I was working with a client-server project based on UDP and 802.11 as a link and physical layer. There, the client was trying to probe some packets in the wireless channel to gauge channel condition. This function is required to set up the transmission speed and estimate packet drop rate in my client application. To carry out that function, it is required to measure the number of re-transmissions (topology is client -----ap ------server: where ----- is wireless channel)that are occurring in IEEE 802.11. In the transport layer, there won't be any re-transmission, as UDP is used, but if the wireless channel is bad (no acknowledgement from the receiver MAC), the IEEE802.11 Wi-Fi NIC will re-transmit. So far I could access the RSSI from ~/proc/net/wireless, which gives an idea about the received signal strength but not about the wireless channel condition. Wireless channel condition could be estimated from number of retransmission. How should I measure the number of re-transmission in IEEE 802.11 layer, Say for 200 packets from application how many re-transmission (from client) in IEEE 802.11 layer ?

Or is there any kernel hack that will stop the IEEE802.11 re-transmission feature? I was using ubuntu 18.04.1.

  • I think you need to clarify the difference between the network layers. Packets are at the network level, where addressing happens (i. e. TCP/IP addresses for TCP and UDP packets); 802.11 doesn't come into play here. That's a specification for the physical and data link layers. The wireless network infrastructure retransmitting is not the same as a host retransmitting a network packet (which doesn't happen over UDP anyhow; that's one of the main differences between UDP and TCP). – DopeGhoti Oct 26 '18 at 17:24
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    @DopeGhoti and to continue with this, you get retransmissions at the physical layer on ethernet as well (Collision Detection, for example) where the controller will back off and retransmit. – Stephen Harris Oct 26 '18 at 18:47
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    Network layer shouldn't be the concern here. How many re-transmission in the IEEE 802.11 is the concern here. – H.Jamil Oct 26 '18 at 18:51
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    That's my point. IEEE 802.11 retransmissions aren't part of the UDP stack. UDP isn't aware of anything the data link layer is doing. – DopeGhoti Oct 26 '18 at 19:55
  • I was asking suggestions about ways to calculate IEEE802.11 re-transmission number in a bad wireless channel condition. UDP was just pointing to the topology. – H.Jamil Oct 26 '18 at 21:47

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