I am currently trying to develop a new module in freeswitch which requires SIP interaction.

In this new mod, the primary decision making will be based on the multipart text received in the SIP INVITE message.

So far, I am able to do the following:

1. upon receiving SIP INVITE, separate the received multipart text

2. do the required processing and take a decision based on this 

Now I want to generate a new SIP INVITE (to a different user)  having a similar structure (i.e. sending out a new text message to the user along with new parameters in SDP).

I was able to generate a SIP INVITE with help of switch_ivr_originate().

I was also able to add the required Multipart Text part in the INVITE.

However, I am not sure how to proceed with adding new SDP part....

(In below sample message, I was able to generate everything in Green but nothing in RED)

So my question is this, where should I make changes to add to SDP.