Asterisk to pass along a 182 Call is Waiting Call

Hi All.

Currently when the asterisk receives a 182 SIP message, it changes this into a 183 session progress message. thereby changing the call origination side.
This issue can be seen in ISDN call waiting scenario where the gateway sends 182 message to Proxy/PBX on receiving the 182 message the proxy Ondo sends the message as it is to the caller side and the caller receives an ALERTING message with a NOTIFICATION IE, whereas using the PBX Asterisk, it changes the received 182 message to 183 and sends it to the caller the caller receives a PROGRESS message.

Plz can anyone help me to shoot out this problem