Flow control of fragmented data transfer

[JaeseungYeom]

To allow a send/recv buffer of a size smaller than that of the entire data file, data need to be split into multiple chunks and sent one at a time.
To avoid overrunning the receiver's buffer in a transmission scheme based on the RMA (remote memory access), a flow control is necessary such that the receiver's buffer is clear to receive new data. For this, we will use a circular buffer and a scheme similar to TPC's flow control where a token(ACK) is sent from the receiver to the sender when a buffer is ready to accept new data. To increase overlapping and hide the control overhead, we many use more than two buffers in rotation. In such as case, the token may specify the number of buffers ready to receive new data.