[reSIProcate] How to differentiate sdp in InviteSessionHandler::onOffer()?

[常铮]

Hi all,

I want to implement Hold and UnHold.
Firstly, A Hold B,
A should send INVITE with sdp(c=IN IP4 0.0.0.0) to B,
then
B call InviteSessionHandler::onOffer(InviteSessionHandle is, const SipMessage& msg, const SdpContents& sdp) 

After a moment, A unHold B,
A should send INVITE with sdp(c=IN IP4 172.25.17.240) to B,
and then
B also call the same function InviteSessionHandler::onOffer(InviteSessionHandle is, const SipMessage& msg, const SdpContents& sdp)

I want to know 
How to differentiate them in 
InviteSessionHandler::onOffer()
{
  ...   
}
 
Thank you very much!

John  Beijing,China