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 the information frames that the
V.42 transmits to the Public Switched Telephone Network (PSTN)
modem. This size governs the maximum number of information
frames that 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
txKwindowSize.