220.127.116.11.1.3 Dequeuing RPC PDUs
If the Sender AvailableWindow is greater than the number of bytes in the first queued RPC PDU, the implementation MUST send queued PDUs in order until either no RPC PDUs remain in the queue or the Sender AvailableWindow is less than the number of bytes in the next queued RPC PDU.
Each time an RPC PDU is dequeued, an implementation MUST do the following:
Increment the BytesSent protocol variable by the number of bytes in the RPC PDU sent.
Decrement the Sender AvailableWindow by the same amount.