall be rejected by the IWF V.42.
The value used for XID negotiations can be provisioned by
component GsmIwfV42 attribute rxN401FrameSize.