[cisco-voip] Weird problem (SIP)

[yy]

Hi all,

I'm having a weird problem here. Currently when I dial to my phone 
connected to a FXS port of my cisco 2600 router, if the user at the FXS 
port does not pick up the phone, the phone rings and waits at 183 (Sip 
protocol message). This is the correct behaviour. However, when I dial 
out to PSTN from my router, and the user at the other end does not pick 
up the phone, I would receive a 200 OK almost immediately. In other 
words, it does not wait at a 183. And when the caller puts does the 
phone, I get a BYE msg instead of a CANCEL. Why is it so?

Please advise :-)

Regards,
YY