1<!-- 2Author: Michael Mehari 3SPDX-FileCopyrightText: 2019 UGent 4SPDX-License-Identifier: AGPL-3.0-or-later 5--> 6 7## 802.11 packet injection 8 9The Linux wireless networking stack (i.e. driver, mac80211, cfg80211, net_dev, user app) is a robust implementation supporting a plethora of wireless devices. As robust as it is, it also has a drawback when it comes to single-layer testing. 10 11Ping and Iperf are well established performance measurement tools. However, using such tools to measure 802.11 PHY performance can be misleading, simply because they touch multiple layers in the network stack. 12 13Luckily, the mac80211 Linux subsystem provides packet injection functionality and it allows us to have finer control over physical layer testing. 14 15To this end, we have adapted a [packetspammer](https://github.com/gnychis/packetspammer) application originally written by Andy Green <[email protected]> and maintained by George Nychis <[email protected]>. 16 17### Build inject_80211 on board 18Userspace program to inject 802.11 packets through mac80211 supported (softmac) wireless devices. 19 20Login/ssh to the board and setup internet connection according to the Quick Start. Then 21``` 22apt install libpcap-dev 23cd openwifi/inject_80211 24make 25``` 26 27### Options of program inject_80211 28 ``` 29-m/--hw_mode <hardware operation mode> (a,g,n) 30-r/--rate_index <rate/MCS index> (0,1,2,3,4,5,6,7) 31-i/--sgi_flag (0,1) 32-n/--num_packets <number of packets> 33-s/--payload_size <payload size in bytes> 34-d/--delay <delay between packets in usec> 35-h this menu 36 ``` 37 38### Example: 39Login/ssh to the board, Then 40``` 41cd openwifi 42./wgd.sh 43./monitor_ch.sh sdr0 11 44./inject_80211/inject_80211 -m n -r 0 -n 64 -s 100 sdr0 45``` 46Or add extra virtual monitor interface on top of sdr0, and inject packets: 47``` 48iw dev sdr0 interface add mon0 type monitor && ifconfig mon0 up 49./inject_80211/inject_80211 -m n -r 0 -n 64 -s 100 mon0 # Inject 10 802.11n packets at 6.5Mbps bitrate and 64bytes size 50``` 51 52### Link performance test 53 54To make a profound experimental analysis on the physical layer performance, we can rely on automation scripts. 55 56The following script will inject 100 802.11n packets at different bitrates and payload sizes. 57 58``` 59#!/bin/bash 60 61HW_MODE='n' 62COUNT=100 63DELAY=1000 64RATE=( 0 1 2 3 4 5 6 7 ) 65SIZE=( $(seq -s' ' 50 100 1450) ) # paload size in bytes 66IF="mon0" 67 68for (( i = 0 ; i < ${#PAYLOAD[@]} ; i++ )) do 69 for (( j = 0 ; j < ${#RATE[@]} ; j++ )) do 70 inject_80211 -m $HW_MODE -n $COUNT -d $DELAY -r ${RATE[$j]} -s ${SIZE[$i]} $IF 71 sleep 1 72 done 73done 74 75``` 76 77On the receiver side, we can use tcpdump to collect the pcap traces. 78 79``` 80iw dev wlan0 interface add mon0 type monitor && ifconfig mon0 up 81tcpdump -i mon0 -w trace.pcap 'wlan addr1 ff:ff:ff:ff:ff:ff and wlan addr2 66:55:44:33:22:11' 82``` 83 84Wlan addresses *ff:ff:ff:ff:ff:ff* and *66:55:44:33:22:11* are specific to our injector application. 85 86Next, we analyze the collected pcap traces using the analysis tool provided. 87 88``` 89analyze_80211 trace.pcap 90``` 91 92An excerpt from a sample analysis looks the following 93 94``` 95HW MODE RATE(Mbps) SGI SIZE(bytes) COUNT Duration(sec) 96======= ========== === =========== ===== ============= 97802.11n 6.5 OFF 54 100 0.11159 98802.11n 13.0 OFF 54 100 0.11264 99802.11n 19.5 OFF 54 100 0.11156 100802.11n 26.0 OFF 54 100 0.11268 101802.11n 39.0 OFF 54 100 0.11333 102802.11n 52.0 OFF 54 100 0.11149 103802.11n 58.5 OFF 54 100 0.11469 104802.11n 65.0 OFF 54 100 0.11408 105``` 106 107