Forgot a few details :
===
cat /etc/debian_version
stretch/sid
===
uname -a
Linux HSZ 4.3.0-1-amd64 #1 SMP Debian 4.3.5-1 (2016-02-06) x86_64 GNU/Linux
===
iwlist wlp2s0 freq
wlp2s0 32 channels in total; available frequencies :
Channel 01 : 2.412 GHz
Channel 02 : 2.417 GHz
Channel 03 : 2.422 GHz
Channel 04 : 2.427 GHz
Channel 05 : 2.432 GHz
Channel 06 : 2.437 GHz
Channel 07 : 2.442 GHz
Channel 08 : 2.447 GHz
Channel 09 : 2.452 GHz
Channel 10 : 2.457 GHz
Channel 11 : 2.462 GHz
Channel 36 : 5.18 GHz
Channel 40 : 5.2 GHz
Channel 44 : 5.22 GHz
Channel 48 : 5.24 GHz
Channel 52 : 5.26 GHz
Channel 56 : 5.28 GHz
Channel 60 : 5.3 GHz
Channel 64 : 5.32 GHz
Channel 100 : 5.5 GHz
Channel 104 : 5.52 GHz
Channel 108 : 5.54 GHz
Channel 112 : 5.56 GHz
Channel 116 : 5.58 GHz
Channel 120 : 5.6 GHz
Channel 124 : 5.62 GHz
Channel 128 : 5.64 GHz
Channel 132 : 5.66 GHz
Channel 136 : 5.68 GHz
Channel 140 : 5.7 GHz
Channel 149 : 5.745 GHz
Channel 153 : 5.765 GHz
Current Frequency:2.442 GHz (Channel 7)
===
iwconfig
wlp2s0 IEEE 802.11abgn ESSID:“xxxxxx”
Mode:Managed Frequency:2.442 GHz Access Point: F4:EC:38:E9:A1:A8
Bit Rate=54 Mb/s Tx-Power=19 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=48/70 Signal level=-62 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:29 Invalid misc:36113 Missed beacon:0