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TCP windows won't save you. TCP has no way to magically know when some buffer is full. Instead it notices packet loss and interprets it as congestion. Which is not what you want, because it can significantly reduce throughput.

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Yes it does, receiver side advertises window as 0 and persist timer kicks in. The send call then blocks until window recovers.

That's the problem when you don't really even have any congestion, but just very high packet loss caused by small buffers. Transfer rate drops to nothing.

With pause frames you can avoid that situation.

There's many types of TCP congestion algos and not all of them require dropped packets to begin the congestion avoidance.

In fact, at the time, I was working at LBL in a lab that developed new congestion avoidance algorithms. The problem was that most of our tuning for was for long-range links, while I was using the cluster for local high performance networking.

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