Speed and CPU usage test:
TEST1)
	Open two ssh sessions: a) and b)
	a)
		while true; do echo "Hit [CTRL+C] to stop!"; speedtest-cli --simple; done

	b)
		sudo htop	# see on CPU usage by IRQ/kworker handlers

TEST2)
	Open two ssh sessions: a) and b)
	a)
		while true; do echo "Hit [CTRL+C] to stop!"; wget -O /dev/null --report-speed=bits http://download.thinkbroadband.com/100MB.zip ; done

	b)
		sudo htop	# see on CPU usage by IRQ/kworker handlers

TEST3)	For TWO modems connected. NOT TESTED!
	Connect 2 modems.
	Setup each of them with
		sudo sakis3g --interactive

	See IP-adresses of modems (ppp0 and ppp1 interfaces)
		sudo ifconfig -a

	Open three ssh sessions: a), b) and c)
		a)
			while true; do echo "Hit [CTRL+C] to stop!"; speedtest-cli --source IP_OF_PPP0 --simple; done
		b)
			while true; do echo "Hit [CTRL+C] to stop!"; speedtest-cli --source IP_OF_PPP1 --simple; done
		c)
			sudo htop	# see on CPU usage by IRQ/kworker handlers