sms_router sleeping when bulking

[Fourat Zouari]

Am doing bulk sms, attacking kannel '/cgi-bin/sendsms' url, and it's going very slowly, when debugging, i see this line in the bearerbox log repeating each 60 MT messages :

2006-05-13 16:38:58 [4556] [8] DEBUG: sms_router: time to sleep 30.00 secs.

Am using SMS-C connexion.
Anyone can help ?
how to increase/decrease this sleep time value ?