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sipvoipsdp

Can a SIP call's media address changed mid-call?

I am referring to the c value of an SDP header. enter image description here

Is it possible that the media stream address changes during a call? And it what scenarios?

Solution

  • It may be changed with re-INVITE or UPDATE. Some example scenarios:

    • PABX system consisting of multiple machines decides to route media through another media endpoint because of e.g. high server load or some other problem with this machine
    • after receiving FAX CNG, CED and/or modem preamble PABX passes the call to fax server
    • call is passed to specialized music-on-hold or IVR server

    Also, addresses advertised in SIP headers or in SDP quite often are not matching real addresses used for communication because of NAT or misconfiguration - for best results B2BUAs often may ignore them.