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When we surf the web, and a page includes a picture that is made up of 10 packets, and one of these packets is dropped, we have to wait for at least one round-trip-time until we see the result.
AQM -- Active Queue Management (AQM) is a strategy to drop or mark packets in router buffers to signal the onset of congestion to the senders and therefore to avoid the buffer to become full. The persistently full buffers in network routers along the Internet paths lead to excessive latency that negatively affect the performance of multimedia flows (e.g. video streaming, VoIP and online gaming). Therefore it's vital to deploy AQM at network routers to assure the low latency, more specifically on the access links such as home routers, access points and modems.
Multiple TCP connections between the same pair of hosts each carry out congestion control on their own. Much efficiency could be gained if such TCP connections would "collaborate" by sharing certain information such as the congestion window (cwnd).
TCP or other protocols can sometimes build "standing queues" in the network: buffers that are filled to a certain level but never allowed to drain because data continuously comes in fast enough to keep the queue filled. This causes a permanent delay growth for all the traffic that traverses the queue. If the sender that causes the standing queue reacts to congestion in some way, it might be best to "flush" the queue, by quickly sending so much data into it that significant loss happens, in the hope that the sender that caused the problem reduces its rate.