who wakes the sendsms thread

Hi,

I am a new user of kannel. I am using kannel with a GSM modem, but I have
noticed this one issue. Suppose I try and send a message using "sendsms" the
message is sent only after some irregular interval. But, if I send a sms
from my mobile, to which the reply is sent using "sendsms" the message is
sent immediately. Also any other queued messages are sent at that time too.

Now I tried looking into the code and was lost in this maze of threads and
locks. On further inspection I figured that the "at2_device_thread" blocks
but was unable to figure out the event which will unblock this thread,
leading to the message being sent.

Please help. Also any architecture guide giving details of the threads and
the locks will be very helpful.

Thanks,
akshat