traffic measurement with STAK on asterisk with g.729

ever wonder how much g729 compare to g711 when it come to use the bandwidth ?, here is the result when I am using STAK, ( stak-1.0b1 on linux) in my asterisk server.

with g711 codec :

./stakrate -r5 -ci eth2 -f  "host  x.x.x.x"
=> Currently 19.57 kBps/100.40  pps, Average: 19.57 kBps/100.40  pps
=> Currently 19.57 kBps/100.40  pps, Average: 19.57 kBps/100.40  pps
=> Currently 19.57 kBps/100.40  pps, Average: 19.57 kBps/100.40  pps
=> Currently 19.61 kBps/100.60  pps, Average: 19.58 kBps/100.45  pps

with g729 codec :

./stakrate -r5 -ci eth2 -f  "host  x.x.x.x"
=> Currently 5.90 kBps/100.40  pps, Average: 5.90 kBps/100.40  pps
=> Currently 5.91 kBps/100.60  pps, Average: 5.90 kBps/100.50  pps
=> Currently 6.75 kBps/101.80  pps, Average: 6.18 kBps/100.93  pps
=> Currently 6.79 kBps/102.20  pps, Average: 6.34 kBps/101.25  pps

almost 1/4.