T-Lib-Initiated Hold-Retrieve RFC 3264
Some SIP endpoints do not accept SDP with an IP address of 0.0.0.0. SIP Server behaves differently if the
Sip-hold-rfc3264 configuration parameter is set to true. A valid SDP is sent in the Invite, but as per the RFC, the attribute flag of the SDP is changed to get the desired functionality.
For example, to hold a call, an SDP with
a=inactive is sent in the SDP. A re-INVITE with the original SDP retrieves the call.