[Freeswitch-dev] Question regarding modification of SDP in INVITE generated by FreeSwitch Server

Akshay Patil ahvpatil at gmail.com
Mon Jan 28 12:14:44 UTC 2019

Hi All,

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.

Any help is appreciated

Akshay Patil

   Content-Type: application/sdp
   Content-Length:   407
a=fmtp:96 0-16
   m=application 4121 UDP MCPTT
   c=IN IP4
   a=fmtp:MCPTT mc_queueing;mc_priority=5;mc_granted;mc_implicit_request

   Content-Type: application/vnd.3gpp.mcptt-info+xml
   Content-Length:   513

   <?xml version="1.0" encoding="UTF-8"?>
   <mcpttinfo xmlns="urn:3gpp:ns:mcpttInfo:1.0" xmlns:xsi="
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