The AvailableWindowAdvertised variable MAY be maintained by implementations of this protocol. Implementations of this protocol MAY implement the flow control algorithm without using this variable. In the latter case, implementations of this protocol can skip the rest of this section.<25>
If an implementation maintains this protocol variable, it SHOULD follow the abstract data model specified in the rest of this section.
As specified in section 22.214.171.124.1.1, each time a receiver sends a flow control acknowledgment to the sender, it MUST advertise the size of the Receiver AvailableWindow field.
The AvailableWindowAdvertised variable keeps track of the value of the Receiver AvailableWindow field the last time the receiver advertised it to the sender. The AvailableWindowAdvertised variable is initialized to be the same size as the ReceiveWindow variable.