This attribute indicates the current value of k that is negotiated
during Exchange Identification (XID). This is the size of flow
control sliding window used for information frames transmitted
from the Public Switched Telephone Network (PSTN) modem. This
size governs the maximum number of information frames that the
peer of the IWF V.42 error-correcting entity can have outstanding
(that is, unacknowledged). The value used for XID negotiations can
be provisioned by component GsmIwfV42 attribute rxKwindowSize.