example swiped from unix.se:
altq on $ext_if cbq bandwidth 640Kb queue { def, ftp, udp, \
http, ssh, icmp }
queue def bandwidth 18% cbq(default borrow red)
queue ftp bandwidth 10% cbq(borrow red)
queue udp bandwidth 30% cbq(borrow red)
queue http bandwidth 20% cbq(borrow red)
queue ssh bandwidth 20% cbq(borrow red) { ssh_interactive, \
ssh_bulk }
queue ssh_interactive priority 7 bandwidth 20%
queue ssh_bulk priority 0 bandwidth 80%
queue icmp bandwidth 2% cbq
pass log quick on $ext_if proto tcp from any to any port ssh \
flags S/SA keep state queue (ssh_bulk, ssh_interactive)
pass in quick on $ext_if proto tcp from any to any port ftp \
flags S/SA keep state queue ftp
pass in quick on $ext_if proto tcp from any to any port www \
flags S/SA keep state queue http
pass out on $ext_if proto udp all keep state queue udp
pass out on $ext_if proto icmp all keep state queue icmp