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Editorial Team
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Asked: 2026-06-18T05:48:44+00:00

I observed a surprising thing that when there are both udp-based and tcp-based applications

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I observed a surprising thing that when there are both udp-based and tcp-based applications sending packets, if the upd-based application sent the packets so fast that the bandwith are nearly filled with udp packets, then the tcp packets would be very hard to send out.

The surprising thing is that though tcp-based application is able to send a few packets out (observed by the return value of write()), the receiver of the tcp packets never receives them. Why? Is that because the tcp-packets arenot finally sent out by the network card? or the tcp packets are actually dropped by routers?

Thanks,
Steve

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1 Answer

  1. Editorial Team

    First, the return value of write() is not an indicator of whether packets were sent. It just indicates that the data was buffered.

    Second, if you are saturating the network with UDP packets there will be a lot of packet loss, and TCP being adaptive will adapt to that by sending packets out more slowly. If the packet loss gets too high TCP can basically stop altogether. The solution is not to saturate the network with UDP packets.

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