SIP Server's Hold operation can be configured to play music while the customer is placed on hold by an agent. The music-on-hold configuration is global — if it is enabled, all held parties hear music; if it is not enabled, all held parties hear silence.
Hold-with-silence only involves stopping the RTP streams. The Retrieve operation resumes the RTP streams.
There are multiple methods for stopping the RTP streams. SIP Server uses IP address 0.0.0.0 in the
c= attribute as the only universally accepted method.
Because some endpoints may change the RTP port address when trying to retrieve a call, the re-INVITE with delayed SDP offer-answer negotiation shown in the following diagram is necessary.