Setup of TFTP to boot OS from PXE

I am trying to network system from network using PXE. I almost done, but have some problem. When I boot my client from PXE I got this on clients' screen: PXE-E11: ARP timeout PXE-E38: TFTP cannot open connection There are some attempts on the Internet to fix it, but nothing concrete, so I will describe my case in details. in this file /etc/default/atftpd I changed **USE_INETD=true** to **USE_INETD=false** then in the file /etc/default/tftpd-hpa I put TFTP_DIRECTORY="/srv/tftp", because srv/tftp was in the end of file /etc/default/atftpd. Then I run sudo /etc/init.d/atftpd start and few last things I typped sudo mount -o loop /home/tux/ubuntu16-Desktop.iso /srv/tftp/ubuntu/ and done with tftp, but it does not work. Do you have ideas to fix it?