An Investigation into Transport Protocols and Data Transport ...

4.2. Protocol Description 56
Where n is number of packets in flight, and s is the size of each packet as
limited by the MTU and MSS. As such, should the physical memory assigned
to the sliding window be restricted, then the number of packets in flight is
restricted and consequently the throughput is also restricted.
Another way of thinking about the BDP is that for a network capacity of
C (i.e. b = C), and an end-to-end latency of T , the required window in order
for a TCP flow to saturate the path is C × T . This is only valid when there
are no competing flows as the presence of network cross traffic is that the
available bandwidth of the network is less than C. However, the presence of
cross traffic may also increase the latency of the flow, and therefore there is
a balancing effect (of the decrease in bandwidth, but an increase in latency).
A full account of this is given in [JPD03].
4.2.3 Flow Control
To prevent a fast sender from overflowing a slow receiver, and hence causing
losses at the receiver (and wasting network resources), TCP implements flow
control [Tan96]. In order to prevent such an occurrence, in every ack the
receiver advertises to the sender its ‘receiver window’ (rwnd) which represents
the number of bytes available for buffering at the TCP receiver before it is
processed and sent up to the receiver Application.
Therefore, if the TCP receiver cannot process the incoming data at the
speed which is being sent, the value of rwnd sent will get smaller as the
socket buffer at the receiver fills.
Through the advertisement of rwnd, the TCP sender can prevent overflowing
the receiver by limiting its maximum allowed window size for transmission.
This mechanism provides a simple, yet elegant way of preventing