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### inject_80211 18Userspace program to inject 802.11 packets through mac80211 supported (softmac) wireless devices. 19 20### Options 21 ``` 22-m/--hw_mode <hardware operation mode> (a,g,n) 23-r/--rate_index <rate/MCS index> (0,1,2,3,4,5,6,7) 24-i/--sgi_flag (0,1) 25-n/--num_packets <number of packets> 26-s/--payload_size <payload size in bytes> 27-d/--delay <delay between packets in usec> 28-h this menu 29 ``` 30 31### Example: 32``` 33iw dev wlan0 interface add mon0 type monitor && ifconfig mon0 up 34inject_80211 -m n -r 0 -n 64 -s 100 mon0 # Inject 10 802.11n packets at 6.5Mbps bitrate and 64bytes size 35``` 36 37### Link performance test 38 39To make a profound experimental analysis on the physical layer performance, we can rely on automation scripts. 40 41The following script will inject 100 802.11n packets at different bitrates and payload sizes. 42 43``` 44#!/bin/bash 45 46HW_MODE='n' 47COUNT=100 48DELAY=1000 49RATE=( 0 1 2 3 4 5 6 7 ) 50SIZE=( $(seq -s' ' 50 100 1450) ) # paload size in bytes 51IF="mon0" 52 53for (( i = 0 ; i < ${#PAYLOAD[@]} ; i++ )) do 54 for (( j = 0 ; j < ${#RATE[@]} ; j++ )) do 55 inject_80211 -m $HW_MODE -n $COUNT -d $DELAY -r ${RATE[$j]} -s ${SIZE[$i]} $IF 56 sleep 1 57 done 58done 59 60``` 61 62On the receiver side, we can use tcpdump to collect the pcap traces. 63 64``` 65iw dev wlan0 interface add mon0 type monitor && ifconfig mon0 up 66tcpdump -i mon0 -w trace.pcap 'wlan addr1 ff:ff:ff:ff:ff:ff and wlan addr2 66:55:44:33:22:11' 67``` 68 69Wlan addresses *ff:ff:ff:ff:ff:ff* and *66:55:44:33:22:11* are specific to our injector application. 70 71Next, we analyze the collected pcap traces using the analysis tool provided. 72 73``` 74analyze_80211 trace.pcap 75``` 76 77An excerpt from a sample analysis looks the following 78 79``` 80HW MODE RATE(Mbps) SGI SIZE(bytes) COUNT Duration(sec) 81======= ========== === =========== ===== ============= 82802.11n 6.5 OFF 54 100 0.11159 83802.11n 13.0 OFF 54 100 0.11264 84802.11n 19.5 OFF 54 100 0.11156 85802.11n 26.0 OFF 54 100 0.11268 86802.11n 39.0 OFF 54 100 0.11333 87802.11n 52.0 OFF 54 100 0.11149 88802.11n 58.5 OFF 54 100 0.11469 89802.11n 65.0 OFF 54 100 0.11408 90``` 91 92