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Assume we talking about the situation of many senders sending packets to a receiver.
Often senders would be the one that control congestion by using sliding window that limits sending rate.

We have: 

 snd_cwnd = min(cwnd,rwnd)

Using explicit or implicit feedback information from network (router,switch), sender would control cwnd to control sending rate.

Normally, rwnd is always big enough that sender only care about cwnd. But if we consider rwnd, using it to limit snd_cwnd, it would make congestion control more efficiently.

rwnd is the number of packets (or bytes) that receiver be able to receive. What I'm concerned about is capability of senders.

Questions:
1. So how do receiver know how many flows sending packets to it?
2. Is there anyway that receiver know the snd_cwnd of sender?

brokenfoot
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Tai Nguyen
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1 Answers1

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This is all very confused.

  1. The number of flows into a receiver isn't relevant to the rwnd of any specific flow. The rwnd is simply the amount of space left in the receive buffer for that flow.

  2. The receiver has no need to know the sender's cwnd. That's the sender's problem.

Your statement that 'normally rwnd is always big enough that sender only cares about cwnd' is simply untrue. The receive window changes with every receive; it is re-advertised with every ACK; and it frequently drops to zero.

Your following statement 'if we consider rwnd, using it to limit cwnd ...' is simply a description of what already happens, as per 'snd_cwnd = min(cwnd, rwnd)'.

Or else it may constitute a completely unexplained proposal to needlessly modify TCP's flow control which has been working for 25 years, and which didn't work for several years before that: I remember several Arpanet freezes in the middle 1980s.

user207421
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  • Thank you EJP. I want to find out about TCP and find if there is any way that can make TCP better. Often sender is the main one in congestion control algorithm. I think that if receiver can inform how many flows to sender, sender will fastly reduce sending rates for fair sharing with others. – Tai Nguyen Apr 25 '14 at 16:09
  • @TaiNguyen But the number of flows into the receiver isn't significant by itself. The significant factors are the RTT and the packet loss rate, and the sender already knows those. – user207421 Apr 25 '14 at 22:17