If you have to upload firmware to a router or a switch with xmodem, get the package lrzsz-0.12.20.tar.gz. Configure it with

tar xvzf lrzsz-0.12.20.tar.gz
cd lrzsz-0.12.20
./configure --disable-nls && sudo make install

Then start a console session with screen

screen /dev/tty.Keyserial1 9600

then, when you are asked from the program up upload the firmware using xmodem, do:

Press ctrl-a
:exec !! lsx -b -X /path/srw2016-24-10086.ros

the upload will start.