A colleague of yours has a cleaver idea for improving the sliding-window protocol: the receiver only sends ACKs when it has received a frame and it...

A colleague of yours has a cleaver idea for improving the sliding-window protocol: the receiver only sends ACKs when it has received a frame and it has room in its buffer for the next frame. Unfortunately for your colleague, the improved sliding-window protocol occasionally deadlocks (the sender has frames the send, the receiver has buffer space for more frames, but no frames are sent). What suggestions would you make to your colleague to fix the protocol? Assume the sequence numbers are properly sized.